Organic field-effect transistors based on Langmuir–Blodgett films of substituted phthalocyanines

Three substituted phthalocyanines (Pcs), two asymmetrical and one symmetrical, named amino-tri-tert-butyl-phthalocyanine (AmBuPc), 1,8-naphthalimide-tri-tert-butyl-phthalocyanine (NaBuPc), and tetra-iso-propoxy-phthalocyaninato copper(II) (i-Pro-CuPc), were used as semiconductor layers in organic field-effect transistors (OFETs) based on their Langmuir–Blodgett (LB) films. These substituted Pcs possess good solubility in common organic solvents. From the long-wavelength absorption edge of their UV–VIS absorption spectra and their electrochemical data, the highest occupied molecular orbital and the lowest unoccupied molecular orbital were determined and the energy band diagram of their OFETs was deduced. The narrower energy gaps of them indicated stronger electron donor–acceptor ability than other symmetrical Pcs because of the substituents at the peripheral ring. The results of their OFETs demonstrated that the LB films of these substituted Pcs can be used as semiconducting layers of OFETs functioned as p-channel accumulation devices. From the electrical characteristics of their OFETs, the channel carrier mobilities of AmBuPc, NaBuPc and i-Pro-CuPc were calculated to be about 2.84×10−5, 4.42×10−4 and 3.25×10−4 cm2 V−1 s−1, respectively.