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发色团之间的电子相互作用导致基态和激发态能级的分裂，CR波段的吸收光谱在近红外（NIR）区域具有特征。本课题旨在揭示影响二聚体自由基阳离子稳定性及其超快动力学的因素。以下是本项目的主要成果，这些成果将有助于开发在近红外区域具有强和超快光响应的分子光子学新材料。1)飞秒激光在1,2 -二甲氧基乙烷中激发硝基和二氰乙烯基取代的苯基吡啶四苯基硼酸盐，在可见光和近红外区域的吸收均在小于1皮秒（ps）的时间内超快上升。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。更快的组分被分配到从二聚体自由基阳离子到氧化四苯基硼酸盐的反向电子转移。较慢的一个被分配到从自由基单体到氧化四苯基硼酸盐的反向电子转移。2)新合成的三氰乙烯基苯基吡啶衍生物在多种溶剂中具有更稳定的自由基和二聚自由基阳离子。用这些材料制备了Langmuir-Blodgett薄膜，并首次在固体薄膜中观察到CR波段，该波段在1000 nm处比在苯中红移明显。3)在以1,3取代丙烷或2,4取代戊烷为桥接的双色基团化合物中观察到分子内二聚体自由基阳离子。在丙烷桥接的硝基苯基吡啶衍生物中，在948和1742 nm处观察到两个CR波段。它们被分配到三明治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.