Abstract
In this theoretical work, we present a spectroscopic analysis of the cis/trans-isomers of a molecular switch, penta-2,4-dienoic acid, attached to gold clusters of different size (1, 2 and 20 gold atoms). We have simulated 4 different spectroscopic techniques: Infrared spectroscopy, normal Raman scattering, absorption spectra and resonance Raman scattering. We discuss how the position and the conformation of the molecule determine the electronic structure and hence, the spectra. The calculations have been performed using density functional theory for the properties of the ground state and time-dependent density functional theory for the excited-state properties. Special emphasis is put on the resonance Raman spectra for the study of the isomers. In the present case, resonance Raman scattering is best suited to discriminate between the isomers on the gold clusters.
Highlights
The remarkable functionalities of molecular switches in nature make it highly desirable to develop artificial systems in a similar fashion.[1]
In presence of metal surfaces, the spectroscopic signals are often dramatically increased and the corresponding techniques have received much attention recently, which is documented in several reviews for surface-enhanced infrared absorption (SEIRA),[16,17,18] sum-frequency generation (SFG),[19,20] surface-enhanced Raman scattering (SERS)
We investigated properties of the excited states and simulated ultraviolet regime (UV) absorption spectra giving insight into how the molecule interacts with the gold cluster at higher energies
Summary
The remarkable functionalities of molecular switches in nature make it highly desirable to develop artificial systems in a similar fashion.[1]. One of the most prominent examples is the retinal isomerization in rhodopsin which is responsible for signal conversion in human vision.[13] Anchoring such switches on surfaces may lead to new functional properties, which are relevant for different fields like molecular electronics, biocompatible devices or sensing.[14] A detailed study of their microscopic properties is vital for the correct understanding of their functionality. Its resonance Raman analog (SERRS).[18,21,22,23,24] Another variant of RS employs sharp tips to exploit the surface effect This tip-enhanced Raman scattering (TERS) yields remarkable spatial resolution in addition to the enhanced signals.[25,26,27,28] the vibrations of a molecule situated between two electrodes can be monitored via inelastic electron tunneling spectroscopy (IETS).[29,30,31,32,33] All these techniques are especially suited for surface analysis in organic electronics, microfluidics or smart materials, where molecular switches are applied.[14,34].
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