Luminescent Organogels Formed by Ionic Self‐Assembly of AIE‐Active Phospholes

Yellow to blue switching of fluorescence by the tuning of the pentaphenylphosphole structure: phosphorus electronic state vs. ring conjugation

The interaction between diphenylacetylene and dichlorophenylphosphine under various conditions is a simple method for the preparation of pentaphenylphosphole derivatives exhibiting fluorescence properties. Depending on the electronic state of the various centers of the phospholic structure, it was possible to obtain molecules with fluorescence, as in the blue area for 1,2,3,4,5-pentaphenyl-2,5-dihydro-phosphole-1-oxide (H₂PPPO), in the yellow area for 1,2,3,4,5-pentaphenylphosphole-1-oxide (PPPO) and in the cyan area for 1,2,3,4,5-pentaphenylphosphole (PPP). The effect of the structure and π-conjugation on the optical properties of these compounds was studied using PPP derivatives as examples. Unusual changes in the optical properties of PPP derivatives in solution and in the crystalline state are explained. In the case of agglomeration of PPPO and PPP molecules, the effect of aggregation-induced emission (AIE) was observed to have weak fluorescence in solution and strong fluorescence in the aggregated state. However, for H₂PPPO, the AIE effect remains mild. With the help of experimental studies, supported by theoretical calculations, the main mechanism of the optical properties of pentaphenylphosphole derivatives has been revealed. It was observed that the intramolecular motions of PPPO and PPP are more limited in the solid state than the motions of H₂PPPO, which is associated with less conjugation of the phenyl rotors of H₂PPPO. The analysis of the structure and distribution of electron density showed why hydrogenation of the phosphole ring leads to a sharp change in the optical properties of pentaphenylphosphole derivatives, while the oxidation of phosphorus does not lead to the disappearance of the AIE effect and to a lesser extent affects the change in the fluorescence wavelength. Thus, it was shown how the regulation of various structural features of the phospholic ring helps to control the optical properties of such compounds.

Trifunctional Silyl Groups as Anchoring Units in the Preparation of Luminescent Phosphole-Silica Hybrids

A synthetic strategy to β-silylphospholes with three methoxy, ethoxy, chloro, hydrido, or phenyl substituents at silicon has been developed, starting from trimethoxy, triethoxy, or triphenyl silyl substituted phenyl phosphanides and 1,4-diphenyl-1,3-butadiyne. These trifunctional silylphospholes were attached to the surface of uniform spheric silica particles (15 μm) and, for comparison, to a polyhedral silsesquioxane (POSS)-trisilanol as a molecular model to explore their luminescent properties in comparison with the free phospholes. Density functional theory calculations were performed to investigate any electronic perturbation of the phosphole system by the trifunctional silyl anchoring unit. For the immobilized phospholes, cross-polarization magic-angle-spinning NMR measurements (¹³C, ²⁹Si, and ³¹P) were carried out to explore the bonding situation to the silica surface. Thermogravimetric analysis and X-ray photoelectron spectroscopy measurements were performed to approximate the amount of phospholes covering the silica surface. Identity and purity of all novel phospholes have been established with standard techniques (multinuclear NMR, mass spectrometry, and elemental analysis) and X-ray diffraction for the POSS derivative.

Phosphetes via Transition Metal Free Ring Closure - Taking the Proper Turn at a Thermodynamic Crossing

A transition metal free route to phosphetes featuring an exocyclic alkene unit is presented. In this approach phosphanides are added to a variety of diynes generating phosphaallylic intermediates which depending on the reaction conditions transform either to phosphetes or the corresponding phospholes. Investigation of the reaction mechanism by combined quantum chemical and experimental means identifies phosphole formation as thermodynamically controlled reaction path, whereas kinetic control furnishes the corresponding phosphetes. Structural and luminescence properties of the rare class of phosphetes are explored, as well as for selected key intermediates.