Synthesis, characterization and semiconducting properties of oligo(2,6-naphthalene)s

Abstract

Oligo(2,6-naphthalene)s (nNs) with the number of repeating unit (n) of 3–5 and dioctyl substituted trimer (DO-3N) and tetramer (DO-4N) were synthesized and characterized. Except of DO-4N that decomposed at 331°C, all other oligomers display good thermal stability with 5% weight loss temperatures beyond 350°C. For 4N and DO-4N, only one phase transition corresponding to melting can be found. However, DO-3N and 5N exhibit multiple phase transitions. The film absorption maximum of the oligomers at the long wavelength exhibits a red-shift with increasing the number of repeating unit. Meanwhile, the highest occupied molecular orbital (HOMO) levels increase from −5.96eV of 3N to −5.91eV of 4N and then −5.85eV of 5N. The introduction of octyl group has negligible effect on the photophysical properties. Highly ordered films of 4N, 5N, DO-3N and DO-4N in which the molecules orient with their long axis standing on the substrates can be prepared by vacuum deposition. Organic thin-film transistors (OTFTs) with top-contact and bottom-gate geometry have been fabricated based on these films. The introduction of octyl groups results in the films with higher order and therefore higher field-effect mobilities (μ) of OTFT devices. Among these oligomers, DO-3N exhibits the highest mobility of 0.50cm2/Vs when the film deposited on the octyltrichlorosilane (OTS) modified substrate.