Mechanisms, recent advancements and perspectives concerning nonconventional luminophores free of classic conjugates but with intrinsic photoluminescence are discussed.

Persistent room-temperature phosphorescence (p-RTP) has drawn extensive attention due to its unique photophysical processes and promising applications in organic light-emitting diodes (OLEDs), [1] biological areas, [2] chemical sensors, [3] optics, [4] and anticounterfeiting technology. [5] Currently, p-RTP systems, however, are normally restricted to inorganic compounds. [6] As promising alternatives, pure organic p-RTP luminogens take advantages of low cost, wide variety, environmental friendliness, good biocompatibility, appreciable stability, and good processability, [7] allowing a wide range of optoelectronic and biological applications. [2] The triplet excitons of organic luminogens, however, are prone to nonradiative relaxations through vibrational stretching and external quenching (i.e., O 2 ), making it difficult to achieve efficient p-RTP. [8] To overcome such barriers, generally, two attempts are endeavored: one is to boost the spin-orbital coupling (SOC) and subsequently promote the intersystem crossing (ISC) processes through incorporation of heavy atoms, [9] heteroatoms, [10] or aromatic carbonyls; [11] the other is to stabilize the triplet excitons in a rigid environment by suppressing nonradiative decay pathways to activate the RTP emission, [12] such as crystal formation, [13] embedding into rigid hosts, [14] polymer assistance, [15] and metal-organic framework (MOF) coordination. [16] Despite exciting advancements have been made in the past few years, fabrication of efficient and robust p-RTP still remains a challenge. First, the p-RTP efficiency (Φ p ) of reported phosphors with the lifetime (〈τ〉 p ) of several hundred milliseconds are generally below 5%, [11a,13a] and moreover, robust p-RTP at complex and changing environments is rare, even though it is essential for diverse applications in data recording, encryption, anticounterfeiting, and bioimaging. [17] For example, when applied in molecular imaging, owing to their long-lasting nature, p-RTP materials can eliminate the need for light irradiation and circumvent the troublesome interference of nanosecond tissue autofluorescence, thus permitting much clearer and more reliable bioimaging with high signal-to-noise ratios. Current methodologies toward biomedical applications, however, mainly adopt nanocrystallization or top-down nanoparticle Pure organic persistent room-temperature phosphorescence (p-RTP) under ambient conditions is attractive but challenging due to the slow intersystem crossing process and susceptibility of triplet excitons. Fabrication of pure organic RTP luminogens with simultaneously high efficiency and ultralong lifetime still remains a daunting job, owing to their conflicting requirements for the T 1 nature of (n,π*) and (π,π*) characteristics, respectively. Herein, a group of amide-based derivatives with efficient p-RTP is developed through the incorporation of spin-orbital-coupling-promoting groups of carbonyl and aromatic π units, giving impressive p-RTP with lifetime and efficiency of up to 710.6 ms and 10.2%,...

It is a textbook knowledge that protein photoluminescence stems from the three aromatic amino acid residues of tryptophan(Trp), tyrosine (Tyr), and phenylalanine (Phe), with predominant contributions from Trp. Recently, inspired by the intrinsic emission of nonaromatic amino acids and poly(amino acids) in concentrated solutions and solids, we revisited protein light emission using bovine serum albumin (BSA) as a model. BSA is virtually nonemissive in dilute solutions (≤0.1 mg mL−1), but highly luminescent upon concentration or aggregation, showing unique concentration‐enhanced emission and aggregation‐induced emission (AIE) characteristics. Notably, apart from well‐documented UV luminescence, bright blue emission is clearly observed. Furthermore, persistent room‐temperature phosphorescence (p‐RTP) is achieved even in the amorphous solids under ambient conditions. This visible emission can be rationalized by the clustering‐triggered emission (CTE) mechanism. These findings not only provide an in‐depth understanding of the emissive properties of proteins, but also hold strong implications for further elucidating the basis of tissue autofluorescence.

The clustering-triggered emission mechanism guides the rational design of nonaromatic polyurethanes with intrinsic emissions including room-temperature phosphorescence.

Novel emitters that do not contain traditional chromophores but only electron-rich moieties (e. g. amine, C=O, À OH, ether, and imide), which are classified as nonconventional luminophores, have been more frequently reported. Although more and more examples have been demonstrated, their emission mechanism remains unclear. The clustering-triggered emission (CTE) mechanism has previously been proposed to rationalize the luminescence of unconventional chromophores. Moreover, great attention has been paid to the distinctive inherent luminescence from nonaromatic biomolecules such as cellulose, starch, sugars, and nonaromatic amino acids and proteins. In this Review, we summarize these unconventional biomolecular luminophores and apply the CTE mechanism to rationalize such a phenomenon. This Review may shed new light on the understanding of intrinsic emission of nonaromatic biomolecules and decipher the intrinsic fluorescence from cells and tissues.