Supramolecular polymerization of permanently dipolar perylene diimide-based diazacoronenes

Abstract

We demonstrate that ground-state dipoles guides the supramolecular assembly and resultant optoelectronic characteristics of perylene diimide-based diazacoronenes (PDACs). The synthetic difficulty of installing permanent ground-state dipoles on planar aromatic systems has largely constrained the exploration of dipole engineering in discotic molecules. Here, we synthesize a family of PDACs with ground-state dipoles between 1 and 6 Debye by installing functional groups on the diazacoronene. Systematically increasing the dipolar character of these PDACs led to red-shifted absorption (477 to 557 nm) and emission spectra (483 to 723 nm), which is consistent with their more negative electrochemical reduction potentials. Density functional theory revealed that sufficiently strong dipoles (PDAC-NMe₂, 6.0 Debye) led to ground-state charge-transfer, which was confirmed by a combination of electrochemical and spectroscopic measurements. Molecular dynamics simulations predicted that PDACs with larger ground-state dipole moments have stronger intramolecular interactions and more well-defined assemblies. Variable-solvent, -concentration, and -temperature aggregation studies were consistent with this trend and, in all cases, revealed that supramolecular polymerization led to more extended electronic delocalization. Additionally, we observed that PDAC assemblies with larger ground state dipoles had enhanced emission lifetimes over their monomer counterparts (τ = 1.8 ns to 5.1 ns for PDAC-NMe₂), whereas assemblies formed from molecules with smaller ground-state dipoles had virtually no change in their excited state lifetimes. Taken together, permanent ground-state dipoles are shown to be a powerful tool to control planar molecular assemblies and their optoelectronic characteristics.