The excited state dynamics and critically regulated factors of reverse intersystem crossing(RISC)in through-space charge transfer(TSCT)molecules have received insufficient attention.Here,five molecules of through spac...The excited state dynamics and critically regulated factors of reverse intersystem crossing(RISC)in through-space charge transfer(TSCT)molecules have received insufficient attention.Here,five molecules of through space/bond charge transfer inducing thermally activated delayed fluorescence(TADF)are prepared,and their excited state charge transfer processes are studied by ultrafast transient absorption and theoretical calculations.DM-Z has a largerΔEST,leading to a longer lifetime of intersystem crossing(ISC),resulting in the lowest photoluminescence quantum yield(PLQY).Oppositely,ISC and RISC are demonstrated to take place with shorter lifetimes for TSCT molecules.The face-to-faceπ-πstacking interactions and electron communication enable DM-B and DM-BX to have an efficient RISC,increasing the weight coefficient of RISC from 1.7%(DM-X)to close to 50%(DM-B and DM-BX)in the solvents,which make DM-BX and DM-B to have a high PLQY.However,partial local excitation in the donor center is observed and the charge transfer is decreased for DM-G and DM-X.The triplet excited state(DM-G)or singlet excited state(DM-X)mainly undergoes inactivation through a non-radiative relaxation process,resulting in less RISC and low PLQY.This work provides theoretical hints to enhance the RISC process in the TADF materials.展开更多
Recently, an effective exciton diffusion length L exceeding 100μm has been reported for organic- inorganic halide perovskites owing to both the high mobility and ultra-long lifetime of the excitons; however, the orig...Recently, an effective exciton diffusion length L exceeding 100μm has been reported for organic- inorganic halide perovskites owing to both the high mobility and ultra-long lifetime of the excitons; however, the origin of ultra-long L is still unclear in nature. In some photoelectric materials, reverse intersystem crossing （RISC） from the triplet to the singlet state can enhance the quantum yield of pho- toluminescence greatly. In this study, our theoretical investigation indicated that the energy difference △E_st between the singlet state and the triplet state of CH_3NH_3Pbl_3 was less than 0.1 eV, which represents one crucial prerequisite for the occurrence of RISC. Meanwhile, the experimental results showed that the photoluminescence lifetime increased with the increasing temperature, a typical feature of RISC. Based on this study, we put forward the hypothesis that the ultra-long lifetime of excitons in organic-inorganic halide perovskite might be caused by the RISC process. This may provide a new insight into the important photophysical properties of such novel photovoltaic materials.展开更多
Circularly polarized luminescence(CPL)materials with delayed fluorescence have attracted much attention due to their ability to efficiently trap triplet state excitons,thereby improving the photoluminescence quantum y...Circularly polarized luminescence(CPL)materials with delayed fluorescence have attracted much attention due to their ability to efficiently trap triplet state excitons,thereby improving the photoluminescence quantum yields of CPL materials.However,much effort has been normally focused on the utilization of T1 excitons but seldom on the utilization of higher excited triplet state T_(n)(n>1)excitons.Rational manipulation of higher excited triplet state T_(n)(n>1)excitons and suppression of Kasha’s rule of CPL materials remains a major challenge.Herein,two gold complex enantiomers((R/S)-BPAuBC)based on axially chiral binaphthyls and 3,6-Di-tert-butylcarbazole groups are synthesized and systematically investigated.These materials exhibit aggregation-induced circularly polarized delayed fluorescence.Circularly polarized delayed fluorescence was found to be enabled by activating high-level reverse intersystem crossing(hRISC).The anti-Kasha phosphorescence at 77 K proves that the exciton has a large population in the high-lying triplet state T_(2),which allows the effective hRISC process to cross back to the singlet state S_(1)and emit delayed fluorescence.In addition,CPL“on-off”switching is further achieved in nanoparticles by acid-base stimulus,showing its potential as an acid-base responsive material.展开更多
The development of circularly polarized multiresonant thermally activated delayed fluorescence materials with fast reverse intersystem crossing(RISC)process remains a challenge.Herein,we introduce high-lying excited s...The development of circularly polarized multiresonant thermally activated delayed fluorescence materials with fast reverse intersystem crossing(RISC)process remains a challenge.Herein,we introduce high-lying excited states to assist the RISC process.Through arranging two known MR-TADF emitters tCzBN and DiKTa at the pseudo-ortho position of a chiral skeleton paracyclophane(PCP),the excitedstate density was increased.The proof-of-concept emitter po-PCP-tCzBN-DiKTa shows nearly three times higher kRISC(5.31×10^(4) s^(−1))than PCP-tCzBN(1.73×10^(4) s^(−1))without compromising color purity and exhibiting circularly polarized luminescence with|gPL|values at the 10^(−4) level.The solution-processed organic light-emitting diodes with po-PCP-tCzBNDiKTa show high maximum external quantum efficiency(EQE_(max))reaching 23%with a moderate efficiency roll-off,showing EQE of 18%and 9%at 100 and 1000 cd/m^(2.)展开更多
The intersystem crossing channels of gaseous 4H-pyran-4-thione were investigated using the CASSCF//TD-B3LYP methods and group theory. Using the effective one-electron spin-orbit Harniltonian, the strengths of spin-orb...The intersystem crossing channels of gaseous 4H-pyran-4-thione were investigated using the CASSCF//TD-B3LYP methods and group theory. Using the effective one-electron spin-orbit Harniltonian, the strengths of spin-orbit coupling were estimated, which plays an essential role in the spin transitions between different spin states. Calculated results show that phosphorescence and non-radiative decay via intersystem crossing to the So state are concurrent processes occurring at the T1 state. A rapid depletion of the S1 state via intersystem crossing to the T1 state can be mediated by the T2 state, if spin relaxation is fast within the triplet levels. Our calculated results are in close agreement with experimental observations.展开更多
