Molecular control and ultrafast dynamics of specific interaction of photogenerated radicals

由于二聚体自由基阳离子的两个生色团之间的电子相互作用导致基态和激发态的能级分裂，CR带的特征是其在近红外(NIR)区域的吸收光谱。本文主要研究了影响二聚体自由基阳离子稳定性的因素及其超快动力学行为。主要研究结果如下：1)飞秒激光激发1，2-二甲氧基乙烷对硝基和二氰基四苯基四苯基吡啶的可见光和近红外区的超快吸收。在近红外区为单指数衰减，寿命约为3ps，在可见光区为双指数衰减，寿命约为3ps和17ps。二聚体自由基阳离子向氧化型四苯基硼酸根的反向电子转移是较快的成分。较慢的是自由基单体向氧化型四苯基硼酸酯的背电子转移。2)新合成的三氰基乙烯基苯并吡啶衍生物在多种溶剂中都能产生更稳定的自由基和二聚自由基阳离子。在此基础上制备了Langmuir-Blodgett薄膜，并首次在1000 nm处观察到固体薄膜中的CR带，该带较苯中的CR带有较大的红移。3)在以1，3-取代丙烷或2，4-取代戊烷为桥联的双色化合物中观察到分子内的二聚体自由基阳离子。在丙烷桥联的硝基苯基吡啶类化合物中，观察到两条CR谱带，分别位于948和1742 nm处。他们被分配到夹心型和部分重叠型二聚体自由基阳离子。

The CR band is characterized by its absorption spectrum in the near-infrared (NIR) region, due to the splitting of the energy levels of both the ground and the excited states resulting from the electronic interaction between two chromophores of the dimer radical cation. In the present research project, efforts were made to elicidate factors affecting the stability of dimer radical cations and their ultrafast dynamics.Followings are the main results from the present project, which will contribute a great deal to the development of novel materials for molecular pohotonics showing strong and ultrafast photoresponses in the near infrared region.1) Femtosecond laser excitation of nitro-and dicyanovinyl-substituted styrylpyridinium tetraphenylborates in 1, 2-dimethoxyethane revealed ultrafast rise of absorptions both in the visible and NIR regions in less than 1 picosecond (ps). The decay was single-exponential in the NIR region with a lifetime of about 3 ps and double-exponential in the visible region with lifetimes of about 3 ps and 17 ps. The faster component was assigned to the back electron transfer from dimer radical cations to oxidized tetraphenylborate. The slower one was assigned to the back electron transfer from radical monomers to oxidized tetraphenylborate.2) Newly synthesized tricyanovinylstyrylpyridinium derivatives gave much more stable radicals and dimer radical cations in a wide variety of solvents. Langmuir-Blodgett films were prepred from these and the CR band was observed for the first time in solid films at 1000 nm which was considerably redshifted than that in benzene.3) Intramolecular dimer radical cations were observed in bichromophoric compounds bridged with 1, 3-substituted propane or 2, 4-substituted pentane. In propane-bridged nitrostyrylpyridinium derivatives, two CR bands were observed with peaks at 948 and 1742 nm. They were assigned to sandwich-and partially overlapped type dimer radical cations.