EFFECT OF MESOPHASE STRUCTURE ON THE INTERMOLECULAR TRIPLET QUENCHINGOF PHOTOEXCITED ZUTPP AND CUTPP MIXTURES

Time-resolved EPR detection of photoexcited Zn- and Cu-tetraphenylporp hyrin (TPP) mixtures oriented in several thermotropic liquid crystals (LCs) is reported. Both the transient triplet EPR spectra of ZnTPP and the doublet ground state CW spectra of CuTPP were recorded and quanti tatively analyzed via line shape analyses over a wide temperature rang e (130-370 K). It is shown that the photoexcited triplet state of ZnTP P is entirely quenched by the photoexcited CuTPP species exclusively i n the fluid smectic phase of a multidomain LC (ZLI-1167), whereas in t he other phases of this LC, as well as in other LCs (E-7 and ZLI-4389) there is no indication of any interaction between the different chrom ophores. The results are interpreted in terms of a ZnTPP-CuTPP transie nt complex formation, which depends on a favorable mutual orientation of the interacting chromophores, specifically imposed by the layers an d multidomain structure of the smectic phase of ZLI-1167.