Development of new photosensitizers(PSs)with high singlet oxygen quantumyield and minimal side effects is of great interest in photodynamic therapy(PDT).Herein,a facile strategy to significantly improve photosensitiza...Development of new photosensitizers(PSs)with high singlet oxygen quantumyield and minimal side effects is of great interest in photodynamic therapy(PDT).Herein,a facile strategy to significantly improve photosensitization has been demonstrated for the first time with two pentamethine dyes connected by a varying alkyl chain resulting in a series of cyanine dimers.The photophysical properties of the dimerswere studied with steady-state optical spectroscopies,a timecorrelated single photon counting technique,and laser flash photolysis spectrometry.X-ray crystallography confirmed that the molecular packing modes of Cy-Bu-D and Cy-He-D were dominated by H-aggregation.The H-aggregation by dimerization suppresses the radiative singlet decay,which helps to stabilize the highly efficient triplet excitation state.Moreover,the dimers show more intensewavelength absorption in the nearinfrared(ɛ1.5-2.0 times more than monomer Cy-H at 650 nm),better singlet oxygen quantum yield,and a longer triplet-state lifetime than monomer Cy-H,providing excellent performance as a triplet PS.In vivo experiments demonstrated that Cy-He-D successfully suppresses tumor growth after PDT treatment.This work is beneficial to the design of novel heavy atom free PSs for PDT-based theranostic systems.展开更多
We report for the first time a practical and simple supramolecular approach to turn fluorophores into photosensitizers(PSs).Using boron dipyrromethene(BODIPY)as a proof-of-concept,eight BODIPY derivatives manifest bri...We report for the first time a practical and simple supramolecular approach to turn fluorophores into photosensitizers(PSs).Using boron dipyrromethene(BODIPY)as a proof-of-concept,eight BODIPY derivatives manifest bright fluorescence and generate negligible singlet oxygen in solution.In contrast,aggregation fails to emit fluorescence and enhances singlet oxygen generation.Experimentally,these aggregates have excellent photodynamic therapy(PDT)performance,and one even exhibits much stronger photocytotoxicity than the commercialized PS Ce6 under identical conditions.Theoretical studies show that this property originated from significantly reduced energy gaps between relevant excited singlet and triplet states,leading to considerably improved intersystem-crossing efficiency.Importantly,a simple disaggregation recovers the original properties of the fluorophores.This reversible switching property between fluorophores and PSs assists the development of smart PDT systems,in which singlet oxygen generation in tumors can be controlled in an intelligent manner after PDT treatment.The present work provides a novel strategy to design heavy-atom-free PSs and may pave the way to the development of smart PDT systems.展开更多
Organic scintillators that efficiently generate bright triplet excitons are of critical importance for highperformance X-ray-excited luminescence in radiation detection.However,the nature of triplet-singlet spinforbid...Organic scintillators that efficiently generate bright triplet excitons are of critical importance for highperformance X-ray-excited luminescence in radiation detection.However,the nature of triplet-singlet spinforbidden transitions in these materials often result in long-lived phosphorescence,which is undesirable for ultrafast X-ray detection and imaging.Here we demonstrate that the effect of hybridized local and charge-transfer(HLCT)excited states enables organic scintillators to exhibit highly efficient and fast radioluminescence(RL)in response to X-ray irradiation.Our experimental and theoretical investigation shows that the oxidized 1,8-naphthalimide-phenothiazine dyad(OMNI-PTZ 2)with HLCT-excited states has an enhanced overlap integral of the highest occupied molecular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO)on MNIπ-orbitals,and moderate donor–acceptor electron interactions.As a result,the RL of these crystals exhibits a 61-fold increase and its monoexponential decay lifetime is three orders of magnitude faster compared to its corresponding thermally activated delayed fluorescence(TADF)molecule MNI-PTZ 1.We further demonstrate the practical utility of the OMNI-PTZ 2(G)in high-performance X-ray detection and imaging,achieving an X-ray dose sensitivity of 97 nGy s−1 and an exceptional spatial resolution of 20 lp/mm.Our study provides a promising molecular design principle for utilizing triplet excitons to develop high-efficiency and fast X-ray scintillators for the development of next-generation flexible and stretchable X-ray imaging detectors.展开更多
Most of acridine based thermally activated delayed fluorescence(TADF)emitters are characterized by advantageous reverse intersystem crossing(RISC)rate(kRISCs)due to the perpendicular orientation of the acridine donor ...Most of acridine based thermally activated delayed fluorescence(TADF)emitters are characterized by advantageous reverse intersystem crossing(RISC)rate(kRISCs)due to the perpendicular orientation of the acridine donor to the acceptor moiety,but suffer from a poor radiation rate(kr)typically in the order of 10^(6) s^(−1).Herein,two sky blue TADF emitters 3,6-DMAC-AD-Py and 3,6-SFAC-AD-Py were developed by linking acridine(DMAC)and spiro-fluorene-acridine(SFAC)donors to 10-(pyridin-2-yl)acridin-9(10H)-one(AD-Py)acceptor.Larger SFAC and electron-deficient pyridyl groups are deliberately incorporated in 3,6-SFACAD-Py since the unique through-space interaction between them is designed to drive the rotation of inner acridine ring in SFAC for enhancing frontier molecular orbitals overlap while keeping a decent TADF behavior.Thus,the kr of 3,6-SFACAD-Py is increased to 1.5×10^(7) s^(−1).Simultaneously,SFAC donors improve spin orbital coupling strength and reduce the energy gaps,generating kRISC of 1.8×10^(6) s^(−1).This is the first acridine donor based TADF emitter realizing kr of 10^(7) s^(−1) and kRISC of 10^(6) s^(−1) by a through-space interaction strategy.3,6-SFACAD-Py enables a highly efficient sky-blue organic light-emitting diode with a maximum external quantum efficiency(EQE)of 34.7%and Commission International de I'Eclairage coordinates of(0.19,0.37).More importantly,the EQE still remained 27.6%and 16.9%at high brightness of 1000 and 10,000 cd m^(−2).展开更多
The reaction of Nb＋ with CS2, producing cationic transition-metal sulfide and CS, was taken as a representative example to elucidate the overall mechanism of reactions of second- row early transition metal ions with ...The reaction of Nb＋ with CS2, producing cationic transition-metal sulfide and CS, was taken as a representative example to elucidate the overall mechanism of reactions of second- row early transition metal ions with CS2. The reactions in both triplet and quintet state were studied by using the UB3LYP density functional method with the Stuttgart pseudo potentials and corresponding basis sets for Nb＋ and the standard 6-311＋G（2d） basis sets for C and S. The geometries for reactants, the transition states, and the products were completely optimized. All the transition states were verified by vibrational analysis and intrinsic reaction coordinate calculations. The results show that the reaction mechanism between niobium ion and CS2 is an insertion-elimination mechanism. Intersystem crossing may occur in the reaction Nb＋ with CS2 and a minimum energy crossing point was found.展开更多
Room-temperature phosphorescence（RTP） materials have attracted great attention due to their involvement of excited triplet states and comparatively long decay lifetimes.In this short review,recent progress on enhanc...Room-temperature phosphorescence（RTP） materials have attracted great attention due to their involvement of excited triplet states and comparatively long decay lifetimes.In this short review,recent progress on enhancement of RTP from purely organic materials is summarized.According to the mechanism of phosphorescence emission,two principles are discussed to construct efficient RTP materials：one is promoting intersystem crossing（ISC） efficiency by using aromatic carbonyl,heavyatom,or/and heterocycle/heteroatom containing compounds;the other is suppressing intramolecular motion and intermolecular collision which can quench excited triplet states,including embedding phosphors into polymers and packing them tightly in crystals.With aforementioned strategies,RTP from purely organic materials was achieved both in fluid and rigid media.展开更多
Thermally activated delayed fluorescence(TADF)organic molecules feature with long-lived delayed fluorescence,because they can undergo not only efficient intersystem crossing(ISC),but also efficient reverse intersystem...Thermally activated delayed fluorescence(TADF)organic molecules feature with long-lived delayed fluorescence,because they can undergo not only efficient intersystem crossing(ISC),but also efficient reverse intersystem crossing(RISC)at room temperature.As a new type of luminescent molecules,they have exhibited successful applications in organic light emitting diodes(OLEDs).Aside from OLEDs,they are also found to have potential applications in time-resolved luminescence imaging based on long-lived fluorescence property.Meanwhile,due to their excited triplet characteristic originated from efficient ISC,they were found to be applied in triplet-triplet annihilation upconversion(TTA-UC),photodynamic therapy(PDT)and organic photocatalytic synthesis.This review briefly summarizes the characteristics and excellent photophysical properties of TADF organic compounds,then covers their applications to date aside from OLEDs based on their highly efficient ISC ability and RISC ability at room temperature.展开更多
Clinical phototheranostic agents suffer from low absorption in near-infrared(NIR)region,decreasing singlet oxygen quantum yield(^(1)O_(2)QY)caused by aggregation in water,and low photothermal conversion efficiency(PCE...Clinical phototheranostic agents suffer from low absorption in near-infrared(NIR)region,decreasing singlet oxygen quantum yield(^(1)O_(2)QY)caused by aggregation in water,and low photothermal conversion efficiency(PCE),all of which are factors weakening their phototheranostic efficacy.Herein,we designed and synthesized a donor-acceptor-donor(D-A-D)structured boron-dipyrromethene derivative(B-2TPA)which exhibited NIR absorption and fluorescence.After being encapsulated in amphiphilic distearoyl phosphoethanolamine polyethyleneglycol 2000(DSPE-PEG-2000),the water-soluble B-2TPA nanoparticles(NPs)had increasing^(1)O_(2)QY(6.7%)due to the intermolecular aggregation-induced decrease in the energy gap between singlet and triplet excited states.Moreover,the quenched fluorescence and stable twisted intramolecular charge transfer in aggregates further increased the PCE of B-2TPA NPs to 60.1%.In vitro and in vivo studies confirmed that B-2TPA NPs could be used in NIR fluorescence and photoacoustic imagingguided synergistic photodynamic and photothermal therapy in tumor treatment.展开更多
Thioxo/dithioxo-naphthalimide is a class of rarely visited fluorophore,first synthesized in 1999.Facile chemistry was devised to achieve mono or dual thionation of the two carbonyl groups of 1,8-naphthalimide.Thionati...Thioxo/dithioxo-naphthalimide is a class of rarely visited fluorophore,first synthesized in 1999.Facile chemistry was devised to achieve mono or dual thionation of the two carbonyl groups of 1,8-naphthalimide.Thionation effectively shifts absorption maximum to longer spectral wavelength,significantly increase absorption coefficients,and dramatically enhances intersystem crossing efficiency with respect to their oxo-analogues.They were first explored as potent photocleavers to induce DNA strand break and novel photosensitizers for photodynamic therapies.In recent years,the unique chemistry of thioxo groups has been harnessed to achieve new applications,such as fluorescent sensors for heave metal ions.These unique photochemical and photophysical characteristics revitalize them intriguing functional molecules to investigate.In this short review,we wish to revisit their first discovery,facile synthesis,and the endeavors on the use of thioxo/dithioxo-naphthalimides for novel chemical and biomedical applications.展开更多
Efficient yield of^(1)O_(2)determines the photocatalytic degradation rate of antibiotics,but the regulatory mechanism for^(1)O_(2)selective generation in O_(2)activation is still lacking exploration.Herein,oxygen vaca...Efficient yield of^(1)O_(2)determines the photocatalytic degradation rate of antibiotics,but the regulatory mechanism for^(1)O_(2)selective generation in O_(2)activation is still lacking exploration.Herein,oxygen vacancy(OV)modification strategy of MIL-125 was successfully practiced to promote the selective generation of^(1)O_(2).Multiple characterizations including extended X-ray absorption fine structure(EXAFS)and electron paramagnetic resonance spectra(EPR)confirmed the formation of oxygen vacancy in OV-MIL-125.The synthesized OV-MIL-125 exhibited greatly enhanced^(1)O_(2)selective(~90%)and antibiotics removal rate in water with high mineralization rate.Dynamics analysis of excitons by transient-steady state fluorescence and phosphorescence,transient absorption spectra(TAS)revealed that oxygen vacancy greatly enhanced the intersystem crossing(ISC)of singlet exciton,promoting triplet exciton generation.Density functional theoretical(DFT)calculation also proved the reduced gap of intersystem(ΔE_(ST))and the modulated highest occupied molecular orbital(HOMO)-lowest unoccupied molecular orbital(LUMO)population which was conducive to intersystem crossing process.Calculation of transition state further confirmed the lower energy barrier forπ^(*)orbital spin flip of O_(2)adsorbed on OV-MIL-125.The Dexter energy transfer involving triplet annihilation dominated the O_(2)activation mechanism to generate^(1)O_(2)instead of the charge transfer to generate O_(2)^(·-)which happened in MIL-125.This study provides new thinking for photocatalytic activation of molecular oxygen and is expected to guide the design of MOF-based catalysts for water treatment.展开更多
2,7-Di（9,9-dimethyl-9H-fluoren-l-yl）-9H-thioxanthen-9-one （DMBFTX） with thermally activated delayed fluorescence （TADF） was well designed and synthesized. The phosphorescent organic lightemitting device （PHOLED...2,7-Di（9,9-dimethyl-9H-fluoren-l-yl）-9H-thioxanthen-9-one （DMBFTX） with thermally activated delayed fluorescence （TADF） was well designed and synthesized. The phosphorescent organic lightemitting device （PHOLED） based on this novel TADF host material displays a stable red phosphorescence region, a peak external quantum efficiency （EQE） value of 12.9% and a low EQE roll-off of 38.8%at a luminance of 10000 cd/m2, which is benefited from the reverse intersystem crossing （RISC） of TADF host and less populated triplet exitons. Notably, the red device based on the TADF host DMBFrX exhibits superior electroluminescence performance and reduced efficiency roll-offcompared with the one hosted by commercially available host 1,3-bis（9-carbazolyl）benzene （mCP）, illustrating the high potential of employing the TADF host material with small energy gap to reduce efficiency roll-off in PHOLED.展开更多
