RESUMO
A B,N-diphenyl-5,10-dihydro-dibenzo-1,4-azaborine, in which both phenyl groups on the boron and nitrogen atoms are planarized to generate a carbazole substructure, was synthesized. The structral constraint around the boron and nitrogen atoms alters the π-conjugation mode and thus the photophysical and electrochemical properties. Specifically, this structurally constrained dibenzoazaborine showed an intense blue emission with a narrow full width at half maximum. One of its derivatives exhibited near infrared absorption in the one-electron-oxidized state.
RESUMO
The precise control of on-off switching is essential to the design of ideal molecular sensors. To understand the switching mechanism theoretically, we selected as representative example a 9-anthryltriphenylstibonium cation, which was reported as a fluoride ion sensor. In this molecule, the first excited singlet state exhibits two minimum geometries, where one of them is emissive and the other one dark. The excited state at the geometry with bright emission is of π-π* character, whereas it is of π-σ* character at the "dark" geometry. Geometry changes in the excited state were identified by geometry optimization and partial potential energy surface (PES) mapping. We also studied Group V homologues of this molecule. A barrierless relaxation pathway after vertical excitation to the "dark" geometry was found for the Sb-containing compound on the excited-states PES, whereas barriers appear in the case of P and As. Molecular orbital analysis suggests that the σ* orbital of the antimony compound is stabilized along such relaxation and that the excited state changes its nature correspondingly. Our results indicate that the size of the central atom is crucial for the design of fluoride sensors with this ligand framework.