Elsevier

Journal of Molecular Structure

Volume 1127, 5 January 2017, Pages 413-418
Journal of Molecular Structure

Synthesis, characterization and air stable semiconductor properties of thiophene-condensed pyrene derivatives

https://doi.org/10.1016/j.molstruc.2016.07.104Get rights and content

Highlights

  • Two air stable thiophene-condensed pyrene derivatives were prepared.

  • Absolute molecular structures were determined by using X-ray analysis.

  • Air stable and p-type semiconducting properties were evaluated.

Abstract

New and simple polyaromatic compounds containing two thiophene rings were prepared via photo-cyclization and their structural and photophysical properties were evaluated via 1H NMR spectroscopy and X-ray crystallographic analysis. On the basis of X-ray analysis, it was determined that the molecular structure of the compound was highly strained and that they contain two hetero [4] helicene moieties. The compounds were investigated as active layer in p-type organic field-effect transistors (p-OFET) in top contact type devices. Notably, the compound containing two thiophene components exhibited very stable p-type semiconducting behavior in moist air.

Introduction

In recent years, polycyclic aromatic hydrocarbons (PAHs) have been attracting great interest owing to their significant photochemical and electrical properties, and have found various applications in organic opto-electronic materials [1], [2], [3], [4], [5]. Planar PAHs such as pentacene, hexacene, pyrene, perylene are readily stacked in solution and crystalline state owing to π–π interactions, and are therefore widely used as components of new materials such as organic semiconductors [6], [7]. In recent year, for example, Nuckolls and co-workers developed a novel approach to the synthesis of a phase-forming, distorted hexa-cata-hexa-benzocoronene derivative, whereby the decisive step was accomplished via photo-cyclization. The material formed columnar liquid-crystalline phases with high charge-carrier mobilities as determined in organic field-effect transistors (OFETs) [8].

On the other hand, the structural and physical properties of “strained” PAHs such as helicene, fullerene and bucky bowl, have also been intensively studied in order to investigate the potential for their use as organic semiconductors with interesting properties compared to those of the various planar compounds [9]. Yamato et al reported the preparation, structural and opto-electrical properties of t-butylated pyrenes and their derivatives [10], [11]. Lakshman et al, meanwhile, reported the preparation and structural properties of the highly strained 1,4-dimethylbenzo[c]phenanthlene [12]. There is a fjord region in the molecule, and the protons located in the fjord region showed strange 1H NMR chemical shifts due to the strained structure.

For flexible electronics, OFETs are indispensable for the fabrication of electronic circuits on plastic substrates [8], [9], [10]. Typically, organic semiconducting materials that have large mobility also have a planar structure. However, their solubility is usually not good, and thus these compounds are not suitable for the synthesis of OFETs via wet processes such as spin-coating and drop-casing. Here, we report the synthesis, characterization and structural properties of highly twisted di-t-butylated polyaromatic compounds containing two thiophene rings. The compounds were prepared via oxidative photo-cyclization, and their structural and photophysical properties were evaluated via 1H NMR, UV-Vis and X-ray crystallographic analysis. The p-type semiconducting properties of the new compounds were evaluated in top contact-type OFET devices, and their air and moisture stabilities were examined over 40 days.

Section snippets

Results and discussion

Reactions of pyrene-based bis Wittig reagent 1 (2,7-di-t-butyllpyrene-4,9-bisethyltrophenylphosphonium dichloride) with thiophene carbaldehyde 2 (2-thiophenecarboxaldehyde 2a, 5-methyl-2-thiophenecarboxaldehyde 2b) successfully proceeded to give the diarylethenyl compounds 3 in excellent yields (>90%, Scheme 1). Subsequently, photo-cyclization of the diarylethenyl compounds 3 under irradiation from a high pressure Hg lamp in the presence of iodine as the oxidative reagent gave the desired

Conclusions

In conclusion, new di-t-butylated polycyclic aromatic hydrocarbons containing two hetero [4]helicene moieties were readily prepared via oxidative photo-cyclization. The compounds have highly twisted π-conjugated systems and also contain two deep fjord regions. They readily form dimers in solution and regulate one-dimensional array columnar packing via intermolecular π–π interactions in the crystalline state. More importantly, it was found that the highly strained aromatic π systems and bulky t

Experimental

All melting points were recorded on As-one hot-stage microscope apparatus and are uncorrected. 1H NMR spectra were recorded on a Bruker AVANCE400S spectrometer in CDCl3 with tetramethylsilane (Me4Si) as an internal reference. Mass spectra were obtained on a Nippon Densi JEOL-DX-300 spectrometer at 75 eV using a direct inlet system. Column chromatography was carried out on silica gel (Wako gel, C-300). The amounts of silica gel used were 10–50 g. Thiophenecarboaldehydes (2a and 2b) are

Additional information

Crystallographic data reported in this manuscript have been deposited with Cambridge Crystallographic Data Centre as supplementary publication no. CCDC948635 for 4a and CCDC1459056 for 4b, respectively. Copies of the data can be obtained free of charge via http://www.ccdc.cam. ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, U.K.; fax: +44 1223 336033; or [email protected]).

Acknowledgments

We are grateful to the Center for Instrumental Analysis in Kyushu Institute of Technology (KITCIA) for the elemental, mass spectral, 1H NMR, and X-ray analyses. We also thank Dr. Kenji Yoza (Bruker AXS JAPAN) for experimental assistance during the twin treatment of the X-ray analysis. The authors also thank the Center for Microelectronic Systems at Kyushu Institute of Technology for fabrication of the Si/SiO2 substrate. This study was financially supported by the Kitakyushu Foundation of

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