Poly(Nipam-Co-Thienoviologen) For Multi-Responsive Smart Windows And Thermo-Controlled Photodynamic Antimicrobial Therapy

Multi-functional copolymers based on NIPAM and thienoviologens with different numbers of thiophene units (n = 1, 2 and 3) were synthesized and their absorption/emission properties were systematically studied. The thienoviologens exhibited significantly decreased energy band gaps (2.21-2.80 eV) compared with methyl viologen (3.70 eV) as well as intense fluorescence emission with up to 92% quantum yield. Different numbers of thiophene units effectively changed the electrochromic and electrofluorochromic behavior of the devices because of the varied conjugation degree. The PNIPAM chains contribute to the thermo-responsive properties which could be observed simultaneously with electrochromic and electrofluorochromic behavior when the temperature varied below and above the LCST (32 degrees C). By combining the thermo-responsive, electrochromic and electrofluorochromic properties of poly(NIPAM-co-TV), multi-responsive smart windows were developed. The thienoviologen units also demonstrate photodynamic antimicrobial activities due to their ability to generate singlet oxygen species upon photo irradiation. With the contribution of thermo-responsive PNIPAM fragments, poly(NIPAM-co-terthienoviologen) is endowed with thermo-controlled antimicrobial activity (CFU reduction = 99.6% for T > LCST and CFU reduction = 63.0% for T < LCST). This discovery successfully integrated thermo-responsive, electrochromic, electrofluorochromic and photodynamic antimicrobial properties into one system and will be greatly beneficial to expand the potential applications of viologen derivatives.