Fluorocarbon-Modified Organic Semiconductors:  Molecular Architecture, Electronic, and Crystal Structure Tuning of Arene- versus Fluoroarene-Thiophene Oligomer Thin-Film Properties

We present here the systematic synthesis and comparative physicochemical characterization of a series of regiochemically varied and core size extension-modulated arene(perfluoroarene)−thiophene oligomers. The molecules investigated are: 5,5‘ ‘-diphenyl-2,2‘:5‘,2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (1), 5,5‘-bis{1-[4-(thien-2-yl)phenyl]}-2,2‘-dithiophene (2), 4,4‘-bis[5-(2,2‘-dithiophenyl)]-biphenyl (3), 5,5‘ ‘-diperfluorophenyl-2,2‘:5‘,2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (4), 5,5‘-bis{1-[4-(thien-2-yl)perfluorophenyl]}-2,2‘-dithiophene (5), 4,4‘-bis[5-(2,2‘-dithiophenyl)]-perfluorobiphenyl (6), 5,5‘ ‘-diperfluorophenyl-2,2‘:5‘,2‘ ‘-tertthiophene (7), 5,5‘-diperfluorophenyl-2,2‘-dihiophene (8), and 5,5-diperfluorophenylthiophene (9). Trends in optical absorption and emission parameters, molecular structures as defined by single-crystal X-ray diffraction, as well as electrochemical redox processes are described. The morphologies and microstructures of the vapor-deposited films grown over a range of growth temperatures have also been characterized. Field-effect transistor (FET) measurements demonstrate that all of these materials are FET-active and, depending on the molecular architecture, exhibit comparably good p- or n-type mobility when optimum film microstructural order is achieved. A very large n-channel mobility of ∼0.5 cm2/Vs with I on/I off ratios > 108 is achieved for films of 4.