Doctor of Philosophy (PhD)
Chemo- and biosensors based on fluorescent conjugated polymer benefit from greater detection sensitivity due to amplification of the electronic perturbations produced by analyte binding. This amplification stems from the exciton-transporting properties of conjugated polymers. A conventional design paradigm relies on the analyte binding events which generate sites of lower energy relative to the polymer energy: either fluorescence quenching sites (turn-off sensors) or bathochromically shifted fluorophores (turn-on sensors). In both type sensors, the excitons migrate to the lower-energy site created by analyte binding.
This dissertation primarily focused the investigation of an alternative paradigm when analyte binding creates higher energy gap sites in the polymer backbone. Such higher-energy gap sites act as “roadblocks” for excitons to reduce their migration length. Decreasing exciton migration length is accompanied by increasing fluorescence intensity, thus generating an amplified turn-on fluorescent response. The new paradigm expands the generality and universality of the signal amplification concept in conjugated polymers, and can be used to design amplifying turn- on fluorescent sensors for various practically useful analytes such as hydrogen sulfide and cysteine.
In the last part of this dissertation, we present a series of poly(p-phenylene ethynylene) thin films prepared by stepwise surface-initiated polymerization. In addition to experimental simplicity and reproducibility of the preparation, and broad variety of compatible building blocks, this method requires low material consumption and no purification for the final bulk thin films. The stepwise surface-initiated polymerization yields dense films of covalently immobilized polymer chains with precisely controlled molecular structure and organization.
Chiang, Chien-Hung, "Higher Energy Gap Control of Fluorescence in Conjugated Polymers" (2018). LSU Doctoral Dissertations. 4516.