The behavior of room temperature phosphorescence quenching and fluorescence enhancing of gadolinium labeled sinoporphyrin sodium(Gd-DVDMS) in the aqueous solution were studied.Gd-DVDMS was characterized by various tec...The behavior of room temperature phosphorescence quenching and fluorescence enhancing of gadolinium labeled sinoporphyrin sodium(Gd-DVDMS) in the aqueous solution were studied.Gd-DVDMS was characterized by various techniques including mass spectra,Fourier transform infrared spectra and transmission electron microscopy.The optical behavior was monitored through UV-vis absorption spectra and photoluminescence spectra.The result shows that the phosphorescence intensity gradually quenches,almost disappears after dissolved 120 min,meanwhile the fluorescence intensity enhances 5 times.The above behavior is attributed to the decreased population of Gd-DVDMS as first excited triplet state(T1),Based on the time-invariant of both absorption spectra and phosphorescence decay curves at710 nm of Gd-DVDMS in different dissolution time,the reason for the decreased population of GdDVDMS in T1 state is that the intersystem crossing from first excited state(S1) to T1 is prevented.In addition,the fluorescent decay curves of Gd-DVDMS initially dissolved in the aqueous solution and dissolved for 120 min were also measured for comparison.The big change in fluorescent lifetime further proves the conclusion that intersystem crossing is prevented,meanwhile,the increase in fluorescence intensity is demonstrated.In this work,the possibility of decomposition of Gd-DVDMS is excluded because the phosphorescence decay curve in Gd-DVDMS aqueous solution is sensible to DVDMS.展开更多
We report on the observation of new fluorescence emission spectral transitions obtained from NO diatomic molecule in the region from ultraviolet （UV） to near infrared （NIR） in a low power glow discharge system. Th...We report on the observation of new fluorescence emission spectral transitions obtained from NO diatomic molecule in the region from ultraviolet （UV） to near infrared （NIR） in a low power glow discharge system. This glow discharge electronic excitation populates different quartet and doublet states of NO in its proximity such as the A2Z （/9 = 2）, b4∑- （υ= 3）, B2М （1） = 4）, and X2Л （u= 33-32） states. Due to inter-system crossing, emission lines originating from these levels to lower lying states are recorded and spectral line assignments are performed. The observed systems include b4∑- a4∏, B21∏-a4∏, a4∏-X2I∏, A2∑X2∏, X2∏-X2∏ （33-15）, X2∏-X2∏ （33-17）, X2∏-X2∏ （33-20）, and X2∏-X2∏ （33- 18）. This new information will conduce to the better understanding of the interesting features of NO molecule. Such parameters that affect the recording of low density of NO molecules are also discussed In addition to the factors such as the time evolution, argon gas concentration relative to NO mixture, the percentage of NO molecular gas concentration, discharge electric current signals and discharge applied voltage are studied. Those factors would enhance the fluorescence signal intensity of NO molecules. The recent results might be significant as reference data for optimizing the glow discharge spectrometer and diagnostics of NO gas.展开更多
The mechanism of photocycloaddition reaction between 6-azauracll and acetone was studied by using semiemptrical SCFMO AMI method. It was found that this reaction is not a concerted one. The calculated results are as f...The mechanism of photocycloaddition reaction between 6-azauracll and acetone was studied by using semiemptrical SCFMO AMI method. It was found that this reaction is not a concerted one. The calculated results are as follows:(1) A T1 state exciplex is on the T1 state energy surface; (2) T exciplex as a reactant will proceed along the energy surface of T1 state to form a diradical intermediate. The energy barrier of this reaction step is 63. 6 kJ/mol; (3) The T1 state diradical intermediate happens to be close in energy to the ground state intermediate with a similar geometry. Such a situation turns out to be very favorable for an intersystem crossing (jump from the T, state to the ground state) ; (4) The final product will be formed from the ground S0 state intermediate via an energy barrier 88. 2 kJ/mol.展开更多
The photochemical reaction of bicyclo[4.1.0]heptane was studied at the complete active space SCF（CASSCF） level with a 6-31G^＊ basis set. A muhireference MP2 algorithm that has been implemented in the Gaussian progr...The photochemical reaction of bicyclo[4.1.0]heptane was studied at the complete active space SCF（CASSCF） level with a 6-31G^＊ basis set. A muhireference MP2 algorithm that has been implemented in the Gaussian program was used to correct the energetics for the dynamic correlation. Starting from the Franck-Condon excitation of bicyclo [ 4.1.0 ] heptane, the reaction is via two bonds＇ breakage to give rise to 1,6-heptdiene. One internal conversion （IC） and two intersystem crossing points（ISC） were located and are discussed separately. The reaction proceeds to its own characteristic product on the ground state.展开更多
基金supported by the National Natural Science Foundation of China(No.22273057)the Universities Joint Laboratory of Guangdong,Hong Kong and Macao(No.2021LSYS009)+2 种基金the Natural Science Foundation of Guangdong Province(Nos.2022A1515011661,2023A1515012631)the Chemistry and Chemical Engineering Guangdong Laboratory(No.1922003)Guangdong Major Project of Basic and Applied Basic Research(No.2019B030302009)。
文摘The excited state dynamics and critically regulated factors of reverse intersystem crossing(RISC)in through-space charge transfer(TSCT)molecules have received insufficient attention.Here,five molecules of through space/bond charge transfer inducing thermally activated delayed fluorescence(TADF)are prepared,and their excited state charge transfer processes are studied by ultrafast transient absorption and theoretical calculations.DM-Z has a largerΔEST,leading to a longer lifetime of intersystem crossing(ISC),resulting in the lowest photoluminescence quantum yield(PLQY).Oppositely,ISC and RISC are demonstrated to take place with shorter lifetimes for TSCT molecules.The face-to-faceπ-πstacking interactions and electron communication enable DM-B and DM-BX to have an efficient RISC,increasing the weight coefficient of RISC from 1.7%(DM-X)to close to 50%(DM-B and DM-BX)in the solvents,which make DM-BX and DM-B to have a high PLQY.However,partial local excitation in the donor center is observed and the charge transfer is decreased for DM-G and DM-X.The triplet excited state(DM-G)or singlet excited state(DM-X)mainly undergoes inactivation through a non-radiative relaxation process,resulting in less RISC and low PLQY.This work provides theoretical hints to enhance the RISC process in the TADF materials.
