Modulating some photophysical properties of cocrystals

Abstract

In this study, nine cocrystals of N-(5-nitropyridin-2-yl)amide derivatives with 3-dimethylaminobenzoic acid (3DMABA) and 4-aminobenzoic acid (4ABA) were synthesized and structurally characterized in order to fine-tune photophysical properties by systematically modifying targets and coformers while maintaining overall structural consistency. The influence of competing factors, such as hydrogen-bonding motifs and steric effects, was examined through deliberate coformer selection and alkyl chain-length variation. The compounds exhibited visible color changes during grinding experiments, which were investigated using UV-visible spectroscopy and computational chemistry. The results show that changing the coformer can effectively modulate photophysical behavior while largely preserving crystal structure, and the competing intermolecular forces do not limit control over key solid-state structural parameters. Furthermore, the observed photophysical properties and colors can be rationalized and predicted based on calculated HOMO–LUMO gaps of donor–acceptor pairs, demonstrating a strategy for controlled design of functional cocrystals.