Novel electrical and optical properties of discotic liquid crystals, substituted phthalocyanine rare-earth metal complexes

Akylthio-group-substituted phthalocyanine rare-earth metal sandwich complexes such as bis[octakis(alkylthio)phthalocyanineato]europium(III) {[(C/sub n/S)/sub 8/Pc]/sub 2/Eu}, bis[octakis(alkylthio)phthalocyaninato]lutetium(III) {[(C/sub n/S)/sub 8/Pc]/sub 2/Lu}, bis[octakis(alkylthio)phthalocyaninato]terbium(lII) {[(C/sub n/S)/sub 8/Pc]/sub 2/Tb} exhibit discotic liquid crystal phases. Photoluminescence (PL) peaks of [(C/sub n/S)/sub 8/Pc]/sub 2/Eu were observed at around 400-600 nm and 730 nm in chloroform solution. However, the strong narrow emission of the Eu/sup 3+/ ion was not observed compared with other Eu-complexes. The intensity and the decay time of the PL peak depend strongly on the phase. They have been explained by taking electronic energy schemes of both phthalocyanine ligands and the Eu/sup 3+/ ion into consideration. The role of the triplet exciton is also discussed. In the photoconductivity (PC) spectra of [(C/sub n/S)/sub 8/Pc]/sub 2/Eu several peaks were observed corresponding to the absorption peaks. The behavior has been discussed in terms of carrier migration along the stack of phthalocyanine cores in the discotic phase. Current-voltage characteristics and dielectric properties of these discotic liquid crystals have also been clarified.