Optoelectronic and structural properties of a family of thiophene functionalized 1,5-dithia-2,4,6,8-tetrazocines

Abstract

The dithiatetrazocine (DTTA) ring has been functionalized with thiophene (5a), 5-hexylthiophene (5b) and 5-bromothiophene (5c), and the optoelectronic and structural properties have been probed. All three derivatives possess low-lying LUMO levels near −3.5 eV and exhibit irreversible reduction and oxidation processes. Inspection of their absorption profiles reveals a small bathochromic shift in λ_max with substitution of the thiophene ring. The HOMO–LUMO band gaps, determined from electrochemical, optical and computational studies, decrease across the series in the following manner: 5a > 5c > 5b. DFT calculated frontier molecular orbitals for 5a–c (R = Me for 5b) indicate delocalized electron density over the entire tricyclic framework for the HOMO, whereas the electron density for the LUMO is localized on the DTTA ring. Single crystal X-ray diffraction on 5b,c show structures consisting of molecules with planar molecular frameworks arranged in slipped π-stack arrays. Although both compounds exhibit close intermolecular interactions, the contacts observed in 5c are between π-stacks, while they are exclusively within the π-stacks for 5b.