Non-linear, cata-Condensed, Polycyclic Aromatic Hydrocarbon Materials: A Generic Approach and Physical Properties

A generic approach to the regiospecific synthesis of halogenated polycyclic aromatics is made possible by the one- or two-directional benzannulation reactions of readily available (ortho-allylaryl)trichloroacetates (the “BHQ” reaction). Palladium-catalysed cross-coupling reactions of the so-formed haloaromatics enable the synthesis of functionalised polycyclic aromatic hydrocarbons (PAHs) with surgical precision. Overall, this new methodology enables the facile mining of chemical space in search of new electronic functional materials.

1 CARE: All polyclic aromatic hydrocarbons should be viewed as being toxic. The synthesis and manipulation of these compounds should be conducted in a well ventilated fume cupboard. Workers should always use appropriate safeguards so that these compounds do not come into contact with the skin. Avoid ingestion and inhalation. These compounds should be viewed as being toxic and having potential carcinogenic and mutagenic activities.   2-(Naphthalene-1ʹ′-yloxy)-1-tetralone 15. [3] 2-Bromo-1-tetralone 14 (15.41 g, 68.5 mmol) was added to a stirring suspension of 1-naphthol (9.86 g, 68.5 mmol) and

-Field Effect Transistors
Field effect transistors were created for compound 28. The thin films were characterised by X-ray diffraction and atomic force microscopy and transistors were created and analysed using conventional thin film transistor techniques.

-Thin Film Deposition
All materials and devices were prepared on heavily doped silicon (n++) substrates with 300 nm of thermally grown silicon dioxide. The substrates were cleaned by washing and sonication in acetone, propan-2-ol and methanol followed by UV-Ozone treatment. The surfaces of the substrates were then treated with octadecyltrichlorosilane (OTS) monolayers to reduce the surface energy, passivate traps and improve thin film growth. OTS treatment was done by spin coating of an OTS solution from chloroform as reported elsewhere. 1 OTS treated substrates were all washed with organic solvents and dried with nitrogen before being transferred to the vacuum chamber for thin film deposition.
Evaporation of the organic semiconductor was performed in a modified Edwards Auto306 vacuum evaporator with a base pressure of 7 x 10 -6 mbar. Nominally 30 nm was deposited onto substrates held at 40 °C at a rate of 0.5 As -1 To create thin film transistors the as prepared substrates were transferred to a separate Edwards Auto500 vacuum evaporator (base pressure 1 x 10 -7 mbar) for gold evaporation. Nominally 50 nm of gold was deposited on top of the organic layers at a rate of 1 As -1 through a shadow mask.

-Thin Film Characterisation
The thin films were characterised using a Park XE100 atomic force microscope in tapping mode and a Bruker D8 discover X-ray diffractometer for out-of-plane Xray diffraction. The compound creates small crystals approximately 0.25 µm 2 large with a thin film roughness of 2.1 nm. The out-of-plane x-ray diffraction allows us to calculate the relative tilt of the molecule to the substrate surface by comparing the 001 reflection with the calculated molecular length from single crystal x-ray diffraction. Using Bragg's law the d-spacing is calculated to be 1.67 nm, using the calculated molecular length of 2.07 nm suggests that the molecule is tilted toward the surface normal at an angle of 36 °.

-Transistor Characterisation
A series of 10 transistors were created via the evaporation of gold electrodes in a top contact bottom gate configuration. The devices were then tested in the saturation regime using the standard equation.
Where, I D is the source-drain current, C i is the capacitance, W the channel width, L the channel length, µ sat is the saturation mobility, V G is the swept gate voltage and V T is the threshold voltage. The transistors had a channel width of 2000 µm and a channel length of 60 µm, the 300 nm silicon dioxide with OTS monolayer was calculated to have a capacitance of approximately 11.4 nFcm -2 . The devices showed good transistor behaviour with an average saturation mobility of 0.03 ± 0.01 cm 2 V -1 s -1 , a threshold of -9 ± 1 V, on/off ratio of 4 x 10 6 and a subthreshold swing of 600 mVdec -1 .