Donocadh P. Lydon

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.

A simple “palladium-free” synthesis of phenyleneethynylene-based molecular materials revisited

Nucleophilic attack of acetylide anions at the two carbonyl moieties of para-quinones readily affords the corresponding diols. Subsequent reduction with stannous chloride affords a number of useful compounds, including 1,4-bis[(trimethylsilyl)ethynyl]benzene, 1,4-bis[(trimethylsilyl)ethynyl]naphthalene and 9,10-bis[(trimethylsilyl)ethynyl]anthracene. Sequential attack by different acetylide anions followed by reduction provides a useful route to differentially substituted compounds including 1-[(4-nonyloxyphenyl)ethynyl]-4-(phenylethynyl)benzene, a new luminescent liquid-crystalline material.

Optical properties of donor–acceptor phenylene-ethynylene systems containing the 6-methylpyran-2-one group as an acceptor

Donor-acceptor phenylene ethynylene systems containing the 6-methylpyran-2-one group, synthesized via classic or microwave-assisted Sonogashira cross-coupling, exhibit pronounced solvatochromism in fluorescence suggesting a highly polar excited state; 4-[4-(4-N,N-dihexylaminophenylethynyl)phenylethynyl]-6-methylpyran-2-one has a fluorescence quantum yield >0.9 in cyclohexane.

The synthesis and liquid crystalline behaviour of alkoxy‐substituted derivatives of 1,4‐bis(phenylethynyl)benzene

Despite the prevalence of organised 1,4‐bis(phenylethynyl)benzene derivatives in molecular electronics, the interest in the photophysics of these systems and the common occurrence of phenylethynyl moeties in molecules that exhibit liquid crystalline phases, the phase behaviour of simple alkoxy‐substituted 1,4‐bis(phenylethynyl)benzene derivatives has not yet been described. Two series of 1,4‐bis(phenylethynyl)benzene derivatives, i.e. 1‐[(4′‐alkoxy)phenylethynyl]‐4‐(phenylethynyl)benzenes (5a–5f) and methyl 4‐[(4″‐alkoxy)phenylethynyl‐4′‐(phenylethynyl)] benzoates (18a–18f) [alkoxy = n‐C4H9 (a), n‐C6H13 (b), n‐C9H19 (c), n‐C12H25 (d), n‐C14H29 (e), n‐C16H33 (f)] have been prepared and characterised. Both series have good chemical stability at temperatures up to 210°C, the derivatives featuring the methyl ester head‐group (18a–18f) offering rather higher melting points and generally stabilising a more diverse range of mesophases at higher temperatures than those found for the simpler compounds (5a–5f). Smectic phases are stabilised by the longer alkoxy substituents, whereas for short and intermediate chain lengths of the simpler system (5a–5c) nematic phases dominate. Diffraction analysis was used to identify the SmBhex phase in (5d–5f) that is stable within a temperature range of approximately 120–140°C. The relationships between the organisation of molecules within these moderate temperature liquid crystalline phases and other self‐organised states (e.g. Langmuir‐Blodgett films) remain to be explored.