Citation
Farid, Ramy Samir (1991) Electron transfer in rigid and semirigid iridium d8d8 donorspaceracceptor complexes. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd06212007154303
Abstract
A series of rigid and semirigid donorspaceracceptor complexes, [Ir(µpz*)(CO)(Ph2POC6H4(CH2)npy[superscript +]R)]2(pz* = 3,5dimethylpyrazolyl; C6H4 = phenylene; py[superscript +] = pyridinium; R = H, 4tertbutyl, and 4amide; and n = 0,1,2, and 3, has been synthesized for the purpose of studying photoinduced electrontransfer (ET) reactions. The spacers separating the iridium center (electron donor, Ir2) and pyridinium cation (electron acceptor, py[superscript +]) are based on terminal phosphinite ligands, consisting of a phenylene group and a number of methylene groups ranging from 0 to 3. Three distinct ET reactions can be studied in each complex: singles excitedstate electron transfer ([superscript 1]ET), triplet excitedstate electron transfer ([superscript 3]ET), and thermal back electron transfer (ET[superscript b]).
Atomic positions, obtained from the Xray crystal structure of [Ir(µpz*)(CO)(Ph2POC6H4CH3]2 were used as a basis for molecular mechanics calculations, furnishing solution structures for the series of Ir2py[superscript +] donoracceptor complexes. These results revealed that the spacers in complexes where n = 0 and n =1 are rigid, and that in complexes where n = 2 and n = 3, the spacers are semirigid, taking on either folded or stretched conformations in fluid solution.
Steadystate and timeresolved emission and absorption experiments were employed to determine [superscript 1]ET, [superscript 3]ET, and ET[superscript b] rates in these complexes. The [superscript 1]ET and [superscript 3]ET rates for the n = 2 and n = 3 complexes exhibit Gaussian freeenergy dependence, in excellent agreement with classical ET theory (n = 2: [lambda] = 1.10 eV, H[subscript DA] = 26 cm[superscript 1]; n = 3: [lambda] = 1.05 eV and H[subscript DA] = 7 cm[superscript 1]). However, the [superscript 1]ET and [superscript 3]ET rates in n = 0 and n = 1 complexes exhibit dramatically different behavior: the [superscript 3]ET rates in these rigid complexes are on the order of 10,000 times slower than the corresponding [superscript 1]ET rates. H[subscript DA]s for the ET[superscript b] reactions (n = 1,2) are similar to those of the corresponding [superscript 1]ET reactions. These results are discussed in terms of the solution structure parameters obtained for the series of donoracceptor complexes. Evidence that throughbond and throughspace couplings play different roles in singles and triplet electron transfer is presented for the first time.
Item Type:  Thesis (Dissertation (Ph.D.)) 

Degree Grantor:  California Institute of Technology 
Division:  Chemistry and Chemical Engineering 
Major Option:  Chemistry 
Thesis Availability:  Restricted to Caltech community only 
Research Advisor(s): 

Thesis Committee: 

Defense Date:  15 January 1991 
Record Number:  CaltechETD:etd06212007154303 
Persistent URL:  http://resolver.caltech.edu/CaltechETD:etd06212007154303 
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  2680 
Collection:  CaltechTHESIS 
Deposited By:  Imported from ETDdb 
Deposited On:  18 Jul 2007 
Last Modified:  26 Dec 2012 02:53 
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