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For in vivo imaging of molecular processes via positron emission tomography (PET) radiotracers of high specific activity are demanded. In case of the most commonly used positron emitter fluorine-18, this is only achievable with no-carrier-added [$^{18}$F]fluoride, which implies nucleophilic methods of $^{18}$F-substitution. Whereas electron deficient aromatic groups can be labelled in one step using nocarrier- added [$^{18}$F]fluoride, electron rich $^{18}$F-labelled aromatic molecules are only available by multistep radiosyntheses or carrier-added electrophilic reactions. Here, diaryliodonium salts represent an alternative, since they have been proven as potent precursor for a direct nucleophilic $^{18}$F-introduction into aromatic molecules. Furthermore, as known from non-radioactive studies, the highly electron rich 2-thienyliodonium leaving group leads to a high regioselectivity in nucleophilic substitution reactions. Consequently, a direct nucleophilic no-carrier-added $^{18}$F-labelling of electron rich arenes via aryl-(2-thienyl)iodonium precursors was developed in this work. The applicability of direct nucleophilic $^{18}$F-labelling was examined in a systematic study on eighteen aryl(2-thienyl)iodonium salts. As electron rich precursors the ortho-, meta- and para- ethoxyphenyl(2-thienyl)iodonium bromides, iodides, tosylates and triflates were synthesised. In addition, para-substituted (R = BnO, CH$_{3}$, H, Cl, Br, I) aryl(2-thienyl)iodonium bromides were prepared as precursors with a systematically varying electron density. As first approach, the general reaction conditions of the nucleophilic $^{18}$F-substitution procedure were optimised. The best conditions for direct nucleophilic no-carrier-added $^{18}$F-labelling via aryl(2-thienyl) iodonium salts were found with dimethylformamide as solvent, a reaction temperature of 130 $\pm$ 3°C and 25 mmol/l as concentration of the precursor. For the effect of bromide, iodide, tosylate and triflate as counter anion on the radiochemical yield (RCY) the ...