Surface-enhanced resonance raman spectra of photochromic crown ether styryl dyes, their model chromophores, and their complexes with Mg2+

The complexation of the derivatives of crown ether styryl dyes betaine 2-[2-(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin-16-yl)ethenyl]-3-(3-sulfopropyl)benzothiazolium (1a) and perchlorate 2-[2-(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin-16-yl)ethenyl]-3-ethylbenzothiazolium (1b) and their molecular fragment 2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin (2) with magnesium cations has been studied by the surface-enhanced Raman scattering (SERS) spectroscopy at very low (down to 10-8 M) concentrations. A detailed comparison of the Raman and SERS spectra of 1a,b and their molecular fragments 2 and perchlorate 2-Me-3-ethyl benzothiazolium (3) enabled one to assign the vibrational modes and propose the model of dye interaction with the silver SERS-active surface. Benzo-15-crown-5 chromophore of 1a,b was found to be adsorbed through its crown ether part so that the plane of benzene ring is nearly perpendicular to the surface of silver el...