Thermally activated delayed fluorescence(TADF)exciplexes,constituted of donor-acceptor moieties,have garnered mounting interest because of their promising potential to obtain high-performance electroluminescent device...Thermally activated delayed fluorescence(TADF)exciplexes,constituted of donor-acceptor moieties,have garnered mounting interest because of their promising potential to obtain high-performance electroluminescent devices.However,the moderate reverse intersystem crossing(RISC)of current reported exciplex systems and the lack of clear molecular design concepts to improve this situation have distinctly hindered the further use of exciplexes in organic light-emitting diodes(OLEDs).Herein,we conduct an exploration of exciplex systems founded upon[2,2]paracyclophane(PCP)-containing donor molecules and a triazine acceptor,which exhibit very fast RISC processes with a rate constant(k_(RISC))up to 8.3×10^(6) s^(-1)benefiting from the efficient interactions between the donor and acceptor fragments induced by the peripheral spatial-blocking of PCP group.Utilizing these deep-blue exciplexes as hosts and a multiple resonance(MR)molecule as emitter,pure-blue narrowband OLEDs with CIE coordinates of(0.124,0.137),a full-width at half-maximum(FWHM)of 23 nm,and a high external quantum efficiency(EQE)of around 30%are accessed.This study paves the way for developing blue OLEDs using PCP-based exciplex materials with an enhanced RISC process.展开更多
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
First-principles calculations are applied for investigating influence of electron donating ability of donor groups in eight thermally activated delayed fluorescence（TADF） molecules on their geometrical structures an...First-principles calculations are applied for investigating influence of electron donating ability of donor groups in eight thermally activated delayed fluorescence（TADF） molecules on their geometrical structures and transition properties as well as reverse intersystem crossing（RISC） processes. Results show that the diphenylamine substitution in the donor part can slightly change the bond angle but decrease bond length between donor and acceptor unit except for the lowest triplet state（Ti） of carbazole-xanthone molecule. As the electron donating ability of donor groups is increased, the overlap between the highest occupied molecular orbital（HOMO） and the lowest unoccupied molecular orbital（LUMO） is decreased. As the diphenylamine groups are added in donor part, the delocalization of HOMO is enlarged,which brings a decreased energy gap(△ES1-T1) between the lowest singlet excited state（S1）and T1 state. Furthermore, with the calculated spin-orbit coupling coefficient(HSO), one finds that the larger value of ■ is, the faster the RISC is. The results show that all investigated molecules are promising candidates as TADF molecules. Overall, a wise molecular design strategy for TADF molecules,in which a small △ES1-T1 can be achieved by enlarging the delocalization of frontier molecular orbitals with large separation between HOMO and LUMO, is proposed.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
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
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
开发了一种具有热激子性质的激发态分子内质子转移(Excited-state intramolecular proton transfer,ESIPT)橙光材料HBT-TPA,该材料以2-(2'-羟基苯基)苯并噻唑(HBT)作为ESIPT单元,修饰以强给电子基团三苯胺(TPA),赋予材料一定的电荷...开发了一种具有热激子性质的激发态分子内质子转移(Excited-state intramolecular proton transfer,ESIPT)橙光材料HBT-TPA,该材料以2-(2'-羟基苯基)苯并噻唑(HBT)作为ESIPT单元,修饰以强给电子基团三苯胺(TPA),赋予材料一定的电荷转移特性,使分子的醇式和酮式异构体激发态均呈现出混合局域电荷转移态(Hybridized local and charge transfer state,HLCT)性质。以HBT-TPA为发光材料制备的OLED器件呈现出橙光发射,其电致光谱的发光峰位于576 nm,对应的国际发光委员会(Commission Internationale de l'Eclairage,CIE)色坐标为(0.5007±0.0016,0.4883±0.0008)。器件的最大外量子效率及最大电流效率分别为2.0%和5.0cd/A,并获得了29.3%~43.9%的激子利用率。器件中较为高效的激子利用率是利用ESIPT发光材料中的酮式异构体通过高能级反向系间窜越(High-lying reverse intersystem crossing,hRISC)的热激子机制来实现的。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
