Phenacyl-Thiophene and Quinone Semiconductors Designed for Solution Processability and Air-Stability in High Mobility n-Channel Field-Effect Transistors

Electron-transporting organic semiconductors (n-channel) for field-effect transistors (FETs) that are processable in common organic solvents or exhibit air-stable operation are rare. This investigation addresses both these challenges through rational molecular design and computational predictions of n-channel FET air-stability. A series of seven phenacyl-thiophene-based materials are reported incorporating systematic variations in molecular Structure and reduction potential. These compounds are as follows: 5,5"'-bis(perfluorophenylcarbonyl)-2,2':5',-2 '':5 '',2"'-quaterthiophene (1),5,5"'-bis(phenacyl)-2.2':5',2 '':5 '',2'''-quaterthiophene (2), poly[5,5"'-(perfluorophenac-2-yl)-4',4 ''-dioctyl-2,2':5',2 '':5 '',2"'-quaterthiophene) (3), 5,5'''-bis(perfluorophenacyl-4,4"'-dioctyl-2,2':5',2 '':5 '',2"'-quaterthiophene (4) 2.7-bis((5-per-fluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (5), 2,7-bis[(5-phenacyl)thiophen-2-yl]-9,10-phenan-threnequinone (6), and 2,7-bis(thio-phen-2-yl)-9,10-phenanthrenequinone, (7). Optical and electrochemical data reveal that phenacyl functionalization significantly depresses the LUMO energies, and introduction of the quinone fragment results in even greater LUMO stabilization. FET measurements reveal that the films of materials 1, 3, 5, and 6 exhibit n-channel activity. Notably, oligomer 1 exhibits one of the highest mu(e) (up to approximate to 0.3cm(2)V(-1)s(-1)) values reported to date for a solution-cast organic semiconductor One Of the first n-channel polymers, 3. exhibits mu(e) approximate to 10(-6) cm(2)V(-1)s(-1) in spin-cast films (mu(e) = 0.02cm(2)V(-1)s(-1) for drop-cast 1:3 blend films): and rare air-stable n-channel material 5 exhibits n-channel FET operation with 0.015 cm(2)V(-1)s(-1), while maintaining it large I-on:off = 10(6) for a period greater than one year in air. The crystal structures of 1 and 2 reveal close herringbone interplanar pi-stacking distances (3.50 and 3.43 angstrom, respectively), whereas the structure of the model quinone compound, 7, exhibits 3.48 angstrom cofacial pi-stacking in it slipped, donor-acceptor motif.