Optical properties of substituted phthalocyanine rare-earth metal complexes

Comparative study of optical properties of alkylthio-group-substituted phthalocyanine rare-earth metal sandwich complexes $\mathrm{([(}{\mathrm{C}}_n{\mathrm{S)}}_{\mathrm{8}}{\mathrm{Pc]}}_{\mathrm{2}}\mathrm{M,M=Eu,Lu,Tb})$ is presented. Photoluminescence and photoconductivity of $\mathrm{[(}{\mathrm{C}}_n{\mathrm{S)}}_{\mathrm{8}}{\mathrm{Pc]}}_{\mathrm{2}}\mathrm{M}$ complex is very weak. Two photoluminescence bands were observed at around 400–650 and 720–800 nm in chloroform solution corresponding to the Soret and Q bands in the absorption spectra, respectively. However, the emission from ${\mathrm{Eu}}^{\text{3+}}$ ion (as well as ${\mathrm{Tb}}^{\text{3+}})$ was not found compared with other Eu complexes because the $\text{5d}$ levels of the ${\mathrm{Eu}}^{\text{3+}}$ ion lie higher than the triplet level of the ligand. The significant enhancement of the photoconductivity of $\mathrm{[(}{\mathrm{C}}_{\mathrm{16}}{\mathrm{S)}}_{\mathrm{8}}{\mathrm{Pc]}}_{\mathrm{2}}\mathrm{M}$ after ${\mathrm{C}}_{60}$ doping is reported. The photoconductivity is positive at the low electric field in the ohmic regime while it becomes negative at the high electric field upon photoexcitation with strongly absorbed light. The negative photoconductivity is attributed to space-charge effects. The mechanism of photoluminescence and photoconductivity are discussed by taking the electronic energy schemes of phthalocyanine ligands and lanthanide ion and ${\mathrm{C}}_{60}$ into consideration.