Electronic and optoelectronic devices based on soft organic and biological polymers may change the way we maintain our environment, generate energy and treat otherwise incurable health conditions, for example, brain trauma. The rational design of such devices is hindered because the relationship between morphology and electronic and optoelectronic behaviours of conjugated or biological polymers is, in general, poorly understood. In this talk, I will describe two of our recent results that offer helpful insights into this complex relationship: (1) We have demonstrated theoretically that torsional disorder in substituted polythiophenes can polarize the excited electron-hole pairs (excitons), and observed this effect directly using single-molecule spectroscopy experiments in a
(theory-driven) collaborative effort. Of particular practical interest is our finding that exciton polarization in conjugated polymers can be controlled with non-bonding interactions, for example, with strategically chosen side-chains; this insight may help manipulate the mechanism of exciton diffusion and charge-separation in organic photovoltaics; (2) We have developed a minimal theoretical framework, which captures in a crude but cost-effective and intuitive way the effects of morphology on fluorescence brightness in a class of fluorescent proteins (Tsien's Class 2). The goal of this work is to guide the rational design of fluorescent bio-sensors, which can detect rearrangements of target proteins via interdomain allostery. As an application, we used this framework to propose a consistent mechanism of a genetically encoded voltage indicator ArcLight, whose mechanism is currently under debate.