Oligo‐ and Polyselenophenes: A Theoretical Study

Recently, a family of conducting polyselenophenes was synthesized, and they were shown to have a number of interesting properties. Here we have studied oligoselenophenes, their cation radicals and dications up to the 50‐mer (50 Se), as well as polyselenophene at the B3LYP/6‐31G(d) level of theory, and compared them with the corresponding oligothiophenes. Although the calculations reveal many similarities between oligo‐ and polyselenophenes and their thiophene‐based counterparts, they also show the important differences between those two types of conjugated systems. Oligo‐ and polyselenophenes have a more quinoid character, lower band gap, and importantly, they are more difficult to twist. The theoretical results suggest that the HOMO–LUMO gap (band gap), bond‐length alternation (BLA), and charge distribution in oligo‐ and polyselenophenes are strongly dependent on inter‐ring twisting, yet twisting costs little energy. The inter‐ring distances in oligo‐ and polyselenophenes are shorter than the related distances in oligothiophenes, whereas the bond lengths within the selenophene rings are comparable to those of the corresponding oligothiophenes. Good news about polyselenophenes: Polyselenophenes are becoming important organic electronic materials. The first in‐depth computational study of oligo‐ and polyselenophenes has been performed. When compared with oligo‐ and polythiophenes, oligo‐ and polyselenophenes have a more quinoid character, lower band gap, and they are more difficult to twist (see graph).