Light Switchable Ionic Conductivity of Arylazopyrazole Modified Polysiloxanes

ABSTRACT Ionic conductivity is a crucial property of polymers used in sensors, actuators, and solid‐state batteries. The ability to precisely switch ionic conductivity with a trigger is essential for enhancing device functionality and enabling advanced applications. Two polysiloxanes modified with a novel hydroxy‐functionalized arylazopyrazole ( AAP ) dye, which have different polarities, were synthesized. The polar polymer was synthesized from polymethylvinylsiloxane through a thiol–ene reaction involving thiopropionic acid. This was followed by esterification of carboxylic acid groups with a substoichiometric quantity of AAP dye. Any remaining unreacted carboxylic acid groups were then esterified with 3‐hydroxypropanenitrile to increase the polymer's polarity. The less polar polymer was synthesized using the same procedure starting from random poly(methylvinyl‐ co ‐dimethyl)siloxane with a 1:3 ratio of methylvinylsiloxy to dimethysiloxy units, except that all the carboxylic acid groups were esterified with AAP . The silicone backbone offers favorable flexibility and a glass transition temperature below 0°C, while the AAP undergoes isomerization upon exposure to UV light. The two polymers behave differently, particularly regarding ionic conductivity after the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. The less polar polymer exhibited light‐dependent complexation of lithium salt, which affected ionic conductivity. Therefore, the less polar polymer exhibited a strong, reversible switch in ion conductivity upon exposure to UV light, while the polar polymer exhibited only minor light‐switchable conductivity. The switching occurs within seconds and is stable for over 100 cycles. The light‐switchable properties make our new material a promising candidate for next‐generation smart devices and sensors.