Amplifying Conjugated Polymers for Fluorescent Chemosensing

Chemo- and biosensors based on fluorescent conjugated polymers 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. In the conventional sensor design paradigm, excitons migrate from the bulk of the polymer to the analyte binding sites which can be either fluorescence quenching sites (turn-off sensors) or lower energy fluorophores (turn-on sensors). In this dissertation, we proposed an alternative design paradigm when analyte binding creates a higher energy gap site in the polymer backbone. In the case of isolated polymer chains in dilute solution, these higher energy gap sites act as “roadblocks” for migrating excitons, effectively limiting the exciton migration length. This is responsible for an amplified enhancement of fluorescence of conjugated polymer sensors. As a proof of concept, we utilized this design principle to develop an amplifying turn-on sensor for organophosphorous warfare agents mimics, and demonstrated substantial signal gain and much broader analyte detection range relative to the corresponding small-molecule analogue. In addition, we utilized this novel “higher energy gap” control concept to develop an amplifying fluorescent conjugated polymer sensor for the detection of hydrogen sulfide. This 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. The last part of this dissertation focuses on the conceptual design of near infrared (NIR) conjugated polymers based on cyanine building blocks. We developed a synthetic approach to this class of fluorescent materials which can eventually become useful in biomedical and bioimaging applications