Benzil-Imidazole Blue Fluorophores and Their Applications in Blue/White Light-Emitting Diodes, Sensing and Anticounterfeiting

Abstract

A series of benzilimidazole-based donor–π–acceptor (D–π–A) blue fluorophores, functionalized at the N1 position of the imidazole ring are designed and synthesized. In solution, solid, and thin-film matrices, the luminophores exhibit deep blue emission with a good quantum yield (∼70%) with excellent thermal stability and show excellent intramolecular charge transfer (ICT) with a large Stokes’ shift (∼8000 cm−1). Due to the excellent fluorescence characteristics in the solid phase, these synthesized fluorophores are utilized to fabricate hybrid white and blue light-emitting diodes (LEDs) and in anticounterfeiting applications. The fabricated blue and white LEDs exhibited high luminous efficiency of radiation values with CIE coordinates that are nearly matched with the NTSC standard and a high color rendering index (CRI) of 86%. Latent fingerprint (LFP) imaging also has been effectively implemented using fluorophores. Additionally, specific structural functionalities of the fluorophores enable them to interact selectively with picric acid (PA) over other nitroaromatic compounds (NACs). The sensing mechanisms are analyzed using nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations. These fluorophores exhibit superior sensing abilities toward PA with high quenching constants (Ksv) of 6.6 × 106 M−1 and ultralow detection limits of 400 ppb. Furthermore, these molecules are found to show remarkable on–off–on fluorescence behavior in response to acid-base vapor interaction and, thus, can be a probable candidate for vapor sensing.