White-light emission from a pyrimidine-carbazole conjugate with tunable phosphorescence-fluorescence dual emission and multicolor emission switching

Synthesis of biaryl-based carbazoles via C-H functionalization and exploration of their anticancer activities

The synthesis of a library of new biaryl-based carbazoles via bidentate directing group-assisted C-H functionalization and preliminary screening of the anticancer properties of biaryl-based carbazoles is reported. While various classes of modified carbazoles are known for their applications in materials and medicinal chemistry, to our knowledge, the biological activities of designed biaryl-based carbazoles have been rarely known. Given the prominence of carbazoles in research in medicinal chemistry, we envisioned the scope for new scaffolds of carbazole-based biaryl structures. We screened the synthesized biaryl-based carbazoles for their anticancer properties against various cancer cell lines such as HeLa (cervical cancer), HCT116 (colon cancer), MDA-MB-231 and MDA-MB-468 (breast cancer). In addition, the hits were also tested in the human embryonic kidney cell line HEK293T to assess their impact on the viability of normal human cells in the presence of these compounds. In this preliminary study, we identified some of the biaryl-based carbazoles as lead compounds with anticancer activities.

Role of Halobenzene Guest Molecules in Modulating Room Temperature Phosphorescence of Benzophenone-Naphthalene Diimide Inclusion Crystals

Materials exhibiting room temperature phosphorescence (RTP) have recently emerged as a subject of significant interest. In this study, we successfully created inclusion crystals by introducing halobenzenes as guests into a host molecule combining benzophenone with naphthalene diimide. This approach led to the creation of fascinating fluorescence and RTP properties dependent on the guest molecules. Notably, crystals containing chlorobenzene showed cyan fluorescence, while those with iodobenzene displayed red RTP. This difference highlights the impact of the guest molecule on the luminescent properties, with the significant external heavy-atom effect of iodobenzene playing a key role in promoting efficient intersystem crossing between the excited singlet and triplet states. Crystals with bromobenzene exhibited a unique blend of fluorescence and RTP, both from benzophenone and naphthalene diimide, highlighting the moderate heavy-atom effect. These findings reveal composite materials with remarkably diverse and interesting optical characteristics.

Mesomerism induced temperature-dependent multicomponent phosphorescence emissions in ClBDBT

Quantum mechanics/molecular mechanics (QM/MM) and molecular dynamics (MD) methods were applied to systematically investigate the temperature-dependent phosphorescence emission of dibenzo[b,d]thiophen-2-yl(4-chlorophenyl)methanone (ClBDBT) and its derivatives. The calculated temperature-dependent spectra on the lowest triplet state (T1) are in good agreement with the experimental observations, which means that the two-component white light emission should stem from the T1 state. The further MD simulations demonstrate the existence of two mesomerism structures at room temperature which can emit two lights simultaneously. The multi-component light emissions induced by mesomerism structures have advantages in balancing the distribution of excitons which could be beneficial to obtain pure white light along with stable Commission Internationale de l'Éclairage (CIE) coordinates. We hope this mesomerism concept can be further used to design new white light emitters based on room-temperature phosphorescence.

Aliphatic Polyesters with White-Light Clusteroluminescence

Single-molecule white-light emission (SMWLE) has many advantages in practical applications; however, the fabrication of SMWLE from nonconjugated luminescent polymers, namely, clusteroluminogens (CLgens), is still a big challenge. Herein, the first example of linear nonconjugated polyesters with SMWLE is reported. Twenty-four kinds of nonconjugated aliphatic polyesters with tunable clusteroluminescence (CL) colors and efficiency were synthesized by the copolymerization of six epoxides and four anhydrides. Experimental and calculation results prove that, at the primary structure level, the balance of structural flexibility and rigidity via adjusting the side-chain length significantly enhances the efficiency of CL without wavelength change. However, altering the chemical structures of the monomer from succinic anhydride to trans-maleic anhydride (MA), cis-MA, and citraconic anhydride (CA), secondary structures of these polyesters change from helix to straight and folding sheet accompanied by gradually red-shifted CL from 460 to 570 nm due to the increase in through-space n-π* interactions, as demonstrated by the computational and experimental results. Then, pure SMWLE with CIE coordination (0.30, 0.32) based on overlapped short-wavelength and long-wavelength CL is achieved in CA-based polyesters. This work not only provides further insights into the emission mechanism of CL but also provides a new strategy to manipulate the properties of CL by regulating the hierarchical structures of CLgens.