基金supported by the National Key R&D Program of China(2022YFE0109000)the National Natural Science Foundation of China(21975152,92256304,U23A20593)+1 种基金the China Postdoctoral Science Foundation(2022M722028)the Deutsche Forschungsgemeinschaft(DFG)under Germany’s Excellence Strategy(3DMM2O-EXC-2082/1-390761711)。
文摘Thermally activated delayed fluorescence(TADF)exciplexes,constituted of donor-acceptor moieties,have garnered mounting interest because of their promising potential to obtain high-performance electroluminescent devices.However,the moderate reverse intersystem crossing(RISC)of current reported exciplex systems and the lack of clear molecular design concepts to improve this situation have distinctly hindered the further use of exciplexes in organic light-emitting diodes(OLEDs).Herein,we conduct an exploration of exciplex systems founded upon[2,2]paracyclophane(PCP)-containing donor molecules and a triazine acceptor,which exhibit very fast RISC processes with a rate constant(k_(RISC))up to 8.3×10^(6) s^(-1)benefiting from the efficient interactions between the donor and acceptor fragments induced by the peripheral spatial-blocking of PCP group.Utilizing these deep-blue exciplexes as hosts and a multiple resonance(MR)molecule as emitter,pure-blue narrowband OLEDs with CIE coordinates of(0.124,0.137),a full-width at half-maximum(FWHM)of 23 nm,and a high external quantum efficiency(EQE)of around 30%are accessed.This study paves the way for developing blue OLEDs using PCP-based exciplex materials with an enhanced RISC process.
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This work was supported by the National Natural Science Foundation of China(No.11374195 and No.21403133),the Taishan Scholar Project of Shandong Province,the Promotive Research Fund for Excellent Young and Middle-aged Scientists of Shandong Province(No.BS2014CL001),and the General Financial Grant from the China Postdoctoral Science Foundation(No.2014M560571).
文摘First-principles calculations are applied for investigating influence of electron donating ability of donor groups in eight thermally activated delayed fluorescence（TADF） molecules on their geometrical structures and transition properties as well as reverse intersystem crossing（RISC） processes. Results show that the diphenylamine substitution in the donor part can slightly change the bond angle but decrease bond length between donor and acceptor unit except for the lowest triplet state（Ti） of carbazole-xanthone molecule. As the electron donating ability of donor groups is increased, the overlap between the highest occupied molecular orbital（HOMO） and the lowest unoccupied molecular orbital（LUMO） is decreased. As the diphenylamine groups are added in donor part, the delocalization of HOMO is enlarged,which brings a decreased energy gap(△ES1-T1) between the lowest singlet excited state（S1）and T1 state. Furthermore, with the calculated spin-orbit coupling coefficient(HSO), one finds that the larger value of ■ is, the faster the RISC is. The results show that all investigated molecules are promising candidates as TADF molecules. Overall, a wise molecular design strategy for TADF molecules,in which a small △ES1-T1 can be achieved by enlarging the delocalization of frontier molecular orbitals with large separation between HOMO and LUMO, is proposed.
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).
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.)
文摘开发了一种具有热激子性质的激发态分子内质子转移(Excited-state intramolecular proton transfer,ESIPT)橙光材料HBT-TPA,该材料以2-(2'-羟基苯基)苯并噻唑(HBT)作为ESIPT单元,修饰以强给电子基团三苯胺(TPA),赋予材料一定的电荷转移特性,使分子的醇式和酮式异构体激发态均呈现出混合局域电荷转移态(Hybridized local and charge transfer state,HLCT)性质。以HBT-TPA为发光材料制备的OLED器件呈现出橙光发射,其电致光谱的发光峰位于576 nm,对应的国际发光委员会(Commission Internationale de l'Eclairage,CIE)色坐标为(0.5007±0.0016,0.4883±0.0008)。器件的最大外量子效率及最大电流效率分别为2.0%和5.0cd/A,并获得了29.3%~43.9%的激子利用率。器件中较为高效的激子利用率是利用ESIPT发光材料中的酮式异构体通过高能级反向系间窜越(High-lying reverse intersystem crossing,hRISC)的热激子机制来实现的。
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.
