The nature of singlet exciton fission in carotenoid aggregates.

Singlet exciton fission allows the fast and efficient generation of two spin triplet states from one photoexcited singlet. It has the potential to improve organic photovoltaics, enabling efficient coupling to the blue to ultraviolet region of the solar spectrum to capture the energy generally lost as waste heat. However, many questions remain about the underlying fission mechanism. The relation between intermolecular geometry and singlet fission rate and yield is poorly understood and remains one of the most significant barriers to the design of new singlet fission sensitizers. Here we explore the structure-property relationship and examine the mechanism of singlet fission in aggregates of astaxanthin, a small polyene. We isolate five distinct supramolecular structures of astaxanthin generated through self-assembly in solution. Each is capable of undergoing intermolecular singlet fission, with rates of triplet generation and annihilation that can be correlated with intermolecular coupling strength. In contrast with the conventional model of singlet fission in linear molecules, we demonstrate that no intermediate states are involved in the triplet formation: instead, singlet fission occurs directly from the initial 1B(u) photoexcited state on ultrafast time scales. This result demands a re-evaluation of current theories of polyene photophysics and highlights the robustness of carotenoid singlet fission.This work was supported by the EPSRC (UK) (EP/G060738/ 1), the European Community (LASERLAB-EUROPE, grant agreement no. 284464, EC’s Seventh Framework Programme; and Marie-Curie ITN-SUPERIOR, PITN-GA-2009-238177), and the Winton Programme for the Physics of Sustainability. G.C. acknowledges support by the European Research Council Advanced Grant STRATUS (ERC-2011-AdG No. 291198). J.C. acknowledges support by the Royal Society Dorothy Hodgkin Fellowship and The University of Sheffield’s Vice- Chancellor’s Fellowship scheme.This is the final published version. It was first made available by ACS at http://pubs.acs.org/doi/abs/10.1021/jacs.5b01130

Mechanisms of spectral shifts in lobster carotenoproteins. The resonance Raman spectra of ovoverdin and the crustacyanins

NRC publication: Ye

Excited state (exciton) interactions in polyene aggregates: J.Raman Spectroscopy

NRC publication: Ye

A RAMAN STUDY OF THE ROTATIONAL ISOMERS OF BICYCLOPROPYL AND VINYLCYCLOPROPANE

Author Institution: Division of Chemistry, National Research Council of CanadaThe $\Delta H$ of isomerization of bicyclopropyl in the liquid and vapor phases was determined from the relative temperature dependence of Raman bands assigned to the gauche and trans isomers. In both phases, the gauche form is more stable, with $\Delta H_{liquid} = -188 \pm 8$ cal/mole, and $\Delta H_{vapor}=-91 \pm 28$ cal/mole, The result for the liquid agrees with previous infrared measurements, but the vapor result conflicts with that derived previously from electron diffraction data. The Raman spectrum of vinylcyclopropane consists of a series of strong bands which persist throughout the solids, liquid, and vapor phases. In the liquid and vapor phases, a second, weaker set of bands is observed, whose intensity relative to that of the first set increases with increasing temperature. Also a third set of bands may be discerned, whose relative intensity decreases with increasing temperature. These observations are consistent with an equilibrium between three types of rotamers. This data and its interpretation will be discussed."

Resonance Raman spectra of lobster shell carotenoproteins and a model astaxanthin aggregate. A possible photobiological function for the yellow protein: Biochemistry

NRC publication: Ye

Improvement of indoor air quality in four problem homes

Peer reviewed: YesNRC publication: Ye

Actions to reduce the impact of construction products on indoor air: outcomes of the European project Healthy Air

The European project - HealthyAir is a network project involving six institutions in Europe on actions and activities that address the effects of construction products on indoor air. Different ways to improve indoor air quality were reviewed, ranging from source control to education of occupants on how to manage the built environment to achieve healthy and acceptable indoor air. Through literature study, organised workshops with scientific experts and building professionals as well as via interviews with three stakeholder groups: producers of construction products, architects and housing corporations; requirements for information, guidance and actions to improve indoor air quality were identified. These requirements formed the basis of a possible approach to improve indoor air quality: education and awareness, regulations and policies and further research and development