A new ultrafast energy funneling material harvests three times more diffusive solar energy for GaInP photovoltaics

There is no theoretical limit in using molecular networks to harvest diffusive sun photons on large areas and funnel them onto much smaller areas of highly efficient but also precious energy-converting materials. The most effective concept reported so far is based on a pool of randomly oriented, light-harvesting donor molecules that funnel all excitation quanta by ultrafast energy transfer to individual light-redirecting acceptor molecules oriented parallel to the energy converters. However, the best practical light-harvesting system could only be discovered by empirical screening of molecules that either align or not within stretched polymers and the maximum absorption wavelength of the empirical system was far away from the solar maximum. No molecular property was known explaining why certain molecules would align very effectively whereas similar molecules did not. Here, we first explore what molecular properties are responsible for a molecule to be aligned. We found a parameter derived directly from the molecular structure with a high predictive power for the alignability. In addition, we found a set of ultrafast funneling molecules that harvest three times more energy in the solar’s spectrum peak for GaInP photovoltaics. A detailed study on the ultrafast dipole moment reorientation dynamics demonstrates that refocusing of the diffusive light is based on ∼15-ps initial dipole moment depolarization followed by ∼50-ps repolarization into desired directions. This provides a detailed understanding of the molecular depolarization/repolarization processes responsible for refocusing diffusively scattered photons without violating the second law of thermodynamics.

The Mechanical Properties of Nucleic Acids

This chapter reviews models which describe the elastic properties of stretched polymers—the Kratky–Porod, Freely Jointed Chain (FJC), and Worm-Like Chain (WLC) models—and the effect of self-avoidance on results derived from these. The models are compared with double-stranded DNA (dsDNA) stretching experiments. Dynamics of a single polymer in the presence (Zimm model) or absence (Rouse model) of hydrodynamic interactions between its segments is described, and results on the dynamics of dsDNA and ssDNA of various lengths are discussed. Theoretical and experimental behaviour of twisted DNA is described, deducing the molecule’s torsional modulus and its coupling between stretching and twisting. After discussing the braiding of two DNA molecules and simulation of the twisting and stretching of DNA molecules, this chapter describes the results of stretching experiments on ssDNA and RNA, where self-avoiding and base-pairing interactions contribute to elastic behaviour.