Synthesis of Polysubstituted Symmetrical BODIPYs via Fischer Carbene Complexes: Theoretical, Photophysical and Electrochemical Evaluation

Abstract

A series of new symmetrical highly substituted BODIPYs 6 a–l was synthesized through a prefunctionalization approach in 35 %–89 % yields from the pyrrole core. This strategy allowed modulation of the substituents at the different positions based on the choice of Fischer's alkynyl carbenes, oxazolones and aldehydes used as precursors. The substituent variation at positions 2, 6, 3 and 5 had the greatest effect on the modulation of their photophysical properties such as absorption (λabs) and emission (λem) wavelengths, extinction coefficient (ϵ), quantum yields (ϕ), Stokes shifts (Δν), fluorescence decay, radiative (krad) and non‐radiative (knr) constants and the CIE 1931 coordinates. Theoretical calculations allowed to corroborate the effect of the substituents of meso‐position on the modification of the dihedral angles. Cyclic voltammetry studies revealed that the BODIPY series presents similar redox potential behavior, being electrochemically active even in successive cycles, which suggests that transport by diffusion is the dominant process.

Bathochromic Shift of Fluorescence Peak in Dipyrrolo[1,2-a:2′,1′-c]quinoxaline by Introducing Each of Electron-Donating and Electron-Withdrawing Substituent

“…To achieve a longer fluorescent peak, the introduction of substituents is one of the more efficient methods. However, the various electronic properties of substituents lead to various changes in the fluorescent peak, i.e., a bathochromic shift or a small change was obtained by introducing the electron-withdrawing substituent in the case of hypsochromic shift by the electron-donating substituent, and vice versa [ 10 , 11 , 12 , 13 , 14 ]. For example, Hirano et al reported the substituent effect of 2-phenylimidazo [1,2- a ]pyrazine-3(7 H )-ones which showed the bathochromic shift on fluorescence spectra with an increase in the electron-withdrawing property [ 15 ].…”

Extended BODIPYs as Red–NIR Laser Radiation Sources with Emission from 610 nm to 750 nm

“…According to the literature, several approaches have been successfully tested to span the delocalized π-system of the dipyrrin core and reach the red–NIR spectral window. The main strategies involve the fusion of aromatic rings (aryls and heterocycles, and even other BODIPYs) [ 21 , 22 , 23 ], peripheral linkage of aromatic frameworks (for instance, styryls and the aforementioned cyclic moieties) [ 24 , 25 , 26 ], replacement of the meso -carbon by nitrogen (aza-BODIPYs) [ 27 , 28 ], grafting electron releasing and withdrawing functionalizations (push-pull BODIPYs) [ 29 , 30 ], and the combination of some of these molecular strategies into a single structure [ 31 ]. From such surveys, we find that the tethering of aromatic frameworks, properly functionalized with electron rich groups, at the pyrrolic β and α positions, is one of the successful strategies to induce pronounced spectral shifts, while retaining the high absorption and emission efficiency characteristics of this family of dyes.…”