Unusual loss of electron mobility upon furan for thiophene substitution in a molecular semiconductor

• Synthesis of a furan based small molecule organic semiconductor.
• Comparison of furan vs thiophene substitution.
• Furan based material shows only hole transport properties.
• Thiophene based materials shows hole and electron transport properties.
• DFT calculations point towards differences in LUMO and LUMO+1 of dimers.

Furan has often been considered as a more sustainable alternative to thiophene in organic electronics. Herein we demonstrate that replacing thiophene with furan in a phthalimide based molecular semiconductor results in a complete loss of electron mobility when evaluated using organic thin film transistors (OTFTs). Although optical, electronic, thermal, and structural characterization show subtle effects substituting furan for thiophene, theoretical dimer modeling employing the respective single crystal structures of the two molecules reveals a loss of degeneracy between the lowest unoccupied molecular orbital (LUMO) and LUMO+1 molecular orbitals in the bifuran-containing molecule. These results demonstrate that minor changes to molecular structure can result in large differences in device performance.

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