The study of purely organic room-temperature phosphorescence (RTP) has drawn increasing attention because of its considerable theoretical research and practical application value. Currently, organic RTP materials with both high efficiency (ΦP  > 20%) and a long lifetime (τP  > 10 s) in air are still scarce due to the lack of related design guidance. Here, a new strategy to increase the phosphorescence performance of organic materials by integrating the RTP host and RTP guest in one doping system to form a triplet exciplex, is reported. With these materials, the high-contrast labeling of tumors in living mice and encrypted patterns in thermal printing are both successfully realized by taking advantage of both the long afterglow time (up to 25 min in aqueous media) and high phosphorescence efficiency (43%).

High Performance of Simple Organic Phosphorescence Host-Guest Materials and their Application in Time-Resolved Bioimaging.

Over the past few decades, graphitic carbon nitride (g-C3 N4 ) has arisen much attention as a promising candidate for photocatalytic hydrogen evolution reaction (HER) owing to its low cost and visible light response ability. However, the unsatisfied HER performance originated from the strong charge recombination of g-C3 N4 severely inhibits the further large-scale application of g-C3 N4 . In this case, the utilization of cocatalysts is a novel frontline in the g-C3 N4 -based photocatalytic systems due to the positive effects of cocatalysts on supressing charge carrier recombination, reducing the HER overpotential, and improving photocatalytic activity. This review summarizes some recent advances about the high-performance cocatalysts based on g-C3 N4 toward HER. Specifically, the functions, design principle, classification, modification strategies of cocatalysts, as well as their intrinsic mechanism for the enhanced photocatalytic HER activity are discussed here. Finally, the pivotal challenges and future developments of cocatalysts in the field of HER are further proposed.

Emerging Cocatalysts on g-C3N4 for Photocatalytic Hydrogen Evolution

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 (CO), carboxyl (–COOH), cyano (CN), thioether (–S–), sulfoxide (SO), sulfone (OSO), 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: characteristics, advancements and perspectives.

In recent years, purely organic room-temperature phosphorescence (RTP) has aroused wide concern and promotes the development of the supramolecular phosphorescence. Different from organic crystallization, polymerization, or matrix rigidification, supramolecular strategy mainly takes advantage of the synergy between supramolecular co-assembly and strong binding by macrocyclic host compounds (cucurbit[n]urils, cyclodextrins, etc.) to overcome deficiencies such as poor processability and water solubility and improves RTP materials' quantum efficiency and lifetime in the solid state or in an aqueous solution. Meanwhile, it expands application, especially in aqueous solution, in cell imaging. Therefore, supramolecular phosphorescence will become a new growth point and will have broad application prospects in chemistry, biology, and material science.This Account focuses on the uniquely synergetic advantages of co-assembly and host-guest interaction from macrocyclic hosts for enhancing RTP. This Account starts with a brief introduction of the recent development of organic RTP materials as well as the host-guest interaction and co-assembly. Then, we introduce a supramolecular solid-state RTP strategy involving an ultrahigh phosphorescent quantum yield via the tight encapsulation of macrocyclic host cucurbit[6]uril, an ultralong lifetime via changing the substituents of phosphors, and long-lived and bright RTP by the synergy of host-guest interaction and polymerization. Meanwhile, the applications of solid-state RTP materials for anti-counterfeiting and data encryption are presented. The third part will be the water-phase supramolecular phosphorescence systems constructed by water-soluble macrocyclic host cucurbit[8]uril. Host-guest interaction and polymerization worked together toward efficient phosphorescence in aqueous solution, and the multi-stage assembly promoted phosphorescent applications such as cell targeted imaging and energy transfer. A humidity sensor and data encryption by the conversion of supramolecular hydrogels and xerogels are also involved. In the summary section, we present perspectives and possible research directions for supramolecular phosphorescence.Furthermore, on the basis of previous research, we would like to conclude and propose the developing concept of "macrocycles enhance guest's phosphorescence", and this concept not only means that the macrocyclic host limits the movement of the guest compound or promotes interactions between guest compounds but also involves the synergetic enhancement centered on macrocyclic compounds via multi-stage supramolecular assembly which further improves the efficiency of RTP, water solubility, and biocompatibility. And we believe that this concept will be able, together with theory of "assembly-induced emission" and "aggregation-induced emission", to accelerate the development of purely organic RTP materials.

