Photoinduced Electron Tunneling in Bridge Molecules

In Ref. [302], a difference by a factor of 5 was found for the rate constants of electron tunneling in rigid bridge molecules P-Q that contained porphyrin P and quinone Q fragments at almost the same distances, but had different mutual orientations of P and Q fragments. 

Theoretical calculations of the dependence of the probability of electron tunneling on mutual orientation of donor and acceptor fragments in bridge molecules were presented in Ref. [304], With the use of a cyclic polyene model to construct wave functions of porphyrin fragments, a number of analytical expressions were obtained for orientation dependence of probabilities of tunneling between these fragments. 

Photoinduced intramolecular electron tunneling was observed also in some other porphyrin containing bridge molecules, such as porphyrin covalently linked to phenolphthalein [308], dimethylaniline — mesoporphyrin II — quinone triad [309], Zn porphyrin-viologen-quinone triad [310], carotenoid — porphyrin -diquinone tetrad [311]. The influence of conformational state of porphyrin-viologen bridge molecules on the rate of PET reactions was studied in Ref. [312]. 

In Refs. [315 316] a synthetic methodology was developed that allows to use transition metal chromophores such as (bipy)Re (CO)3 in studies of PET across rigid organic spacers. Intramolecular PET from 1,3-benzodithiafulvene to Re1 over 16 A via trans-1,4-cyclohexane spacer at 298 K followed by dark charge recombination was found to occur in the nanosecond time scale. 

In Ref. [317] the temperature independence of the intramolecular electron transfer reaction in a cofacial Zinc porphyrin-quinone cage molecule was observed in the range 80-300 K and interpreted in terms of non-adiabatic electron tunneling. 

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