Ion exchange processes and environmental effects in chromophoric self-assembled superlattices. Manipulation of microstructure and large enhancements in nonlinear optical response

Stephen B. Roscoe, Shlomo Yitzchaik, Ashok K. Kakkar, Tobin J Marks, Weiping Lin, George K. Wong

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

This contribution reports on the anion exchange characteristics of self-assembled monolayers composed of high-β stilbazolium chloride moieties as assessed by X-ray photoelectron spectroscopy, optical spectroscopy, and polarized second harmonic generation (SHG) spectroscopy. At moderate chromophore surface coverages (∼1 × 1014 molecules/cm2) in acetonitrile or methanol, replacement of ∼60 % of the Cl-counterions by I-, p-aminobenzenesulfonate, or 4-[4-[(diethylamino)phenyl]azo]benzenesulfonate (ethyl orange) is observed. However, negligible exchange is detected at higher chromophore surface coverages (≥2 × 1014 molecules/cm2) or when the monolayer is functionalized with a siloxane overlayer. Polarized SHG measurements at 1064 nm reveal ion exchange-induced increases in χzzz(2) of 34%, 25%, and 44% for I-, p-aminobenzenesulfonate, and ethyl orange, respectively. However, changes in the average chromophore orientation angle with respect to the surface normal are ≤2°, implicating changes in anioncation pairing as the source of the large enhancements in χzzz(2).

Original languageEnglish
Pages (from-to)1337-1339
Number of pages3
JournalLangmuir
Volume10
Issue number5
Publication statusPublished - 1994

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Colloid and Surface Chemistry

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