Recent advances in organic fluorescent dyes and responsive materials: from molecular design to functional biomedical applications.

The structural versatility, excellent sensitivity and bio-compatibility of organic fluorophores and responsive luminescent materials have made them essential detection and bio-imaging tools in the recent past. The capacity to precisely adjust photophysical parameters like absorption/emission wavelength, quantum yield, luminescence, and response has been made possible through rational design and synthesis approaches. Emphasis is placed on rational synthetic approaches guided by factors such as structure-photophysical relationships, structure-activity relationships and response pathways controlling fluorescence tenability. This work offers a critical and comprehensive review of the chemistry and functional applications of the most recent organic fluorescent dyes and other materials in biology. Key approaches in rational functionalization of these compounds include modifications to functional groups, extending π-conjugation systems, and attachment of various heteroatoms, among other approaches. These chemistry approaches aim to enhance near-infrared emission, fluorescence intensity quantification (ratiometry), and turn-on sensitivity in vitro and in vivo. Various classes of fluorophores including boron-dipyrromethene, coumarins, and cyanines, among others are explored in this work. Their biological compatibility, selective targeting efficacy, and signal-to-noise ratio reduction are also discussed vis-à-vis clinical applicability of fluorescent materials. Finally, the prevailing challenges and future prospects in this interesting area are addressed.