Theoretical investigation of the structure and conformational behaviour of small selenophene oligomers

The molecular structure and the conformational behaviour of selenophene, 2,2′-biselenophene (α-2Se), 2,2′:5′,2″-terselenophene (α-3Se) and 2,2′:5′,2″:5″,2″′-quaterselenophene (α-4Se) were determined through conventional ab initio and density functional calculations using a polarized valence double zeta basis set. Hartree—Fock (HF) calculations predict very flat four-fold torsional potentials where the minimum energy conformations correspond to anti—gauche structures and the less stable conformations to the syn form. The planar and perpendicular conformations are transition states. Zero point vibrational energy corrections have negligible effects. B3LYP calculations favour π-electron interactions suggesting that the planar anti form is the ground state of α-oligoselenophenes. Torsional potentials were analysed by a Fourier procedure in terms of non-bonding and conjugative interactions and were compared with corresponding data in sulfur analogues.