Salzmann Susanne, Martinez-Junza Víctor, Zorn Björn, Braslavsky Silvia E, Mansurova Madina, Marian Christel M, Gärtner Wolfgang
Institute of Theoretical and Computational Chemistry, Heinrich Heine University, Düsseldorf, Universitätsstrasse 1, Geb. 26.32, 40225 Düsseldorf, Germany.
J Phys Chem A. 2009 Aug 20;113(33):9365-75. doi: 10.1021/jp905724b.
Four different riboflavin (RF) derivatives, two electronically modified compounds (1- and 5-deazariboflavin, 1DRF and 5DRF) and two sterically modified compounds (7,8-didemethyl- and 8-isopropylriboflavin, DMRF and iprRF), were subjected to a combination of time-resolved measurements (absorption and fluorescence) and high-level quantum chemical investigations. Both alkyl-modified flavins showed similar fluorescence properties as the parent compound, yet 5DRF had a larger quantum yield of fluorescence (PhiF = 0.52) than RF (PhiF = 0.27). Interestingly, 1DRF did not show fluorescence at all under these steady state conditions. The triplet quantum yield was different for the modified flavins such that no triplet formation was found for 1DRF, whereas the other compounds all formed triplet states (PhiTR for 5DRF of 0.64 and 0.50 and 0.23 for iprRF and DMRF, respectively). The triplet states of the two alkyl-modified flavins decayed with similar time constants as the parent compound, whereas a shorter lifetime was measured for 5DRF (tauTR = 15 micros, compared to tauTR = 29 micros for RF). In the calculations, the flavin derivatives were modeled as lumiflavins, that is, without the ribityl chain. We conclude that for aqueous solutions of DMRF, iprRF, and 5DRF intersystem crossing (ISC) takes place from the S1 1(pipi*) to the T2 3(pipi*) state by a vibronic spin-orbit coupling mechanism, a process common to most flavins, whereas ISC is slow in excited 1DRF due to the absence of a close-by triplet state.
对四种不同的核黄素（RF）衍生物进行了时间分辨测量（吸收和荧光）与高水平量子化学研究相结合的实验。这四种衍生物包括两种电子修饰化合物（1-去氮核黄素和5-去氮核黄素，1DRF和5DRF）以及两种空间修饰化合物（7,8-二去甲基核黄素和8-异丙基核黄素，DMRF和iprRF）。两种烷基修饰的黄素与母体化合物表现出相似的荧光性质，但5DRF的荧光量子产率（ΦF = 0.52）高于RF（ΦF = 0.27）。有趣的是，在这些稳态条件下，1DRF根本不显示荧光。修饰黄素的三重态量子产率各不相同，1DRF未发现三重态形成，而其他化合物均形成三重态（5DRF的ΦTR为0.64，iprRF和DMRF的分别为0.50和0.23）。两种烷基修饰黄素的三重态衰变时间常数与母体化合物相似，但5DRF的寿命较短（τTR = 15微秒，而RF的τTR = 29微秒）。在计算中，黄素衍生物被建模为发光黄素，即没有核糖醇链。我们得出结论，对于DMRF、iprRF和5DRF的水溶液，系间窜越（ISC）通过振动自旋轨道耦合机制从S1 1（ππ*）态发生到T2 3（ππ*）态，这是大多数黄素常见的过程，而在激发的1DRF中ISC较慢，因为不存在附近的三重态。
