Supramolecular Design of Highly Efficient Two-Component Molecular Hybrids toward Structure and Emission Properties Tailoring

Exploiting molecular systems to attain tunable emission characteristics out of the organic fluorophore is of great pertinence for the construction of solid-state luminescent materials owing to their fascinating applications in optoelectronics. Herein, we have designed three charge transfer (CT) molecular assemblies utilizing carbazole luminophores (9-benzoyl carbazole (BC), 9-(para-tolyl carbazole (TC), and N-(4-formylphenyl)carbazole (FC)) as donor compounds and 1,2,4,5-tetracyanobenzene (TCNB) as an acceptor building block to tailor the structure and emission properties. Unlike TC and FC, BC has a carbonyl spacer between carbazole and phenyl group, which allow more short contacts and, therefore, effect the binary crystalline self-assembly. Detail structural and spectroscopic studies revealed the formation of alternate sandwich motifs between the donors and acceptor in a cofacial fashion, which resulted in tunable molecular structure and photophysical properties. Cocrystals XII and XIII present identical emissions due to the similar molecular packing modes (DAD center dot center dot center dot DAD) and stoichiometric ratio (2:1), whereas cocrystal XI exhibits varied molecular packing features (DADA) and molar ratio (3:2) with yellow-green fluorescence. The present study demonstrates the significance of molecular design as an effective route that could fine-tune the molecular packing, stoichiometry, and luminescence characteristics, thereby bringing out efficient optical properties out of the single component via cocrystal strategy for construction of novel solid state luminescent materials.