No abstract

No abstract

By analyzing stationary absorption and fluorescence spectra of several α-oligothiophenes in dichloromethane at room temperature, the S1 ← S0 zero−zero transition energies and Huang−Rhys parameters are determined. Reorientational behaviors of the α-oligothiophenes in dichloromethane are also investigated by femtosecond time-resolved fluorescence spectroscopy. The reorientational relaxation observed for each α-oligothiophene in its first excited state is interpreted in terms of revolution of a hydrodynamic prolate ellipsoid of which the emission transition dipole is aligned along the long molecular axis. Our results show that a hydrodynamic slip model could successfully explain the reorientation times of α-terthiophene, α-quaterthiophene, and α-quinquethiophene in dichloromethane at 288 K, by modeling these molecules as prolate ellipsoids with dimensions consistent with their van der Waals volumes.

We report stationary fluorescence, fluorescence excitation spectra, site-selective fluorescence spectra, and femtosecond time-resolved fluorescence spectra of vacuum-evaporated α- quaterthiophene (T4) and α-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.

No abstract