Poly(NIPAM-co-thienoviologen) for multi-responsive smart windows and thermo-controlled photodynamic antimicrobial therapy

Abstract

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 °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.