Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, Maryland 21250 United States.
Syngene International Ltd., Biocon Park, 560099 Bengaluru, India.
J Phys Chem A. 2021 Mar 25;125(11):2294-2307. doi: 10.1021/acs.jpca.0c11639. Epub 2021 Mar 16.
The solvent-dependent photophysics of two 4-amino-substituted 1,8-naphthalene imides () were studied using fluorescence spectroscopy and laser flash photolysis. The compounds were functionalized with water-soluble 2,2'(ethylenedioxy) diethylamine groups, yielding a monomer () and a dimer (). The radiative and nonradiative singlet-state deactivation processes of and were quantified in 10 solvents and at different pH values. The fluorescence quantum yield for the dimer in water was more than 100× lower than in other solvents, or for the monomeric . The enhanced nonradiative decay of aqueous solutions of dimeric is accompanied by biexponential decay kinetics, suggesting equilibration with a dark excited state. An oxygen-quenchable triplet state (T) of was produced upon 416 nm excitation in both water and -octanol. In water, the T state evolved into a long-lived transient that was unreactive toward oxygen or several electron donors. This species was not observed in -octanol. The transient observed upon 416 nm excitation of in water was extremely weak. However, production of T in both and was evidenced by the photoinduced electron transfer to methyl viologen, albeit in low quantum yield (0.0503 and 0.00778 for and , respectively). The photophysics and reactivity are consistent with the production of an intramolecular charge transfer (ICT) state that is stabilized in water. Significantly, this stabilization enhances nonradiative decay pathways, particularly in the dimer. The results indicate that the photochemistry of these compounds can be environmentally mediated, switching from radical- to triplet-initiated processes.
两种 4-氨基取代的 1,8-萘二甲酰亚胺 () 的溶剂依赖性光物理性质使用荧光光谱和激光闪光光解研究。这些化合物用水溶性 2,2'-(乙二氧基)二乙胺基团进行功能化，得到单体 () 和二聚体 ()。 和 的单重态辐射和非辐射弛豫过程在 10 种溶剂中和不同的 pH 值下进行了定量。在水中，二聚体的荧光量子产率比其他溶剂或单体 低 100 倍以上。水相中二聚体增强的非辐射衰减伴随着双指数衰减动力学，表明与暗激发态平衡。在水和正辛醇中，用 416nm 激发产生了可被氧气猝灭的三重态 (T)。在水中，T 态演变成一种对氧气或几种电子供体无反应的长寿命瞬态。在正辛醇中未观察到该物种。在水相中用 416nm 激发 时观察到的瞬态非常弱。然而，通过向甲基紫精进行光诱导电子转移，证明了 在 和 中都产生了 T，尽管量子产率较低（分别为 0.0503 和 0.00778）。光物理性质和反应性与形成稳定在水中的分子内电荷转移 (ICT) 态一致。重要的是，这种稳定增强了非辐射衰减途径，特别是在二聚体中。结果表明，这些化合物的光化学可以被环境介导，从自由基引发过程转换为三重态引发过程。
