UV-vis-NIR and Raman spectroelectrochemical studies on viologen cation radicals: Evidence for the presence of various types of aggregate species

Chongmok Lee, Young Mi Lee, Myung Sun Moon, Sang Hee Park, Joon Woo Park, Kyung Gon Kim, Seung-Joon Jeon

Research output: Contribution to journalArticle

45 Citations (Scopus)

Abstract

The spectral changes of 1-e- reduced species of unsymmetric viologens, l-methyl-1′-alkyl-4,4′-bipyridinium (C1CnV2+: n = 1, 8, 9, 12, 14, 16, 18) and 2-e- reduced species of bisviologens linked by polymethylene chains (C1V2+CnV2+C1: n = 3, 5, 8, 10) have been investigated spectroelectrochemically in the region from 350 to 1500 nm. Subtracting the contribution of the monomeric viologen cation radical from the spectra of reduced viologens, we obtained spectra of aggregates of viologen cation radicals. Three different spectral types were observed: Type I, the usual dimer spectrum of viologen cation radicals exhibiting structureless bands around 880 (band I), 530 (band II) and 360 nm (band III); Type II, red-shifts of the bands I and II of the Type I spectrum to as far as 1120 and 540 nm respectively; Type III, band positions similar to those of the Type I spectrum, but band II exhibiting a shoulder at around 510 nm and the bandwidth of band III much narrower than that of the corresponding band in the Type I spectrum. The Type I spectrum is shown with C1CnV·+ when n is less than 8. The Type II spectrum is observed with C1CnV·+ when n ≥ 9 and C1V·+CnV·+C 1 when n ≥ 8. Addition of cetyltrimethylammonium bromide (CTAB) to the solutions showing the Type II spectrum caused a spectral change towards Type I. The Type III spectrum is shown with C4C4V·+ in the presence of γ-cyclodextrin and C1V·+C3V·+C 1. The Raman spectra of viologen cation radicals showing Type I and II spectra exhibit doublet features at 1507/1527 and 1334/1351 cm-1, whereas singlet bands are observed for solutions showing the Type III spectrum. We attributed the Type I spectrum to face-to-face viologen radical dimers, the Type II spectrum to higher aggregates of viologen radicals, and the Type III spectrum to a viologen radical dimer with oblique stacking of the viologen rings.

Original languageEnglish
Pages (from-to)139-144
Number of pages6
JournalJournal of Electroanalytical Chemistry
Volume416
Issue number1-2
DOIs
Publication statusPublished - 1996 Nov 1

    Fingerprint

Keywords

  • Aggregate species
  • Raman spectroscopy
  • UV-vis-NIR
  • Viologen cation radicals

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Analytical Chemistry
  • Electrochemistry

Cite this