Tuning the Photonic Behavior of Symmetrical bis-BODIPY Architectures: The Key Role of the Spacer Moiety

Abstract

Herein we describe the synthesis, computationally assisted spectroscopy, and lasing properties of a new library of symmetric bridged bis-BODIPYs that differ in the nature of the spacer. Access to a series of BODIPY dimers is straightforward through synthetic modifications of the pending ortho-hydroxymethyl group of readily available C-8 (meso) ortho-hydroxymethyl phenyl BODIPYs. In this way, we have carried out the first systematic study of the photonic behavior of symmetric bridged bis-BODIPYs, which is effectively modulated by the length and/or stereoelectronic properties of the spacer unit. The designed bis-BODIPYs display bright fluorescence and laser emission in non-polar media. The fluorescence response is governed by the induction of a non-emissive intramolecular charge transfer (ICT) process, which is significantly enhanced in polar media. The effectiveness of the fluorescence quenching and also the prevailing charge transfer mechanism (from the spacer itself or between the BODIPY units) rely directly on the electron-releasing ability of the spacer. Moreover, the linker moiety can also promote intramolecular excitonic interactions, leading to excimer-like emission characterized by new spectral bands and the lengthening of lifetimes. The substantial influence of the bridging moiety on the emission behavior of these BODIPY dyads and their solvent-sensitivity highlight the intricate molecular dynamics upon excitation in multichromophoric systems. In this regard, the present work represents a breakthrough in the complex relationship between the molecular structure of the chromophores and their photophysical signatures, thus providing key guidelines for rationalizing the design of tailored bis-BODIPYs with potential advanced applications.

Aggregation enhances luminescence and photosensitization properties of a hexaiodo-BODIPY

“…It is known that the presence of multiple chromophores in close proximity often leads to exciton coupling between dyes thereby resulting in significant changes in the absorption and emission properties. [56][57][58][59] Thus, the presence of three BODIPY units around the central phenyl ring plausibly promotes intramolecular interactions thereby resulting in quenching of fluorescence. The observation of negligible difference in the absorbance but a significant red-shift in the emission maximum of B 3 as compared to B and B 2 (Table 1) suggests excited state interactions.…”

A Concise Route to Water-Soluble 2,6-Disubstituted BODIPY-Carbohydrate Fluorophores by Direct Ferrier-Type C-Glycosylation

“…The fluorescence response of 16 is lower than that of its corresponding monomeric precursor, especially in polar media (Figure and Table S3). Similar results were previously reported for nonglycosylated urea-bridged bis-BODIPYs. , As mentioned above, each chromophoric fragment retains its molecular identity after covalent assembly, thus showing isoenergetic excited states and electronic transitions that enable energy and electron transfer processes. The migration of energy between bridged BODIPY units could quench the fluorescence through the dissipation of excitation energy as heat, but it solely cannot explain the marked solvent-sensitive fluorescence response of 16 .…”

“…The migration of energy between bridged BODIPY units could quench the fluorescence through the dissipation of excitation energy as heat, but it solely cannot explain the marked solvent-sensitive fluorescence response of 16 . Such polarity-triggered fluorescence quenching was ascribed to an additional nonradiative pathway such as photoinduced electron transfer (PET) between the pair of identical BODIPYs electronically decoupled in the ground state. − This electron transfer mechanism with no electrostatic driving force is enhanced by the solvent polarity, thus decreasing the fluorescence efficiency in polar media (Figure and Table S3).…”