Soluble and highly fluorescent conjugated polymer network: non-oxidative reversible doping, cell imaging and anticancer activity

Herein, we report two soluble and highly fluorescent triazine-based conjugated polymer networks (TCPNs) by conjugating a thiophene (donor) unit with a triazine ring (acceptor) through a phenyl linker. The 3-substituted thiophene moiety with alkyl and oligoethylene glycol side chains is rationally introduced into the polymeric network to improve its solubility and the effect of the side chain polarity on its optical, band gap, conductivity and biological activities was also investigated. When both TCPNs were reacted with a Lewis acid and base respectively, significant optical switching and a conductivity change were observed, indicating efficient non-oxidative doping/de-doping. Both TCPNs exhibit remarkable stability after several switching cycles from their neutral to doped states and vice versa. Doping of the TCPN through the addition of a Lewis acid is also studied via DFT, which clearly shows a narrowing of the band gap. To the best of our knowledge, this may be the first demonstration of the non-oxidative doping of a triazine-based CPN to control the conjugation, color and conductivity. Furthermore, these TCPNs show gelation after doping with a Lewis acid, resulting in the formation of a conducting gel. It is also observed that both TCPNs can enter cells to simultaneously exhibit abilities of fluorescence imaging and cancer cell inhibition. Thus, the described study showcases the potential scope of tuning the optical properties of triazine-based conjugated polymer networks for electronic and optoelectronic applications, as well as the probable use of these polymers for cell imaging and chemotherapeutic applications.