Photoinduced Processes in Molecular-Inorganic Materials - Design Strategies for Control of Photophysical and Photochemical Processes

Abstract: Sunlight is the most abundant renewable energy resource on Earth and has the potential to provide our society with clean energy. Despite this abundancy, solar energy corresponds to only a minority of the global energy production. Two major reasons for this are the limited efficiencies of solar cells and the difficulty of storing solar energy. The work presented within this Thesis aims to investigate ways of overcoming these issues. A process called singlet fission could be utilized to increase the efficiency of solar cell. The storage issue of solar energy could be circumvented by producing fuels (i.e. solar fuels) instead of electricity from sunlight. The work presented herein has been dedicated to mechanistic studies of photo-induced processes in molecular/inorganic materials. The aim has been to gather knowledge about how the materials can be designed to obtain control of the photoinduced processes; so that one process can be favored over another. Molecular/inorganic materials were used because of their favorable characteristics compared to molecules or inorganic materials alone in terms of combining the stability of inorganic materials with the tunability of molecules. In this work, a derivative of the well-known singlet fission molecule 1,3-diphenylisobenzofuran was attached to various semiconductor films in solvents of different polarities. Studies of these materials revealed that utilizing semiconductors with a relatively low conduction band energy in a non-polar environment is favorable for achieving singlet fission followed by injection from the triplet excited state. Further, studies of molecular/semiconductor materials with both photosensitizer and catalyst molecules attached to the surfaces revealed that the charge separated lifetime between the photosensitizer and the semiconductor can be significantly extended by design of a patterned film of two different semiconductors. These studies further revealed that two-electron transfer from the conduction band to an attached molecular catalyst is possible; thus, these materials are promising for use in solar fuel generating assemblies. The results presented herein can be useful for future design of molecular/inorganic materials to achieve singlet fission as well as multi-electron transfer necessary for generating solar fuels.

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