Formation of merocyanine self-assembled monolayer and its nonlinear optical properties probed by second-harmonic generation and surface plasmon resonance

Kazuma Tsuboi, Kazuhiko Seki, Yukio Ouchi, Katsuhiko Fujita, Kotaro Kajikawa

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19 Citations (Scopus)

Abstract

Nonlinear optical responses of a self-assembled monolayer (SAM) containing merocyanine chromophore, 1-alkyl-4-(4-hydroxystyryl) pyridinium bromide (HSP), on gold in water and in ethanol were studied by second-harmonic generation (SHG). The pH dependence of the SHG response clearly showed a solvatochromic characteristic of the merocyanine from a protonated form to a zwitterionic form. A large second-order susceptibility χzzz = 5.0 × 10-1 esu (2.1 × 102 pm/V) was found in a basic solution of ethanol where the merocyanine is in the zwitterionic form. Combination of the SHG and surface plasmon resonance (SPR) spectroscopy measurements also provides us with details of the formation process of the merocyanine SAMs in the ethanol solution of the HSP-terminated-alkyldisulfide, ω, ω′-dithiodi[l-undecyl-4-(4-hydroxystyryl)pyridinium bromide](HSPC11SS). A considerable difference was found in the kinetics between SPR and SHG, because SHG probes the molecules in a noncentrosymmetric fashion on the gold surface while SPR probes the optical thickness of the film. The difference enabled us to separate the chemisorption from the physisorption in the adsorption process. Interestingly, both probes showed slower kinetics in the solution of higher concentration, suggesting association of the disulfide molecules in the solution of high concentration.

Original languageEnglish
Pages (from-to)607-613
Number of pages7
JournalJapanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers
Volume42
Issue number2 A
DOIs
Publication statusPublished - Feb 2003

All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Physics and Astronomy(all)

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