Determination of molecular anisotropy in thin films of discotic assemblies using attenuated total reflectance UV-visible spectroscopy

Ware H. Flora, Sergio B. Mendes, Walter J. Doherty, Steven S Saavedra, Neal R Armstrong

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

We report here an investigation of absorbance anisotropy in highly ordered, single bilayer (ca. 5.6 nm) Langmuir-Blodgett (LB) thin films of discotic liquid-crystalline phthalocyanines, using a recently introduced broad-band attenuated total reflectance (ATR) spectroscopic technique, capable of measuring dichroism in such films in the UV-visible optical region down to absorbances of ca. 0.003 absorbance units. On the basis of the ATR measurements of LB-deposited films, a thorough treatment was established to determine the ensemble average of the Cartesian components and the associated optical anisotropy of transition dipoles in the molecular film. In an effort to recover order parameters of molecular orientation, those results were interpreted with a circular dipole model, which is the expected model for the isolated molecule based on symmetry properties. We measured a strong dipole component normal to the film plane that cannot be explained in terms of a truly circular model, indicating that the molecular transition dipoles were perturbed upon aggregation. The utility of the experimental approach was further demonstrated by (a) investigating the effect of substrate modifiers (methyl- and phenyl-terminated silanes) on the ordering within the phthalocyanine film and (b) the effect of water immersion and re-annealing of the thin film on molecular ordering and optical anisotropy.

Original languageEnglish (US)
Pages (from-to)360-368
Number of pages9
JournalLangmuir
Volume21
Issue number1
DOIs
StatePublished - Jan 4 2005

Fingerprint

assemblies
Anisotropy
Spectroscopy
dipoles
reflectance
Thin films
anisotropy
Optical anisotropy
thin films
spectroscopy
water immersion
Silanes
Langmuir-Blodgett films
silanes
Molecular orientation
Reflectometers
dichroism
Dichroism
broadband
Agglomeration

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Colloid and Surface Chemistry

Cite this

Determination of molecular anisotropy in thin films of discotic assemblies using attenuated total reflectance UV-visible spectroscopy. / Flora, Ware H.; Mendes, Sergio B.; Doherty, Walter J.; Saavedra, Steven S; Armstrong, Neal R.

In: Langmuir, Vol. 21, No. 1, 04.01.2005, p. 360-368.

Research output: Contribution to journalArticle

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