Optically Active Phthalocyaninato−Polysiloxane Constructed from Achiral Monomers: From Noncovalent Assembly to Covalent Polymer

Abstract

In this paper, we reported that optically active supramolecular assemblies of an achiral phthalocyanine derivative, silicon 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine dihydroxide (Pc 1), could be easily achieved through the Langmuir and Langmuir−Schaefer (LS) technique. We have found that the LS film of Pc 1 showed weak Cotton effect (CE) when it was subjected to the circular dichroism (CD) measurements. The chirality of the LS film was suggested to be due to the spontaneous symmetry breaking occurred at the air/water interface. More interestingly, such assemblies connected through the noncovalent bond could be further converted into covalent bond under heating at 180 °C in a high vacuum for 10 h. UV−vis spectra and FT-IR have confirmed the polymerization of Pc 1 in the LS film during the heating, which resulted in the formation of the corresponding phthalocyaninato−polysiloxane (PcPs 2) polymer. Stronger Cotton effect was detected for the thin solid film of PcPs 2 compared with that of the Pc 1 LS film, suggesting that more efficient exciton coupling existed between the covalently linked phthalocyanine chromophore in the polymer PcPs 2. The investigation provided an easy way of constructing optically active polymeric PcPs films exclusively from achiral monomer unit by the preassembly of monomer through interfacial organization.