The Influence of the pi-Conjugated Spacer on Photophysical Properties of Difluoroboranyls Derived from Amides Carrying a Donor Group

摘要

A series of difluoroboranyls derived from amides carrying a variable pi-conjugated spacer between the electron-donating (D) and electron-accepting (A) groups was synthesized and characterized with H-1, B-11 C-13, N-15, and F-19 NMR, electronic absorption, fluorescence spectroscopies, and first-principle calculations. The D-to-A distance in the series varied from 1.5 to 4.5 angstrom, causing bathochromic shifts of both the absorption and fluorescence maxima by more than 120 and 213 nm, respectively. These trends are rationalized by quantum-mechanical calculations that allow for quantification of the charge transfer distance. Theoretical calculations were also performed to determine the vibronic couplings and thus to reproduce the experimental band shapes.