This mini-review on the photophysics of poly-alkyl thiophenes (e.g., P3HT) and its blends with electron-acceptor moeties such as fullerenes (e.g., PCBM) and carbon nanotubes focuses on highlights of recent literature on spectroscopic probes of exciton formation, diffusion, charge-separation, and transport in these materials. The literature in this area is vast: more than 3000 papers have been published in on P3HT (and related materials) and applications to organic solar energy harvesting devices over the last 20 years. Thus, no single review can capture the breadth and depth of this research. Here, we attempt to highlight some of the exciting new research efforts aimed at understanding photophysical processes in organic photovoltaic materials. This mini-review is organized as follows: First, a summary of the theoretical framework commonly used to describe fundamental physical processes of charge generation in organic (polymeric) semiconductor materials is presented. We then discuss recent exciting results on ultrafast spectroscopic probes of exciton dynamics in these materials. Finally, we present highlights of new research on polymer nanostructures (nanoparticles and nanofibers) and their exciting applications to organic photovoltaics. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Chirality in molecular systems plays profoundly important roles in chemistry and physics. Most chemistry students are introduced to the concept of chirality through demonstrations of the interaction of chiral molecules with polarized light manifested as an “optical rotation” leading to the “(+)” and “(−)” [or dextrorotatory (d-) and levorotatory (l-)] designations of chiral compounds, with the subsequent determination of absolute stereochemical configuration by chemical or physical means enabling application of the familiar “R” and “S” labels. Although the intrinsic molecular parameters that control the dissymmetric light-matter interaction in chiral systems are well understood, we have only recently begun to ask questions regarding the role of local molecular environment and hidden heterogeneities associated with the ensemble-averaged molecular chiroptical response. In this mini-review, we discuss some of our recent research on application of single-molecule spectroscopy as a tool for probing heterogeneities and fluctuations of chiroptical dissymmetries in condensed phase. Chirality 21:E265–E276, 2009. © 2009 Wiley-Liss, Inc.

We present results of fluorescence excitation circular dichroism studies of the chiroptical response of single (bridged triarylamine) helicene molecules immobilized at a polymer interface. We extract directly dissymmetry parameters, and corresponding probability distributions, associated with the single-molecule fluorescence excitation associated with modulation of a circular polarized excitation field for three different excitation wavelengths (405, 440, 457 nm) showing circular dichroism in bulk films. The observed single molecule chiroptical response is anomalously large in comparison with the results of time-dependent density functional calculations, and the observed defocused emission patterns seem to indicate a higher multipole nature to the transition probed. Our results provide new insights into chiroptical properties of chiral fluorophores that are hidden under the extensive averaging associated with conventional chiroptical probes. Chirality, 2008. © 2008 Wiley-Liss, Inc.