Light‐Stimulated Formation and Dissociation of Supramolecular Donor–Acceptor Complexes between Eosin and Bipyridinium Azobenzenes: Design of Molecular Electronic Devices for the Piezoelectrical Transduction of Recorded Optical Signals

Abstract

Abstract The photoisomerizable electron acceptors, trans ‐4,4′‐bis( N ‐methylpyridinium)azobenzene, ( 1t ), and trans ‐3,3′‐bis( N ‐methylpyridinium)azobenzene, ( 2t ), exhibit photoswitchable binding affinities to eosin. While the trans isomers, ( 1t ) or ( 2t ) exhibit high association affinities ( K a = 8.3 × 10 3 M −1 and 3.8 × 10 4 M −1 , respectively), the cis isomers ( 1c ) or ( 2c ) reveal lower binding affinities ( K a = 3.4 × 10 3 M −1 and 1.4 × 10 4 M −1 , respectively). The formation of the supramolecular donor–acceptor complexes between the eosin and the electron acceptors is associated with an absorbance change of the chromophore. This enables the cyclic spectroscopic transduction of the optically‐induced formation and dissociation of the complexes upon photoisomerization between the respective trans and cis states. An eosin monolayer was assembled onto the Au‐electrodes associated with a quartz piezoelectric crystal. The eosin‐functionalized crystal was employed for the microgravimetric, quartz‐crystal‐microbalance analyses of the association of ( 1t ), ( 2t ), ( 1c ), or ( 2c ) to the crystal interface. The microgravimetric analyses allowed the characterization of the kinetics of association of the electron acceptors to the monolayer and the association constants between the isomers ( 1t ), ( 2t ), ( 1c ), and ( 2c ) with the eosin monolayer. By cyclic photoisomerization of the electron‐acceptor between the trans and cis states, reversible piezoelectric transduction of the formation of the complexes with ( 1t ) or ( 2t ) at the monolayer interface, and their dissociation upon photoisomerization to ( 1c ) or ( 2c ) was accomplished.