The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample o...The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample of cold molecules, initially distributed over several vibrational levels, has thus been transfered into a single selected vibrational level of the singlet X^1∑g ground electronic state. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. In this paper we briefly report the main experimental results and then address, in a detailed way by computer simulations, the perspectives for a ＂complete＂ cooling of the molecules, including also the rotational degree of freedom. Since the pumping process strongly depends on the relative shape of the ground and excited potential curves, ro-vibrational cooling through different excited states is theoretically compared.展开更多
A new star-shaped molecule StOF-Br_3 containing oligofluorenes and halogen atoms(Bromine) has been synthesized and studied by Scanning Tunneling Microscopy(STM) at the highly oriented pyrolytic graphite(HOPG) surface....A new star-shaped molecule StOF-Br_3 containing oligofluorenes and halogen atoms(Bromine) has been synthesized and studied by Scanning Tunneling Microscopy(STM) at the highly oriented pyrolytic graphite(HOPG) surface.We have obtained the high-resolution self-assembled STM images,from which the highly ordered and closely packed non-porous arrangements of the StOF-Br_3 molecular selfassemblies at the heptanoic acid/HOPG surface could be observed.The molecular models and selfassembled StOF-Br_3 architectures have been given in the following text.Besides,we have also figured out the surface free energy by the density functional theory(DFT) calculation,which proved that the halogen...halogen interaction was strong enough to stabilize the ordered molecular self-assemblies.This work verifies the existence of bromine...bromine interactions,and meanwhile provides a kind of effective approach for quickly building ordered molecular nanoarchitectures with large areas and different geometries.展开更多
Coherent control has been achieved in atoms and small molecules in gas phase during the past few decades.An intriguing demonstration of coherent control is a so-called“dark pulse”that cancels 2-photon transition pro...Coherent control has been achieved in atoms and small molecules in gas phase during the past few decades.An intriguing demonstration of coherent control is a so-called“dark pulse”that cancels 2-photon transition probabilities despite exposing the target to the full power spectrum of transform-limited laser pulses.However,for larger functional molecules in condensed phase at room temperature,ensemble measurements do typically not allow exerting full control over competing pathways due to the unavoidable influence of the surrounding(mostly complex)environment.Here,we demonstrate room-temperature coherent control exploiting a nonresonant 2-photon transition into a higher excited state of single conjugated polymer chains embedded in a disordered matrix,including proof-of-principle experiments on bulk films.To manipulate the 2-photon transition probability,we exploit complex pulse sequences,created by a systematically varied cosinusoidal spectral phase applied to the excitation laser spectrum.For single molecules,the phase-dependent response varies from molecule to molecule,which reflects the spectral heterogeneity(position,linewidth)of their 2-photon transitions.These data indicate that coherent control of single molecules requires optimization of parameters for each individual molecule.The experimental data are reproduced by a simple model that allows to directly retrieve the 2-photon absorption spectrum of each single molecule.Our coherent-control approach is a powerful and robust way to obtain spectral characteristics of higher excited states of single molecules and to manipulate the excited-state dynamics in condensed phase at room temperature.It holds the potential to be useful for the characterization of complex organic functional materials.展开更多
Star-shaped oligothiophenes with hexakis（fluoren-2-yl）benzene （HFB） as cores were designed and synthesized. Grafting thiophene units to HFB results in a bond flattening of the core, and makes the molecules a flipp...Star-shaped oligothiophenes with hexakis（fluoren-2-yl）benzene （HFB） as cores were designed and synthesized. Grafting thiophene units to HFB results in a bond flattening of the core, and makes the molecules a flipping-twist shape. Their thermal, photophysical and electrochemical properties were studied. Highly cross-linked conjugated polymers can be produced by electropolymerization of T1-T3.展开更多
The effect of protector molecules on the formation of tetrahedral Pt nanocrystals during the H 2 reduction of aqueous K 2PtCl 6 solution was investigated. It was shown that the addition of sodium lactate or gluconate,...The effect of protector molecules on the formation of tetrahedral Pt nanocrystals during the H 2 reduction of aqueous K 2PtCl 6 solution was investigated. It was shown that the addition of sodium lactate or gluconate, which were good protectors for the synthesis of tetrahedral Ni nanocrystals, cannot result in the formation of tetrahedral Pt nanocrystals. On the other hand, the use of polyvinylpyrrolidone(PVP) for the protector has lead to fairly high selectivity(78%—83%) for the tetrahedral shape of Pt nanocrystals. Raman spectral results indicate that there is an interaction between the CO group of PVP and the surface of tetrahedral Pt nanocrystals. Such an interaction could be important in inducing the formation of tetrahedral Pt nanocrystals.展开更多
文摘The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample of cold molecules, initially distributed over several vibrational levels, has thus been transfered into a single selected vibrational level of the singlet X^1∑g ground electronic state. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. In this paper we briefly report the main experimental results and then address, in a detailed way by computer simulations, the perspectives for a ＂complete＂ cooling of the molecules, including also the rotational degree of freedom. Since the pumping process strongly depends on the relative shape of the ground and excited potential curves, ro-vibrational cooling through different excited states is theoretically compared.
