Crystallization-induced dual emission from metal- and heavy atom-free aromatic acids and esters

Pure organic materials exhibiting room temperature phosphorescence (RTP) have significant fundamental importance and promising optoelectronic and biological applications. Exploration of metal- and heavy atom-free pure organic phosphors, however, remains challenging because achieving emissive triplet relaxation that outcompetes the vibrational loss is difficult without metal or heavy atoms. In this contribution, in contrast to aggregation-caused quenching (ACQ) normally observed in conventional chromophores, a unique phenomenon of crystallization-induced dual emission (CIDE), namely, simultaneously boosted fluorescence and phosphorescence upon crystallization, is observed in a group of pure organic aromatic acids and esters at ambient conditions. Moreover, two triplet-involved relaxations of delayed fluorescence (DF) and phosphorescence are activated. Such efficient intrinsic emission from both singlet and triplet states in a single compound without employing metal or heavy atoms is suitable for a variety of fundamental research and applications.