Covalently Tethered Assemblies Improve Energetic Homogeneity and Exciton Transport in Organic Materials

Abstract

Structural and functional heterogeneity is a consequence of the weak noncovalent interactions that direct the formation of organic materials from solution precursors. While covalent tethering of solution-phase assemblies provides a compelling strategy to enhance intermolecular order, the effects of this tethering strategy on the formed solid-state materials remain unestablished. This work uses pump−probe microscopy to compare excited-state dynamics in thin films fabricated from tethered perylene bisimide assemblies to those fabricated from noncovalent assemblies. On average, tethered films exhibit faster and more homogeneous excited-state lifetimes, consistent with stronger and more uniform intermolecular coupling. Optical measurements of excited-state diffusion show that the tethered film has ∼75% faster transport than the control film. Kinetic Monte Carlo modeling suggests that the reduction of site energetic disorder is sufficient to quantitatively explain the difference in diffusion coefficients. These results provide strong support that covalent tethering is a promising strategy to enhance the structural and energetic ordering in molecular materials.

Probing Excited State Delocalization and Charge Separation in Hierarchical Perylene Diimide Materials with Time-Resolved Broadband Microscopy

“…These mesoscale materials, which spontaneously assemble on a substrate, enable us to carefully isolate and interrogate rod-like structures like those shown in Figure C to compare with the EQ-PDI film. We were unable to measure X-ray diffraction patterns from either sample while maintaining the morphologies shown in Figure , however materials derived from structurally similar monomeric precursors show π–π stacking distances of 3.45 Å in drop cast films …”