Multicolor Photoluminescence of a Hybrid Film via the Dual-Emitting Strategy of an Inorganic Fluorescent Au Nanocluster and an Organic Room-Temperature Phosphorescent Copolymer

Luminescence Properties of Hoechst 33258 in Polyvinyl Alcohol Films

We report a comprehensive investigation of the photophysical properties of Hoechst 33258 (HOE) embedded in polyvinyl alcohol (PVA) films. HOE displays a bright, highly polarized, blue fluorescence emission centered at 430 nm, indicating effective immobilization within the polymer matrix of PVA. Its fluorescence quantum yield is notably high (~0.74), as determined relative to a quinine sulfate standard. In addition, we observed that HOE-doped PVA films exhibit room temperature phosphorescence (RTP) that remains visible for several seconds after UV excitation ceases. The slightly negative phosphorescence anisotropy implies that the triplet-singlet radiative transition is orthogonal to the singlet-singlet transition governing fluorescence. Notably, we observed that direct triplet-state excitation at longer wavelengths (beyond the primary absorption band) produces highly polarized RTP. We believe this possibility of direct triplet-state excitation opens new avenues for studying RTP in polymer-immobilized molecules.

Photofunctional Gold Nanocluster Composites for Bioapplications

Gold nanoclusters (AuNCs), with customized structures and diverse optical properties, are promising optical materials. Constructing composite systems by the assembly and incorporation of AuNCs can utilize their optical properties to achieve diagnostic and therapeutic applications in the biological field. Therefore, the exploration of the assembly behaviors of AuNCs and the enhancement of their performance has attracted widespread interest. In this review, we introduce multiple interactions and assembly modes that are prevalent in nanocomposites and microcomposites based on AuNCs. Then, the functions of AuNC composites for bioapplications are demonstrated in detail. These composite systems have inherited and enhanced the inherent optical performances of the AuNCs to meet diverse requirements for biological sensing and optical treatments. Finally, we discuss the prospects of AuNC composites and highlight the challenges and opportunities in biomedical applications.

Polymerization Based on Modified β-Cyclodextrin Achieves Efficient Phosphorescence Energy Transfer for Anti-Counterfeiting

Supramolecular polymerization can not only activate guest phosphorescence, but also promote phosphorescence Förster resonance energy transfer and induce effective delayed fluorescence. Herein, the solid supramolecular assemblies of ternary copolymers based on acrylamide, modified β-cyclodextrin (CD), and carbazole (CZ) are reported. After doping with polyvinyl alcohol (PVA) and dyes, a NIR luminescence supramolecular composite with a lifetime of 1.07 s, an energy transfer efficiency of up to 97.4% is achieved through tandem phosphorescence energy transfer. The ternary copolymers can realize macrocyclic enrichment of dyes in comparison to CZ and acrylamide copolymers without CD, which can facilitate energy transfer between triplet and singlet with a high donor-acceptor ratio. Additionally, the flexible polymeric films exhibit regulable lifetime, tunable luminescence color, and repeatable switchable afterglow by adjusting the excitation wavelength, donor-acceptor ratio, and wet/dry stimuli. The luminescence materials are successfully applied to information encryption and anti-counterfeiting.

Activating Molecular Room-Temperature Phosphorescence by Manipulating Excited-State Energy Levels in Poly(vinyl alcohol) Matrix

Poly(vinyl alcohol) (PVA) has been found as a wonderful matrix for chromophores to boost their room-temperature phosphorescence (RTP) character by forming abundant hydrogen bonding. Despite the well-utilized protective effect, the constructive role in accelerating the intersystem crossing is less investigated. Here, we focus on its role in manipulating the excited-state energy level to facilitate multiple intersystem crossing channels. Six benzoyl carbazole derivatives do not emit RTP in their solutions, powders, or crystals but exhibit significantly persistent RTP signals when embedded into the PVA matrix. Charge-transfer excited states were trapped by cofacial stacking in crystal, which blocks the intersystem crossing channels. In the PVA matrix, the allowed broad distribution of charge-transfer states covers the locally excited states, offering multiple intersystem crossing pathways via spin-vibronic orbit coupling. Consequently, efficient and persistent heavy-atom-free phosphors have been developed with the highest quantum yields of 7.7% and the longest lifetime of 2.3 s.

