Facile synthesis of phenothiazine-pyrazine-based donor-acceptor-donor regioisomers: Influence of molecular geometry on aggregation-induced emission

Abstract

Aggregation-induced emission (AIE) fluorescent molecules are in great demand due to the wide range of applications. In this article, three regioisomers namely, o-PyPTZ, m-PyPTZ and p-PyPTZ, with pyrazine (Py) as acceptor and phenothiazine (PTZ) as donor, were rationally designed and synthesized. Phenothiazine moieties are attached to pyrazine core as peripheral groups at 2,3- 2,5- and 2,6-positions. The attachment of bulky PTZ pendants at different position of pyrazine core could influence the molecular packing modes, resulting in discrete photophysical and electronic properties. The resulting regioisomers are weakly fluorescent in dilute solutions but highly emissive upon aggregate formation, verifying their AIE activities. They are thermally and morphologically stable with degradation temperature of 372–407 °C. Single-crystal structures of three isomers indicate their twisted conformation. A detailed comparison of the photophysical, electronic and structural properties of these isomers has been made with a view to studying the outcome of the positional change.