Dipole-dipole and exchange energy transfer in different types of porphyrin chemical dimers

摘要

Experimental and theoretical studies of the singlet and triplet state deactivation in porphyrin and chlorin homo- (both free bases and metallocomplexes (Zn, Cu, Ni)) and heterodimers of various types in a wide temperature range have been carried out.Rigid dimers of cyclopentaneporphyrins as well as more flexible ethane-bisporphyrins and ethane-bischlorins with -CH_2-CH_2- spacers have been investigated. First singlet/triplet states of the dimer subunits are involved in weak dipole-dipole/exchange interactions that result in pico-anosecond excitation energy transfer (ET). In homodimers at temperature lower than 77 K when essential spectral inhomogeneity exists and in heterodimers the ET is directed to the longer wave centers. Exchange d-pi effectsplay the main role in excitation deactivation in heterodimers containing Cu ions. In heterodimers containing Ni ions, very fast energy transfer takes place to low-energy d-levels of Ni. Free bases of ethane-'sporphyrins have been shown to quench singlet oxygen by about an order of magnitude more effectively than the initial monomeric compounds. In the case of homo- and hetero-etlwne-toporphyrins containing metal ions, quenching efficiency depends both on the dimer composition and on the nature of themetal ions.