Straightforward Access to Multifunctional π-Conjugated P-Heterocycles Featuring an Internal Ylidic Bond

Synthesis, Structures, and Properties for PIII-Doped Hetero-Buckybowls and Their Phosphonium Salts

Doping polycyclic aromatic hydrocarbons with heteroatoms enables manipulation of their electronic structures. Herein, the structures and properties of phosphorus (P) doped heterosumanenes (HSEs) are regulated by varying the valence states of P-dopant. The phosphine sulfide (PV) and chalcogens (S, Se, Te) co-doped HSEs (1-3) are reduced to trivalent phosphorus (PIII) doped analogues 4-6. Then, the PIII-dopants on 4-6 are converted to phosphonium salts (R4P+), giving 7-9. The valence states of P-dopant show great influence on molecular geometries and electronic structures. Taking P and S co-doped HSEs as example, bowl-depths increase in the order of 1 (PV)<7 (R4P+)<4 (PIII), and the HOMO energy levels and HOMO-LUMO gaps increase to be 7<1<4. Consistent with the theoretical calculation, the first oxidation potentials decrease and the absorption/emission bands show blue shift from 7 to 1 to 4. The transformation of PV to PIII leads to large variations on the coordination with Ag+, owing to the alteration of coordination site from P=S to PIII. The phosphonium salts show ring-opening of phosphole rings under electrochemical reduction. It is found that chalcogen atoms play pivotal roles on coordination patterns of coordination complexes and the conversion rates of ring-opening reactions.

Synthesis of P-Containing Polycyclic Aromatic Hydrocarbons from Alkynyl-phosphonium Salts

This work presents a straightforward method for synthesizing a series of phosphorus-containing polycyclic aromatic hydrocarbons (P-PAHs) featuring an internal ylidic bond. The method involves anion exchange, alkyne annulation, and deprotonation reactions, enabling the efficient production of cyclic phosphonium salts, which serve as pivotal intermediates in the synthesis of P-PAHs. The alkyne annulation reaction exhibits high regioselectivity, ensuring the successful synthesis of λ5-phosphaphenanthrene isomers. Additionally, the incorporation of electron-withdrawing groups effectively stabilizes the internal ylidic bond of P-PAHs.

Phospha-cyanines in Their Ideal Polymethine State: Synthesis and Structure-Property Relationships

We report the synthesis and full characterization of a family of phosphorus-containing polymethine cyanines (phospha-cyanines). The compounds are easily prepared in two steps, starting from readily available phosphanes. The impact of the P-substituents and the counterions on the structural and optical properties is investigated through a joint experimental/theoretical approach. Based on the study of the single-crystal X-ray diffraction structures, all phospha-cyanines present a bond length alternation close to zero, independently of the substituents and counterions, which indicates an ideal polymethine state. All these compounds display the typical cyanine-like UV-vis absorption with an intense and sharp transition with a vibronic shoulder despite possessing a reverse electronic configuration compared to "classical" cyanines. Time-dependent density-functional theory calculations allowed us to fully rationalize the optical properties (absorption/emission wavelengths, luminescence quantum yields). Interestingly, due to the tetrahedral shape of the P atom, the optical properties are independent of the counterion, which is in marked contrast with N-analogues, which enables predictive engineering of the phospha-cyanines regardless of the medium in which they are used.

Azaphosphinines and their derivatives

Six-membered heterocycles containing one phosphorus and one nitrogen atom, known as azaphosphinines, have existed in the shadows of their single heteroatom-containing analogues for almost 150 years. Despite this, recent chemistry has seen a rapid increase in publications concerning this uncommon scaffold. Azaphosphinines exist in one of six isomers-there are three possible orientations of the pnictogen atoms and in each of these, the phosphorus is in one of two valences (PIIIvs. PV). This review aims to outline and inform on the synthesis and applications of all six isomers. PV-oxo azaphosphinines are of particular interest to this review as many of the discussed heterocycles either form as the pentavalent species directly or oxidize to this over time. In very recent years the published applications of azaphosphinines have blossomed into subjects spanning several fields of chemistry such as asymmetric catalysis, supramolecular association, cellular imaging, and medicinal chemistry.

Three-Component Synthesis of Dioxaphosphorane-Fused Diphosphacycles Exhibiting Unique Dynamic Fluorescence "On/Off" Properties

Rigidly planar polycyclic phosphacycles featuring an internal dioxaphosphorane are promising photofunctional materials. However, the lack of efficient synthetic methods resulted in limited structural diversities which significantly hampered extensive study. Herein, we report a straightforward three-component synthesis of novel dioxaphosphorane-fused diphosphacycles with distinctive photophysical properties. Control experiments and theory calculations were performed to account for a plausible reaction mechanism. We also systematically investigated the structure-property relationships of these unprecedented platforms by combining experiments (X-ray analysis, optical and redox properties) and theoretical computations. Based on their unique structure and properties, a novel fluorescent switch for pH sensing was revealed by a dynamic ring-opening/ring-closing process.