Donocadh P. Lydon

Durham University, Durham, ENG, United Kingdom

Are you Donocadh P. Lydon?

Claim your profile

Publications (18)57.32 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper describes the preparation of Langmuir−Blodgett (LB) films comprised of an oligomeric phenylene−ethynylene (OPE) derivative, 4-[4-(phenylethynyl)-phenylethynyl] benzoic acid (BPEBA). Analysis of the surface pressure and surface potential vs area per molecule isotherms reveal that good quality monolayer films can be formed at surface pressures of 15 mN/m. The monolayers were transferred onto solid substrates with a Z-type deposition and a transfer ratio of 1. Raman and surface-enhanced Raman spectroscopy (SERS) studies reveal that the films are physisorbed onto silver metal substrates. The morphology of the deposited films was analyzed by means of atomic force microscopy (AFM), revealing the formation of homogeneous layers free of three-dimensional defects. The optical and emissive properties of the LB films were determined, with significant blue-shifted absorption spectra indicating the formation of two-dimensional H aggregates in the films. In addition, a significant Stokes shift in the excitation and emission spectra of the films is indicative of a distribution of molecular conformations around the long molecular axis in the solidlike monolayer environment. Scanning tunneling microscopy (STM) studies of single layer BPEBA LB films were performed. The tip−sample distance has been calibrated carefully to obtain I−V curves above the LB film. I−V curves are unexpectedly symmetrical in spite of the asymmetric contacts of the molecule with the tip and the substrate. Single molecule conductance for BPEBA has also been determined and the similarity of these results to I−V data for BPEBA incorporated in LB films indicates that lateral (intermolecular) conductance is negligible for electrical measurements using the STM configuration.
    Chemistry of Materials - CHEM MATER. 02/2010; 22(6).
  • [Show abstract] [Hide abstract]
    ABSTRACT: The miscibility of a conjugated “molecular wire” candidate and an “insulating” fatty acid within a thin film has been comprehensively analyzed. Specifically, Langmuir and Langmuir–Blodgett films containing mixtures of 4-[4′-(4″-hexyloxyphenylethynyl)-phenylethynyl]-aniline (HBPEB amine) and behenic acid (BA) have been prepared, characterized, and their miscibility compared with that of mixtures of 4-[4′-(4″-hexyloxyphenylethynyl)-phenylethynyl]-benzoic acid (HBPEB acid) and BA studied previously. Surface pressure vs. area per molecule isotherms were recorded, with negligible excess areas per molecule at high surface pressures suggesting either complete miscibility or immiscibility of the two materials. The Langmuir films were transferred onto solid supports to fabricate Langmuir–Blodgett (LB) films which were characterized by SPM probe techniques. Scanning Polarization Force Microscopy (SPFM) undoubtedly shows good miscibility of the two materials in the films with no evidence of phase separation, in contrast with the HBPEB acid–BA system where phase separation occurs for HBPEB acid mole fractions over the 0.1–0.8 range.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2009; 346:170-176. · 2.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Liquid Crystals 02/2008; 35(2):119-132. · 1.96 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Langmuir and Langmuir–Blodgett (LB) films of two “wire-like” oligo(phenylene–ethynylene) methyl ester derivatives, namely methyl-4-[(4″-(nonyloxyphenylethynyl)-4′-(phenylethynyl)]-benzoate and methyl-4-[(4″-hexadecyloxyphenylethynyl)-4′-(phenylethynyl]-benzoate (abbreviated as C9BPEB and C16BPEB), have been prepared and characterized. Surface pressure isotherms for both materials have been obtained, with C9BPEB showing more expanded monolayers. An analysis of the reflection spectra of monolayer films at the air–water interface suggests the formation of H-aggregates, and supports an organizational model in which tilt angles of C16BPEB and C9BPEB molecules with respect to the water surface are approximately 70° and 60°, respectively. The sequential transfer of monolayers of these BPEB ester derivatives onto solid substrates results in a Z-type deposition in the case of C9BPEB and Y-type for C16BPEB. The current–voltage (I–V) characteristics of LB monolayers are relatively symmetrical for both films, with the asymmetric contacts more evident in the I–V C16BPEB characteristics.
