The ground state (S0) geometry of the firefly luciferin (LH2) was optimized by both DFT B3LYP and CASSCF methods. The vertical excitation energies (Tv) of three low-lying states (S1, S2, and S3) were calculated by TD-...The ground state (S0) geometry of the firefly luciferin (LH2) was optimized by both DFT B3LYP and CASSCF methods. The vertical excitation energies (Tv) of three low-lying states (S1, S2, and S3) were calculated by TD-DFT B3LYP//CASSCF method. The S1 geometry was optimized by CASSCF method. Its Tv and the transition energy (Te) were calculated by MS-CASPT2//CASSCF method. Both the TD-DFT and MS-CASPT2 calculated S1 state Tv values agree with the experimental one. The IPEA shift greatly affects the MS-CASPT2 calculated Tv values. Some important excited states of LH2 and oxyluciferin (oxyLH2) are charge-transfer states and have more than one dominant configuration, so for deeply researching the firefly bioluminescence, the multireference calculations are desired.展开更多
In this work, we report the first CASPT2//CASSCF study of the mechanism of the photodecarboxylation of N-phthaloylglycine. The charge transfer excited state S CT （ 1∏∏＊） is initially populated upon irradiation at...In this work, we report the first CASPT2//CASSCF study of the mechanism of the photodecarboxylation of N-phthaloylglycine. The charge transfer excited state S CT （ 1∏∏＊） is initially populated upon irradiation at 266 nm. As a result of a fast internal conversion to the lowest excited singlet state S CT-N （ 1∏∏＊）, this state becomes a favorable precursor state for proton transfer, which triggers decarboxylation. Actually, the excited state intramolecular proton transfer （ESIPT） and decarboxylation processes proceed in an asynchronous concerted way. The ESIPT process is accomplished in the S CT-N （ 1∏∏＊） state, but the CO 2 molecule is finally formed in the ground state via the S CT /S 0 conical intersection. Azomethine ylide is formed in the ground state as a complex with CO 2 . A barrier of ~15 kcal/mol indicates that azomethine ylide is stable in the ground state, which is consistent with the experimental findings. This work provides mechanistic details about the formation of azomethine ylide by photoreaction of N-phthaloylglycine.展开更多
基金Supported by the National Natural Science Foundation of China (Grant No. 20673012)the Major State Basic Research Development Programs (Grant No. 2004CB719903)
文摘The ground state (S0) geometry of the firefly luciferin (LH2) was optimized by both DFT B3LYP and CASSCF methods. The vertical excitation energies (Tv) of three low-lying states (S1, S2, and S3) were calculated by TD-DFT B3LYP//CASSCF method. The S1 geometry was optimized by CASSCF method. Its Tv and the transition energy (Te) were calculated by MS-CASPT2//CASSCF method. Both the TD-DFT and MS-CASPT2 calculated S1 state Tv values agree with the experimental one. The IPEA shift greatly affects the MS-CASPT2 calculated Tv values. Some important excited states of LH2 and oxyluciferin (oxyLH2) are charge-transfer states and have more than one dominant configuration, so for deeply researching the firefly bioluminescence, the multireference calculations are desired.
基金supported by the National Natural Science Foundation of China (21033002)the National Basic Research Program of China(2011CB808503)
文摘In this work, we report the first CASPT2//CASSCF study of the mechanism of the photodecarboxylation of N-phthaloylglycine. The charge transfer excited state S CT （ 1∏∏＊） is initially populated upon irradiation at 266 nm. As a result of a fast internal conversion to the lowest excited singlet state S CT-N （ 1∏∏＊）, this state becomes a favorable precursor state for proton transfer, which triggers decarboxylation. Actually, the excited state intramolecular proton transfer （ESIPT） and decarboxylation processes proceed in an asynchronous concerted way. The ESIPT process is accomplished in the S CT-N （ 1∏∏＊） state, but the CO 2 molecule is finally formed in the ground state via the S CT /S 0 conical intersection. Azomethine ylide is formed in the ground state as a complex with CO 2 . A barrier of ~15 kcal/mol indicates that azomethine ylide is stable in the ground state, which is consistent with the experimental findings. This work provides mechanistic details about the formation of azomethine ylide by photoreaction of N-phthaloylglycine.
