Photoactivation of distal carbonyl groups in steroidal ketones: Intramolecular energy transfer control of multiplicity

Long-Range Through-Bond Photoactivated σ Bond Cleavage in Steroids. Intramolecular Sensitized Debromination1

“…The TPSO fluorescence efficiency (0.010) and lifetime (2.1 ns) in a model system, 3α-(triphenylsilyloxy)-5α-androstane ( 1), are similar to those observed for the DPSO group (0.005 and 1.2 ns, respectively) …”

Photophysics and Mechanisms of Intramolecular Electronic Energy Transfer in Bichromophoric Molecular Systems: Solution and Supersonic Jet Studies

“…This pioneering work was followed over the years by a plethora of studies of other bichromophoric molecules were intramolecular sensitization, as a result of intra-EET was the photochemical route leading to the observed reactions. [378][379][380][381][382][383][384][385][386][387][388][389][390][391][392][393][394][395][396] The approach adopted in these earlier studies involved two different classes of molecules. The first class consisted of bifunctional acyclics which were flexible and relatively free of conformational constraints.…”

“…In the second class of molecules welldefined cyclic substrates allowed a detailed study of the dependence of the observed triplet-triplet photophysical and photochemical energy transfer processes on the chromophore geometry. [379][380][381][382][383][384][385] These studies were later [386][387][388][389][390][391][392][393][394][395][396] extended to address problems of photochemical activation of distal functional groups in polyfunctional molecules, in particular the antenna-initiated photochemistry in trifunctional steroids should be noted. The photochemistry study was complemented by investigating the fluorescence spectroscopy of the bichromophoric molecule which revealed that the photochemical reaction was initiated by a singlet-singlet intra-EET process.…”

“…There are, however, some studies of the photochemical aspects of intra-EET . The major contributions to the understanding of photochemistry involving intra-EET in bichromophoric molecules were made by Morrison and co-workers. ,,− Morrison has pointed out that in the photochemistry of trans -4-hexen-2-one 377 one of the products the isomeric cis -4-hexen-2-one was produced as a result of an intra-EET process from the excited carbonyl chromophore to the nonconjugated double bond. This study was followed by photochemistry performed on two other bichromophoric molecules .…”

“…Morrison's conclusion was that “absorption of light at one site of the molecule results in a chemical reaction at a second, nonconjugated site”. This pioneering work was followed over the years by a plethora of studies of other bichromophoric molecules were intramolecular sensitization, as a result of intra-EET was the photochemical route leading to the observed reactions. − The approach adopted in these earlier studies involved two different classes of molecules. The first class consisted of bifunctional acyclics which were flexible and relatively free of conformational constraints.…”