화학공학소재연구정보센터
Journal of Chemical Physics, Vol.109, No.19, 8442-8450, 1998
Fluorescence from molecules and aggregates in polycrystalline thin films of alpha-oligothiophenes
We report stationary fluorescence, fluorescence excitation spectra, site-selective fluorescence spectra, and femtosecond time-resolved fluorescence spectra of vacuum-evaporated alpha-quaterthiophene (T4) and alpha-quinquethiophene (T5) polycrystalline thin films at various temperatures. It is found that the fluorescence spectrum of each compound studied is a superposition of emission spectra originated from energetically and spatially separated fluorescent species or sites, which are suggested to be disordered-molecules, pre-aggregates, aggregates, and physical defects. The disordered molecules lying at grain boundaries display a solutionlike fluorescence decay feature. Multiple fluorescence spectra with identical vibrational developments from pre-aggregate species are observed in the T5 film. A long-lived fluorescence decay component observed in the T4 film is attributed to the dipole-allowed transition in the aggregates. A slow rise observed in the time-resolved fluorescence of the T4 film is interpreted in terms of energy transfer from the energetically high-lying species to the physical defects in crystal.