基金The financial supports of the National Natural Science Foundation of China (grant nos. 21373042, 21677029 and 51402036)the Fundamental Research Funds for the Central Universities (grant no. DUT15YQ109)
文摘Recently, an effective exciton diffusion length L exceeding 100μm has been reported for organic- inorganic halide perovskites owing to both the high mobility and ultra-long lifetime of the excitons; however, the origin of ultra-long L is still unclear in nature. In some photoelectric materials, reverse intersystem crossing （RISC） from the triplet to the singlet state can enhance the quantum yield of pho- toluminescence greatly. In this study, our theoretical investigation indicated that the energy difference △E_st between the singlet state and the triplet state of CH_3NH_3Pbl_3 was less than 0.1 eV, which represents one crucial prerequisite for the occurrence of RISC. Meanwhile, the experimental results showed that the photoluminescence lifetime increased with the increasing temperature, a typical feature of RISC. Based on this study, we put forward the hypothesis that the ultra-long lifetime of excitons in organic-inorganic halide perovskite might be caused by the RISC process. This may provide a new insight into the important photophysical properties of such novel photovoltaic materials.
基金support from the National Natural Science Foundation of China(52003298)the Natural Science Foundation of Jiangsu Province(BK20200578)+4 种基金funding from the Beijing University of Technology(049000513202 and 049000514123564)support of the Research Grants Council of Hong Kong(C6014-20W)the Innovation and Technology Commission(ITC-CNERC14SC01)Shenzhen Key Laboratory of Functional Aggregate Materials(ZDSYS20211021111400001)the Science Technology Innovation Commission of Shenzhen Municipality(KQTD20210811090142053 and JCYJ2022081810-3007014).
文摘Circularly polarized luminescence(CPL)materials with delayed fluorescence have attracted much attention due to their ability to efficiently trap triplet state excitons,thereby improving the photoluminescence quantum yields of CPL materials.However,much effort has been normally focused on the utilization of T1 excitons but seldom on the utilization of higher excited triplet state T_(n)(n>1)excitons.Rational manipulation of higher excited triplet state T_(n)(n>1)excitons and suppression of Kasha’s rule of CPL materials remains a major challenge.Herein,two gold complex enantiomers((R/S)-BPAuBC)based on axially chiral binaphthyls and 3,6-Di-tert-butylcarbazole groups are synthesized and systematically investigated.These materials exhibit aggregation-induced circularly polarized delayed fluorescence.Circularly polarized delayed fluorescence was found to be enabled by activating high-level reverse intersystem crossing(hRISC).The anti-Kasha phosphorescence at 77 K proves that the exciton has a large population in the high-lying triplet state T_(2),which allows the effective hRISC process to cross back to the singlet state S_(1)and emit delayed fluorescence.In addition,CPL“on-off”switching is further achieved in nanoparticles by acid-base stimulus,showing its potential as an acid-base responsive material.
基金the China Scholarship Council(grant no.202106310038)for supportsupport from the China Postdoctoral Science Foundation(grant no.2022TQ0227)+2 种基金the Natural Science Foundation of Jiangsu Province,China(grant no.BK20230508)the China Scholarship Council(grant no.201906250199)support from the National Natural Science Foundation of China(grant no.52130304)the Suzhou Key Laboratory of Functional Nano&Soft Materials,the Collaborative Innovation Center of Suzhou Nano Science&Technology,the 111 Project.
文摘The development of circularly polarized multiresonant thermally activated delayed fluorescence materials with fast reverse intersystem crossing(RISC)process remains a challenge.Herein,we introduce high-lying excited states to assist the RISC process.Through arranging two known MR-TADF emitters tCzBN and DiKTa at the pseudo-ortho position of a chiral skeleton paracyclophane(PCP),the excitedstate density was increased.The proof-of-concept emitter po-PCP-tCzBN-DiKTa shows nearly three times higher kRISC(5.31×10^(4) s^(−1))than PCP-tCzBN(1.73×10^(4) s^(−1))without compromising color purity and exhibiting circularly polarized luminescence with|gPL|values at the 10^(−4) level.The solution-processed organic light-emitting diodes with po-PCP-tCzBNDiKTa show high maximum external quantum efficiency(EQE_(max))reaching 23%with a moderate efficiency roll-off,showing EQE of 18%and 9%at 100 and 1000 cd/m^(2.)
文摘The intersystem crossing channels of gaseous 4H-pyran-4-thione were investigated using the CASSCF//TD-B3LYP methods and group theory. Using the effective one-electron spin-orbit Harniltonian, the strengths of spin-orbit coupling were estimated, which plays an essential role in the spin transitions between different spin states. Calculated results show that phosphorescence and non-radiative decay via intersystem crossing to the So state are concurrent processes occurring at the T1 state. A rapid depletion of the S1 state via intersystem crossing to the T1 state can be mediated by the T2 state, if spin relaxation is fast within the triplet levels. Our calculated results are in close agreement with experimental observations.
