Nonconventional macromolecular luminogens with aggregation‐induced emission characteristics

Abstract

Nonconventional luminogens without classic conjugated structures have drawn increasing interests owing to their fundamental importance and promising applications. These luminogens generally bear such subgroups as tertiary amine, C = C, C≡N, C = O, OH, ether, and imide. The emission mechanism, however, remains under debate. Different assumptions like oxidation or acidification of tertiary amines, aggregation of C = O groups, as well as clustering and electron cloud overlap are proposed. Unlike concentration quenching and aggregation‐caused quenching (ACQ) that are normally observed in traditional luminogens, many of these unorthodox luminogens exhibit unique aggregation‐induced emission (AIE) characteristics, regardless of their molecular architectures. This review summarizes varying unorthodox luminogens with AIE features, aiming to outline the recent advances in this exciting area, with focus on the macromolecular systems. In light of the reported results, clustering‐triggered emission mechanism, namely clustering of diverse subgroups with subsequent electron cloud overlap and conformation rigidification can well rationalize the photophysical behaviors of most systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 560–574

Aggregate Science: From Structures to Properties

“…Nonconjugated luminogens that exhibit a clusterization-triggered emission (CTE) effect, known as clusteroluminogens, have recently emerged as new frontier of photonics. [188][189][190][191][192][193][194][195][196][197][198] Clusteroluminogens, including nonconjugated polymers, small molecules and metal clusters, are often nonluminescent as molecular species. [199] As shown in Figure 11A, the isolated molecules possess a large energy gap (∆E 1 ) due to the lack of through-bond conjugation resulting in ∆E 1 always corresponding to an ultraviolet emission that is weak in intensity, and invisible in wavelength to the eye, and may even be below the detection limit of spectrophotometers.…”

Fluorescent linear polyurea based on toluene diisocyanate: Easy preparation, broad emission and potential applications

“…As such, this type of new fluorescence is referred to as intrinsic photoluminescence (IPL) [4] or nontraditional intrinsic luminescence [5]. As to the mechanism of this type of fluorescence emission, the cluster-trigged emission (CTE) proposed by Tang et al [20,21], has been widely accepted, which suggests that the emission is owing to the formation of clusters when the polymer reaches a high concentration, caused by the intra-and interchain interactions of their electron-rich groups by sharing their lone-pair electrons. This CTE mechanism is similar to the AIE mechanism proposed also by these authors earlier [22,23], from the view point that the emission is caused by structural rigidification of their non-emissive moieties, due to the restriction of inter-and intramolecular mobility.…”

A new approach to developing diagnostics and therapeutics: Aggregation‐induced emission‐based fluorescence turn‐on

“…The AIE molecular configuration easily forms loose packing, which suppresses the distance‐dependent intermolecular quenching to allow intense fluorescence in the aggregated state. Another possible mechanism is clustering‐triggered emission . For AIEgens without conventional fluorogens, electron‐rich atoms can form clusters upon aggregation.…”

“…Another possible mechanism is clustering-triggered emission. 46,47 For AIEgens without conventional fluorogens, electron-rich atoms can form clusters upon aggregation. Subsequently, electron clouds overlap to afford extended delocalization and rigid conformations and are thus easily excited and radiatively deactivated.…”