Radiation and Photo Chemistry Division, Bhabha Atomic Research Center, Mumbai-400085, India.
J Phys Chem B. 2010 Jul 1;114(25):8327-34. doi: 10.1021/jp101643c.
The aggregation behavior of 5,10,15-trisphenyl-20-(3,4-dihydroxy phenyl) porphyrin (L) in aqueous solution has been studied as a function of pH and concentration with the help of steady state absorption and emission spectroscopy. Our studies revealed that, for a particular concentration range, molecules of L undergo a reversible aggregation process and form two different aggregates at two different pH ranges, namely, J- and H-aggregates. We have monitored the excited state lifetimes of different aggregates by picosecond time-resolved emission spectroscopy and found that the emission lifetime of L reduces drastically with the formation of these aggregates. To study the dynamics associated with the excited state of both non-aggregated and aggregated (both J and H) porphyrins in an ultrafast time domain, we have carried out femtosecond transient absorption spectroscopy in the visible region following excitation of the respective samples at 400 nm. In addition to other de-excitation channels, another extra 100 fs (major) component for H-aggregates and 200 fs (major) component for J-aggregates has been observed and attributed to the exciton decay components of the respective aggregates.
本文借助稳态吸收和发射光谱，研究了 5,10,15-三苯基-20-(3,4-二羟基苯基)卟啉（L）在水溶液中的聚集行为与 pH 值和浓度的关系。我们的研究表明，对于特定的浓度范围，L 分子经历了一个可逆的聚集过程，并在两个不同的 pH 值范围内形成了两种不同的聚集体，即 J-聚集体和 H-聚集体。我们通过皮秒时间分辨发射光谱监测了不同聚集体的激发态寿命，发现 L 的发射寿命随着这些聚集体的形成而急剧降低。为了在超快时间域内研究非聚集态和聚集态（J 和 H 聚集态）卟啉的激发态动力学，我们在 400nm 处激发相应的样品后，在可见区域进行了飞秒瞬态吸收光谱研究。除了其他去激发通道之外，还观察到 H-聚集体的 100fs（主要）和 J-聚集体的 200fs（主要）额外的超快成分，并将其归因于相应聚集体的激子衰减成分。
