Search

Nonconventional luminophores devoid of remarkable conjugates have attracted considerable attention due to their unique luminescence behaviors, updated luminescence mechanism of organics and promising applications in optoelectronic, biological and medical fields. Unlike classic luminogens consisting of molecular segments with greatly extended electron delocalization, these unorthodox luminophores generally possess nonconjugated structures based on subgroups such as ether (-O-), hydroxyl (-OH), halogens, carbonyl (CO), carboxyl (-COOH), cyano (CN), thioether (-S-), sulfoxide (SO), sulfone (OSO), phosphate, and aliphatic amine, as well as their grouped functionalities like amide, imide, anhydride and ureido. They can exhibit intriguing intrinsic luminescence, generally featuring concentration-enhanced emission, aggregation-induced emission, excitation-dependent luminescence and prevailing phosphorescence. Herein, we review the recent progress in exploring these nonconventional luminophores and discuss the current challenges and future perspectives. Notably, different mechanisms are reviewed and the clustering-triggered emission (CTE) mechanism is highlighted, which emphasizes the clustering of the above mentioned electron rich moieties and consequent electron delocalization along with conformation rigidification. The CTE mechanism seems widely applicable for diversified natural, synthetic and supramolecular systems.

Nonconventional luminophores without significant conjugations generally possess excitation-dependent photoluminescence (PL) owing to the coexistence of diverse clustered chromophores, which strongly implies the possibility of achieving color-tunable PL and/or persistent room temperature phosphorescence (p-RTP) from their crystals assisted by effective intermolecular interactions. Compared with traditional luminogens, however, nonconventional luminophores generally suffer from poor PL efficiencies. Here, inspired by the highly stable double-helix structure and multiple hydrogen bonds in DNA, we report a series of planar or twisted nonconventional luminophores based on hydantoin (HA), demonstrating unprecedentedly high PL/p-RTP efficiencies and p-RTP lifetimes of up to 87.5%/21.8% and 1.74 s, respectively, accompanying color-tunable p-RTP from sky-blue to yellowish-green. These findings will advance the exploitation of efficient nonconventional luminophores and provide deeper mechanistic insights into the origin of color-tunable p-RTP.

Compounds bearing aliphatic amines could be emissive under proper conditions. Their ionized counterparts, quaternary ammonium salts (QASs), which are widely used as phase-transfer catalysts, ionic liquids, disinfectants and surfactants, however, are known as luminescence quenchers and thought to be nonemissive. Here we report the unprecedented intrinsic fluorescence-phosphorescence dual emission from a diversity of QASs, which can also be finely regulated by excitation wavelength, alkyl chain length, counter ions, mechanical stimuli, etc. The bright photoluminescence along with distinct afterglow and tunable multicolor emissions enables advanced multimode anticounterfeiting for QAS solids. This finding refreshes the cognition of QASs and would inspire emerging applications by utilizing their intrinsic luminescence. Furthermore, it opens opportunities for the investigation of QAS related processes and functions in a photophysical approach and affords strong implications for the fabrication of novel nonconventional luminophores.