Probing organization and communication at layered interfaces

Maciej Mazur 2Monika J. Dominska 1Paweł G. Krysiński 2Gary J. Blanchard 1

1. Michigan State University, Department of Chemistry (MSU), East Lansing, MI 48824, United States
2. Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland

Abstract

Many present-day technologies, such as catalysis, chemical sensing and nanoelectronics, rely on phenomena that proceed at interfaces. Because of the limited structural control we can exert over solid surfaces, an attractive strategy for tailoring interfaces to specific purposes is growing monolayers or multilayers onto them. Such adlayers can be prepared by several methods, with Langmuir-Blodgett and self-assembly being the most useful and widely used approaches for interface structural control. The chemical modification of interfaces requires the development and use of measurement techniques that are capable of probing the interfaces once formed. Both electrochemistry and spectroscopy are useful for this task, depending on the interface used. For both electrochemical and spectroscopic measurements, the incorporation of probe molecules into the modified interface enhances the sensitivity and specificity of the information gained. Fluorescent spectroscopic probes have proven especially useful because they can be detected with high sensitivity and in some cases the details of their emission profile are reflective of their immediate environment. We use pyrene as an optical and electrochemical probe for this work because of its ability to sense the "polarity" of its microenvironment through the intensity ratio of two emission bands. These two bands respond differently to the dielectric properties of the chromophore immediate environment. For substituted pyrene, the emission band ratio environment dependence is somewhat less sensitive than for pyrene because of the reduction in symmetry, but if chosen properly, substituted pyrene can be used as a probe of interface local environment. We report on organization and intermolecular communication within several interfacial systems as a function of interface composition and for immersion of the interface in selected solvents. The co-deposition of selected molecules with pyrene derivatives has a measurable effect on the pyrene emission spectrum, and the details of this effect depend on the identity of the surface modifier. We gauge the sensitivity of vibronic band intensities in the emission spectrum of pyrene by co-immobilizing hydrophobic molecules, demonstrate energy transfer in the system of two spectrally overlapped chromophores, and demonstrate that pyrene can communicate with other electrochemically active species within the interface. The average distance between molecules in these interfaces is nanometers, close enough for efficient communication. This fact is important from fundamental and technological standpoints, as in the construction of sensors and the design of nanoelectronics, and in understanding chemical deposition at heterogeneous interfaces.

 

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Presentation: Tutorial lecture at SMCBS'2005 Workshop, by Gary J. Blanchard
See On-line Journal of SMCBS'2005 Workshop

Submitted: 2005-07-26 20:22
Revised:   2009-06-07 00:44