Synthesis, optical properties, crystal structures and phase behaviour of selectively fluorinated 1,4-bis(4′-pyridylethynyl)benzenes, 4-(phenylethynyl)pyridines and 9,10-bis(4′-pyridylethynyl)-anthracene, and a Zn(NO₃)₂ coordination polymer

A series of selectively fluorinated and non-fluorinated rigid rods based on the 4-pyridylethynyl group, namely 1,4-bis(4'-pyridylethynyl)benzene (1a), 1,4-bis(4'-pyridylethynyl)tetrafluorobenzene (1b), 1,4-bis(2',3',5',6'-tetrafluoropyridylethynyl)benzene (1c), 1,4-bis(2',3',5',6'-tetrafluoropyridylethynyl) tetrafluorobenzene (1d), 9,10-bis(4'-pyridylethynyl)anthracene (2), 4-(pentafluorophenylethynyl)pyridine (3a) and 4-(phenylethynyl)- tetrafluoropyridine (3b) were prepared in good yields using Pd/Cu-catalysed Sonogashira cross-coupling reactions and/or lithium chemistry involving nucleophilic aromatic substitution. UV-Vis absorption and fluorescence spectra for 1a-d and 2 are reported. The X-ray crystal structures of 1b, 1c, 2, 3a and 3b show a variety of packing motifs, none of which involve arene-perfluoroarene stacking. The phase behaviour of 1a-1c has been studied by differential thermal analysis and transmitted polarised light microscopy. Compound 1b exhibits an ordered phase between 227.6 and 272.5 °C which is either hexatic B or crystal B. A 1:1 complex (4) between 1b and Zn(NO₃)₂ has been prepared; its crystal structure consists of zig-zag polymer chains held together by hydrogen bonds.