Hidalgo José, Sánchez-Coronilla Antonio, Balón Manuel, Asunción Muñoz María, Carmona Carmen
Departamento de Química Física, Facultad de Farmacia, Universidad de Sevilla, 41012, Sevilla, Spain.
Photochem Photobiol Sci. 2009 Mar;8(3):414-20. doi: 10.1039/b816776a. Epub 2009 Jan 20.
A systematic study of the influence of the gradual temperature decrease on the UV-vis absorption and fluorescence emission spectra of betacarboline, 9H-pyrido[3,4-b]indole, BC, and other model systems, such as BC plus N(9)-methyl-9H-pyrido[3,4-b]indole, MBC, and BC plus pyridine, PY, has been carried out in 2-methylbutane, 2MB. These studies have allowed the conclusion that the temperature decrease favours the formation of hydrogen-bonded self-associated BC aggregates. The initial red shifts of the absorption and emission bands and the fluorescence quenching have been ascribed to the formation of hydrogen bond BC dimers with a proton transfer structure, PTC. In these adducts, the fluorescence is quenched by an electron-driven proton transfer process. However, because the quenching rate constant decreases upon decreasing the temperature, the emission intensity later increases without modification of the wavelength maxima. At the lowest temperatures, these dimeric PTC complexes further aggregate. We propose that they form ground state cyclic tetrameric adducts in which both nitrogen atoms of each BC unit are hydrogen bonded. The tautomeric forms of these tetrameric complexes, generated by a quadruple proton transfer, emit dual fluorescence, from its locally excited state, LE, and its intramolecular charge transfer state, ICT.
在2-甲基丁烷（2MB）中，对温度逐渐降低对β-咔啉（9H-吡啶并[3,4-b]吲哚，BC）以及其他模型体系（如BC加N(9)-甲基-9H-吡啶并[3,4-b]吲哚，MBC，和BC加吡啶，PY）的紫外可见吸收光谱和荧光发射光谱的影响进行了系统研究。这些研究得出结论，温度降低有利于形成氢键自缔合的BC聚集体。吸收带和发射带的初始红移以及荧光猝灭归因于具有质子转移结构（PTC）的氢键BC二聚体的形成。在这些加合物中，荧光通过电子驱动的质子转移过程猝灭。然而，由于猝灭速率常数随温度降低而减小，发射强度随后增加，且波长最大值不变。在最低温度下，这些二聚体PTC配合物进一步聚集。我们认为它们形成基态环状四聚体加合物，其中每个BC单元的两个氮原子都形成氢键。这些通过四重质子转移产生的四聚体配合物的互变异构形式从其局部激发态（LE）和分子内电荷转移态（ICT）发出双重荧光。
