Tuning the Electronic Structure of BODIPY-Coumarin Ratiometric Fluorescent Sensors for Accurate Microviscosity Monitoring Applications.

Abstract

Fluorescent molecular rotors (FMRs) have emerged as versatile tools for assessing microviscosity in biological and physicochemical environments. This study presents the design, synthesis, and characterization of two novel ratiometric viscosity sensors based on BODIPY-Coumarin derivatives, in which the chromophores are electronically isolated by an ester bridge. This structural feature aims to mitigate polarity-dependent effects and optimize their ratiometric performance. The synthesis was carried out through a multistep approach, including microwave-assisted esterification, achieving high yields. Structural characterization, based on single-crystal X-ray diffraction and DFT calculations, confirmed the electronic isolation of the chromophores, while photophysical studies revealed polarity-independent emission from the BODIPY fragment. Both sensors exhibited high sensitivity to viscosity variations over a broad range in DMSO/glycerol mixtures. These findings highlight the potential of these FMRs as advanced tools for microenvironment studies, providing a promising platform for future applications in biochemistry and materials science.