Pereira Robson Valentim, Gehlen Marcelo Henrique
Instituto de Química de São Carlos, Universidade de São Paulo, 13566-590, São Carlos-SP, Brazil.
J Phys Chem A. 2006 Jun 22;110(24):7539-46. doi: 10.1021/jp0561470.
Fluorochromic dyes derived from 9-aminoacridinium containing a vinylene function with electron withdrawing groups such as diethyl [(acridinium-9-ylamino)methylene]malonate (I), ethyl [(acridinium-9-ylamino)methylene]cyanoacetate (II), [(acridinium-9-ylamino)methylene]malononitrile (III), are prepared and studied in their monoprotonated form. Absorption spectra of the new dyes are red shifted compared to that of the precursor dye. The observed dual fluorescence and multiexponential decay are ascribed to normal emission from the acridinium chromophore in addition to excited-state intramolecular charge transfer (ESICT) process. However, biexponential decay character is observed only for the dicyano derivative (compound III), whereas for the two other systems, more complex kinetics and a three-component decay is recovered. The analysis of the fluorescence decays in different solvents for the first two compounds reveals two short-lived components in the range of 160-350 ps and 1.1-3.0 ns, related to formation and decay of the ESICT state, plus a third one with decay time of about 9 ns, which is ascribed to the normal emission from the acridinium chromophore as an enol tautomer or as an intramolecular H-bond conformer (closed form tautomer). For the dicyano derivative, in which the absence of carbonyl group precludes the H-bond interaction, the biexponential fitting reveals a slightly fast formation rate of the ESICT state with values on the order of 10(10) s(-1), whereas its decay time is between 0.6 and 3.2 ns, depending on the solvent used.
制备了含亚乙烯基官能团且带有吸电子基团的9-氨基吖啶鎓衍生的荧光染料，如二乙基[(吖啶鎓-9-基氨基)亚甲基]丙二酸酯（I）、乙基[(吖啶鎓-9-基氨基)亚甲基]氰基乙酸酯（II）、[(吖啶鎓-9-基氨基)亚甲基]丙二腈（III），并对其单质子化形式进行了研究。与前体染料相比，新染料的吸收光谱发生了红移。观察到的双重荧光和多指数衰减归因于吖啶鎓发色团的正常发射以及激发态分子内电荷转移（ESICT）过程。然而，仅二氰基衍生物（化合物III）观察到双指数衰减特征，而对于其他两个体系，恢复了更复杂的动力学和三组分衰减。对前两种化合物在不同溶剂中的荧光衰减分析显示，有两个短寿命组分，范围在160 - 350 ps和1.1 - 3.0 ns，与ESICT态的形成和衰减有关，还有第三个组分，衰减时间约为9 ns，这归因于吖啶鎓发色团作为烯醇互变异构体或分子内氢键构象体（封闭形式互变异构体）的正常发射。对于二氰基衍生物，由于不存在羰基，排除了氢键相互作用，双指数拟合显示ESICT态的形成速率略快，值约为10(10) s(-1)，而其衰减时间在0.6至3.2 ns之间，取决于所用溶剂。
