Photophysics of the mixed (phthalocyaninato)(porphyrinato) rare earth [terbium (III) and europium (III)] double- and triple-decker sandwich compounds

Ground state electronic absorption and photoluminescent properties of a series of porphyrin and phthalocyanine mixed rare earth triple- and double-decker complexes, namely [(TClPP)M(Pc)M(TClPP)] (a), [(TClPP)M(Pc)M(Pc)] (b) and [(TClPP)M(Pc)] (c) [Pc = phthalocyaninate; TClPP = eso-tetrakis(4-chlorophenyl)porphyrinate; M = Tb (1a–1c), Eu (2a–2c)] have been investigated comparatively. The optical properties analogous to each other for these sandwich compounds suggests that internal π–π interactions between each macrocycles within the compounds defining the electronic properties of the chromophores brought within van der Waals distance. Besides, the unexpected phosphorescence bands of the terbium containing double- and triple-deckers, arising from 3T(π, π*) state of the compounds indicates that rare earth metals chelated in the highly conjugated macrocyclic compounds play no direct role in the stable states, but determine the relaxation rates and pathways of the excited states following photoexcitation of sandwich-type tetrapyrrolic complexes.