Date of Award

Spring 1-1-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Niels H. Damrauer

Second Advisor

Justin C. Johnson

Third Advisor

Gordana Dukovic

Fourth Advisor

Joel D. Eaves

Fifth Advisor

Oana R. Luca

Abstract

Singlet fission (SF) is a spin-allowed process wherein a singlet excited state on one molecule shares its energy with a neighbor to create a pair of spin-coupled triplet states. This process has the potential to significantly improve solar cell efficiency as part of a carrier multiplication cell, and thus deserves robust understanding. The factors which govern the efficiency and rate of SF are explored in three systems: polycrystalline tetracene (Tc); a rigid, tetracene-inspired covalent dimer (BT1); and its (triisopropylsilylethynyl)-substituted derivative (TIPS-BT1). For polycrystalline Tc, films of two different polymorphs are prepared with the complementary variable of grain size. Crystallite size affects SF in one polymorph but not the other, highlighting the complex interplay between chromophore coupling and large-scale effects in the solid phase. In BT1, the role of coupling is isolated from long-range effects by reduction of the problem to a covalent dimer. With unfavorable coupling due to symmetry and poor energetics, slow SF in BT1 is largely out-competed by other loss processes. In TIPS-BT1, improved stability and solubility allow for in-depth photophysical studies. In a nonpolar environment, the excited dimer relaxes emissively with no apparent singlet fission. In a polar environment, two distinct states emit—one monomer-like and one dimer-like—with the latter in equilibrium with a dark state. These findings provide a foundation of mechanistic details for contrasting with future dimers based on this molecular platform. There, through systematic changes to energetics and coupling, we expect significant improvements to SF accompanied by deep mechanistic insight.

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