Single-Component White Light Emission from a Metal-Coordinated Cyclotriveratrylene-Based Coordination Polymer

A coordination polymer, namely, [Cd₃L(H₂O)₃]·DMA·4H₂O (1) (DMA = N,N-dimethylacetamide), was prepared by the solvothermal reaction of cyclotriveratrylene-based ligand 5,6,12,13,19,20-hexacarboxy-methoxy-cyclotriveratrylene (H₆L) and Cd(NO₃)₂·4H₂O. In 1, a two-dimensional structure was constructed by the connection of hexanuclear Cd-O clusters and L^6- anions. Photoluminescence measurements indicated that 1 displayed tunable photoluminescence through the variation of the excitation wavelength. Significantly, the white light emission of 1 can be observed with a broad excitation wavelength range from 320 to 385 nm. When 1 is excited by 385 nm light, its chromatic coordinate is (0.29, 0.34), which is located very close to the pure white light region (0.33, 0.33). Meanwhile, the color temperature (CCT) is 7994 K, which corresponds well to "cold" white light.

In Situ Synthesis of Gold Nanoclusters in Covalent Organic Frameworks with Enhanced Photodynamic Properties and Antibacterial Performance

In this work, ultrasmall gold nanoclusters (AuNCs) have been in situ synthesized in nanopores of covalent organic framework (COF) nanoparticles, which exhibited enhanced fluorescence, improved photosensitizing capabilities, and promising antibacterial performance. A small organic molecule, 1-vinylimidazole (Vim), was diffused into the nanopores of imine-based COFs and served as a reducing agent and capping ligand for the in situ synthesis of ultrasmall AuNCs. The as-obtained AuNCs were homogeneously distributed throughout the COF nanoparticles whose fluorescence intensity was enhanced remarkably. Due to the efficient electron transfer between AuNCs and COFs and increased separation of photogenerated electron-hole pairs, the light-triggered reactive oxygen species (ROS) production of COFs was prominently enhanced by AuNCs. Moreover, the obtained nanocomposites exhibited an efficient photodynamic killing behavior on Escherichia coli under visible light exposure. Thus, we provide a facile strategy to prepare COF/AuNC nanocomposites for ROS-related applications.

Local Constraints on Junctions to Strengthen Near-Infrared Phosphorescence of Organic Dyes

A strategy involving the effect of the local constraint on junctions for doping-induced phosphorescence was proposed to increase the rigidity of hydrogen-bonded polymer to inhibit the nonradiative decay of the organic phosphorescent dyes and was verified by bromophenol blue (BPB) derivatives as the near-infrared (NIR) phosphorescent dye. It is shown that the effect of local constraints on junctions of β-cyclodextrin in the poly(vinyl alcohol) (PVA-LCPN) matrix can effectively improve the quantum yields of NIR phosphorescence of BPB derivatives. On the basis of the verification and optimization of the system through response surface analysis, the quantum yield of TBPB@PVA-LCPN film based on NIR emission could be increased up to 77% compared with that of TBPB@PVA, reaching 5.3%, and the quantum yield in the NIR region could be improved to 3.6%. The results of response surface analysis are consistent with the phenomenon of our proposed strategy, which can inspire the production of organic materials with NIR RTP emission. Together, this could inform efficient and cheap strategies for increasing the quantum yield of the doping RTP materials.

Encapsulation of gold nanoclusters: stabilization and more

Gold nanoparticles with only a few atoms, known as gold nanoclusters (AuNCs), have dimensions below 2 nm and feature singular properties such as size dependent luminescence. AuNCs are also highly photostable and have catalytic activity, low toxicity and good biocompatibility. With these properties, they are extremely promising candidates for application in bioimaging, sensing and catalysis. However, when stabilized only with small capping ligands, their use is hindered by lack of colloidal stability. Encapsulation of the AuNCs can contribute to provide a more robust protection and even to improve their properties. Here, we review the encapsulation of AuNCs in polymers, silica and metal organic frameworks (MOFs) for applications in bioimaging, sensing and catalysis.

