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A comprehensive photophysical characterization of a new class of naphthalene derivatives of the important α-oligothiophenes (αn’s) has been undertaken in solution at room (293 K) and low (77 K) temperature. This includes absorption and fluorescence spectra, fluorescence quantum yields (φF), and lifetimes (τF), as a function of temperature and solvent. Triplet–triplet absorption spectra and triplet formation quantum yields (φT) were also determined. From the above, all the rate constants for the radiative (kF) and radiationless (kIC and kISC) have been calculated. It is shown that the lowest singlet excited state is an allowed π,π* state in all solvents. The results show that although the behavior of the oligomers is similar to their parent compounds (αn’s), significant differences are observed. By comparison of the extinction coefficients of the naph(αn’s) and the (αn’s), a good correlation was found between naph(αn) and α(n+1). On the basis of this proposed pairing, a consistent blue-shift was observed in the absorption maxima between the compounds here considered and the reference α-oligothiophenes. This indicates that there is some significant twist between the naphthalene and the αn chromophores. The most favorable inter-ring angle between the two chromophores, naphthalene and αn, was predicted on the basis of comparison with theory.

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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.