Synthesis of Chromophores Extension for Nonlinear Optics Applications
Abstract
(Cholesteryl)benzoateethynylene oligomers having 3, 5 and 7 repeat units and the homologue polymer were synthesized by a divergence-convergence approach by the Sonogashira-Heck reaction. Their chemical structure was analyzed by 1H, 13C NMR, UV-Vis, fluorescence spectroscopy and circular dichroism. X-Ray diffraction patterns of all the materials show only a first order peak at 2.05 deg in 2(theta), indicative of a lamellar order within a distance of 4.3 nm. This is twice the calculated distance of a molecule in its more extended conformation, i.e. of 2.15 nm, and is consistent with a disordered Smectic A phase for the trimer and pentamer and a nematic phase for the heptamer and polymer. The most probable model of organization corresponds to a supramolecular assembly in bilayers, where the cholesteryl chains are oriented in an opposite sense, i.e. in a back-to-back "comb like" fashion. Since the molecular shape of the materials is consistent with brick or board-like structures and the molecules are stacked in blocks randomly oriented, the (cholesteryl)benzoateethynylene materials could be described as Sanidic LCs as a general term to classify their mesomorphic behavior. Optical properties are discussed in terms of the conjugation length and the terminal groups, iodine or in one case, hydrogen. In general the results confirm that all the molecules assume in solution a more planar conformational geometry when passing from the ground to the excited state. Circular dichroism spectra measured were consistent with the observed structural properties.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 31, 2012
- Accession Number
- ADA580521
Entities
People
- Eduardo Arias
- Ivana Moggio
- Ronald Ziolo