Realization of Single-Phase White-Light-Emitting Materials with Time-Evolution Ultralong Room-Temperature Phosphorescence by Coordination Assemblies

Two Cd-based supramolecular coordination polymers, [Cd₃(CzIP)₃(DMF)₂] (1) and [Cd₂(CzIP)₂(DMF)₄] (2), were synthesized by using 5-(carbazol-9-yl) isophthalate (CzIP) as ligands. These two compounds exhibit multiple luminescence emissions; apart from fluorescence, time- and temperature-dependent ultralong phosphorescence (RTP) were also achieved under room conditions. Significantly, compound 1 has a long-lived afterglow of 0.93 s at 545 nm under ambient conditions. Compound 2 shows nearly pure white-light emission with CIE coordinates of (0.33, 0.33) via the dual emission of fluorescence and phosphorescence. It has come to our attention that it is the first example of a luminescent coordination polymer with single-phase white-light emission and color-evolution RTP. In addition, the long-lived RTP materials can be used in time-dependent anticounterfeiting and white-light-emitting diodes. Experimental and singlet and triplet state calculations indicate that both C-H···π interaction and inter- and intramolecular charge transfer interactions could be beneficial to the emission of ultralong RTP.

Luminescent polymorphic crystals: mechanoresponsive and multicolor-emissive properties

Polymorphic organic crystals that can switch their photophysical properties in response to mechanical stimuli are highlighted.

Negative Thermal Quenching of Photoluminescence from Liquid-Crystalline Molecules in Condensed Phases

The luminescence of materials in condensed phases is affected by not only their molecular structures but also their aggregated structures. In this study, we designed new liquid-crystalline luminescent materials based on biphenylacetylene with a bulky trimethylsilyl terminal group and a flexible alkoxy chain. The luminescence properties of the prepared materials were evaluated, with a particular focus on the effects of phase transitions, which cause changes in the aggregated structures. The length of the flexible chain had no effect on the luminescence in solution. However, in crystals, the luminescence spectral shape depended on the chain length because varying the chain length altered the crystal structure. Interestingly, negative thermal quenching of the luminescence from these materials was observed in condensed phases, with the isotropic phase obtained at high temperatures exhibiting a considerable increase in luminescence intensity. This thermal enhancement of the luminescence suggests that the less- or nonemissive aggregates formed in crystals are dissociated in the isotropic phase. These findings can contribute toward the development of new material design concepts for useful luminescent materials at high temperatures.

Metal-Free Organic Luminophores that Exhibit Dual Fluorescence and Phosphorescence Emission at Room Temperature

Dual-fluorescent-phosphorescent compounds have attracted increasing attention in various fields, such as bio-imaging, data protection/encryption, ratiometric luminescence sensing, and white-light emission. Conventional dual-emissive compounds contain a phosphorescent organometallic complex of a precious metal, such as iridium or platinum. However, the use of precious metals in organic materials has several drawbacks. This Minireview focuses on precious-metal-free organic light-emitting materials that exhibit dual fluorescence and phosphorescence emission in the solid state at room temperature to produce bimodal steady-state emission spectra. The dual emitters presented herein are categorized into the following six compound classes: (1) difluoroboron diaroylmethanes, (2) diarylketones, (3) diarylsulfones, (4) triazines and pyrimidines, (5) fused phenazines, and (6) N-arylcarbazoles.

Dual emission in purely organic materials for optoelectronic applications

Purely organic molecules, which emit light by dual emissive (DE) pathways, have received increased attention in the last decade. These materials are now being utilized in practical optoelectronic, sensing and biomedical applications. In order to further extend the application of the DE emitters, it is crucial to gain a fundamental understanding of the links between the molecular structure and the underlying photophysical processes. This review categorizes the types of DE according to the spin multiplicity and time range of the emission, with emphasis on recent experimental advances. The design rules towards novel DE molecular candidates, the most perspective types of DE and possible future applications are outlined. These exciting developments highlight the opportunities for new materials synthesis and pave the way for accelerated future innovation and developments in this area.