Electron-transporting organic semiconductors (n-channel) for fieldeffect 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 (FETs) 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-perfluorophenacyl)thiophen-2-yl)-9,10phenanthrenequinone (5), 2,7-bis[(5phenacyl)thiophen-2-yl]-9,10-phenanthrenequinone (6), and 2,7-bis(thiophen-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, μe (up to ≈0.3 Cm 2V-1S-1) values reported to date for a solutioncast organic semiconductor; one of the first n-channel polymers, 3, exhibits μe ≈ 10-6 Cm2V -1S-1 in spin-cast films (μc = 0.02 cm 2 V-1S-1 for drop-cast 1:3 blend films); and rare air-stable n-channel material 5 exhibits n-channel FET operation with μe = 0.015 cm2V-1s-1, while maintaining a large Ion:off= 106 for a period greater than one year in air. The crystal structures of 1 and 2 reveal close herringbone interplanar π-stacking distances (3.50 and 3.43 Å, respectively), whereas the structure of the model quinone compound, 7, exhibits 3.48 Å cofacial π-stacking in a slipped, donor-acceptor motif.
ASJC Scopus subject areas
- Organic Chemistry