Department of Chemistry and Biochemistry and the Center for Nano- and Molecular Science and Technology, University of Texas at Austin, Austin, Texas 78712, USA.
J Phys Chem B. 2009 Nov 5;113(44):14619-28. doi: 10.1021/jp906740n.
Single-particle fluorescence spectroelectrochemistry was used to investigate the electrochemical oxidation of isolated, immobilized particles of the conjugated polymers BEH-PPV and MEH-PPV at an indium tin oxide (ITO) electrode immersed in an electrolyte solution. Two types of particles were investigated: (i) polymer single molecules (SM) and (ii) nanoparticle (NP) aggregates of multiple polymer single molecules. For the BEH-PPV polymer, the observation of nearly identical lowest oxidation potentials for different SM in the ensemble is evidence for effective electrostatic screening by the surrounding electrolyte solution. A combination of Monte Carlo simulations and application of Poisson-Boltzmann solvers were used to model the charging of polymer single molecules and nanoparticles in the electrochemical environment. The results indicate that the penetration of electrolyte anions into the polymer nanoparticles is necessary to produce the observed narrow fluorescence quenching vs oxidation potential curves. Finally, fluorescence-lifetime single-molecule spectroelectrochemical (SMS-EC) data revealed that at low potential an excited state reduction process (i.e., electron transfer from ITO to the polymer) is probably the dominant fluorescence quenching process.
采用单粒子荧光光谱电化学方法研究了在浸入电解质溶液的氧化铟锡（ITO）电极上，共轭聚合物 BEH-PPV 和 MEH-PPV 分离固定化粒子的电化学氧化。研究了两种类型的粒子：（i）聚合物单分子（SM）和（ii）多个聚合物单分子的纳米颗粒（NP）聚集体。对于 BEH-PPV 聚合物，对于集合体中不同 SM 的几乎相同的最低氧化电势的观察结果证明了周围电解质溶液的有效静电屏蔽。使用蒙特卡罗模拟和泊松-玻尔兹曼求解器的组合来模拟电化学环境中聚合物单分子和纳米颗粒的充电。结果表明，电解质阴离子渗透到聚合物纳米颗粒中是产生观察到的窄荧光猝灭与氧化电势曲线所必需的。最后，荧光寿命单分子光谱电化学（SMS-EC）数据表明，在低电势下，激发态还原过程（即，从 ITO 到聚合物的电子转移）可能是主要的荧光猝灭过程。
