Enhanced Intersystem Crossing Rate in Polymethine-Like Molecules: Sulfur-Containing Squaraines versus Oxygen-Containing Analogues

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• 作者：Davorin Peceli ; Honghua Hu ; Dmitry A. Fishman ; Scott Webster ; Olga V. Przhonska ; Vladimir V. Kurdyukov ; Yurii L. Slominsky ; Alexey I. Tolmachev ; Alexey D. Kachkovski ; Andrey O. Gerasov ; Art毛m E. Masunov ; David J. Hagan ; Eric W. Van Stryland
• 刊名：The Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：March 21, 2013
• 年：2013
• 卷：117
• 期：11
• 页码：2333-2346
• 全文大小：633K
• 年卷期：v.117,no.11(March 21, 2013)
• ISSN：1520-5215

文摘

Two different approaches to increase intersystem crossing rates in polymethine-like molecules are presented: traditional heavy-atom substitution and molecular levels engineering. Linear and nonlinear optical properties of a series of polymethine dyes with Br- and Se-atom substitution, and a series of new squaraine molecules, where one or two oxygen atoms in a squaraine bridge are replaced with sulfur atoms, are investigated. A consequence of the oxygen-to-sulfur substitution in squaraines is the inversion of their lowest-lying 蟺蟺* and n蟺* states leading to a significant reduction of singlet鈥搕riplet energy difference and opening of an additional intersystem channel of relaxation. Experimental studies show that triplet quantum yields for polymethine dyes with heavy-atom substitutions are small (not more than 10%), while for sulfur-containing squaraines these values reach almost unity. Linear spectroscopic characterization includes absorption, fluorescence, quantum yield, anisotropy, and singlet oxygen generation measurements. Nonlinear characterization, performed by picosecond and femtosecond laser systems (pump鈥損robe and Z-scan measurements), includes measurements of the triplet quantum yields, excited state absorption, two-photon absorption, and singlet and triplet state lifetimes. Experimental results are in agreement with density functional theory calculations allowing determination of the energy positions, spin鈥搊rbital coupling, and electronic configurations of the lowest electronic transitions.