Spectroscopic studies of bithiazole oligomers and related polymers.

Conjugated polymers are widely studied because they can be doped and thus used in electronic devices as conducting polymers. Polythiophene is perhaps the most studied conjugated polymer. Poly(4,4'-dinonyl-2,2 '-bithiazole) (PNBT) is similar to polythiophene, and is studied here, as well as the NBT monomer, dimer, trimer, and pentamer. Absorbance, emission, excitation, polarized UV-Vis, IR, and Raman spectroscopy. Isolated 2,2'-bithiazole dimer in quaterphenyl matrix has a Stokes shift of 1800 cm-1 and overlapping absorbance and emission origins. Poly(4,4'-bis(p-dodecylphenyl)-2,2 '-bithiazole-5,5'diyl), (DBT) with its side chains that hinder crystallinity, is also investigated and compared to PNBT spectra. DBT solid state spectra are 800 cm-1 to lower energy than solution spectra. Absorbance and emission PNBT shifts from solution to solid by 3900 cm-1 and 5800 cm-1 respectively. These results imply that PNBT spectra are from Davydov splitting of a band of states. IR and Raman spectra are dominated by ring modes containing C-S and C=N vibrations, and the same 700 cm-1 and 1650 cm -1 modes are also resolved in the monomer electronic spectra. Dimer molecules aligned on Teflon give absorbance spectra with two oppositely polarized components, suggesting Davydov splitting. Trimer and pentamer emission spectra change in peak position and relative ratio, suggesting emission is from trap species whose content dependent on processing. The three dimensional planar packing of PNBT is responsible for solvatochromism. Spectral signatures that are recurrent in this series are also noted in several other conducting polymers and are commented on in light of intermolecular and intramolecular forces. A mathematical model that attributes spectral changes to conformational changes is proposed. Emission spectra that are narrower than absorbance spectra, and absorbance spectra that are featured result from this model. Alternatively, spectral shifts of 4000 to 6000 cm-1 are also explained by intramolecular forces (Davydov splitting), as the inter-planar distance of 3.6A is consistent with strong pi-pi interactions. Solution spectroscopic data is consistent with intramolecular pi-pi overlap theories (FEMO, KUHN, etc.), but solid state results indicate both strong intramolecular and intermolecular interactions. Oligomer and polymer absorbance and emission maxima are plotted to give theoretical band gaps of 19400 cm-1 (solid) and 24400 cm-1 (solution).PhDPolymer chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132738/2/9990848.pd