Chemistry and Chemical Biology ETDs

Edwards Niles

Publication Date

2-14-2014

Abstract

This thesis employs variants of spectroscopic techniques to evaluate intermolecular interactions between P3HT chains in solution and in the solid state. Emphasis was put on understanding not only how intermolecular interactions within P3HT chains affect electronic properties, but also to assess changes due to the addition of weak and strong electron acceptors. To this end, optical and magnetic spectroscopies were focused on to correlate observed changes in electronic properties to physical changes in the polymer structure. To assess changes in intermolecular interactions, self-assembly was used to form P3HT nanofibers and were studied using resonance Raman, and transient absorption, and temperature- and pressure-dependent photoluminescence spectroscopy. Nanofiber spectra revealed an increase in intrachain order, a change in aggregation and the utility of self-assembly to control P3HT chain interactions. Resonance Raman, and optical absorption of different wt/wt loadings of P3HT/PCBM blends were measured to study the effect of weak acceptor interactions on thin film morphology and photocurrent output in donor/acceptor blends. The changes in optical spectra lineshapes were fit with the weakly coupled H-aggregate model to reveal decreases in the relative amounts of aggregated/unaggregated P3HT chains as weight fraction of PCBM increased. Electron paramagnet and nuclear magnetic resonance were combined with pre-resonance Raman and optical absorption to evaluate charge transfer salts. The electronic structure was altered the addition of a strong electron acceptor that formally oxidized a segment of the polymer chain. Paramagnetic signals were observed with EPR after radicals formed in donor/acceptor blends that coincided with observations of new low energy absorption bands and changes in chemical shift. The Raman spectra revealed increased backbone planarity after ground state complexation and led to the conclusion that strong acceptor blends enhanced planarity of polymer chains after charge separation.

Project Sponsors

UNM NMR

Language

English

Keywords

P3HT, NMR, EPR, RAMAN, CHARGE TRANSFER

Document Type

Dissertation

Degree Name

Physical Chemistry

Level of Degree

Doctoral

Department Name

Department of Chemistry and Chemical Biology

First Committee Member (Chair)

QIN, YANG

Second Committee Member

HABTEYES, TEREFE

Third Committee Member

DUNLAP, DAVID

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