Influence of substitution pattern and enhanced π-conjugation on a family of thiophene functionalized 1,5-dithia-2,4,6,8-tetrazocines

A versatile, one-pot synthetic route to prepare a series of 1,5,2,4,6,8-dithiatetrazocines (DTTA) functionalized with 4-hexylthiophen-2-yl, 5-(thiophen-2′-yl)thiophen-2-yl and 5-(5′-hexylthiophen-2′-yl)thiophen-2-yl is described. The latter two compounds mark the first reported examples of π-extended DTTA systems. Comparative spectroscopic, computational and structural studies were carried out on this family of heterocycles to investigate the influence of the substitution pattern, in addition to enhanced conjugation, on the optoelectronic and solid-state properties. These studies revealed a slight increase in the optical energy gap upon displacement of the alkyl chain from the 5- to the 4-position in hexylthienyl functionalized DTTA, whereas extension of the conjugation diminishes the HOMO–LUMO gap. In the solid-state, variation in alkyl substituent plays an important role, contrary to what was previously observed for aryl functionalized DTTA derivatives.