Supramolecular Purely Organic Room-Temperature Phosphorescence.

The design and characterization of purely organic room-temperature phosphorescent (RTP) materials for optoelectronic applications is currently the focus of research in the field of organic electronics. Particularly, with the merits of preparation controllability and modulation flexibility, host-guest material systems are encouraging candidates that can prepare high-performance RTP materials. By regulating the interaction between host and guest molecules, it can effectively control the quantum efficiency, luminescent lifetime, and color of host-guest RTP materials, and even produce RTP emission with stimuli-responsive features, holding tremendous potential in diverse applications such as encryption and anti-counterfeiting, organic light-emitting diodes, sensing, optical recording, etc. Here a roundup of rapid achievement in construction strategies, molecule systems, and diversity of applications of host-guest material systems is outlined. Intrinsic correlations between the molecular properties and a survey of recent significant advances in the development of host-guest RTP materials divided into three systems including rigid matrix, exciplex, and sensitization are presented. Providing an insightful understanding of host-guest RTP materials and offering a promising platform for high throughput screening of RTP systems with inherent advantages of simple material preparation, low-cost, versatile resource, and controllably modulated properties for a wide range of applications is intended.

Recent Advances on Host-Guest Material Systems toward Organic Room Temperature Phosphorescence.

Purely organic room-temperature phosphorescence has attracted attention for bioimaging but can be quenched in aqueous systems. Here we report a water-soluble ultralong organic room-temperature phosphorescent supramolecular polymer by combining cucurbit[n]uril (CB[7], CB[8]) and hyaluronic acid (HA) as a tumor-targeting ligand conjugated to a 4-(4-bromophenyl)pyridin-1-ium bromide (BrBP) phosphor. The result shows that CB[7] mediated pseudorotaxane polymer CB[7]/HA–BrBP changes from small spherical aggregates to a linear array, whereas complexation with CB[8] results in biaxial pseudorotaxane polymer CB[8]/HA–BrBP which transforms to relatively large aggregates. Owing to the more stable 1:2 inclusion complex between CB[8] and BrBP and the multiple hydrogen bonds, this supramolecular polymer has ultralong purely organic RTP lifetime in water up to 4.33 ms with a quantum yield of 7.58%. Benefiting from the targeting property of HA, this supramolecular polymer is successfully applied for cancer cell targeted phosphorescence imaging of mitochondria. Room-temperature phosphorescence has attracted attention for bioimaging, but quenching in aqueous systems is an issue. Here, the authors report on the synthesis of a water soluble organic phosphorescent polymer and demonstrate application is cancer cell targeting and imaging.

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Ultralong purely organic aqueous phosphorescence supramolecular polymer for targeted tumor cell imaging.

Constructing ultralong organic phosphorescent materials possessing a high quantum yield is challenging. Herein, assemblies of purely organic supramolecular pins composed of alkyl-bridged phenylpyridinium salts and cucurbit[8]uril (CB[8]) are reported. Different from "one host with two guests" and "head-to-tail" binding, the binding formation of supramolecular pins is "one host with one guest" and "head-to-head," which overcomes electrostatic repulsion and promotes intramolecular charge transfer. The supramolecular pin 1/CB[8] displays afterglow with high phosphorescence quantum yield (99.38%) after incorporation into a rigid matrix, which is the highest yield reported to date for phosphorescent materials. Moreover, multicolor photoluminescence can be obtained by different excitation wavelengths and ratios of host to guest. Owing to the redshift of the absorption, the supramolecular pins are applied for targeted phosphorescence imaging of mitochondria. This work will provide a reasonable supramolecular strategy to achieve redshifted and efficient phosphorescence both in the solid state and in aqueous solution.

Zhixue Liu

Papers

Ultralong purely organic aqueous phosphorescence supramolecular polymer for targeted tumor cell imaging.

Supramolecular Pins with Ultralong Efficient Phosphorescence

Organic supramolecular aggregates based on water‐soluble cyclodextrins and calixarenes

A highly efficient light-harvesting system with sequential energy transfer based on a multicharged supramolecular assembly

Controllable Singlet Oxygen Generation in Water Based on Cyclodextrin Secondary Assembly for Targeted Photodynamic Therapy.