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

Abstract

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.