A study of intramolecular energy transfer in steroid analogues
Abstract
The compounds 3β-dimethylphenylsiloxy-16-ethylidene-5α-androstane (1), 3α-dimethylphenylsiloxy-16-ethylidene-5α-androstane (2), 3-ethylidene-16-β-dimethylphenylsiloxy-5-α-androstane (3), and 3-ethylidene-16-α-dimethylphenylsiloxy-5-α-androstane (4) were prepared to answer questions about the efficiency of TTET to and from positions C3 and C16 in steroidal molecular photonic wires. Irradiation of these compounds with 254 nm light resulted in the absorption of photons by the donor chromophore, followed by triplet-triplet excited-state energy transfer (TTET) to the ethylidene acceptor. The result is Z→E isomerization of the ethylidene group. This energy transfer occurs both intra- and intermolecularly at the 5 mM concentration used in the study of these compounds. The quantum efficiencies of isomerization (ΦZ→E) for compounds 1 and 2 are 0.044 ± .005 and 0.046 ± .003, respectively. A complete set of rate constants were obtained by kinetic analyses of compounds 1 and 2 using model compounds. The rate constants for intramolecular triplet-triplet energy transfer (kintraTTET) for 1 and 2 are 7.6 x 10 6 s-1 and 6.6 x 106 s-1, respectively. The rates of kintraTTET for C3 to C16 are faster than those for C3 to C17, suggesting that the C16 acceptor is a much better quencher of the triplet state of the DPSO group than the C17 acceptor. Surprisingly, the kintraTTET values of 1 and 2 are closer than one would have expected considering that the geometry of 1 adopts the all-trans arrangement known to be ideal for through-bond interaction. Kinetic studies of 3 and 4 could not be completed due to the inability to resolve the double bond isomers.
Degree
Ph.D.
Advisors
Morrison, Purdue University.
Subject Area
Organic chemistry|Biochemistry
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