Bimanes in retrospect: An in-depth analysis of their chemical evolution and applications of derivatives over the last half century

Over the last five decades, bimane derivatives have been of great interest due to their unique fluorescence properties and a wide range of applications in several scientific disciplines including Chemistry, Biology, Material Sciences and Physics. This chapter provides the first detailed overlook at the chemical aspects of bimane derivatives evolution: synthesis, structural modifications, and applications for different purposes. Bimanes are low molecular weight heterobicyclic compounds introduced by Kosower and colleagues in the late 1970s. Their core structure, consisting of two fused pyrazolinone rings, exists as syn- and anti-isomers, each exhibiting distinct photophysical properties. syn-Bimanes are highly fluorescent and photostable, making them ideal for biological imaging, protein labeling, and diagnostics. anti-Bimanes show weak fluorescence but can exhibit phosphorescence at low temperatures. The synthesis of bimanes typically involves constructing a pyrazolinone ring, followed by cyclization to produce the bimane core. The choice of base in the last step dictates the formation of the syn- and anti-isomers. Chemical modifications at the α and β positions have enhanced their optical properties for targeted applications. Bimanes also serve as ligands in metal complexes, forming highly sensitive chemical sensors. They find applications in heat-resistant explosive materials, fluorescence sensors, photoremovable protecting groups, glycosidic linkers, laser dyes, and chemical sensors. Density Functional Theory (DFT) calculations can aid predicting their photophysical properties, guiding the development of new derivatives. Despite some limitations, such as low stability under basic conditions or in the presence of strong nucleophiles, ongoing research aims, among other things, to develop water-soluble bimanes for effective use in living cells, promising a bright future for these versatile molecules.