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Interplay of structural dynamics and electronic effects in an engineered assembly of pentacene in a metal-organic framework.

Ritesh HaldarMariana KozlowskaMichael GanschowSamrat GhoshMarius JakobyHongye ChenFarhad GhalamiWeiwei XieShahriar HeidrichYusuke TsutsuiJan FreudenbergShu SekiIan A HowardBryce S RichardsUwe H F BunzMarcus ElstnerWolfgang WenzelChristof Wöll
Published in: Chemical science (2021)
Charge carrier mobility is an important figure of merit to evaluate organic semiconductor (OSC) materials. In aggregated OSCs, this quantity is determined by inter-chromophoric electronic and vibrational coupling. These key parameters sensitively depend on structural properties, including the density of defects. We have employed a new type of crystalline assembly strategy to engineer the arrangement of the OSC pentacene in a structure not realized as crystals to date. Our approach is based on metal-organic frameworks (MOFs), in which suitably substituted pentacenes act as ditopic linkers and assemble into highly ordered π-stacks with long-range order. Layer-by-layer fabrication of the MOF yields arrays of electronically coupled pentacene chains, running parallel to the substrate surface. Detailed photophysical studies reveal strong, anisotropic inter-pentacene electronic coupling, leading to efficient charge delocalization. Despite a high degree of structural order and pronounced dispersion of the 1D-bands for the static arrangement, our experimental results demonstrate hopping-like charge transport with an activation energy of 64 meV dominating the band transport over a wide range of temperatures. A thorough combined quantum mechanical and molecular dynamics investigation identifies frustrated localized rotations of the pentacene cores as the reason for the breakdown of band transport and paves the way for a crystal engineering strategy of molecular OSCs that independently varies the arrangement of the molecular cores and their vibrational degrees of freedom.
Keyphrases
  • metal organic framework
  • molecular dynamics
  • density functional theory
  • room temperature
  • energy transfer
  • molecular dynamics simulations
  • ionic liquid
  • single molecule
  • single cell
  • dna methylation
  • high density