Synthesis and Photophysical Properties of Carbazole-Functionalized Diazaphosphepines via Sequent P-N Chemistry

Phosphorus-Nitrogen Heterocycles Derived from Chelating N-Donor Ligands: Historical Advances, Recent Highlights, and Outlook

The exploration of phosphorus-nitrogen heterocycles derived from chelating N-donor ligands is an area of research that has lagged behind the development of similar heterocycles based on other main group elements, most notably boron. The fact that phosphorus and nitrogen are both group 15 elements and that their compounds are most commonly viewed as Lewis bases likely contributes to this observation. However, through judicious ligand design and creative use of phosphorus sources that render phosphorus as Lewis acidic and/or electron poor, a variety of heterocyclic architectures are possible. In this article, we highlight selected examples of phosphorus adducts of bidentate, tridentate, and tetradentate N-donor ligands that have shown utility as functional molecular materials, in small molecule activation and catalysis, and as therapeutics and diagnostics in chemical biology. Finally, we look forward to the future of this emerging area and provide commentary on the unique opportunities available to researchers working within the field of phosphorus-nitrogen heterocycle chemistry.

Synthetic Strategies for 3,6-Substituted Carbazole-based Polymers and Their Opto-Electronic Applications-A Review

The use of conducting polymers in devices makes them desirable due to their allowance for the fabrication of flexible, lightweight, and potentially inexpensive devices. This review explores the synthetic strategies and characterizations of 3,6-substituted carbazole-based polymers, emphasizing the influence of these modifications on their electronic structure and absorption properties. Polymers containing carbazole substituents are widely studied due to their unique optical and electronic properties, high electron-donating ability, and photoconductivity. The structural adaptability of the carbazole with the 3,6-substitution makes it as an outstanding candidate for their integration into polymers and also possesses improved stability and triplet energy. The role of intramolecular charge transfer (ICT) was highlighted by donor-acceptor architectures with tailoring energy levels to extract their advantageous physicochemical characteristics and optimized performances. Collectively, this comprehensive review delves into the burgeoning field of 3,6-substituted carbazole-based polymers and their crucial role in advancing optoelectronic applications. By amalgamating materials design, synthetic strategies, and application-driven insights, the review serves as a valuable resource for researchers to understand the structure-property relationships and foster innovative solutions for next-generation opto-electronic applications.

Dithieno[3,2-b; 2',3'-f]phosphepinium-Based Near-Infrared Fluorophores: px-π* Conjugation Inherent to Seven-Membered Phosphacycles

Positively charged phosphorus-containing heterocycles are characteristic core skeletons for functional molecules. While various phosphonium-containing five- or six-membered-ring compounds have been reported, the seven-membered-ring phosphepinium have not been fully studied yet. In this study, dithieno[3,2-b; 2',3'-f]phosphepinium ions containing electron-donating aminophenyl groups were synthesized. An X-ray crystallographic analysis of the resulting donor-acceptor-donor dyes revealed a bent conformation of the central seven-membered ring. These compounds exhibit fluorescence in the near-infrared region with a bathochromic shift of ca. 70 nm compared to a phosphepine oxide congener and a large Stokes shift. High fluorescence quantum yields were obtained even in polar solvents due to the suppression of the nonradiative decay process. A theoretical study revealed that the phosphepinium skeleton is highly electron-accepting owing to the orbital interaction between a px orbital of the phosphonium moiety and a π* orbital of the 1,3,5-hexatriene moiety. Due to the lower-lying px orbital in the phosphonium moiety compared to that of the phosphine oxide and the bent conformation of the seven-membered ring, the phosphepinium ring permits effective px-π* conjugation. A large structural relaxation with a contribution of a quinoidal resonance structure is suggested in the excited state, which should be responsible for the bright emission with a large Stokes shift.

Phenoxaphosphonium Mixed Ylides in Ring Expansion Reaction

Treatment of mixed phosphonium-iodonium ylides featuring a six-membered phenoxaphosphonium fragment with aqueous tetrafluoroboronic acid induces a rearrangement, resulting in expansion of the phosphacycle and oxidation of the phosphorus atom. The target difficult-to-access dibenzo[b,f][1,4]oxaphosphepine oxides (3 examples) were isolated in excellent yields (up to 95%) as mixtures of stereoisomers. Hydrolysis of a five-membered mixed ylide, a dibenzophosphole derivative, predominantly preserves the phosphole system with cycle expansion occurring as a side process.