CQFM-Centro de Química-Física Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
Photochem Photobiol Sci. 2013 Nov;12(11):1948-59. doi: 10.1039/c3pp50132a.
This study presents several new squarylium dyes derived from benzothiazole and benzoselenazole with several structural variations, namely the nature of the heteroaromatic ring and the length of the N,N'-dialkyl groups. Before being investigated in connection with their effect on living cells and/or tissues, these novel compounds were characterized, namely with respect to the determination of their main photophysical parameters. Therefore, a study of the ground state absorption, fluorescence emission (quantum yields and lifetimes) and singlet oxygen generation quantum yields was performed for all the compounds synthesized in order to evaluate their efficiency as photosensitizers. An increase of the alkyl chain length from ethyl to hexyl did not produce a clear change in the fluorescence quantum yields, showing no influence on the photoisomerization process. Heavy atom inclusion (Se instead of S) enhanced the singlet oxygen generation efficiency and decreased the intensity of the fluorescence emission. The external heavy atom effect (I(-) as a counterion instead of CF3SO3(-)) produced a significant increase in the singlet oxygen formation quantum yield (about 20%). Transient absorption studies in aerated and oxygen free samples revealed that the photoisomerization process, which could compete with the triplet state formation for all dyes in solution, is a negligible pathway for the excited state deactivation, in accordance with the rigidity introduced by the squaric ring into the polymethine chain of the dye, both in chloroform and ethanol. However, in the case of the chloroform solution a new transient was detected in air equilibrated solutions, resulting from a reaction of the excited squarylium dye in the singlet state with CHCl3˙, and assigned to the radical cation (SQ(+)˙) of the dye.
本研究提出了几种新的方酸染料，它们源自苯并噻唑和苯并硒唑，具有几种结构变化，即杂芳环的性质和 N，N'-二烷基的长度。在研究它们对活细胞和/或组织的影响之前，对这些新型化合物进行了表征，即确定了它们的主要光物理参数。因此，对所有合成的化合物进行了基态吸收、荧光发射（量子产率和寿命）和单线态氧生成量子产率的研究，以评估它们作为光增敏剂的效率。烷基链从乙基增加到己基并没有使荧光量子产率产生明显变化，表明对光异构化过程没有影响。重原子（Se 代替 S）的包含增加了单线态氧生成效率，并降低了荧光发射强度。外部重原子效应（I(-)作为抗衡离子而不是 CF3SO3(-)）使单线态氧形成量子产率显著增加（约 20%）。在有氧和无氧样品中的瞬态吸收研究表明，光异构化过程可能与所有染料在溶液中的三重态形成竞争，但对于激发态失活来说是微不足道的途径，这与 squaric 环在染料的聚甲川链中引入的刚性一致，无论是在氯仿还是乙醇中。然而，在氯仿溶液中，在空气平衡溶液中检测到一种新的瞬态，它是由处于单重态的激发方酸染料与 CHCl3˙反应产生的，并且被分配给染料的自由基阳离子（SQ(+)˙）。
