Discrete boronate ester ladders from the dynamic covalent self-assembly of oligo(phenylene ethynylene) derivatives and phenylenebis(boronic acid)†
Three increasingly π-conjugated covalent organic polygons have been prepared by the dynamic covalent condensation of catechol-based oligo(phenylene ethynylene) derivatives with phenylenebis(boronic acid). The assemblies represent a series of boronate ester “ladders” wherein two electron rich oligo(phenylene ethynylene) “rungs” are bridged by electron deficient aryl boronate ester “rails”, resulting in quasi-two-dimensional oligomers of increasing size. Spectroscopic and computational investigations suggest that the ladders exhibit a greater effective conjugation length than comparable oligo(phenylene ethynylene) compounds not bridged by aryl boronate esters. Different conformations, substitutions, and constitutions of boronate ester ladders are also modeled to gain further insight into their influence on π-conjugation and HOMO–LUMO gaps of isolated one-dimensional versus bridged, quasi-two-dimensional conjugated organic materials.