Anni M, Della Sala F, Raganato M F, Fabiano E, Lattante S, Cingolani R, Gigli G, Barbarella G, Favaretto L, Görling A
National Nanotechnology Laboratory (NNL) of INFM, Dipartimento di Ingegneria dell'Innovazione, Università degli Studi di Lecce, Via per Arnesano, 73100 Lecce, Italy.
J Phys Chem B. 2005 Mar 31;109(12):6004-11. doi: 10.1021/jp046465j.
The intramolecular radiative and nonradiative relaxation processes of three thiophene-S,S-dioxide derivatives with different molecular rigidity are investigated in different solutions and in inert matrix. We show that the fluorescence quantum efficiency and the relaxation dynamics are strongly dependent on the environment viscosity, whereas they are almost independent of the environment polarity. We demonstrate that this strong dependence is due to an environment dependent nonradiative decay rate, whereas no relevant variations of the radiative decay rate are observed. We demonstrate that the dipole coupling with the solvent does not provide an efficient nonradiative decay channel and that the S(n) - S(1) vibrational relaxation is very efficient in all of the molecules and for all of the investigated environments. Moreover first-principles time-dependent density-functional theory calculations in the correct, i.e., excited-state, molecular conformation, suggest that significant contributions of intersystem crossing to the triplet manifold can be excluded. We then conclude that the main nonradiative process determining the fluorescence quantum efficiency of this class of molecules is S(1) - S(0) internal conversion (IC). An explanation for the IC rate dependence in terms of the environment viscosity, molecular rigidity, S(1) - S(0) energy-gap, and molecular volume is presented.
研究了三种具有不同分子刚性的噻吩 - S,S - 二氧化物衍生物在不同溶液和惰性基质中的分子内辐射和非辐射弛豫过程。我们发现荧光量子效率和弛豫动力学强烈依赖于环境粘度，而几乎与环境极性无关。我们证明这种强烈依赖性是由于环境依赖的非辐射衰减率，而未观察到辐射衰减率的相关变化。我们证明与溶剂的偶极耦合不会提供有效的非辐射衰减通道，并且S(n) - S(1)振动弛豫在所有分子和所有研究环境中都非常有效。此外，在正确的即激发态分子构象下进行的第一性原理含时密度泛函理论计算表明，可以排除系间窜越对三重态流形的显著贡献。然后我们得出结论，决定这类分子荧光量子效率的主要非辐射过程是S(1) - S(0)内转换（IC）。给出了关于IC速率依赖性与环境粘度、分子刚性、S(1) - S(0)能隙和分子体积之间关系的解释。
