Crystalline pseudorotaxane enabling dual-wavelength photothermal mechanical actuation

Abstract

We report the synthesis and photothermal-mechanical conversion behavior of a photoresponsive pseudorotaxane comprising an ammonium salt bearing ferrocenyl and anthryl groups as the axle and dibenzo[24]crown-8 (DB24C8) as the macrocyclic ring. In the crystalline state, the pseudorotaxane exhibits notable void spaces around the ferrocene and anthryl substituents, with void volume increasing from 12.7% to 17.3% over the temperature range of −173 °C to 77 °C. The crystals display characteristic photoabsorption at 375 nm and 445 nm, attributed to the anthryl and ferrocenyl units, respectively, enabling efficient photothermal conversion. Upon incorporation into a poly(n-butyl methacrylate) (PBMA) matrix, the crystal-dispersed film undergoes significant temperature increases from 27 °C to 72 °C and 69 °C when irradiated at 375 nm and 445 nm, respectively, resulting in light-induced film expansion. This expansion translates into pronounced photoactuated lifting and bending motions, which are significantly greater than those observed in films containing only the axle or lacking the anthryl moiety. These findings demonstrate the utility of ferrocenyl–anthryl-functionalized crystalline pseudorotaxanes in the development of photomechanical materials, soft actuators, and optically responsive mechanical systems.