Ferrocene triplet states

The quenching of the trans dimer with oxygen and ferrocene indicates that this product is formed almost entirely from the triplet state. It is possible to calculate the amount of triplet-derived product in benzene by subtracting the amount of product obtained in the presence of oxygen from the amount of product obtained in the absence of oxygen. Such a calculation indicates that acenaphthylene triplets in benzene give both trans and cis dimers in the ratio of 74 26. The triplet state accounts for almost all of the trans product and about 10% of the cis product. The break in the slope of the Stem-Volmer plot for the trans dimer (Figure 10.3) may be attributed to the presence of two excited species which are quenched at different rates. These two species could be (a) two different monomeric acenaphthylene triplet states 7 and T2 or (b) a monomeric acenaphthylene triplet state 7 and a triplet excimer. This second triplet species is of relatively minor importance in the overall reaction since less than 5% of the total product in an unquenched reaction is due to this species. 

Ge(TPP)R2, Ge(TPP)(Fc)Ph, and Ge(TPP)Fc2) the spectrum after 2 /us was consistent with a triplet excited state, although this decayed much faster for the fer-rocenyl complexes. Addition of ferrocene to Ge(TPP)R2 also quenches triplet lifetimes. A similar situation was observed for the indium complexes In(Por)R, and the triplet-state quenching was attributed to an energy transfer process from the excited-state triplet to ferrocene. In the case of the germanium porphyrins, the longer-lived triplet state in Ge(TPP)R2 is responsible for the Ge—C bond homolysis, and both inter- and intramolecular quenching by ferrocene is observed. 

It is typical that the photorearrangement 57 - 58 proceeds readily.37 This seems to rule out the triplet state of the rearranging molecule 57, reasoning that the ferrocene part of the molecule would very probably act as a triplet quencher,35 as is the case with other ferrocene derivatives structurally able to undergo triplet photoreactions.36 On the other hand, the reaction 55 - 56 cannot be sensitized with acetophenone33 (ET = 73.6 kcal mole-1 32ft). 

The copolymers of type 67 exhibit the characteristic photochemical depolymerization noted for polysilanes, a source of their potential as photoresist materials. However, the presence of the ferrocenyl substituents results in a significant retardation of this depolymerization, presumably due to the ability of ferrocene to quench the triplet state responsible for the polysilane photochemistry164. Polymers of type 67 can be regarded as polysilanes with reversible redox behaviour. 

The first example of Ndm and Ybm luminescence sensitized by Ru11 and ferrocene appeared in 2000. The authors noticed that [Ru(bpy)3]2+ has an intersystem crossing yield near unity and that it enables excitation with visible light up to 500 run. On the other hand, ferrocene has weaker absorption bands in the visible spectrum, but its low-lying triplet state (wl3 300 cm-1) matches fairly well the Ndm (4F3/2, 11300 cm-1) and Ybm (2Fs/2,... 

Ferrocene is easily oxidized (F , +0.49 V versus SCE) and has a relatively low-lying (c. 1.8 eV) very short-lived triplet state. Therefore, with many common chromo-... 

Since the triplet energy of ferrocene is similar to that of anthracene the potential energy surface of isomerization of styrylferrocene in the triplet state is considered as similar to that of one-way isomerizing anthrylethenes. However, the substitution of a phenyl group in stilbene by a ferrocenyl group suppressed the efficiency of isomerization due to the acceleration of deactivation of the cis and trans triplet state before undergoing isomerization around the double bond a very short life-... 

With ferrocene as quencher and triphenylene as sensitizer the cis trans isomerization of several 4-nitrostilbenes has been examined [201], From linear plots of ([t]/[c])sens versus [Q], larger slope/intercept ratios were found as compared to direct excitation conditions (Table 8). A cis -> trans pathway partly bypassing the triplet state accounts for this difference (Section VI). Plots of ([t]/[c])scns as a function of the azulene or ferrocene concentrations are shown in Figure 10 for three stilbenes. 

Since the lowest triplet state of nitrostilbenes at room temperature can be probed by laser flash photolysis, quenching rate constants could be measured directly [188,200], Values for kq are close to the diffusion-controlled limit (Table 17). Comparable results have been obtained for naphthyl-[410] and 2-anthrylethylenes [433] and for ADBs [33, 143, 145-147, 232, 411], For substituted 1-NPEs, conclusions about the position of the triplet equilibrium were drawn on the basis of rate constants for quenching by ferrocene and oxygen [441]. 

Table 4 Rate constants for the quenching of triplet states by ferrocene in ethanol solution 828...

The topological control of such polymerization reactions has been the subject of recent extensive reviews,52 and the same phenomenon in 2,5-distyrylpyrazine has been further discussed.53 The true photopolymerization process discussed here is typified by the u.v.-induced polymerization of AW -polymethylenebis-(maleimides) discussed above,51 and a complete study of the kinetics of the process is included in this series of papers. The conclusion is reached that the triplet state of the chromophore is the reactive species this can be quenched by the addition of ferrocene or 3,3,4,4-tetramethyl-l,2-diazetine 1,2-dioxide. The kinetics of a further example of true photopolymerization, the reductive photocopolymerization of diaryl ketones, have been compared with those of the photoreduction of the model compound benzophenone and found to be similar.53 The photoreductive poly-recombination of the diaryl ketones shown in Schemes 2 and 3 has been studied extensively.54... 

Some previous reports of uphill quenching of triplet states by ferrocene may have arisen from assignment of too high a value for the energy of Tx ferrocene... 

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