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

Three substituted phthalocyanines (Pcs), two asymmetrical and one symmetric al, named amino-tri-tert-butyl-phthalocyanine (AmBuPc), 1.8-naphthalimide-t ri-tert-butyl-phthalocyanine (NaBuPc), and tetra-iso-propoxy-phthalocyanina to copper(II) (i-Pro-CuPc), were used as semiconductor layers in organic fi eld-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 ban d diagram of their OFETs was deduced. The narrower energy gaps of them indi cated stronger electron donor-acceptor ability than other symmetrical Pcs b ecause of the substituents at the peripheral ring. The results of their OFE Ts demonstrated that the LB films of these substituted Pcs can be used as s emiconducting layers of OFETs functioned as p-channel accumulation devices. From the electrical characteristics of their OFETs. the channel carrier mo bilities of AmBuPc, NaBuPc and i-Pro-CuPc were calculated to be about 2.84 x 10(-5), 4.42 x 10(-4) and 3.25 x 10(-4) cm(2) V-1 s(-1), respectively. (C ) 2001 Elsevier Science B.V. All rights reserved.