Theoretical study of the structure-property relationship in phosphole monomers

Use of the DFT method with the B3LYP functional offers an efficient way for determining geometries of phosphole structures. It also provides inversion barriers in good agreement with experiment. The molecular orbital MP2 meth od is better suited to calculate the relative stability of the considered i somers. Combination of geometric (Julg index) and magnetic (NICS) criteria leads to an interesting approach to analyze the pi-electron delocalization and/or aromaticity in conjugated heterocyclic systems and can be used for i nvestigation of much larger oligomers. It thus allows us to confirm that pl anarizing the phosphorus atom in phosphole monomers leads to a greater conj ugation over the butadienic pi-system and that substituents, characterized by a strongly pronounced pi-system, exhibit a large extent of conjugation w ith the pi-diene moiety of the heterocyclic system. In push-pull systems su ch as 2-BH2-5-NH2-1H-phosphole, the electron delocalization along the pi-di ene system is even more pronounced than in phospholes with strongly pronoun ced pi-systems. The employed approach is also used to analyze the relations hip between electron conjugation and the phosphorus inversion barrier. More relevant for chemical applications is the result that the computational st udy provides a method of fine-tuning of phosphole building blocks, which ma y enable us to obtain higher pi-conjugation along the polymer backbone.