Radiation and Photochemistry Division, Bhabha Atomic Research Center, Mumbai 400085, India.
Chemphyschem. 2009 Dec 7;10(17):2995-3012. doi: 10.1002/cphc.200900325.
The dynamics of the excited states of 3- and 4-aminofluoren-9-ones (3AF and 4AF, respectively) are investigated in different kinds of solvents by using a subpicosecond time-resolved absorption spectroscopic technique. They undergo hydrogen-bonding interaction with protic solvents in both the ground and excited states. However, this interaction is more significant in the lowest excited singlet (S(1)) state because of its substantial intramolecular charge-transfer character. Significant differences in the spectroscopic characteristics and temporal dynamics of the S(1) states of 3AF and 4AF in aprotic and protic solvents reveal that the intermolecular hydrogen-bonding interaction between the S(1) state and protic solvents plays an important role in its relaxation process. Perfect linear correlation between the relaxation times of the S(1) state and the longitudinal relaxation times (tau(L)) of alcoholic solvents confirms the prediction regarding the solvation process via hydrogen-bond reorganization. In the case of weakly interacting systems, the relaxation process can be well described by a dipolar solvation-like process involving rotation of the OH groups of the alcoholic solvents, whereas in solvents having a strong hydrogen-bond-donating ability, for example, methanol and trifluoroethanol, it involves the conversion of the non-hydrogen-bonded form to the hydrogen-bonded complex of the S(1) state. Efficient radiationless deactivation of the S(1) state of the aminofluorenones by protic solvents is successfully explained by the energy-gap law, by using the energy of the fully solvated S(1) state determined from the time-resolved spectroscopic data.
研究了 3-和 4-氨基芴-9-酮（分别为 3AF 和 4AF）在不同溶剂中的激发态动力学，使用亚皮秒时间分辨吸收光谱技术。它们在基态和激发态都与质子溶剂发生氢键相互作用。然而，由于其显著的分子内电荷转移特性，这种相互作用在最低激发单线态（S(1)）中更为显著。3AF 和 4AF 在非质子和质子溶剂中 S(1)态的光谱特征和时间动态的显著差异表明，S(1)态与质子溶剂之间的分子间氢键相互作用在其弛豫过程中起着重要作用。S(1)态弛豫时间与醇溶剂的纵向弛豫时间（tau(L)）之间的完美线性相关证实了通过氢键重排进行溶剂化过程的预测。在相互作用较弱的体系中，弛豫过程可以很好地用涉及醇溶剂的 OH 基团旋转的偶极溶剂化过程来描述，而在具有较强氢键供体能力的溶剂中，例如甲醇和三氟乙醇，它涉及到非氢键结合形式到 S(1)态氢键配合物的转化。质子溶剂通过有效的无辐射猝灭成功地解释了氨基芴酮的 S(1)态的猝灭，这是通过使用从时间分辨光谱数据确定的完全溶剂化的 S(1)态的能量来解释的。
