Synthesis, Properties, and Functionalization of Nonsymmetric 8-MethylthioBODIPYs

Five new nonsymmetric BODIPY dyes based on the Biellmann methodology [NSBBs (nonsymmetrical Biellmann BODIPYs)] were prepared by condensation of pairs of different pyrroles with thiophosgene. Treatment of the resulting thioketones with MeI and BF3·Et2O/TEA yielded a wide range of products in a simple manner, with selective alkylation of each pyrrole of the indacene core and with controlled functionalization at the meso position. A comprehensive combined photophysical and computational study has been conducted to determine the impact of the alkylation pattern, as well as the role of the conformational freedom and electron coupling of 8‐phenyl and 8‐methylthio groups on the spectroscopic signatures of BODIPYs. The results and conclusions reached are compared with those for previously reported related analogues. We intend to provide key structural guidelines with regard to the factors that trigger the fluorescence responses and spectral shifts of multifunctional fluorophores of this family. New nonsymmetric 8‐methylthioBODIPYs featuring selective alkylation of the pyrrole systems were synthesized and their specific functionalization at the meso position was achieved. The combined photophysical and computational characterization of these dyes provides key structural guidelines for modulation of their spectral band positions, as well as their fluorescence responses.