Ultralong organic room-temperature phosphorescence, multiple stimulus responsiveness and high-level anti-counterfeiting based on multifunctional carbazolyl imidazolopyridine

Abstract

Ultralong organic room-temperature phosphorescence materials induced by host−guest doping and the underlying mechanism have become the current research focus. Furthermore, high-level anti-counterfeiting and information encryption require multifunctional luminescent materials. Here, CzIP and L-CzIP with push−pull electronic system are successfully constructed by imidazopyridine units and commercial/self-made carbazole. The comparison experiment results indicate that trace isomer doping not only shows slight influence on crystal stacking and molecular space conformation but also significantly changes fluorescence and phosphorescence spectra and phosphorescence lifetime by boosting intersystem spin–orbit coupling. Non-radiative relaxation of CzIP and L-CzIP can be effectively inhibited by polymethyl methacrylate (PMMA) doping but not for crystallize. PMMA doping further confirms intrinsic phosphorescent characteristic of L-CzIP, whose room-temperature phosphorescence lifetime (84.83 ms) is close to that of CzIP (100.14 ms). Concentration-dependent fluorescent and phosphorescent emission and dynamic phosphorescent emission are also observed for CzIP in PMMA film. More importantly, a new aminopyridine/CzIP-doped system gives room-temperature phosphorescence lifetimes of 657.56 ms and afterglow lifetimes of 4 s. Notably, CzIP also shows high-contrast mechanochromism, selective response and differentiation to HCl, CF3COOH, and CH3COOH, and excellent detection capability to picric acid in aqueous medium and solid state. Finally, various anti-counterfeiting and encryption patterns are successfully constructed based on multifunction of CzIP. This work not only provides a multifunctional luminous material but also more importantly provides a theoretical basis and experimental guidance for designing novel ultralong organic room-temperature phosphorescence materials and achieving high-level anti-counterfeiting and encryption.