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 [(Ph_3P)_3CuX, (MePh_ 2P)_3CuX, (DIPHOS)CuCl; X = Cl, Br, I and DIPHOS = Ph_ 2P(CH_2)_2PPh_2]. 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 (HePh_2P)_3CuX. The sensitization mechanism of the L_3CuX complexes is proposed as a bimolecular energy transfer process in which energy transfer takes place through the metal centered orbitals. The efficiency of the (MePh_ 2P)_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 L_mCu_nCl_n (L = Ph_3P, MePh_2P; 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 L_mCu_nCl_n complexes (Ph_3P<< MePh_2P) toward ligand dissociation is attributed to the larger steric requirements of Ph_3P in comparison to MePh_2P. Evidence for ground state complexation of NBD and the L_mCu_nCl_n compounds (m:n < 3:1) is shown. Photoexcitation of the (NBD) L_mCu_nCl_n (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 -> a_pi transition. Coordination to copper() halides brings about an enhancement of the l -> a_pi transition of the ligand. The term o,d ->a_pi is used to describe the lowest electronic transition of the complexes indicating that both the o 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-pi-system (a_pi ). The photophysical properties of Zn(II), Cu(I), and Ni(O) complexes of MePh_2P are shown to follow the concept of a o,d -> a_pi electronic transition.
| Identifer | oai:union.ndltd.org:UTAHS/oai:digitalcommons.usu.edu:etd-8310 |
| Date | 01 May 1983 |
| Creators | Fife, Dennis J. |
| Publisher | DigitalCommons@USU |
| Source Sets | Utah State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | All Graduate Theses and Dissertations |
| Rights | Copyright for this work is held by the author. Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user. For more information contact digitalcommons@usu.edu. |
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