Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Chemistry and Biochemistry

Committee Chair(s)

William M. Moore (Committee Chair)


William M. Moore


Karen W. Morse


This research has focused on the sensitized photoisomerization step of a solar energy storage system based on the interconversion of norbornadiene (NBD) and quadricyclane (Q). Sensitizers studied in the photoisomerization were arylphosphine complexes of copper(I) halides [(Ph3P)3CuX, (MePh2P)3CuX, (DIPHOS)CuCl; X = Cl, Br, I and DIPHOS = Ph2P(CH2)2PPh2]. The lowest electronic excited state of the complexes can be an effective triplet energy sensitizer as evidenced by a maximum quantum yield of 1.0 with (MePh2P)3CuX. The sensitization mechanism of the L3CuX complexes is proposed as a bimolecular energy transfer process in which energy transfer takes place through the metal centered orbitals. The efficiency of the (MePh2P)3CuX sensitizers is unprecedented by other reported inorganic or organic sensitizers; however, ligand dissociation of the complexes in dilute solutions detracts from their otherwise attractive features. The free ligands undergo rapid photodecomposition and are extremely poor sensitizers of the NBD/Q system. The ligand dissociation of the LmCunCln (L = Ph3P, MePh2P; m:n = 3:1, 2:1, 4:2, 3:2, 2:2) complexes was modeled by use of vapor pressure osmometry and UV absorption. The equilibria and equilibrium constants of dissociation were determined for benzene solutions at 37 °C. The stability of the LmCunCln complexes (Ph3P<2P) toward ligand dissociation is attributed to the larger steric requirements of Ph3P in comparison to MePh2P. Evidence for ground state complexation of NBD and the LmCunCln compounds (m:n < 3:1) is shown. Photoexcitation of the (NBD) LmCunCln (m:n < 3:1) complexes can produce Q but with quantum efficiencies < 1.0. Photophysical properties of the arylphosphines and their copper(I) halide complexes are reported. The lowest electronic transition of the phosphines associated with an obscured absorption band at ~300nm is classified as an ℓ → aπ transition. Coordination to copper(I) halides brings about an enhancement of the ℓ → aπ transition of the ligand. The term σ,d → aπ is used to describe the lowest electronic transition of the complexes indicating that both the σ bond of the phosphorus lone electron pair to the metal and the d-d orbital bonding of the metal to the phosphorus are involved in an electron excitation from the phosphorus to an antibonding phenyl-π-system (aπ). The photophysical properties of Zn(II), Cu(I), and Ni(0) complexes of MePh2P are shown to follow the concept of a σ,d → aπ electronic transition.



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