Photoactivation of distal functional groups in polyfunctional molecules

Intramolecular Singlet−Singlet and Triplet−Triplet Energy Transfer in Adamantyl-Linked Trichromophores

“…When the energy transfer process is intramolecular, superexchange involving through-bond transfer may also be operative. This latter process is usually most effective when the saturated hydrocarbon structure linking the chromophores is rigid and the bonds in the linker are all trans. − , We therefore expectated that 3 would be more effective in promoting through-bond superexchange than the flexibly linked compounds 1 and 2 and that a faster SSET rate could potentially be observed. It was anticipated that this factor would have the greatest influence on the interaction between the central and terminal chromophores.…”

“…Intramolecular charge and energy transfer in bichromophores has been the subject of considerable interest in recent years. Particular attention has been paid to the kinetics of transfer processes and how they are affected by molecular conformation, the rigidity or flexibility of the connecting bridges, and interchromophore distance. − The observed relationships between the efficiency of transfer and these parameters have been used to investigate the importance of dipole-induced dipole (Förster) and electron exchange (Dexter) transfer mechanisms, as well as the participation of through-bond and through-space transfer routes. For systems that are limited to through-space pathways, it is generally accepted that the dipole-induced dipole mechanism is important at large interchromophore separations while the exchange mechanism predominates at shorter distances.…”

“…For systems that are limited to through-space pathways, it is generally accepted that the dipole-induced dipole mechanism is important at large interchromophore separations while the exchange mechanism predominates at shorter distances. The through-bond superexchange mechanism appears to be favored for molecules in which the chromophores are joined by rigid saturated hydrocarbon bridges such as those synthesized and characterized, for example, by Closs, − Morrison, − Paddon-Row and Verhoeven, − Zimmerman, and others, − including ourselves . In these bridges, orbital overlap facilitating a super-exchange interaction is provided by an “all-trans” arrangement of the σ bonds.…”

“…Compound 3 differs from 1 and 2 in the nature of the connecting bridges between chromophores; in 3 , the chromophores are linked by 1,3-substituted adamantyl groups. As in polychromophores utilizing cyclohexyl, trans -decalin, and steroidal spacers, − rotational flexibility in this molecule is now limited to the single bonds between chromophore and bridge and the central bond in the biphenyl group. We thus anticipated that through-bond transfer may play a more important role here than in 1 and 2 .…”

Photochemistry of Polyfunctional Molecules. Development of Antenna Chromophores for Self‐sensitized Photoreduction of Ketones*

“…Less attention has been paid to the potential utilization of intra-SET in organic synthesis. As part of our general interest in the photoactivation of distal groups in polyfunctional molecules (Morrison, 1987), recent efforts in our laboratory have been directed toward developing a methodology for achieving the selective photoreduction of a single carbonyl group in multi-ketonic systems using intra-SET. We have shown (Morrison et al, 1986) that in prototype aryl ketones containing a non-removable aryl "antenna", e.g., the trans-(3) and cis-decalones(4), excitation of the benzenoid chromophore to the corresponding alcohols in 47 and 26% yields, respectively.…”