Triplet state excitation

The charge transfer that occurs on photoexcitation changes the pAa values of substituents on bpy or related ligands. Because the substituents become more basic as a result of the MLCT nature of the triplet states, excited-state proton transfers can occur. There have been many studies of such reactions of Ru complexes, but few on analogous Os complexes until recently (233). 

Many examples of collisions with changes in local permutational symmetry are known. The Cundall technique31,32,190 used to measure triplet yields to photoexcited benzene involves the transfer of triplet-state excitation energy... 

The role of the triplet state in biological and biochemical systems continues to receive wide attention. Photoexcited triplet states of prophins and derivatives (389), prophyrins (390), aromatic amino acids (390), aromatic amines (391), and monoanionic thymine (392) have been observed at 77°K. Shiga and Piette (393) confirmed the interpretation of ESR data on triplet-state excitation in proteins by a simultaneous phosphorescence study. 

In other solvents (ether, cyclohexane, acetone), the cycloaddition does not take place, only reduction of the double bond is observed. As regards the two monooxiranes of ewdo-bicyclopentadiene, in the course of acetone-sensitized photolysis only enrio-4-oxatetracycloundec-9-ene 136 is changed. Photoreduction of the double bond proceeds by a free-radical mechanism there is no interaction between the triplet-state excited olefin and the oxirane part. ... 

Section XII. 1,3-Dlphenyllsobenzofuran (DPBF) is a highly reactive (ky > 7 x 10 sec l see ref. 186) and widely used reference 02-acceptor. The overall kinetics of its photooxidation was now reinvestigated by Stevens and Small (ref. H). It was found that the triplet-state excited molecules of DPBF act as very efficient 02 quenchers, k = 2 x 10 sec l in benzene. 

Eor the metal-ion chelates of interest here, the triplet state excitation is mainly... 

With reference to the molecular axis frame of Fig. 16, it is recalled from the ODMR results that the ligand-localized triplet state excitation in Rh(TTB)+ is on the fragment (of Cj symmetry) marked with the single asterisk. We consider now, as in Sect. 6.2, that the transition moment for radiative decay of the triplet state is determined by (Hsqc) of Eq. (19), with a major contribution from the SOC... 

For triplet states, excitation yield values up to unity were measured for the energy-deficient system fluoranthene/lO-methyl-phenothiazine [14,18]. The estimation of the triplet yield was carried out by interception with cis-stilbene (p. 57). 

---