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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Intramolecular Charge Transfer with Fluorazene and N-Phenylpyrrole
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Intramolecular Charge Transfer with Fluorazene and N-Phenylpyrrole

机译：氟腈和N-苯基吡咯的分子内电荷转移

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摘要

The reaction from the initially prepared locally excited (LE) precursor to the intramolecular charge transfer (ICT) state of the planarized fluorazene (FPP) is investigated and compared with its flexible counterpart N-phenylpyrrole (PP). The fluorescence spectra of FPP and PP at 25 °C in solvents of different polarity reveal that the onset of a LE f ICT reaction occurs at lower polarity (tetrahydrofuran, ε ) 7.39) for FPP than for PP (1,2-dichloroethane, ε ) 10.4). In accordance with this observation, the ICT reaction enthalpy -ΔH is larger for FPP than for PP, 16.7 versus 6.7 kJ/mol in ethyl cyanide (EtCN). The larger ICT efficiency of FPP is related to the smaller energy gap between the two lowest excited singlet states ΔE(S1,S2): 3680 cm-1 for FPP and 4070 cm-1 for PP in n-hexane, as would be expected in the context of the PICT model. From picosecond fluorescence decays in EtCN at -45 °C it is found that the LE f ICT reaction rate constant ka of FPP is with 9.8 × 1010 s-1 considerably larger than that of PP with 3.9 × 1010 s-1. From femtosecond transient absorption spectra in acetonitrile (MeCN) at 22 °C, an ICT reaction time of 1.6 ps is obtained for FPP, shorter than the 4.0 ps determined for PP. The results show that a perpendicular twist of the pyrrole and phenyl subgroups is not required for an efficient ICT reaction with PP, the planarization of FPP even making this reaction faster. The similarity of the ESA spectra of FPP with those of PP in MeCN, with ICT absorption maxima at 365 nm (FPP) and 370 nm (PP), leads to the conclusion that both ICT states have a planar structure.
机译：研究了从最初制备的局部激发（LE）前体到平面化芴（FPP）的分子内电荷转移（ICT）状态的反应，并将其与相应的柔性N-苯基吡咯（PP）进行了比较。 FPP和PP在25°C下在不同极性溶剂中的荧光光谱表明，与PP（1,2-二氯乙烷，ε）相比，FPP的LE f ICT反应的发生在较低极性下（四氢呋喃，ε）7.39）。 ）10.4）。根据这一观察，FPP的ICT反应焓-ΔH比PP大，在氰化乙酯（EtCN）中为16.7对6.7 kJ / mol。 FPP的较高ICT效率与两个最低激发单重态ΔE（S1，S2）之间的能隙较小有关：正己烷中，FPP为3680 cm-1，PP为4070 cm-1。 PICT模型的上下文。从EtCN在-45°C的皮秒荧光衰减发现，FPP的LE f ICT反应速率常数ka为9.8×1010 s-1，比PP的LE f ICT反应速率常数ka为3.9×1010 s-1。从22°C在乙腈（MeCN）中的飞秒瞬态吸收光谱中，FPP的ICT反应时间为1.6 ps，短于PP的4.0 ps。结果表明，与PP进行有效的ICT反应不需要吡咯和苯基亚基的垂直扭曲，FPP的平面化甚至使该反应更快。 FPP的ESA光谱与MeCN中的PP的光谱相似，在365 nm（FPP）和370 nm（PP）处的ICT吸收最大值，得出的结论是，两种ICT状态均具有平面结构。

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