Phosphorescence Tuning through Heavy Atom Placement in Unsymmetrical Difluoroboron β‐Diketonate Materials

Large-Scale Preparation for Multicolor Stimulus-Responsive Room-Temperature Phosphorescence Paper via Cellulose Heterogeneous Reaction

The large-scale preparation of sustainable room-temperature phosphorescence (RTP) materials, particularly those with stimulus-response properties, is attractive but remains challenging. This study develops a facile heterogeneous B─O covalent bonding strategy to anchor arylboronic acid chromophores to cellulose chains using pure water as a solvent, resulting in multicolor RTP cellulose. The rigid environment provided by the B─O covalent bonds and hydrogen bonds promotes the triplet population and suppresses quenching, leading to an excellent lifetime of 1.42 s for the target RTP cellulose. By increasing the degree of chromophore conjugation, the afterglow colors can be tuned from blue to green and then to red. Motivated by this finding, a papermaking production line is built to convert paper pulp reacted with an arylboronic acid additive into multicolor RTP paper on a large scale. Furthermore, the RTP paper is sensitive to water because of the destruction of hydrogen bonds, and the stimuli-response can be repeated in response to water/heat stimuli. The RTP paper can be folded into 3D afterglow origami handicrafts and anti-counterfeiting packing boxes or used for stimulus-responsive information encryption. This success paves the way for the development of large-scale, eco-friendly, and practical stimuli-responsive RTP materials.

Polymer-Based Long-Lived Phosphorescence Materials over a Broad Temperature Based on Coumarin Derivatives as Information Anti-Counterfeiting

The development of new polymer-based room-temperature phosphorescence materials is of great significance. By a special molecule design and a set of feasible property-enhancing strategies, coumarin derivatives (CMDs, M_a-M_f) were doped into polyvinyl alcohol (PVA), polyacrylamide (PAM), corn starch, and polyacrylonitrile (PAN) as information anti-counterfeiting. CMDs-doped PVA and CMDs-doped corn starch films showed long-lived phosphorescence emissions up to 1246 ms (M_a-PVA) and 697 ms (M_a-corn starch), reaching over 10 s afterglow under naked eye observation under ambient conditions. Significantly, CMDs-doped PAM films can display long-lived phosphorescence emissions in a wide temperature range (100-430 K). For example, the M_e-PAM film has a phosphorescence lifetime of 16 ms at 430 K. The use of PAM with the strong polarity and rigidity has expanded the temperature range of long-life polymer-based phosphorescent materials. The present long-lived phosphorescent systems provide the possibility for developing new polymer-based organic afterglow materials with robust phosphorescence.

Recent advances in the synthesis of luminescent tetra-coordinated boron compounds

Tetra-coordinated boron compounds offer a plethora of luminescent materials. Different chelation around the boron center (O,O-, N,C-, N,O-, and N,N-) has been explored to tune the electronic and photophysical properties of tetra-coordinated boron compounds. A number of fascinating molecules with interesting properties such as aggregation induced emission, mechanochromism and tunable emission by changing the solvent polarity were realised. Owing to their rich and unique properties, some of the molecules have shown applications in making optoelectronic devices, probes and so on. This perspective provides an overview of the recent developments of tetra-coordinated boron compounds and their potential applications.

Recent Advances on Host-Guest Material Systems toward 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.

Modulating Tri-Mode Emission for Single-Component White Organic Afterglow

Achieving single-component white organic afterglow remains a great challenge owing to the difficulties in simultaneously supporting long-lived emissions from varied excited states of a molecule for complementary afterglow. Here, an extraordinary tri-mode emission from the radiative decays of singlet (S₁ ), triplet (T₁ ), and stabilized triplet (T₁ ^* ) excited states was proposed to afford white afterglow through modulating the singlet-triplet splitting energy (ΔE_ST ) and exciton trapping depth (E_TD ). Low-lying T₁ * for yellow afterglow was constructed by H-aggregation engineering with large E_TD and trace isomer doping, while high-lying T₁ and S₁ for blue afterglow with thermally activated emission feature were realized by reducing ΔE_ST through donor-acceptor molecular design. Therefore, the single-component white afterglow with high efficiency of 14.1 % and a lifetime of 0.61 s was achieved by rationally regulating the afterglow intensity ratios of complementary emissions from S₁ , T₁ , and T₁ *.

Direct photo-induced reductive Heck cyclization of indoles for the efficient preparation of polycyclic indolinyl compounds

The photo-induced cleavage of C(sp2)-Cl bonds is an appealing synthetic tool in organic synthesis, but usually requires the use of high UV light, photocatalysts and/or photosensitizers. Herein is described a direct photo-induced chloroarene activation with UVA/blue LEDs that can be used in the reductive Heck cyclization of indoles and without the use of a photocatalyst or photosensitizer. The indole compounds examined display room-temperature phosphorescence. The photochemical reaction tolerates a panel of functional groups including esters, alcohols, amides, cyano and alkenes (27 examples, 50-88% yields), and can be used to prepare polycyclic compounds and perform the functionalization of natural product analogues in moderate to good yields. Mechanistic experiments, including time-resolved absorption spectroscopy, are supportive of photo-induced electron transfer between the indole substrate and DIPEA, with the formation of radical intermediates in the photo-induced dearomatization reaction.

