Environmental photochemistry of Nitro-PAHs:: Direct observation of ultrafast intersystem crossing in 1-nitropyrene
Environmental photochemistry of Nitro-PAHs:: Direct observation of ultrafast intersystem crossing in 1-nitropyrene
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DOI：
10.1021/jp803847q
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发表时间：
2008-07-17
影响因子：
2.9
通讯作者：
Arce, Rafael
中科院分区：
文献类型：
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作者：
Crespo-Hernandez, Carlos E.;Burdzinski, Gotard;Arce, Rafael
介绍了在环己烷和己烷溶液中对1 - 硝基芘（一种环境关注的硝基多环芳烃）进行的飞秒宽带瞬态吸收实验。瞬态吸收光谱表明存在三种物质，分别归属于弗兰克 - 康登激发的最低单重态（S - 1）、结构弛豫的S态以及最低激发三重态。早期的光谱变化根据构象动力学来解释；主要是由于硝基在S - 1态的超快旋转。这种激发态弛豫之后是系间窜越，时间常数为7皮秒。CIS/6 - 31G(d,p)计算预测硝基 - 芳香族扭转角的平面化是主要的核弛豫坐标，从基态在HF/6 - 31G(d,p)理论水平的32.8度（在B3LYP/6 - 31++G(d,p)为27.46度）到S态的0.07度。在TDDFT/6 - 31++G(d,p)和TDDFT/IEFPCM/6 - 31++G(d,p)理论水平的垂直激发能预测了一个小的能隙（
Femtosecond broadband transient absorption experiments of 1-nitropyrene, a nitro-polycyclic aromatic hydrocarbon of environmental concern are presented in cyclohexane and hexane solutions. The transient absorption spectra show the presence of three species that are assigned to the Franck-Condon excited lowest singlet (S-1) state, the structurally relaxed S, state, and the lowest excited triplet state. The spectral changes at early times are interpreted in terms of conformational dynamics; primarily due to an ultrafast rotation of the nitro group in the S-1 state. This excited state relaxation is followed by intersystem crossing with a time constant of 7 ps. CIS/6-31G(d,p) calculations predict planarization of the nitro-aromatic torsional angle as the major nuclear relaxation coordinate, from 32.8 degrees at the HF/6-31 G(d,p) level of theory in the ground state (27.46 degrees at B3LYP/6-31++G(d,p)) to 0.07 degrees in the S, state. Vertical excitation energies at the TDDFT/6-31++G(d,p) and TDDFT/IEFPCM/6-31++G(d,p) levels of theory predict a small energy gap (