金纳米粒子降低吸附态细菌叶绿素a荧光量子效率的机理研究

A Possible Mechanism for the Reduced Fluorescence Quantum Efficiency of Bacteriochlorophyll aMolecules Adsorbed on the Gold Nanoparticles

本文通过比较细菌叶绿素a(BChl a)吸附于Au纳米颗粒表面前后吸收光谱、荧光光谱、绝对量子产率和荧光寿命的变化,研究金纳米颗粒表面对吸附态细菌叶绿素a(BChl a)自发荧光辐射过程的影响。结果表明,BChl a吸附到Au纳米颗粒表面后,单体和二聚体BChl a吸收峰位均红移约3nm;BChl a单体发射的荧光峰位置从784nm红移到791nm,BChl a二聚体发射的荧光峰位置从684nm红移到689nm,二者荧光均发生淬灭;荧光量子效率降低;荧光寿命在误差范围内保持不变。原因可能来自两个方面:(1)BChl a吸附到Au导电表面后使得与自发辐射跃迁速率相关的光子能态密度变小,从而使BChl a自发辐射速率降低;(2)BChl a与纳米Au颗粒表面间的无辐射能量转移导致吸附态BChl a非辐射速率增大。

By comparison of the absorption spectra,fluorescence spectra,absolute quantum yields and the fluorescence lifetimes of Bacteriochlorophyll a（BChl a）before and after adsorption onto the surface of Au nanoparticles,we examined the surface-adsorption effect on the spontaneous fluorescence process of the BChl amolecules when adsorbed on the Au nanoparticles.It is found that the absorption peaks of both the monomeric and the dimeric BChl aare red shifted about 3nm,while the corresponding emission peak of the monomer is red shifted from 784 nm to 791 nm,and that of dimmer from 684 nm to 689 nm.We found that the fluorescence intensity for both the monomer and the dimmer were decreased after the adsorption,in correspondence with the observed decreased absolute fluorescence quantum yields,however the measured florescence lifetimes remain unchanged,within the experimental error.A possible account for the observed phenomenon can be two folds：（1）the conducting surface of Au nanoparticle could reduce the photon density states for the adsorbed BChl amolecules in the spontaneous fluorescence transition process;（2）occurrence of the non-radiative energy transfer between BChl aand Au nanoparticle would lead to a larger nonradiative decay rate for the adsorbed BChl amolecules.