Rational design of signal amplifying fluorescent conjugated polymers for environmental monitoring applications: Recent advances and perspectives

Conjugated polymers (CPs), especially those with donor-acceptor architecture have emerged as a pioneering class of fluorescent material in the field of sensing owing to their multiple exciting features such as high fluorescence quantum yield, good photostability and excellent sensitivity. The remarkable features of CPs are attributed to the presence of delocalized pi-electrons in their backbone structure, which facilitate remarkable sensing response through the unique phenomenon known as "molecular-wire effect". Various types of interactions such as donor-acceptor interactions, hydrogen bonding, pi-pi stacking, and electrostatic interactions are possible between receptor-tagged CPs and the target molecule. These interactions bring them in close proximity and play a vital role in achieving selective sensing. This review paper summarizes the recent progress (especially during past ten years) that has been made in the area of fluorescent CPs for chemical sensing applications with special emphasis on environmental monitoring. Following an introduction into the research area, the first large section describes various synthetic methods (mostly transition-metal catalyzed cross-coupling reactions) and unique properties of CPs. Next section emphasizes the unique phenomenon of "molecular-wire effect", advantages of using CPs as a sensory material, and various fluorescence sensing mechanisms induced by different coordination interactions. Later in the manuscript, we discuss CP-based fluorometric sensors that have been developed for detecting various environmental pollutants, including toxic ions, pesticides, antibiotics, nitro aromatics, and more. The final concluding section gives viewpoints on the present status, current challenges, and an outlook on potential future trends.