Tuning Luminescence and Conductivity through Controlled Growth of Polymorphous Molecular Crystals

Abstract

Clear structure–property correlation is of crucial importance for molecular materials for optical and electronic application. Here, a new intramolecular charge transfer compound (E)-2-{4-[4-(9H-carbazol-9-yl)styryl]benzylidene}malononitrile (TCBR) with a dicyanovinyl group as the electron acceptor and a carbazole group as the electron donor is designed and synthesized. Four different single crystals based on the cis and trans isomeric forms of this compound are grown simultaneously, which are both kinetically and thermodynamically stable. The different packing modes give rise to a dynamic crystal structure change, leading to dramatically different optical and electronic properties. The closer packing can effectively promote the π–π interactions to increase the exciton coupling and orbital overlap between neighbor molecules in crystals, which produces a redshift fluorescence emission and good conductivity. This permits one to tune the packing molecules in the solid state to specific applications in a more precise way. The results of this study highlight the power of designing new functional molecules for optical and electronic applications.