Substituent-Driven Modulation of Structural, Photophysical, and Antimicrobial Properties in 2-Arylbenzo-[f]-coumarins.

2-Arylbenzo-[f]-coumarins represent an underexplored class of extended conjugated systems with remarkable potential in optoelectronics and biomedical research. In this study, we unveil how subtle substituent variations (-H, -OMe, -CH3, -NHAc, -Ph, and extended N-aryl groups) at the 2-position dramatically reshape the structural, vibrational, and photophysical landscapes of benzo[f]coumarins. Single-crystal X-ray diffraction reveals substituent-controlled torsional twists that dictate molecular packing and supramolecular interactions. Vibrational fingerprints, probed by FTIR, Raman spectroscopy, and validated by DFT, show distinct shifts in key marker bands, offering a sensitive handle to track electronic perturbations. Striking photophysical modulations emerge, with unusual emission shifts and biexponential lifetimes pointing to multiple emissive states. Beyond fundamental insights, these molecular nuances translate into function-BC-H and BC-OMe display promising antimicrobial activity against S. aureus and C. albicans, opening avenues toward bioimaging and theranostic applications. By bridging structure-vibration-photophysics-function correlations, this work provides a compelling blueprint for the rational design of next-generation coumarin-based materials with tunable performance.