On the Aggregation Behaviour and Spectroscopic Properties of Alkylated and Annelated Boron‐Dipyrromethene (BODIPY) Dyes in Aqueous Solution

Abstract

The 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.

Modulating the Optical Properties of BODIPY Dyes by Noncovalent Dimerization within a Flexible Coordination Cage

“… 16 − 19 An additional advantage of BODIPY dyes is that their optical properties are strongly dependent on and can be modulated by the degree of dye aggregation as well as the mutual orientation of the dye molecules within the aggregates. 20 The optical properties of such aggregates are typically rationalized by Kasha’s molecular exciton theory, which was described 21 4 years before the first synthesis 22 of BODIPY. According to this model, dipole–dipole interactions between two chromophore units split the energy of the excited state within the dimer into two energy levels.…”

What is Best Strategy for Water Soluble Fluorescence Dyes?—A Case Study Using Long Fluorescence Lifetime DAOTA Dyes**

“…8,9 Dye aggregation may lead to unwanted changes in absorption and emission spectra, reduced fluorescence intensity and lifetime. [10][11][12][13] But even when aggregates are avoided e.g. by high dilution, moderate water-solubility may still lead to problems arising from hydrophobic interactions with other amphiphilic solutes such as biomacromolecules.…”

A modular approach toward producing nanotherapeutics targeting the innate immune system

“…2, F and G ). The differences in mean fluorescence intensity (MFI) between the two types of model prodrugs likely stem from differences in their distribution within the nanocarrier ( 4 , 16 ). These results show that our combined nanobiologic and lipophilic prodrug approach can be used to efficiently deliver drugs to myeloid (progenitor) cells in the bone marrow.…”