A large basis set of α-oligothiophenes with two to seven rings (α2−α7), also including thiophene, α1, have been investigated in five solvents regarding absorption, fluorescence and phosphorescence, quantum yields of fluorescence (φF) and triplet formation (φT), lifetimes of fluorescence and the triplet state, quantum yields of singlet oxygen production (φΔ), all rate constants kF, kIC, kISC, and several of the foregoing as a function of temperature. Ten different theoretical calculations across several levels including three levels of ab initio have been carried out regarding which conformer is lowest in energy and the ΔH's among all conformers of α2, α3 and α5, as well as calculations of transitions energies of the α-oligothiophenes. We have shown that the (l) 1Bu state is the lowest singlet state for all α2−α7 in any solvent, in contradiction to previous predictions for the higher members. Based on absorption and fluorescence data and calculations of atomic charges in S0 and S1, the ground state is twis...