Evolution of BODIPY/aza-BODIPY dyes for organic photoredox/energy transfer catalysis

Over the past few decades, photocatalysis has been established as a rapidly escalating research area to catalyse the chemical reactions induced by visible light through single electron transfer (SET) and energy transfer (EnT) processes between a photocatalyst and an organic substrate. The conventional photocatalysts such as transition metal catalysts used for organic synthetic transformations face some drawbacks such as weak visible light absorbance, expensive, potentially toxic, and difficult to synthesize. As well as organic photocatalysts, for instance, xanthene dyes like Eosin Y and Rose Bengal exhibit inefficiency to harvest the broadband light source, difficulty to modify the molecular structure, as a result of which the redox potentials of the photocatalysts cannot be readily tuned with different substrates. Photoredox/energy transfer catalysis is the capable embodiment for tomorrow's synthetic research and hence, there is a dire need to overcome the limitations and to develop highly efficient photocatalysts that promote the sustainable energy, and interestingly BODIPY falls in that category. Being the most versatile and widely discussed organic fluorophore, BODIPY has considerable impact on different fields such as fluorescence imaging, photodynamic theory, functionalized materials, optoelectronics and has majorly influenced the field of organic synthesis by its most dynamic property as a photosensitizer. This review article widely discusses the application of the BODIPY/aza-BODIPY dye as a photocatalyst for photoredox/energy transfer catalytic organic reactions to produce simple to highly functionalized organic molecules. BODIPY molecule displays highly desirable chemical and physical properties such as high absorbance in the visible region, remarkable thermal and photochemical stabilities, high fluorescence quantum yield, and modularity, making it the more efficient photocatalyst over the popular conventional photocatalysts. In addition, green/NIR light-absorbing BODIPY photocatalysts with long-lived triplet excited state are utilized to elevate SET and EnT processes for selective photocatalysis under mild condition. This review presents a broad perspective of BODIPY/aza-BODIPY based photocatalysts in synthetic organic transformation and its significant advances over other conventional dyes.