Photoelectron Transfer between a Magnesium-Free-Base Porphyrin Heterodimer and Duroquinone. Selective Excitation and Time-Resolved EPR Studies

Article abstract of DOI:10.1021/j100152a026

The photoexcited triplet state of a cofacial heterodimer, , comprised of Mg and H2 porphyrins, and photoinduced electron transfer (ET) between the heterodimer and duroquinone in 1:1 mixture of CH2Cl2/ethanol were studied by selective laser excitation combined with time-resolved CW or with pulsed EPR spectroscopies.ET originates from the photoexcited triplet or triplet radical pair states.Upon photoexcitation of the Mg subunit (580 nm), a noticeable delay time of ca.20 ns in ET is observed, whereas with photoexcitation of the H2 part (620 nm), no delay time in ET is noticed.The dependence of ET upon excitation wavelength is interpreted in terms of the formation and participation of a charge-transfer state that is operative at 205 K.The delay time is attributed to an intradimer ET that produces the triplet radical pair state ³.+-H2^.->.Photoexcitation at 620 nm results in ET via the lower-lying triplet of H2 without involvement of the chargetransfer state.