Abraham Bindu, McMasters Sun, Mullan Mellisa A, Kelly Lisa A
Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, Maryland, USA.
J Am Chem Soc. 2004 Apr 7;126(13):4293-300. doi: 10.1021/ja0389265.
A series of water-soluble 1,4,5,8-naphthalene diimide derivatives has been prepared and their redox and photophysical properties characterized. From laser flash photolysis studies, the triplet excited state of N,N'-bis[2-(N-pyridinium)ethyl]-1,4,5,8-naphthalene diimide (NDI-pyr) was found to undergo oxidative quenching with the electron donors DABCO, tyrosine, and tryptophan as expected from thermodynamics. Interestingly, the reactivities of naphthalene diimides (NDI) possessing alpha- and beta-carboxylic acid substituents (R = -CH2COO-, -C(CH3)2COO-, and -CH2CH2COO-) were strikingly different. In these compounds, the transient produced upon 355 nm excitation did not react with the electron donors. Instead, this transient reacted rapidly (k > 10(8)-10(9) M-1 s-1) with known electron acceptors, benzyl viologen and ferricyanide. The transient spectrum of the carboxyalkyl-substituted naphthalimides observed immediately after the laser pulse was nearly identical to the one-electron-reduced form of 1,4,5,8-naphthalene diimide (produced independently using the bis-pyridinium-substituted naphthaldiimide). From our studies, we conclude that the transient produced upon nanosecond laser flash photolysis of NDI-(CH2)nCOO- is the species produced upon intramolecular electron transfer from the carboxylate moiety to the singlet excited state of NDI. In separate experiments, we verified that the singlet excited state of NDI-pyr does, indeed, react intermolecularly with acetate, alanine, and glycine. The process is further substantiated using thermodynamic driving force calculations. The results offer new prospects of the efficient photochemical production of reactive carbon-centered radicals.
已制备了一系列水溶性1,4,5,8-萘二酰亚胺衍生物，并对其氧化还原和光物理性质进行了表征。通过激光闪光光解研究发现，N,N'-双[2-(N-吡啶基)乙基]-1,4,5,8-萘二酰亚胺（NDI-pyr）的三重激发态如热力学预期的那样，会与电子给体DABCO、酪氨酸和色氨酸发生氧化猝灭。有趣的是，具有α-和β-羧酸取代基（R = -CH2COO-、-C(CH3)2COO-和-CH2CH2COO-）的萘二酰亚胺（NDI）的反应性显著不同。在这些化合物中，355 nm激发产生的瞬态不与电子给体反应。相反，该瞬态与已知的电子受体苄基紫精和铁氰化物迅速反应（k > 10(8)-10(9) M-1 s-1）。激光脉冲后立即观察到的羧基烷基取代萘酰亚胺的瞬态光谱与1,4,5,8-萘二酰亚胺的单电子还原形式（使用双吡啶基取代的萘二酰亚胺独立产生）几乎相同。从我们的研究中，我们得出结论，NDI-(CH2)nCOO-的纳秒激光闪光光解产生的瞬态是由羧酸根基团向NDI的单重激发态进行分子内电子转移产生的物种。在单独的实验中，我们验证了NDI-pyr的单重激发态确实与乙酸盐、丙氨酸和甘氨酸发生分子间反应。使用热力学驱动力计算进一步证实了该过程。这些结果为高效光化学产生活性碳中心自由基提供了新的前景。
