Ultrafast photoresponses of organized molecular assemblies

超快光响应材料和器件的发展对于全光信息处理技术的近期实施至关重要。就上述问题而言，更有希望的方法之一是本项目的主题。它主要涉及几种有组织的分子组装体的超快光响应的构建和检查。1)通过离子交换，通过H_2S气体与分散的Cd^2离子反应，在Nafion膜、两亲物自组装膜和其他系统中制备尺寸量子化的CdS纳米粒子。 CdS 纳米粒子的尺寸和表面状态通过各种处理来控制。2) 采用在 400 nm 激发的飞秒泵浦-探针方法研究了激子形成引起的瞬时漂白。除 LB 薄膜外，所有样品均在小于 1 ps 的时间尺度上表现出非常快的漂白响应。漂白光谱及其恢复率明显取决于颗粒尺寸和尺寸分布、表面状态或微环境。在 Nafion 薄膜中，“大”纳米颗粒（5 nm）的漂白光谱很宽，并且在恢复过程中峰发生红移。对于“小”纳米粒子（3.4 nm），漂白光谱的峰值位于较短的波长处，并且在恢复过程中没有表现出光谱偏移。3）在对取代苯乙烯基吡啶鎓四苯基硼酸盐的激发下，可见光和近红外（NIR）区域的瞬态吸收出现在不到 1 ps 的时间内。可见光区域的衰减由快速和慢速分量组成，而近红外区域的衰减是单指数的。可见光区域快速成分的寿命与近红外吸收的寿命相对应。发现从二聚体自由基阳离子到氧化四苯硼酸盐的反向电子转移反应比单体自由基的反向电子转移反应更快。

The development of ultrafast photoresponsive materials and devices is essential for the near future implementation of all-optical information processing technology. One of the more promising approaches with respect to the above is the subject of the present project. It deals primarily with the construction and examination of ultrafast photoresponses of several organized molecular assemblies.1) Size-quantized CdS nano-particles were prepared in Nafion films, self-assembled films of amphiphiles, and other systems by reacting H_2S gas with Cd^<2+> ions dispersed, by ion-exchange. The size and the surface state of the CdS nano-particles were controlled by various treatments.2) Transient bleaching, by exciton formation, was studied with a fs pump-probe method excited at 400 nm. All samples except the LB films showed a very fast bleaching response on a time scale of less than 1 ps. The bleached spectra and their recovery rate depended markedly on the particle size and size distribution, the surface states, or the microenvironments. In Nafion films, the bleached spectra for "large" nano-particles (5 nm) were broad and the peaks red-shifted during the recovery process. For "small" nano-particles (3.4 nm), the peak of the bleached spectrum was at shorter wave-lengths and showed no spectral shift during the recovery process.3) Transient absorptions in the visible and the near infrared (NIR) regions appeared in less than 1 ps upon excitation of p-substituted styrylpyridinium tetraphenylborates. The decay in the visible region was composed of a fast and a slow component, whereas it was single exponential in the NIR region. The lifetime of the fast component in the visible region corresponded with that of the NIR absorption. The reverse electron transfer reaction from dimer radical cations to oxidized tetraphenylborate was found to be faster than that from monomer radicals.