Processes of charge separation in porphyrin-quinone compounds with a rigid bridge

3 Processes of charge separation in porphyrin-quinone compounds with a rigid bridge 

Another example of compounds with the fixed mutual location of porphyrin and quinone are the porphyrin-quinone compounds with a rigid bridge. Charge photoseparation in P-L-Q molecules in which L is the trip-ticene bridge, P is tetraphenylporphin, TPP, or its zinc complex, and Q is benzoquinone, BQ, naphthoquinone, NQ, or anthraquinone, AQ, has been studied [55]. The distance between the centres of P and Q fragments in these 

Quantum yields, p, of the quenching of the fluorescence of the porphyrin fragment and free energy changes, — AG°, for the electron transfer reaction from the P fragment to the Q fragment of P-L Q molecules in methylene chloride solution [55] 

The efficiency of luminescence quenching (see Table 1) was found to correlate with the change in the free energy, — AG°, of the electron transfer reaction estimated according to the formula (see Chap. 7, Sect. 4.2) 

The charge photoseparation in porphyrin-quinone compounds with a rigid bicyclo[2.2.2]octyl bridge, ensuring a distance between the centres of P and Q of about 16 A, has been studied [57]. The rate constant of intramolecular electron transfer from P to Q was found to depend on the dielectric properties of the medium and reached 3.3 x 107s 1 for a solution of P-L-Q in propionitrile. 

3 Processes of Charge Separation in Porphyrin-Quinone Compounds with a Rigid Bridge 

Further, using Eq, (1) for the dependence of the probability of electron tunneling lfrom P to Q, one can easily calculate ae l,4Aandve 1019 s 1. But, if instead of the intercentral distance, the shortest distance between P and Q is used as R, the value v,. 1016 s 1 is obtained. 

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