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 (ϕ_F) and triplet formation (ϕ_T), lifetimes of fluorescence and the triplet state, quantum yields of singlet oxygen production (ϕ_Δ), all rate constants k_F, k_IC, k_ISC, 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 twisted while the excited state is planar (quinoidal-like). Significant charge transfer occurs between S₀ and S₁ but not S₀ and T₁. For all α2−α7, ϕ_IC is small, k⁰_F is approximately constant while k_ISC decreases significantly from α2 to α7. The decrease is k_ISC is believed to arise from a decrease in matrix elements of the type ⟨Ψ_CT|H‘|³Ψ₁⟩. The essential lack of phosphorescence is assigned as originating from inter-ring twisting mode coupling between T₁ and S₀. Triplet energy transfer to ³O₂ to produce ¹O₂ is highly efficient for α2−α5. Based on all data, the first αn representative of α-polythiophene is α5.