Photophysical studies of a room temperature phosphorescent Cd(ii) based MOF and its application towards ratiometric detection of Hg2+ ions in water

A cadmium based MOF showed room temperature phosphorescence and interacted very selectively with Hg²⁺ ions. The phosphorescence emission at 520 nm gradually disappeared while low intensity fluorescence at 383 nm gradually increased.

One-pot synthesis of β-cyclodextrin modified Au nanoclusters with near-infrared emission

β-Cyclodextrin modified gold nanoclusters with near-infrared emission were facilely and successfully prepared based on a one-pot and green supramolecular macrocycle modification strategy.

Facile synthesis of a micro-scale MOF host–guest with long-lasting phosphorescence and enhanced optoelectronic performance

Micro-scale MOF host–guest with tunable phosphorescence and enhanced optoelectronic performance can be obtained by a facile and scalable precipitation process in aqueous solution.

Heavy-atom-free amorphous materials with facile preparation and efficient room-temperature phosphorescence emission

Amorphous pure organic room-temperature phosphorescent small molecules without heavy atoms were designed and facilely preparedviamodification of heavy-atom-free luminophores onto β-cyclodextrin.

Dual fluorescence of tetraphenylethylene-substituted pyrenes with aggregation-induced emission characteristics for white-light emission

This article presents a new strategy to achieve white-light emission from single tetraphenylethylene-substituted pyrenes (TPE-Pys) with aggregation-induced emission (AIE) characteristics. TPE-Pys were synthesized by a Pd-catalyzed coupling reaction of a boronic acid or pinacol ester of pyrene and tetraphenylethylene (TPE) derivatives and showed multicolor emission by introducing different substituents on the phenyl rings of TPE. TPE-Pys with a TPE unit at the 1-position and asymmetric TPE units at 2,7-positions show dual fluorescence in THF/water mixtures to realize white-light emission with CIE coordinates of (x = 0.30 and y = 0.41) and (x = 0.21 and y = 0.16), respectively. The structure-property relationship of TPE-Pys were investigated to elucidate the origin of the white emission. The results showed that due to the weak electronic interaction of pyrene and its chromophoric units at the 2,7-positions and the constraint of the rotation of the TPE unit at the 1-position of pyrene, each component can exhibit its own emission color. The combination of appropriate colors gives rise to white-light emission. Such a principle of molecular design may open a new avenue for preparing advanced multicolor and multifunctional optical materials for organic electronics.

Amorphous Pure Organic Polymers for Heavy-Atom-Free Efficient Room-Temperature Phosphorescence Emission

Pure organic, heavy-atom-free room-temperature phosphorescence (RTP) materials have attracted much attention and have potential applications in photoelectric and biochemical material fields owing to their rich excited state properties. They offer long luminescent lifetime, diversified design, and facile preparation. However, recent achievements of efficient phosphorescence under ambient conditions mainly focus on ordered crystal lattices or embedding into rigid matrices, which require strict growth conditions and have poor reproducibility. Herein, we developed a concise approach to give RTP with a decent quantum yield and ultralong phosphorescence lifetime in the amorphous state by radical binary copolymerization of acrylamide and different phosphors with oxygen-containing functional groups. The cross-linked hydrogen-bonding networks between the polymeric chains immobilize phosphors to suppress non-radiative transitions and provide a microenvironment to shield quenchers.

Secondary inner filter effect allows extremely efficient pure white light emission by spatially separated organic fluorophores

White light emission with 70 ± 3% efficiency under dilute conditions was obtained via the secondary inner filter effect between 2-(1-pyrenyl)benzimidazole (PyBIM) and pyrelene monoimide (PMI).