仿生色素薄膜的荧光光谱研究

本文利用柱层析法从天然产物中提取分离了叶绿素a(Chl-a)和胡罗h素C(Car),并按Langmuir-Blodgett单分子膜技术制备了Chl-a单分子膜、Chl-a与Car的混合单分子膜。实验中还引入了硬脂酸起辅助支撑作用,选用的硬脂酸与Chl-a的摩尔比为10:1。挂膜载片为经过疏水处理的玻璃片。为制作模仿天然光合膜集光天线系统的功能,我们以Car为给体Chl-a为受体,Caf与Chl-a的摩尔比为5:1、50:1和125:1;这里选用的比例远大于集光天线的色素比例。用荧光光谱的测量发现,L-B膜内的色素分子有特殊的集聚态,这种状态有助于实现高效的激子转移。作者指出,由于二维的L-B膜上会发生Frster型和激子型两种能量转移的协同作用,所以在Car与Chl-a的摩尔比125:1时Chl-a的荧光无相应衰减。Chl-a单分子膜的荧光带为677nm和766nm。吸附在层析纸上Chl-a的荧光,仅长波带有明显位移。

FLUORESCENCE SPECTRUM OF BIOMIMETIC PIGMENT FILM

One approach to the utilization of solar energy is the development of devices that mimic natural photosynthesis. Such artificial photosynthesis efforts would be aided by a better understanding of the primary photochemical steps that occur in the natural process of photosynthesis. As a result our studies emphasize the mechanistic and structural detial of photosynthetic antenna system this appears to be crucial to the design of artificial solar energy devices. Chlorophyll a (Chl-a) has long been known as the major light-absorbing pigment in photosynthetic antenna systems Furthermore, the light absorbed by some carotenoides (accessory pigments) is photosynthesis active. The accessory pigments can transfer their absorbed energy to Chl-a Energy transfer has been considered the mechanism by Förster In types of artificial mono-layers,Chl-a and carotene (Car) are isolated from spinach in the usual manner of extraction followed by purification by column chromatography. In order to investigate the interaction between Chl-a and Car in a monolayer assembly, attempts are made to build up two different types of assembly on glass plate by conventional Langmuir-Blodgett techniques. One type is a monolayer film consisting of Chl-a and octadecoic acid with molar ratio of 1:10. As the artificial molecular monolayer of Chl-a forms aggregates, its fluorescence spectrum has a main peak at 677nm and a secondary peak at around 766nm(Fig.1). The main peak of Chl-a luminescence in the monolayer is shifted by 16nm to the long-wave band when compared with its state in the solution. This shift is apparently due to an increase of aggregate forms in the monolayer with respect to the solution. A new maximum (766nm) appears in the Chl-a fluorescence spectrum. It is due to the aggregate form of pigment The other type is a Car-Chl-a mixed monolayers with molar ratio 5:l;50:l;and 125:1 The two bands all appear in the cases of Car as donor and Chl-a as acceptor And then the luminescence intensities have nonlinear decay with the decrease of Chl-a molecule (Fig.2). The general idea is that Car helps the artificial antenna system to catch more of the incident light energy because they can take up excited light. The accessory pigments can transfer their absorbed energy to Chl-a Experiments show that the limited Förster transfer distance is about 100Å But as a result of the cooperation of exciton transfer and Förster transfer, the distance increaces. The result suggests that exciton transfer should play an important role in luminescence of biomimetic pigment films.