Department of Chemistry, University of Coimbra, P3004-535 Coimbra, Portugal.
Phys Chem Chem Phys. 2012 Feb 7;14(5):1778-83. doi: 10.1039/c2cp23266a. Epub 2011 Dec 14.
A comprehensive investigation of the solution photophysics of a 5,5'-methylene-bridged polymeric indigo, a statistical copolymer consisting of indigo and N-acetylindigo units, was performed in organic solvents at room temperature and further compared with indigo. A complete spectral and photophysical characterization based on photoacoustic calorimetry, steady-state and time-resolved fluorescence data was undertaken. A fluorescence quantum yield of 0.00037 and an intersystem crossing singlet-to-triplet quantum yield of 0.006 (close to the value for indigo) were obtained, leading to a value of 0.9936 for the S(1) → S(0) internal conversion (IC) quantum yield. Spectral and photophysical characteristics similar to indigo were obtained with, however, a special signature: it (mainly) decays single exponentially (in contrast with indigo, found to decay bi-exponentially), with a decay time value of 40-50 ps and an even more efficient S(1) → S(0) IC deactivation channel, related to an efficient energy migration within an energetic ladder of the polymer chromophoric segments. The photochemistry of this polymer, namely the degradation under light excitation, was also investigated and the obtained photoreaction quantum yield (ϕ(R)) in DMF was found to be 0.003, which is lower than the previously determined value for indigo in the same solvent (ϕ(R) = 0.0078). The overall data indicate that although the polymer and indigo have a close finger-print, the former is more stable which is suggested to be due to the additional intramolecular energy transfer process (within different chromophoric units) found with the polymer.
对 5,5'-亚甲基桥联聚合靛蓝（一种由靛蓝和 N-乙酰靛蓝单元组成的统计共聚物）在室温下的溶液光物理进行了全面研究，并与靛蓝进行了进一步比较。基于光声量热法、稳态和时间分辨荧光数据进行了完整的光谱和光物理特性表征。获得了荧光量子产率为 0.00037 和单线态到三线态系间窜越的量子产率为 0.006（接近靛蓝的值），导致 S(1)→S(0)内转换（IC）量子产率为 0.9936。获得了与靛蓝相似的光谱和光物理特性，然而，具有一个特殊特征：它（主要）以单指数衰减（与发现双指数衰减的靛蓝相反），衰减时间值为 40-50 ps，并且具有更有效的 S(1)→S(0) IC 失活通道，与聚合物发色团段的能量梯级内的有效能量迁移有关。还研究了该聚合物的光化学，即在光激发下的降解，在 DMF 中获得的光化学反应量子产率（ϕ(R)）为 0.003，低于在相同溶剂中先前确定的靛蓝值（ϕ(R) = 0.0078）。总体数据表明，尽管聚合物和靛蓝具有密切的指纹，但前者更稳定，这被认为是由于聚合物中发现的额外的分子内能量转移过程（在不同的发色团单元之间）。