基金This work was supported by National Natural Science Foundation of China(project 22090011)NSFCLiaoning United Fund(U1908202).
文摘Development of new photosensitizers(PSs)with high singlet oxygen quantumyield and minimal side effects is of great interest in photodynamic therapy(PDT).Herein,a facile strategy to significantly improve photosensitization has been demonstrated for the first time with two pentamethine dyes connected by a varying alkyl chain resulting in a series of cyanine dimers.The photophysical properties of the dimerswere studied with steady-state optical spectroscopies,a timecorrelated single photon counting technique,and laser flash photolysis spectrometry.X-ray crystallography confirmed that the molecular packing modes of Cy-Bu-D and Cy-He-D were dominated by H-aggregation.The H-aggregation by dimerization suppresses the radiative singlet decay,which helps to stabilize the highly efficient triplet excitation state.Moreover,the dimers show more intensewavelength absorption in the nearinfrared(ɛ1.5-2.0 times more than monomer Cy-H at 650 nm),better singlet oxygen quantum yield,and a longer triplet-state lifetime than monomer Cy-H,providing excellent performance as a triplet PS.In vivo experiments demonstrated that Cy-He-D successfully suppresses tumor growth after PDT treatment.This work is beneficial to the design of novel heavy atom free PSs for PDT-based theranostic systems.
基金This research was made possible as a result of generous grants from the National Natural Science Foundation of China(nos.22177014,21971023,21688102 and 21525206).
文摘We report for the first time a practical and simple supramolecular approach to turn fluorophores into photosensitizers(PSs).Using boron dipyrromethene(BODIPY)as a proof-of-concept,eight BODIPY derivatives manifest bright fluorescence and generate negligible singlet oxygen in solution.In contrast,aggregation fails to emit fluorescence and enhances singlet oxygen generation.Experimentally,these aggregates have excellent photodynamic therapy(PDT)performance,and one even exhibits much stronger photocytotoxicity than the commercialized PS Ce6 under identical conditions.Theoretical studies show that this property originated from significantly reduced energy gaps between relevant excited singlet and triplet states,leading to considerably improved intersystem-crossing efficiency.Importantly,a simple disaggregation recovers the original properties of the fluorophores.This reversible switching property between fluorophores and PSs assists the development of smart PDT systems,in which singlet oxygen generation in tumors can be controlled in an intelligent manner after PDT treatment.The present work provides a novel strategy to design heavy-atom-free PSs and may pave the way to the development of smart PDT systems.
基金supported by the National Key R&D Program of China(grant no.2020YFA0709900)the National Natural Science Foundation of China(grant nos.21971041,22201042,22027805,62134003,and 22104016)+2 种基金the Natural Science Foundation of Fujian Province(grant nos.2020J01447,2022J06008,and 2022J0121)the Research Foundation of Education Bureau of Fujian Province(grant no.JAT210001)the Fuzhou University Testing Fund of Precious Apparatus(grant no.2022T001).
文摘Organic scintillators that efficiently generate bright triplet excitons are of critical importance for highperformance X-ray-excited luminescence in radiation detection.However,the nature of triplet-singlet spinforbidden transitions in these materials often result in long-lived phosphorescence,which is undesirable for ultrafast X-ray detection and imaging.Here we demonstrate that the effect of hybridized local and charge-transfer(HLCT)excited states enables organic scintillators to exhibit highly efficient and fast radioluminescence(RL)in response to X-ray irradiation.Our experimental and theoretical investigation shows that the oxidized 1,8-naphthalimide-phenothiazine dyad(OMNI-PTZ 2)with HLCT-excited states has an enhanced overlap integral of the highest occupied molecular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO)on MNIπ-orbitals,and moderate donor–acceptor electron interactions.As a result,the RL of these crystals exhibits a 61-fold increase and its monoexponential decay lifetime is three orders of magnitude faster compared to its corresponding thermally activated delayed fluorescence(TADF)molecule MNI-PTZ 1.We further demonstrate the practical utility of the OMNI-PTZ 2(G)in high-performance X-ray detection and imaging,achieving an X-ray dose sensitivity of 97 nGy s−1 and an exceptional spatial resolution of 20 lp/mm.Our study provides a promising molecular design principle for utilizing triplet excitons to develop high-efficiency and fast X-ray scintillators for the development of next-generation flexible and stretchable X-ray imaging detectors.
基金the National Natural Science Foundation of China(22078051,22478063,22408035)the Fundamental Research Funds for the Central Universities(DUT22-LAB610)the Open Fund of the Key Laboratory of Advanced Display and System Applications,Ministry of Education,Shanghai University(OF202401)for financial support of this work.
文摘Most of acridine based thermally activated delayed fluorescence(TADF)emitters are characterized by advantageous reverse intersystem crossing(RISC)rate(kRISCs)due to the perpendicular orientation of the acridine donor to the acceptor moiety,but suffer from a poor radiation rate(kr)typically in the order of 10^(6) s^(−1).Herein,two sky blue TADF emitters 3,6-DMAC-AD-Py and 3,6-SFAC-AD-Py were developed by linking acridine(DMAC)and spiro-fluorene-acridine(SFAC)donors to 10-(pyridin-2-yl)acridin-9(10H)-one(AD-Py)acceptor.Larger SFAC and electron-deficient pyridyl groups are deliberately incorporated in 3,6-SFACAD-Py since the unique through-space interaction between them is designed to drive the rotation of inner acridine ring in SFAC for enhancing frontier molecular orbitals overlap while keeping a decent TADF behavior.Thus,the kr of 3,6-SFACAD-Py is increased to 1.5×10^(7) s^(−1).Simultaneously,SFAC donors improve spin orbital coupling strength and reduce the energy gaps,generating kRISC of 1.8×10^(6) s^(−1).This is the first acridine donor based TADF emitter realizing kr of 10^(7) s^(−1) and kRISC of 10^(6) s^(−1) by a through-space interaction strategy.3,6-SFACAD-Py enables a highly efficient sky-blue organic light-emitting diode with a maximum external quantum efficiency(EQE)of 34.7%and Commission International de I'Eclairage coordinates of(0.19,0.37).More importantly,the EQE still remained 27.6%and 16.9%at high brightness of 1000 and 10,000 cd m^(−2).
