Single Molecule Biophysics

Engineering the optical properties of organic semiconductors by manipulating their conformation

Organic Semiconductors or conjugated polymers are synthetic light emitting molecules that combine the electronic properties of semiconductors with the mechanical properties of plastics. This makes conjugated polymers extraordinarily useful as active materials in a wide range of devices such as organic light emitting diodes, photovoltaic devices, thin film transistors and chemical sensors. Despite their semiconductor like electronic properties, the excitations in conjugated polymers are not delocalized over the entire polymer chain. Instead twists and kinks along the polymer backbone break the conjugation and localize the excitons on separate chromophores. The optical properties of conjugated polymers are determined both by the structure of individual chromophores and also by interactions of the chromophores with each other and their surroundings. A molecular level understanding of conjugated polymers therefore requires a precise knowledge of how polymer conformation influences optical properties. We plan to resolve this relationship using the combined single molecule fluorescence-Atomic Force Microscope that our lab is developing.

A single organic semiconductor molecule will be stretched by an AFM cantilever and the resulting changes in fluorescence emission, fluorescence spectra and photon antibunching will be measured and correlated with changes in polymer confirmation.