Mechanism of the phototransfer of electrons from zinc porphyrins to carbon tetrachloride in glassy matrices

Hole-Burning Study of Primary Photochemistry of Metalloporphyrins in Reactive Solvent Glasses

“…It was proven that the green light absorbed during the lifetime of the T 1 state of the pigment leads to the photoionization which obviously takes place in the highly excited triplet state. In striking contrast to the conclusions of refs −11, the photon gating unequivocally indicates that the photooxidation of metalloporphyrins is a two-quantum process involving the triplet state, similar to classical two-quantum reactions of polycyclic arenes and aromatic amines under ultraviolet excitation. , …”

“…In this case the reaction rate should increase linearly with concentration, since the number of acceptor particles in the closest coordination sphere of the pigment molecule is proportional to concentration. As a result of fast relaxation of the T n state (probably several picoseconds), the electron transfer by means of long-range (∼15 nm) tunneling in the sense expressed in refs −8 has no time to occur. The yield of permanent hole formation is not further increased when the pigment becomes fully surrounded by acceptor molecules.…”

“…Evidence for quenching processes of porphyrins in the S 1 state in cryogenic solid solutions is scarce. ,,, The intensity of ZnTPP fluorescence in frozen ethanol at 80 K was reported to decrease by a factor of ∼4 in the presence of 0.3 M methylviologen . It was noted that even in chemically bound porphyrin−viologen compounds connected with flexible chains the donor and acceptor moieties tend to reside in close proximity in the solid matrix .…”

“…It is difficult to determine solely on the basis of optical data whether the spectra are modified by interactions with counteranions or radicals (CCl 4 •- , CCl 3 • , Cl - ), solvation of central Mg ion, or more extensive substitution and addition reactions at the π-radical itself. The electron spin resonance method may prove invaluable for proper characterization of the photooxidation products. − , The efficiency of MgOEP photolysis in different media containing 2.5 M CCl 4 is somewhat dependent on the polarity of matrix. The highest value of Φ 2 (0.01) is observed in highly dipolar ethanol and propylene carbonate.…”

Long Range Electron Tunneling in Biological and Model Systems

“…At the same time according to the evaluations made Khairutdinov (1985). Khairutdinov (1985) and Khairutdinov TpivPP-mezo-tetra (u,a,a,a,-0-pivalamidophenyl) porphyn; HPtme-hematoporphyrin-IX tetramethyl ester; EP-etioporphyrin-l . by Strekova et al (1981) electron transfer from triplet excited zinc and magnesium porphyrins to CC14 is also energetically permitted. But as has been stated above electron tunneling energy differs from the donor electron binding energy, thus the absence of electron transfer from 'MP to CC14 points to a decreased Frank-Condon F factor value for the reactions of 'MP as compared with the electron transfer reaction with IMP.…”