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

The photoisomerizable electron accepters, trans-4,4'-bis(N-methylpyrid inium)azobenzene, (1t), and trans-3,3'-bis(N-methylpyridinium)azobenze ne, (2t), exhibit photoswitchable binding affinities to eosin. While t he trans isomers, (1t) or (2t) exhibit high association affinities (K- 1= 8.3 x 10(3) M-1 and 3.8 x 10(4) M-1, respectively), the cis isomers (1c) or (2c) reveal lower binding affinities (K-a = 3.4 x 10(3) M-1 a nd 1.4 x 10(4) M-1, respectively). The formation of the supramolecular donor-acceptor complexes between the eosin and the electron accepters is associated with an absorbance change of the chromophore. This enab les the cyclic spectroscopic transduction of the optically-induced for mation and dissociation of the complexes upon photoisomerization betwe en the respective trans and cis states. An eosin monolayer was assembl ed onto the Au-electrodes associated with a quartz piezoelectric cryst al. The eosin-functionalized crystal was employed for the microgravime tric, quartz-crystal-microbalance analyses of the association of (It), (2t), (1c), or (2c) to the crystal interface. The microgravimetric an alyses allowed the characterization of the kinetics of association of the electron accepters to the monolayer and the association constants between the isomers (1t), (2t), (1c), and (2c) with the eosin monolaye r. By cyclic photoisomerization of the electron-acceptor between the t rans and cis states, reversible piezoelectric transduction of the form ation of the complexes with (1t) or (2t) at the monolayer interface, a nd their dissociation upon photoisomerization to (1c) or (2c) was acco mplished.