BODIPY Compounds Substituted on Boron

BODIPY compounds are important organic dyes with exceptional spectral and photophysical properties and numerous applications in different scientific fields. Their widespread applications have flourished due to their easy structural modifications, which enable preparation of different molecular structures with tunable spectral and photophysical properties. To date researchers mostly devoted efforts to modify BODIPY meso-position or pyrrole rings, whereas substitution of fluorine atoms remained not widely explored. However, chemistry on the boron atom is possible, and it enables tuning of photophysical properties of the dyes, without tackling their spectral properties. Furthermore, modifications on boron affect solubility and aggregation propensity of the molecules. This review article highlights methods for the preparation of B-substituted compounds and the most important reactions on the boron of the BODIPY dyes. They were divided into reactions promoted by Lewis acid (AlCl3, or BCl3), or bases such as alkoxides and organometallic reagents. By use of these two methodologies it is possible to clave B-F bonds and substitute them with B-C, B-N, or B-O bonds from different nucleophiles. A special emphasis in this review is given to still underdeveloped photochemical reactions on the boron atom of BODIPY dyes. These reactions have potential to be used in the development of a new line of BODIPY photo-cleavable protective groups (also known as photocages) with bio-medicinal and photo-pharmacological applications, such as drug delivery.