Expanding the fluorescent window of nitro‐substituted Triphenylamines through combined steric and electronic engineering

The fluorescence of nitroaromatic fluorophores is highly sensitive to their environment and often exhibits a narrow “fluorescent window” in both solution and solid states. This limitation arises from the various fluorescence‐quenching pathways, including S 1 → T n intersystem crossing (ISC), formation of a twisted intramolecular charge transfer (TICT) state, and antiparallel molecular stacking. Here, we report a series of nitro‐substituted triphenylamines (nitro‐TPAs), in particular the pentiptycene‐derived nitro‐TPAs P X series, to investigate whether combined steric and electronic engineering can broaden the fluorescent window across a wide polarity range and in the solid state. While substituent electronic effects tune the push‐pull character, the bulky pentiptycene scaffold shields the nitrogen center from solvation and suppresses intermolecular stacking in the solid phase. Notably, the isocyanide derivative PNC exhibits fluorescence in all six tested solvents, n‐ hexane, toluene, dichloromethane, N,N ‐dimethylformamide, and acetonitrile, as well as in both crystalline and powdered forms. This work demonstrates the effectiveness of integrating steric and electronic strategies to expand the fluorescence window of flexible nitroaromatic systems.