Relaxation dynamics of photoluminescent excitons in structurally modulated polytmophene thin film

Summary form only given. Optical properties of polythiophene and its derivatives are important for their applications to an organic opto-electronics and a nonlinear-optics. For these subjects, the behavior of the exciton generated in the polymers should be revealed in detail. Dynamics of photoluminescent exciton is considered to connected with the local electronic structure of the conjugated polymers. In this study, relaxation, dynamics of the photoluminescent exciton in structurally modulated polythiophene thin films was investigated. Polythiophene films were prepared on ITO-glass electrode by electropolymerization of several monomers, such as thiophene, 3-metylthiophene, 2,2´-bithiophene and 2,2´:5´,2-terthiophene, in CH/sub 3/CN solution containing 0. I M LiClO/sub 4/. After the polymerization, the films were completely dedoped by electrochemical reduction then used for the optical measurements. Transient spectra of the photoluminescence were measured with ps laser flash photolysis system (Excitation: SHG of Ti-sapphire laser; 395 nm, FWHM 200 fs; Detector: 3-D single photon counting system using streak scope). All the decay curves of the photoluminescence were multi-exponential suggesting the presence of inhomogeneous quenching sites. Observed lifetimes of the excitons were varied by changing the starting monomers. The lifetime of poly(terthiophene) was obviously longer than those of poly(bithiophene) and poly(3-methylthiophene). These tendencies are considered to reflect the structural modulation of the polymers depending on the starting monomers. Interestingly, the photoluminescence spectra and their lifetimes changed according to the thickness of the films. As their thickness decrease, the photoluminescence shift to higher energy region and the lifetime of the exciton decrease, where the quantum-size effect is suggested.