Date of Completion
Emily Jarvis PhD
Density functional theory (DFT) was employed to investigate dodecaphenyltetracene as well as similar molecules containing differing backbone lengths and electron withdrawing groups with interest in manipulating the twist to lower the LUMO level for increased electron mobility. Optimization and frequency time-independent calculations followed by time-dependent (TD-DFT) energy calculations were performed at the B3LYP/G-311G level of theory to analyze electronic trends as a result of increased backbone length and consequently distorted end-to-end molecular twist. These calculations demonstrate a linear relationship with negative slope between the estimated HOMO-LUMO, fundamental, and optical gaps as a function of the number of fused rings along the polycyclic backbone. Contrasting these energy gaps with a separate series of identical molecules fixed into a planar configuration, the optimized twisted molecules display a pronounced red shift from steric hindrance due to phenyl substituents. In addition to the excitation energies, we applied a theoretical model for predicting exciton binding energy in planar polycyclic aromatic hydrocarbons to our series of twisted analogs, demonstrating a negligible effect of intramolecular twist on exciton binding energy. Evaluating higher levels of theory that incorporate dispersion and solvation effects, we found that our original gas-phase calculations sufficiently capture trends in expected excitation energies.
Tully, Grace and Jarvis, Emily A., "Isolating the electronic effects of systematic twist in highly substituted aromatic hydrocarbons using density functional theory" (2023). Honors Thesis. 471.