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A tryptophan imprinted merocyanine copolymer exhibits transport properties towards the polymer-registered substrate; the photoisomerized spiropyran copolymer is non-permeable towards the substrate and the imprinted information is erased.

Multiple layers of glucose oxidase (or glutathione reductase) on Au electrodes can be activated and deactivated reversibly by a ferrocene–nitrospiropyran (or a bipyridinium–nitrospiropyran) acting as a photoisomerizable electron relay. The anchoring of the first enzyme layer to the surface of the electrode is shown schematically below.

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The control of interfacial electron transfer reactions at monolayer-modified electrodes attracted extensive research efforts 1-4 recently. Densely-packed monolayers assembled onto electrode surfaces perturb the electrochemical communication with redoxactive compounds solubilized in the electrolyte, 1 where charged monolayers induce the electrostatic control of interfacial electron transfer with charged electroactive substrates. 2,3 The electron transfer rates within redox-active monolayers were shown to depend on the distance separating the electroactive group from the electrode. 4 Receptor-functionalized monolayer electrodes were used to control electron transfer at the electrode interface by complementary association of the substrate to the receptor monolayer. 5,6 For example, a -cyclodextrin monolayer-modified electrode was applied to concentrate a ferrocene electroactive substrate at the electrode surface by its association to the receptor cavity. 6 The chemistry of donor-acceptor complexes formed between xanthene dyes and N,N′-dialkyl-4,4′bipyridinium salts was characterized by us in the solid state and in solution. 7 The xanthene dyes-bipyridinium complexes are stabilized by charge transfer and π-π interactions as well as electrostatic attraction and exhibit association constants in the range K a ) 10 3 -10 4 M -1 . By utilizing the photoisomerizable N-methyl-N′- [4-(phenylazo)benzyl]-4,4′-bipyridinium electron acceptor (1), photostimulated formation and dissociation of the donor-acceptor complex with the eosin dye (2) were demonstrated. 8 The cis-azobenzene-bipyridinium electron acceptor 1b exhibits high affinity for 2, while the trans isomer 1a associates only weakly to eosin 2. The increased affinity of 1b to eosin was attributed to the high dipole moment (ca. 3.0 D) of the cis-azobenzene unit. 8 Here we wish to report on the photostimulated interactions of the azobenzene-bipyridinium electron acceptor 1 with an eosin monolayer-modified Auelectrode. The photoinduced formation and dissociation of the supramolecular complexes between 1 and the eosin monolayer are transduced as amperometric or quartz-crystal-microbalance, QCM, signals. The systems represent a means for the amperometric or QCM transduction of recorded optical signals.The eosin monolayer was assembled on a Au-electrode or a Au-electrode associated with a quartz crystal (9 MHz), 9 as outlined in Scheme 1. A primary cystamine monolayer 10 was assembled on the Au-electrode and was further modified with eosin isothiocyanate (3) to yield the eosin-modified monolayer. By following the frequency changes of the quartz crystal (∆f) upon the stepwise modification of the electrode, we estimate the surface density 11 of the eosin units on the Au surface to be 6.63 × 10 -10 mole cm -2 . Figure 1(A) (curve a) shows the cyclic voltammogram of the trans isomer (1a), in the presence of the eosin-modified monolayer electrode. Figure 1(A) (curve b) shows the cyclic voltammogram of the cis isomer (1b) in the presence of the eosin-modified electrode. Figure 1(...