Temperature-Dependent Raman Spectroscopy of Conjugated Thiophenes and a Photochromic Molecule

Voiceover

Presenter(s)

Jessica Bair

Abstract or Description

Diarylethene (DAE) derivatives are a class of conjugated molecules that undergo reversible photoisomerization reactions that lead to a change in the absorption spectrum of the molecule. In the DAE derivative chosen in these experiments, the conjugated components of interest include two sterically hindered phenyl groups whose equilibrium angles sit them out of plane from the central portion of the molecule. These experiments sought out to examine the changes that temperature imposes on the geometry of this system via Raman spectroscopy. To gain a better understanding of these effects in DAE, the same experimental methods were performed on the simpler 2,5-diphenylthiophene (DPT) and by extension, 2-phenylthiophene (PT). It was discovered that while there is a general heating effect on vibrational frequencies that is characterized by a red shift in all molecules, some modes do not display the same heating effect. For DAE, two such frequencies have been assigned at 1600 cm⁻¹ (localized ethylenic stretching at the phenyl rings) and 1100 cm⁻¹ (C-C aromatic stretch/C-H bend).  These indicate that the behavior of the phenyl rings situated outside of the planar complex may be affected geometrically by a change in temperature.

Mentor

Christopher G. Elles