Multitiered 2D pi-stacked conjugated polymers based on pseudo-geminal disubstituted [2.2]paracyclophane

Interchain interactions between pi-systems have a strong effect on the electronic structure of conjugated organic materials. This influence has previously been explored by the spectroscopic and electrochemical characterization of molecules in which pairs of conjugated oligomers are held in a stacked fashion by attachment to a rigid scaffold. We have prepared a new polymer which uses a pseudo-geminal disubstituted [2.2]paracyclophane scaffold to hold 1,4-bis(phenylethynyl)-2,5-dialkoxybenzene (PE(3)) chromophores in a pi-stacked fashion over their entire length and in an extended multitier arrangement. Solutions of this new polymer display a Stokes shift of 171 nm, compared to just ca. 30 nm for previous models in which only the terminal phenyl rings of the PE(3) chromophore are held in a stacked arrangement. This suggests that interchain interactions of pi-systems over their entire length in a multitier assembly provides for relaxation of the excited state to a stable "phane" electronic state which is responsible for emission. This stabilization is not available in the stacked dimer or other regioisomers of the polymer which possess lesser degrees of overlap. Thus, the architecture of the soluble polymer mimics that of segments of conjugated polymers in semiconducting thin films and will provide a platform for the exploration of the nature of charge carriers and excitons in these important materials.