Pechmann Dye-Based Molecules Containing Fluorobenzene Moieties for Ambipolar Organic Semiconductors

Two hybrid A(2)-D-A(1)-D-A(2) (A = acceptor, D = donor) molecules, that is, (E)-5,5'-bis[5-(4-fluorophenyl)thiophen-2-yl]-1,1'-dioctyl-[3,3'-bipyrrolylidene]-2,2'(1H,1'H)-dione (FBBPD) and (E)-1,1'-dioctyl-5,5'-bis[5-(3,4,5-trifluorophenyl)thiophen-2-yl]-[3,3'-bipyrrolylidene]-2,2'(1H,1'H)-dione (TFBBPD), were synthesized and characterized. Each of these compounds contain the Pechmann dye derivative (E)-[3,3'-bipyrrolylidene]-2,2'(1H,1'H)-dione (BPD) as the electron-accepting core, which is flanked by an electron-donor moiety (i.e., thiophene) and other electron acceptors (i.e., 4-fluorobenzene or 3,4,5-trifluorobenzene). Organic field-effect transistor (OFET) results of FBBPD show ambipolar properties with electron (mu(max)(e)) and hole mobilities (mu(max)(h)) up to 0.20 and 0.023 cm(2)V(-1) s(-1), respectively. In comparison, the electron and hole mobilities of the OFET based on TFBBPD, which contains a more electron-accepting moiety, are higher (mu(max)(e) = 0.58 cm(2)V(-1) s(-1) and mu(max)(h) = 0.054 cm(2)V(-1) s(-1)). X-ray diffraction and atomic force microscopy studies were carried out to investigate the variations in the mobilities. Overall, these studies show the potential of BPD in hybrid D-A molecules to act as the electron-acceptor moiety in organic semiconducting studies.