文摘The reaction of Nb＋ with CS2, producing cationic transition-metal sulfide and CS, was taken as a representative example to elucidate the overall mechanism of reactions of second- row early transition metal ions with CS2. The reactions in both triplet and quintet state were studied by using the UB3LYP density functional method with the Stuttgart pseudo potentials and corresponding basis sets for Nb＋ and the standard 6-311＋G（2d） basis sets for C and S. The geometries for reactants, the transition states, and the products were completely optimized. All the transition states were verified by vibrational analysis and intrinsic reaction coordinate calculations. The results show that the reaction mechanism between niobium ion and CS2 is an insertion-elimination mechanism. Intersystem crossing may occur in the reaction Nb＋ with CS2 and a minimum energy crossing point was found.
基金the financial support from The National Basic Research Program of China(No.2014CB643802)Ministry of Science and Technology(No.2016YFB0401001)the State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals
文摘Room-temperature phosphorescence（RTP） materials have attracted great attention due to their involvement of excited triplet states and comparatively long decay lifetimes.In this short review,recent progress on enhancement of RTP from purely organic materials is summarized.According to the mechanism of phosphorescence emission,two principles are discussed to construct efficient RTP materials：one is promoting intersystem crossing（ISC） efficiency by using aromatic carbonyl,heavyatom,or/and heterocycle/heteroatom containing compounds;the other is suppressing intramolecular motion and intermolecular collision which can quench excited triplet states,including embedding phosphors into polymers and packing them tightly in crystals.With aforementioned strategies,RTP from purely organic materials was achieved both in fluid and rigid media.
基金financially supported by the National Natural Science Foundation of China(Nos.21877011,21576038,21421005)the Talent Fund of Shandong Collaborative Innovation Center of Eco-Chemical Engineering(No.XTCXYX03)
文摘Thermally activated delayed fluorescence(TADF)organic molecules feature with long-lived delayed fluorescence,because they can undergo not only efficient intersystem crossing(ISC),but also efficient reverse intersystem crossing(RISC)at room temperature.As a new type of luminescent molecules,they have exhibited successful applications in organic light emitting diodes(OLEDs).Aside from OLEDs,they are also found to have potential applications in time-resolved luminescence imaging based on long-lived fluorescence property.Meanwhile,due to their excited triplet characteristic originated from efficient ISC,they were found to be applied in triplet-triplet annihilation upconversion(TTA-UC),photodynamic therapy(PDT)and organic photocatalytic synthesis.This review briefly summarizes the characteristics and excellent photophysical properties of TADF organic compounds,then covers their applications to date aside from OLEDs based on their highly efficient ISC ability and RISC ability at room temperature.
基金supported by National Key Research and Development Program of China(No.2022YFA1207600)National Natural Science Foundation of China(Nos.62175262,62375289)+2 种基金The Science and Technology Innovation Program of Hunan Province(No.2022RC1201)The Climb Plan of Hunan Cancer Hospital(No.ZX2021005)The Hunan Provincial Natural Science Foundation of China(No.2023JJ60464)。
文摘Clinical phototheranostic agents suffer from low absorption in near-infrared(NIR)region,decreasing singlet oxygen quantum yield(^(1)O_(2)QY)caused by aggregation in water,and low photothermal conversion efficiency(PCE),all of which are factors weakening their phototheranostic efficacy.Herein,we designed and synthesized a donor-acceptor-donor(D-A-D)structured boron-dipyrromethene derivative(B-2TPA)which exhibited NIR absorption and fluorescence.After being encapsulated in amphiphilic distearoyl phosphoethanolamine polyethyleneglycol 2000(DSPE-PEG-2000),the water-soluble B-2TPA nanoparticles(NPs)had increasing^(1)O_(2)QY(6.7%)due to the intermolecular aggregation-induced decrease in the energy gap between singlet and triplet excited states.Moreover,the quenched fluorescence and stable twisted intramolecular charge transfer in aggregates further increased the PCE of B-2TPA NPs to 60.1%.In vitro and in vivo studies confirmed that B-2TPA NPs could be used in NIR fluorescence and photoacoustic imagingguided synergistic photodynamic and photothermal therapy in tumor treatment.
基金the National Natural Science Foundation of China(Nos.21822805 and 21908065)Shanghai Municipal Science and Technology Commission(No.18DZ1112703)China Postdoctoral Science Foundation(No.2019M651427)。
文摘Thioxo/dithioxo-naphthalimide is a class of rarely visited fluorophore,first synthesized in 1999.Facile chemistry was devised to achieve mono or dual thionation of the two carbonyl groups of 1,8-naphthalimide.Thionation effectively shifts absorption maximum to longer spectral wavelength,significantly increase absorption coefficients,and dramatically enhances intersystem crossing efficiency with respect to their oxo-analogues.They were first explored as potent photocleavers to induce DNA strand break and novel photosensitizers for photodynamic therapies.In recent years,the unique chemistry of thioxo groups has been harnessed to achieve new applications,such as fluorescent sensors for heave metal ions.These unique photochemical and photophysical characteristics revitalize them intriguing functional molecules to investigate.In this short review,we wish to revisit their first discovery,facile synthesis,and the endeavors on the use of thioxo/dithioxo-naphthalimides for novel chemical and biomedical applications.
基金supported by the National Natural Science Foundation of China(Nos.22276086 and 21976078)the Natural Science Foundation of Jiangxi Province(Nos.20202ACB213001 and20232BAB213029)。
文摘Efficient yield of^(1)O_(2)determines the photocatalytic degradation rate of antibiotics,but the regulatory mechanism for^(1)O_(2)selective generation in O_(2)activation is still lacking exploration.Herein,oxygen vacancy(OV)modification strategy of MIL-125 was successfully practiced to promote the selective generation of^(1)O_(2).Multiple characterizations including extended X-ray absorption fine structure(EXAFS)and electron paramagnetic resonance spectra(EPR)confirmed the formation of oxygen vacancy in OV-MIL-125.The synthesized OV-MIL-125 exhibited greatly enhanced^(1)O_(2)selective(~90%)and antibiotics removal rate in water with high mineralization rate.Dynamics analysis of excitons by transient-steady state fluorescence and phosphorescence,transient absorption spectra(TAS)revealed that oxygen vacancy greatly enhanced the intersystem crossing(ISC)of singlet exciton,promoting triplet exciton generation.Density functional theoretical(DFT)calculation also proved the reduced gap of intersystem(ΔE_(ST))and the modulated highest occupied molecular orbital(HOMO)-lowest unoccupied molecular orbital(LUMO)population which was conducive to intersystem crossing process.Calculation of transition state further confirmed the lower energy barrier forπ^(*)orbital spin flip of O_(2)adsorbed on OV-MIL-125.The Dexter energy transfer involving triplet annihilation dominated the O_(2)activation mechanism to generate^(1)O_(2)instead of the charge transfer to generate O_(2)^(·-)which happened in MIL-125.This study provides new thinking for photocatalytic activation of molecular oxygen and is expected to guide the design of MOF-based catalysts for water treatment.