Activating Room-Temperature Phosphorescence of Organic Luminophores via External Heavy-Atom Effect and Rigidity of Ionic Polymer Matrix*

Pure organic room-temperature phosphorescence (RTP) materials have attracted wide attention for their easy preparation, low toxicity, and applications in various fields like bioimaging and anti-counterfeiting. Developing phosphorescent systems with more universality and less difficulty in synthesis has long been the pursuit of materials scientists. By employing a polymeric quaternary ammonium salt with an ionic bonding matrix and heavy atoms, commercial fluorescent dyes are directly endowed with phosphorescence emission. In a single amorphous polymer, the external heavy-atom effect generates excited triplet states and the rigid polymer matrix stabilizes them. This study put forward a new general strategy to design and develop pure organic RTP materials starting from existing library of organic dyes without complicated chemical synthesis.

Recent advances in dioxaborine-based fluorescent materials for bioimaging applications

Fluorescent materials are continuously contributing to important advances in the field of bioimaging. Among these materials, dioxaborine-based fluorescent materials (DBFM) are arousing growing interest. Due to their rigid structures conferred by a cyclic boron complex, DBFM possess appealing photophysical properties including high extinction coefficients and quantum yields as well as emission in the near infrared, enhanced photostability and high two-photon absorption. We herein discuss the recent advances of DBFM that found use in bioimaging applications. This review covers the development of fluorescent molecular probes for biomolecules (DNA, proteins), small molecules (cysteine, H₂O₂, oxygen), ions and the environment (polarity, viscosity) as well as polymers and nanomaterials used in bioimaging. This review aims at providing a comprehensive and critical insight on DBFM by highlighting the assets of these promising materials in bioimaging but also by pointing out their limitations that would require further developments.

Recent developments in stimuli-responsive luminescent polymers composed of boron compounds

This review summarizes recent developments in stimuli-responsive luminescent polymers with boron chromophores, including three- and four-coordinated compounds. Sensing mechanisms based on the features of boron and polymer structures are described.

Long-Lived Room-Temperature Phosphorescence for Visual and Quantitative Detection of Oxygen

An unconventional organic molecule (TBBU) showing obvious long-lived room temperature phosphorescence (RTP) is reported. X-ray single crystal analysis demonstrates that TBBU molecules are packed in a unique fashion with side-by-side arranged intermolecular aromatic rings, which is entirely different from the RTP molecules reported to date. Theoretical calculations verify that the extraordinary intermolecular interaction between neighboring molecules plays an important role in RTP of TBBU crystals. More importantly, the polymer film doped with TBBU inherits its distinctive RTP property, which is highly sensitive to oxygen. The color of the doped film changes and its RTP lifetime drops abruptly through a dynamic collisional quenching mechanism with increasing oxygen fraction, enabling visual and quantitative detection of oxygen. Through analyzing the grayscale of the phosphorescence images, a facile method is developed for rapid, visual, and quantitative detection of oxygen in the air.

Theoretical insights into UV-Vis absorption spectra of difluoroboron β-diketonates with an extended π system: An analysis based on DFT and TD-DFT calculations

The UV-Vis absorption spectra of difluoroboron β-diketonates with aromatic substituents at the β-carbon are studied thoroughly using DFT and TD-DFT with the CAM-B3LYP functional. The complicated experimental spectra of these dyes can be correctly interpreted by considering their structural features. A closer look at the calculated data shows that the conformational flexibility of these compounds markedly influences their spectral shape. For the complexes with an extended π system, several conformers with significantly different absorption spectra are present in the equilibrium mixture in solution. Introducing a donor group alters the electronic structure of the complexes, so the charge distribution asymmetry in the molecules increases and the nature of the electronic transitions changes. Thus, both types of substituents, aromatic and donor ones, affect the spectral shape. Understanding their roles may help one to explain the absorption spectra of these and similar compounds and predict their response to analytes and other factors.

Spectroscopic and quantum chemical study of difluoroboron β-diketonate luminophores: Isomeric acetylnaphtholate chelates

The electronic structure and optical properties of the isomeric difluoroboron β-diketonates, 2,2-difluoro-4-methylnaphtho-[2,1-e]-1,3,2-dioxaborin (I) and 2,2-difluoro-4-methylnaphtho-[1,2-e]-1,3,2-dioxaborin (II), were studied by means of X-ray photoelectron, absorption and luminescence spectroscopies. The experimental results were interpreted using high-level ab initio quantum chemical computations, including the algebraic-diagrammatic construction method for the polarization propagator of the second and third orders (ADC(2) and ADC(3)), the outer-valence Green's function (OVGF) method, and the time-dependent density functional (TDDFT) approach. The X-ray photoelectron measurements were assigned in the entire energy range using the results of the Kohn-Sham orbital calculations which employed the B3LYP functional. Pronounced hypsochromic shift of crystal-state fluorescence was observed in I upon the lowering of temperature, which can be explained by the deterioration of the conditions for excimers formation. According to our results, remarkable feature of II, absent in I, is its phosphorescence at room temperature. Basing on our calculations, a decay mechanism for the S₁ state was proposed, explaining the observed differences in the phosphorescence of I and II.