Involvement of Triplet Excited States and Olefin Radical Cations in Electron-Transfer Cycloreversion of Four-Membered Ring Compounds Photosensitized by (Thia)pyrylium Salts

2002 ◽  
Vol 67 (12) ◽  
pp. 4138-4142 ◽  
Author(s):  
Miguel A. Miranda ◽  
M. Angeles Izquierdo ◽  
Francisco Galindo
Keyword(s):  
Electron Transfer ◽  
Excited States ◽  
Radical Cations ◽  
Membered Ring ◽  
Pyrylium Salts ◽  
Ring Compounds ◽  
Triplet Excited States

Electron Transfer from the Singlet and Triplet Excited States of Ru(dcbpy)2(NCS)2into Nanocrystalline TiO2Thin Films

2002 ◽  
Vol 106 (17) ◽  
pp. 4396-4404 ◽  
Author(s):  
Jani Kallioinen ◽  
Gábor Benkö ◽  
Villy Sundström ◽  
Jouko E. I. Korppi-Tommola ◽  
Arkady P. Yartsev
Keyword(s):  
Electron Transfer ◽  
Excited States ◽  
Triplet Excited States

scholarly journals Orthogonally Aligned Cyclic BODIPY Arrays with Long-lived Triplet Excited States as Efficient Heavy-Atom-Free Photosensitizers

2021 ◽  
Author(s):  
Zhaoyang Zhu ◽  
Xue Zhang ◽  
Xing Guo ◽  
Qing-Hua Wu ◽  
Zhongxin Li ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Energy Transfer ◽  
Excited State ◽  
Excited States ◽  
Heavy Atom ◽  
Triplet Excited State ◽  
Transfer Processes ◽  
Excited State Lifetimes ◽  
Triplet Excited States

Photosensitizers with long triplet excited state lifetimes are key to their efficient electron transfer or energy transfer processes. Herein, we report a novel class of cyclic trimeric BODIPY arrays which...

scholarly journals Long-lived triplet charge-separated state in naphthalenediimide based donor–acceptor systems

2021 ◽  
Author(s):  
Alexander Aster ◽  
Christopher Rumble ◽  
Anna-Bea Bornhof ◽  
Hsin-Hua Huang ◽  
Naomi Sakai ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited States ◽  
Donor Acceptor ◽  
Triplet Excited States ◽  
Ultrafast Electron Transfer

Ultrafast electron transfer from singlet and triplet excited states in equilibrium results in the population of both singlet and triplet charge-separated states.

scholarly journals Divergent Photocatalytic Reactions of α-Ketoesters Under Triplet Sensitization and Photoredox Conditions

2020 ◽  
Author(s):  
Jian Zheng ◽  
Xiao Dong ◽  
Tehshik Yoon
Keyword(s):  
Electron Transfer ◽  
Energy Transfer ◽  
Transition Metal ◽  
Excited States ◽  
Reactive Intermediates ◽  
Organic Substrates ◽  
Reaction Conditions ◽  
Electron Transfer Pathways ◽  
Photocatalytic Reactions ◽  
Triplet Excited States

The long-lived triplet excited states of transition metal photocatalysts can activate organic substrates via either energy- or electron-transfer pathways, and the rates of these processes can be influenced by rational tuning of the reaction conditions. The characteristic reactive intermediates that are generated by each of these activation modalities, however, are distinct and can exhibit very different reactivity patterns. Herein, we show that the photocatalytic reactions of benzoylformate esters with alkenes can be directed towards either Paternò–Büchi cycloadditions under conditions that favor energy transfer or allylic functionalization reactions under superficially similar conditions that favor electron transfer. These studies provide a framework for designing other divergent photocatalytic methods that produce different sets of reaction outcomes under photoredox and triplet sensitization conditions.

Stereoselective O2-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

2003 ◽  
Vol 81 (6) ◽  
pp. 673-679 ◽  
Author(s):  
Jack Saltiel ◽  
Govindarajan Krishnamoorthy ◽  
Zhennian Huang ◽  
Dong-Hoon Ko ◽  
Shujun Wang
Keyword(s):  
Excited States ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Radical Cations ◽  
Intersystem Crossing ◽  
Kinetic Isotope ◽  
Polar Environment ◽  
Central Bond ◽  
Isomerization Pathway ◽  
Triplet Excited States

Irradiation of all-trans-1,6-diphenyl-1,3,5-hexatriene (ttt-DPH) in degassed acetonitrile (AN) gives ctt- and tct-DPH, relatively inefficiently, mainly via isomerization in the singlet excited state. The triplet contribution to the photoisomerization is small due to a very low intersystem crossing yield (ϕis = 0.01). Central bond isomerization is quenched in the presence of air by a factor of 1.4, consistent with the expected quenching of the lowest singlet and triplet excited states by oxygen. However, the presence of air enhances terminal bond photoisomerization by nearly twofold. Triplet-sensitized ttt-DPH photoisomerization favors tct-DPH formation and is quenched by oxygen. It follows that the interaction of singlet-excited ttt-DPH with O2 suppresses isomerization to tct-DPH but opens a new isomerization pathway to ctt-DPH. The presence of dimethylfuran, a singlet O2 trap, has no effect on the photoisomerization, eliminating the possible involvement of singlet O2 in this new reaction. ttt-DPH radical cations are ruled out as intermediates because the presence of fumaronitrile, which leads to their formation, suppresses both central and terminal bond photoisomerizations. In contrast to acetonitrile, ctt-DPH formation is quenched by oxygen in methylcyclohexane, suggesting the requirement of a polar environment. Strikingly different deuterium isotope effects distinguish the direct and O2-induced photoisomerization pathways. A comparative study of ttt-DPH-d0 with ttt-DPH-d2 and ttt-DPH-d4, involving deuteration of one and both terminal double bonds, reveals an inverse kinetic isotope effect (kHox/kDox = 0.92) for the O2-induced reaction. An attractive mechanism for the new oxygen-induced photoisomerization involves charge transfer from the S1 state of ttt-DPH to oxygen followed by collapse of the exciplex to either a zwitterionic or a biradicaloid species through bonding at one of the benzylic positions. Rotation about the new single bond in this intermediate followed by reversion to DPH and O2 gives the observed result. Key words: diphenylhexatrienes, trans-cis photoisomerization, oxygen sensitization.

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