Fundamental studies to emerging applications of pyrrole-BF₂ (BOPHY) fluorophores

BF₂-based fluorophores, such as the well-known BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dye, are prevalently used in diverse research areas (e.g., bioimaging and chemosensing) as they exhibit promising features including high quantum yields, fine-tuned absorption and emission spectra as well as good photostability and biocompatibility. While BODIPY dyes are most commonly used in such applications, other BF₂-based fluorophores, such as BOPHY (bis(difluoroboron)-1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine - which possess their own characteristic features - are rising in popularity and are being used in a range of applications spanning from molecular sensors to photosensitizers for solar cells. This review examines select examples of BOPHY dyes to highlight the progression of their development while detailing their syntheses and photophysical properties including structure-property relationships. Applications of a number of substituted BOPHYs made by the methods described in this review are also presented.