Abstract
In this study, we report the synthesis, characterization, and chiroptical properties of azo-group-containing chiral salen type Schiff base Ni(II), Cu(II), and Zn(II) complexes absorbed on gold nanoparticles (AuNPs) of 10 nm diameters. Induced circular dichroism (CD) around the plasmon region from the chiral species weakly adsorbed on the surface of AuNP were observed when there were appropriate dipole–dipole interactions at the initial states. Spectral changes were also observed by not only cis-trans photoisomerization of azo-groups but also changes of orientation due to Weigert effect of azo-dyes after linearly polarized UV light irradiation. Spatial features were discussed based on dipole-dipole interactions mainly within an exciton framework.
Highlights
Despite having an identical chemical formula, some compounds show differences in chemical properties or optical properties
When they have specific bonds, the magnitude of induced circular dichroism (CD) spectra increases or decreases depending on the direction of the dipole moments
Overall electric dipole moment would be along the metal-to-middle point of chiral centers direction similar to the analogous chiral salen-type complexes [12]
Summary
Despite having an identical chemical formula, some compounds show differences in chemical properties or optical properties. When chiral metal compounds are adsorbed on AuNP (or nanostructured surface of gold substrates), interaction of the chiroptical signals between their dipole moments may be caused by surface plasmon resonance [4,5,9]. Some types of exciton mechanisms have been proposed for theoretical predictions or experimental explanation [10,11] The importance of both magnitude and direction (phenomenologically speaking, parallel arrangement) of electric transition dipole moments (longer molecular axis) of some chiral metal complexes and (vertical vector of) AuNP has been investigated experimentally [12,13,14]
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