The first solution-processable n-type phthalocyaninato copper semiconductor: tuning the semiconducting nature via peripheral electron-withdrawing octyloxycarbonyl substituents

A series of unsymmetrical phthalocyaninato copper complexes simultaneously incorporating electron-withdrawing and electron-donating substituents at the phthalocyanine periphery Cu{Pc(15C5) [(COOC8H17)(6)]} (2), Cu{Pc[(adj-15C5)(2)][(COOC8H17)(4)]} (3), Cu{Pc[(opp-15C5)(2)][(COOC8H17)(4)]} (4), Cu{Pc(15C5)(3)[(COOC8H17)(2)]} (5) were prepared and isolated. For comparative studies, symmetrical analogues including 2,3,9,10,16,17,24,25-octakis(octyloxycarbonyl)phthalocyaninato copper complex Cu[Pc(COOC8H17)(8)] (1) and 2,3,9,10,16,17,24,25-tetrakis(15-crown-5) phthalocyaninato copper complex Cu[Pc(15C5)(4)] (6) were also prepared. Their electrochemistry was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). With the help of a solution-based self-assembly process, these compounds were fabricated into organic field effect transistors (OFETs) with top contact configuration on hexamethyldisilazane (HMDS)-treated SiO2/Si substrate. In line with the electrochemical investigation results, a p-type OFET with a carrier mobility (for holes) of 0.06 cm(2) V-1 s(-1) was shown for Cu[Pc(15C5)(4)] (6) with electron-donating 15-crown-5 as the sole type of peripheral substituent. In contrast, n-type devices with a carrier mobility (for electrons) of 6.7 x 10(-6)-1.6 x 10(-4) cm(2) V-1 s(-1) were achieved for 1-5 with electron-withdrawing octyloxycarbonyl substituents at the peripheral positions of phthalocyanine ring, indicating the significant effect of electron-withdrawing octyloxycarbonyl substituents on tuning the nature of phthalocyanine organic semiconductors. The present results represent the first example of solution-processed n-type phthalocyanine-based OFET devices.