Executive Summary : | Generation of long-lived charge separated (CS) state has been an important objective of photoinduced electron transfer (PET) research for a long period of time, as the long-lived CS state has the potential for converting solar energy into useful chemical potential. For example, long-lived CS state of suitable energy can be used for water splitting reaction. In this proposal, two strategies for the generation of long-lived photoinduced charge separated states are envisaged. The first involves generation of donor-acceptor nano-assemblies using the inclusion binding interaction of adamantane in beta-cyclodextrin cavity. In aqueous solution donor-linked beta-cyclodextrin and acceptor-linked adamantane undergo self-assembly to form an inclusion complex. Preliminary results from our lab suggest that, in carefully designed systems the inclusion complex self-assembles into hierarchical nano-structures. We observed that photoexcitation of the assemblies leads to formation of long-lived CS states. In the project we plan to explore such systems in detail to understand the mechanistic aspects of nano-structure formation and survival of photoinduced CS state.
The second strategy involved direct generation of long-lived triplet CS states by electron transfer from aromatic hydrocarbon triplets to acceptor molecules such as methyl viologen. It is known that tris-bipyridylruthenium(II) complexes when linked to aromatic hydrocarbons (AH) such as pyrene or anthracene transfer their triplet excitation to the hydrocarbons when irradiated. If suitable acceptor or donor moieties are attached to the hydrocarbons, it is envisaged that electron transfer would occur from the triplet of the hydrocarbons leading to formation of triplet CS states. Since recombination is slow in triplet CS states, we envisage that the CS states formed will be long-lived. Several Ru(bpy)-spacer-AH-spacer-Acceptor type systems will be designed and long-lived CS state formation in these systems will be studied.
Water splitting reaction to generate molecular hydrogen will be attempted using the long-lived CS states and suitable sacrificial donor systems. |