Electronic Energy Transfer in Conjugated Organic Dendrimers and Polymers

177 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2005.This study examines energy transfer in phenylacetylene (PA) dendrimers and the conjugated polymer poly(2-methoxy 5-[2'-ethylhexyloxy]-p-phenylene vinylene) (MEH-PPV). The fundamental absorbing and emitting chromophores in the PA dendrimers are elucidated via steady-state and time-resolved spectroscopy on specially synthesized PA dendrons, and comparison with ab initio calculations. The results are explained by using a variable coupling exciton model. Coherence effects in a model two-level system with trap are examined using Haken-Strobl model with the goal of illustrating how the trapping time, coherence time, and molecular topology all affect the overall efficiency of a light-harvesting network. Several issues are identified, including the dephasing-induced decoupling the trap from the rest of the network, the nonlinear dependence of trapping rate on the coherence time, and the role of network size and connectivity in determining the effect of the coherence time on efficiency. We investigate the energy transfer in MEH-PPV using femtosecond degenerate pump-probe experiments at 298 K and 4 K, and show that by using a simple model to account for inhomogeneous broadening, vibrational lineshape, and the intramolecular Stokes shift, we can obtain semi-quantitative agreement with the experimental results. To directly measure the time-dependent diffusion rate of singlet excitons in MEH-PPH, we utilize a novel femtosecond pump-dump-probe anisotropy experiment. This technique is also used to measure anomalous rotational diffusion of Coumarin 153 as a "proof-of-concept" experiment.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD