Room temperature phosphorescence from natural products: Crystallization matters

Abstract

Efficient room temperature phosphorescence is observed in natural compounds and polymers such as starch, cellulose, bovine serum albumin (BSA), and some other carbohydrates. Whereas being practically nonluminescent in solutions and TLC plates, they emit bright phosphorescence in the crystalline states with lifetime up to microseconds, exhibiting crystallization-induced phosphorescence (CIP) characteristics. The CIP of these natural products without any conventional chromophores offers a new platform for the exploration of conceptually novel luminogens. room temperature phosphorescence, natural products, cellulose, starch, bovine serum albumin

Emission and Emissive Mechanism of Nonaromatic Oxygen Clusters

“…Attractively, all three compounds exhibit intrinsic luminescence and, in cryogenic conditions (i.e., at 77 K), impressive persistent phosphorescence was observed. Furthermore, even obvious RTP was recorded for xylitol crystals . Therefore, such intriguing results further proved the validity of the CTE mechanism, which is also enlightening in the discovery and design of novel luminophores .…”

“…Recently, we proposed the clustering‐triggered emission (CTE) mechanism to rationalize the unique photophysical behaviors of nonconventional luminophores . Namely, the clustering of nonconventional chromophores bearing π and lone‐paired ( n ) electrons and subsequent electron cloud overlap together with simultaneous conformation rigidification can rationalize the emission .…”

“…Despite the absence of conjugation in PEG, overlaps of electronic clouds provided by oxygen atoms, according to the CTE mechanism, may afford bright photoluminescence (PL) through proper contact of oxygen in the aggregated states. Exactly, under 312 nm UV irradiation, PEG powders could exhilaratingly emit blue light with a quantum efficiency ( Φ ) of 8.1% ( Figure a).…”

“…For xylitol crystals, the structured molecular arrangement ( Figure ) promotes close clustering of O atoms, expanding the delocalization of n electrons, and rigidified conformations, which not only efficiently inhibits the nonradiative deactivation of triplet emission, but also duly precludes the quenching effects of oxygen or water. To summarize, RTP was attractively detected in the emission process of xylitol crystals due to the facilitation of the intersystem crossing (ISC) process and rigidified conformations (Figure d) . Furthermore, single crystal structure of xylitol was analyzed to gain further insights .…”

Clustering‐Triggered Emission of Nonconjugated Polyacrylonitrile

“…Very recently, we observed the intriguing light emission from common rice. Subsequent examination of its main component, namely starch, and other natural products like cellulose, glucose, and dextran illustrated similar photophysical behaviors . Based on these results, it is assumed that the formation of clusters of electron rich oxygen with lone pairs is accountable for the light emission .…”