Electrochemical and Quartz-Crystal-Microbalance Transduction of Light-Controlled Supramolecular Interactions at Monolayer-Functionalized Electrodes

Abstract

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(...

Potential-controlled molecular machinery of bipyridinium monolayer-functionalized surfaces: an electrochemical and contact angle analysisElectronic supplementary information (ESI) available: experimental details on the electrode modification, electrochemical and contact angle measurements. See http://www.rsc.org/suppdata/cc/b3/b303845a/

“…1, curve (a), steps (4) and ( 5), respectively. In a reference system, a short chain tethered bipyridinium monolayer was assembled on a Au electrode by the coupling of N-methyl-NA-carboxyethyl-4,4A-bipyridinium 8 (2) to the mercaptoethanol monolayer, Scheme 1. The surface coverage of the bipyridinium units is 4.6 3 10 211 mol cm 22 (12% of a densely packed monolayer).…”

A β-amino-cyclodextrin monolayer-modified Au electrode: a command surface for the amperometric and microgravimetric transduction of optical signals recorded by a photoisomerizable bipyridinium–azobenzene diad

“…10 Recently, the assembly of functionalized photoisomerizable monolayers onto electrode surfaces enabled the amperometric and piezoelectric transduction of optical signals recorded by the monolayer. [11][12][13] Here, we report on the use of a b-amino-cyclodextrin monolayer-modified Au electrode as a command surface for electrochemical transduction of optical signals, recorded by N-methyl-NA-[1-phenylazobenzyl]-4,4A-bipyridinium 1.…”

Preparation of molecularly imprinted polymer membrane with blending trimethoprim-MIP and polysulfone and its transport properties

“…Another approach for the synthesis of the imprinted polymer membranes was in situ crosslinking polymerization. The main problem with this approach was the high levels of cross-linking traditionally used in molecular imprinting for achieving a desirable selectivity, which made the imprinted polymer membranes have poor mechanical stability [12,13]. Moreover, for the approach in which plate membrane served as the supporting membrane, molecular template polymer was coated on the surface where the imprinted polymer membrane was prepared [14].…”