Crystal Engineering in Oligorylenes: The Quest for Optimized Crystal Packing and Enhanced Charge Transport

Area of Science:

• Materials Science
• Organic Electronics
• Crystallography

Background:

• Crystal structure is crucial for organic semiconductor performance in devices like organic field-effect transistors (OFETs).
• Molecular packing in organic semiconductors dictates charge transport properties.

Purpose of the Study:

• To investigate the effect of peri-position substitution on the crystal structure and molecular packing of oligorylene derivatives.
• To understand how different molecular orientations influence intermolecular interactions and charge transport.

Main Methods:

• Crystal structure elucidation of substituted oligorylenes.
• Hirschfeld surface analysis to study intermolecular interactions.
• Fabrication of organic field-effect transistors (OFETs) to measure charge carrier mobility.
• Field-Induced Time-Resolved Microwave Conductivity (FI-TRMC) measurements.

Main Results:

• Unsymmetrical oligorylene derivatives form sandwich herringbone (SHB) motifs, while symmetrical ones form typical herringbone (HB) motifs.
• Peri-substitution often leads to "end-to-face" orientation, promoting C-H-π interactions but not enhancing charge transport.
• Tetramethyl perylene (TMP) exhibits an HB structure with "edge-to-face" orientation, facilitating beneficial C-H-π and π-π interactions.
• TMP achieved a mobility of 0.05 cm²/Vs in OFETs and 0.2 cm²/Vs via FI-TRMC.

Conclusions:

• Crystal engineering via peri-substitution can control molecular packing in oligorylenes.
• "End-to-face" orientation, while stabilizing, does not improve charge transport.
• "Edge-to-face" orientation in TMP, coupled with specific interactions, is key to enhanced charge carrier mobility in OFETs.