Abstract
AbstractThe tendency of boron‐dipyrromethene (BODIPY) dyes to associate in water is well known, and usually a cause for inferior fluorescence properties. Synthetic efforts to chemically improve BODIPYs’ water solubility and minimize this problem have been numerous in the past. However, a deeper understanding of the phenomena responsible for fluorescence quenching is still required. Commonly, the spectroscopic behaviour in aqueous media has been attributed to aggregate or excimer formation, with such works often centring on a single BODIPY family. Herein, we provide an integrating discussion including very diverse types of BODIPY dyes. Our studies revealed that even subtle structural changes can distinctly affect the association behaviour of the fluorophores in water, involving different photophysical processes. The palette of behaviour found ranges from unperturbed emission, to the formation of H or J aggregates and excimers, to the involvement of tightly bound, pre‐formed excimers. These results are a first step to a more generalized understanding of spectroscopic properties vs. structure, facilitating future molecular design of BODIPYs, especially as probes for biological applications.
Highlights
BODIPYs have grown disproportionately high over the last two decades (Figure 1) and the literature reporting the synthesis of new BODIPYs and a description of their optical and chemical properties in organic media is abundant.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
Before we present our results, it is helpful to reflect the current state of knowledge on BODIPY association in water
BODIPY dyes that can be well dissolved in water commonly display identical or very similar spectroscopic properties in aqueous and organic media
Summary
BODIPYs have grown disproportionately high over the last two decades (Figure 1) and the literature reporting the synthesis of new BODIPYs and a description of their optical and chemical properties in organic media is abundant.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] rather few efforts have been devoted to the study of their properties in aqueous solutions.[18,19,20,21,22,23,24,25,26,27,28] This is surprising because on one hand the peculiarities of the application of BODIPYs in water are long since documented even by commercial suppliers[29] yet on the other hand many of the aspired applications such as fluorescence labeling or sensing essentially require operation in aqueous solution. BODIPYs (DHNBDP-H, DHNBDP-Me, DHNBDP-Ph) and three phenanthrene-fused dyes (PBDP-Ph, PBDP-DMA, PBDP-CN), carrying chemical groups with distinctly different electron donating or accepting character in the para-position of the meso-substituent (Scheme 2) Most of these derivatives are highly fluorescent in organic solvents, and especially interesting are the BBDP,[47] DHNBDP[48] and PBDP[44,49] dyes, because they show a strong fluorescence in the red-NIR spectral region
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