基金supported by National Natural Science Foundation of China(No. 61605158)the Science and TechnologyDepartment of Shaanxi Province(No. 2016JQ2028)the Education Department of Shaanxi Province(No. 16JK1790)
文摘2,7-Di（9,9-dimethyl-9H-fluoren-l-yl）-9H-thioxanthen-9-one （DMBFTX） with thermally activated delayed fluorescence （TADF） was well designed and synthesized. The phosphorescent organic lightemitting device （PHOLED） based on this novel TADF host material displays a stable red phosphorescence region, a peak external quantum efficiency （EQE） value of 12.9% and a low EQE roll-off of 38.8%at a luminance of 10000 cd/m2, which is benefited from the reverse intersystem crossing （RISC） of TADF host and less populated triplet exitons. Notably, the red device based on the TADF host DMBFrX exhibits superior electroluminescence performance and reduced efficiency roll-offcompared with the one hosted by commercially available host 1,3-bis（9-carbazolyl）benzene （mCP）, illustrating the high potential of employing the TADF host material with small energy gap to reduce efficiency roll-off in PHOLED.
基金supported by the National Natural Science Foundation of China (81571720,81530052,81727809)。
文摘The behavior of room temperature phosphorescence quenching and fluorescence enhancing of gadolinium labeled sinoporphyrin sodium(Gd-DVDMS) in the aqueous solution were studied.Gd-DVDMS was characterized by various techniques including mass spectra,Fourier transform infrared spectra and transmission electron microscopy.The optical behavior was monitored through UV-vis absorption spectra and photoluminescence spectra.The result shows that the phosphorescence intensity gradually quenches,almost disappears after dissolved 120 min,meanwhile the fluorescence intensity enhances 5 times.The above behavior is attributed to the decreased population of Gd-DVDMS as first excited triplet state(T1),Based on the time-invariant of both absorption spectra and phosphorescence decay curves at710 nm of Gd-DVDMS in different dissolution time,the reason for the decreased population of GdDVDMS in T1 state is that the intersystem crossing from first excited state(S1) to T1 is prevented.In addition,the fluorescent decay curves of Gd-DVDMS initially dissolved in the aqueous solution and dissolved for 120 min were also measured for comparison.The big change in fluorescent lifetime further proves the conclusion that intersystem crossing is prevented,meanwhile,the increase in fluorescence intensity is demonstrated.In this work,the possibility of decomposition of Gd-DVDMS is excluded because the phosphorescence decay curve in Gd-DVDMS aqueous solution is sensible to DVDMS.
基金Project supported by the Funds from Laser Sciences and Interactions Department,National Institute of Laser Enhanced Sciences(NILES),Cairo University,Giza,Egyptthe Fund from the Department of Physics,Faculty of Science for Girls,Imam Abdulrahman Ben Faisal University(x-Dammam University)+1 种基金the Fund from Dammam 31441,Saudi Arabiathe Physics Department of King Fahd University of Petroleum and Minerals(KFUPM),Dhahran,Saudi Arabia
文摘We report on the observation of new fluorescence emission spectral transitions obtained from NO diatomic molecule in the region from ultraviolet （UV） to near infrared （NIR） in a low power glow discharge system. This glow discharge electronic excitation populates different quartet and doublet states of NO in its proximity such as the A2Z （/9 = 2）, b4∑- （υ= 3）, B2М （1） = 4）, and X2Л （u= 33-32） states. Due to inter-system crossing, emission lines originating from these levels to lower lying states are recorded and spectral line assignments are performed. The observed systems include b4∑- a4∏, B21∏-a4∏, a4∏-X2I∏, A2∑X2∏, X2∏-X2∏ （33-15）, X2∏-X2∏ （33-17）, X2∏-X2∏ （33-20）, and X2∏-X2∏ （33- 18）. This new information will conduce to the better understanding of the interesting features of NO molecule. Such parameters that affect the recording of low density of NO molecules are also discussed In addition to the factors such as the time evolution, argon gas concentration relative to NO mixture, the percentage of NO molecular gas concentration, discharge electric current signals and discharge applied voltage are studied. Those factors would enhance the fluorescence signal intensity of NO molecules. The recent results might be significant as reference data for optimizing the glow discharge spectrometer and diagnostics of NO gas.
文摘The mechanism of photocycloaddition reaction between 6-azauracll and acetone was studied by using semiemptrical SCFMO AMI method. It was found that this reaction is not a concerted one. The calculated results are as follows:(1) A T1 state exciplex is on the T1 state energy surface; (2) T exciplex as a reactant will proceed along the energy surface of T1 state to form a diradical intermediate. The energy barrier of this reaction step is 63. 6 kJ/mol; (3) The T1 state diradical intermediate happens to be close in energy to the ground state intermediate with a similar geometry. Such a situation turns out to be very favorable for an intersystem crossing (jump from the T, state to the ground state) ; (4) The final product will be formed from the ground S0 state intermediate via an energy barrier 88. 2 kJ/mol.
基金Supported by the Yunnan Provincial Science and Technology Department(No. 2003A0003M)
文摘The photochemical reaction of bicyclo[4.1.0]heptane was studied at the complete active space SCF（CASSCF） level with a 6-31G^＊ basis set. A muhireference MP2 algorithm that has been implemented in the Gaussian program was used to correct the energetics for the dynamic correlation. Starting from the Franck-Condon excitation of bicyclo [ 4.1.0 ] heptane, the reaction is via two bonds＇ breakage to give rise to 1,6-heptdiene. One internal conversion （IC） and two intersystem crossing points（ISC） were located and are discussed separately. The reaction proceeds to its own characteristic product on the ground state.