基金The financial supports from the National Natural Science Foundation of China(NSFC,Nos.21773041 and 21327805)the National Basic Research Program of China(No.2016YFA0200700)。
文摘A new star-shaped molecule StOF-Br_3 containing oligofluorenes and halogen atoms(Bromine) has been synthesized and studied by Scanning Tunneling Microscopy(STM) at the highly oriented pyrolytic graphite(HOPG) surface.We have obtained the high-resolution self-assembled STM images,from which the highly ordered and closely packed non-porous arrangements of the StOF-Br_3 molecular selfassemblies at the heptanoic acid/HOPG surface could be observed.The molecular models and selfassembled StOF-Br_3 architectures have been given in the following text.Besides,we have also figured out the surface free energy by the density functional theory(DFT) calculation,which proved that the halogen...halogen interaction was strong enough to stabilize the ordered molecular self-assemblies.This work verifies the existence of bromine...bromine interactions,and meanwhile provides a kind of effective approach for quickly building ordered molecular nanoarchitectures with large areas and different geometries.
基金supported by the China Scholarship Council(no.202006170068).
文摘Coherent control has been achieved in atoms and small molecules in gas phase during the past few decades.An intriguing demonstration of coherent control is a so-called“dark pulse”that cancels 2-photon transition probabilities despite exposing the target to the full power spectrum of transform-limited laser pulses.However,for larger functional molecules in condensed phase at room temperature,ensemble measurements do typically not allow exerting full control over competing pathways due to the unavoidable influence of the surrounding(mostly complex)environment.Here,we demonstrate room-temperature coherent control exploiting a nonresonant 2-photon transition into a higher excited state of single conjugated polymer chains embedded in a disordered matrix,including proof-of-principle experiments on bulk films.To manipulate the 2-photon transition probability,we exploit complex pulse sequences,created by a systematically varied cosinusoidal spectral phase applied to the excitation laser spectrum.For single molecules,the phase-dependent response varies from molecule to molecule,which reflects the spectral heterogeneity(position,linewidth)of their 2-photon transitions.These data indicate that coherent control of single molecules requires optimization of parameters for each individual molecule.The experimental data are reproduced by a simple model that allows to directly retrieve the 2-photon absorption spectrum of each single molecule.Our coherent-control approach is a powerful and robust way to obtain spectral characteristics of higher excited states of single molecules and to manipulate the excited-state dynamics in condensed phase at room temperature.It holds the potential to be useful for the characterization of complex organic functional materials.
基金supported by the National Science Fund for Distinguished Young Scholars of China(No. 51125013)
文摘Star-shaped oligothiophenes with hexakis（fluoren-2-yl）benzene （HFB） as cores were designed and synthesized. Grafting thiophene units to HFB results in a bond flattening of the core, and makes the molecules a flipping-twist shape. Their thermal, photophysical and electrochemical properties were studied. Highly cross-linked conjugated polymers can be produced by electropolymerization of T1-T3.
文摘The effect of protector molecules on the formation of tetrahedral Pt nanocrystals during the H 2 reduction of aqueous K 2PtCl 6 solution was investigated. It was shown that the addition of sodium lactate or gluconate, which were good protectors for the synthesis of tetrahedral Ni nanocrystals, cannot result in the formation of tetrahedral Pt nanocrystals. On the other hand, the use of polyvinylpyrrolidone(PVP) for the protector has lead to fairly high selectivity(78%—83%) for the tetrahedral shape of Pt nanocrystals. Raman spectral results indicate that there is an interaction between the CO group of PVP and the surface of tetrahedral Pt nanocrystals. Such an interaction could be important in inducing the formation of tetrahedral Pt nanocrystals.
