A spectroscopic study has been performed on selected substituted 2,2’-bithiophenes. Absorption and fluorescence spectra of bithiophenes (BT) substituted with alkyl and alkoxy groups in positions 4,4’ and 3,3’ have been measured in solvents of various polarity and viscosity. AMI and ZINDO/S semiempirical calculations have also been performed on all molecules in order to evaluate the torsional potential energy surfaces and the singlet-singlet transition energies. It is found by a combined theoretical and experimental technique in which 3,3’-derivatives are more twisted than their 4,4’-analogs in the ground state. After excitation, molecules relax to much more planar SI excited states. The sole exceptions are 3,3’-alkoxybithiophene derivatives which seem to remain in the same conformation in their respective relaxed SI excited state. For molecules in their Ti excited states, planar and perpendicular conformations are the most stable. It is also observed that fluorescence quantum yields of all bithiophene derivatives are weak but weaker for 3,3’-substituted compounds. Results are interpreted in terms of a possible substitutional effect on the intersystem crossing process involved in these systems.