    Surface Science 01/2008; 602(24):3683-3687. · 1.87 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Mixed films containing a conjugated “molecular wire” candidate and an “insulating” fatty acid have been prepared by the Langmuir–Blodgett technique. Specifically, this paper reports the fabrication of mixed films as well as miscibility studies of 4-[4-(4-hexyloxyphenylethynyl)phenylethynyl]benzoic acid (HBPEB) and docosanoic (or behenic) acid (BA). Surface pressure vs. area per molecule isotherms were recorded, with excess area and excess Gibbs energy of mixing calculated. Surface potential-area per molecule isotherms were also recorded for mixtures over the whole range of mole fractions, with negative deviations from the additivity rule revealing orientational changes induced in the HBPEB molecules. The Langmuir films were transferred onto solid supports and characterized by SPM techniques, with atomic force microscopy (AFM) revealing that well-ordered, defect-free films are obtained. The use of scanning polarization force microscopy (SPFM), which provides non-contact imaging based on differences in surface charge distribution, i.e., surface potential, provides complimentary information regarding distribution of the components within the mixed films. From the comprehensive miscibility study performed, which includes thermodynamic and imaging methods, it can be concluded that the wire-like molecule and the fatty acid are miscible over the 0–0.1 and 0.8–1 ranges of HBPEB mole fraction while phase separation occurs for HBPEB mole fractions over the 0.1–0.8 range.
    Soft Matter 01/2008; 4:1508-1514. · 4.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper reports the assembly of well-defined molecular films from 4-[4-(4-hexyloxyphenylethynyl)-phenylethynyl]-aniline (HBPEB amine), an oligomeric phenylene ethynylene (OPE) derivative, by means of the Langmuir–Blodgett technique. Initially, Langmuir films of HBPEB amine were prepared at the air–water interface and characterized with surface pressure vs area per molecule isotherms. Brewster Angle Microscopy was used to map the different phases of the monolayer at the air–water interface. UV–vis reflection spectroscopy showed a blue shift of 20 nm of the reflection spectrum of the Langmuir film with respect to the spectrum of a chloroform solution of HBPEB amine, which indicates that two-dimensional H-aggregates are formed at the air–water interface. The monolayers were transferred onto solid substrates with a Y-type deposition and a transfer ratio of 1. The excellent transfer characteristics permitted the construction of films comprising up to 150 layers, with a uniform architecture. The LB films fabricated from HBPEB amine show a blue shift of ca. 30 nm with respect to the chloroform solution of HBPEB amine, likely arising from a change in the orientation of the molecular transition dipole with respect to the surface normal in the solid-supported films in comparison with the Langmuir films at the air–water interface. The current–voltage (I−V) characteristics of LB monolayers are unexpectedly symmetrical, the asymmetric contacts not being apparent from the observed I−V characteristics.
    Chemistry of Materials - CHEM MATER. 12/2007; 20(1).
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper reports the fabrication and characterization of Langmuir and Langmuir-Blodgett (LB) films incorporating an oligo(phenylene-ethynylene) (OPE) derivative, namely, 4-[4-(4-hexyloxyphenylethynyl)-phenylethynyl]-benzoic acid (HBPEB). Conditions appropriate for deposition of monolayers of HBPEB at the air-water interface have been established and the resulting Langmuir films characterized by a combination of surface pressure and surface potential versus area per molecule isotherms, Brewster angle microscopy, and ultraviolet reflection spectroscopy. The Langmuir films are readily transferred onto solid substrates, and one-layer LB films transferred at several surface pressures onto mica substrates have been analyzed by means of atomic force microscopy, from which it can be concluded that 14 mN/m is an optimum surface pressure of transference, giving well-ordered homogeneous films without three-dimensional defects and a low surface roughness. The optical and emissive properties of the LB films have been determined with significant blue-shifted absorption spectra indicating formation of two-dimensional H aggregates and a Stokes shift illustrating the effects of the solid-like environment on the molecular chromophore.
    The Journal of Physical Chemistry B 07/2007; 111(25):7201-9. · 3.61 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A molecular dyad has been synthesized in which the main chromophore is a 1,4-diethynylated benzene residue terminated with pyrene moieties, this latter unit acting as a single chromophore. A spiropyran group has been condensed to the central phenylene ring so as to position a weak electron donor close to the pyrene unit. Illumination of the pyrene-based chromophore leads to formation of a fluorescent exciplex in polar solvents but pyrene-like fluorescence is observed in nonpolar solvents. The exciplex has a lifetime of a few nanoseconds and undergoes intersystem crossing to the pyrene-like triplet state with low efficiency. Attaching a 4-nitrobenzene group to the open end of the spiropyran unit creates a new route for decay of the exciplex whereby the triplet state of the spiropyran is formed. Nonradiative decay of this latter species results in ring opening to form the corresponding merocyanine species. Rate constants for the various steps have been obtained from time-resolved fluorescence spectroscopy carried out over a modest temperature range. Under visible light illumination, the merocyanine form reverts to the original spiropyran geometry so that the cycle is closed. Energy transfer from the pyrene chromophore to the merocyanine unit leads to an increased rate of ring closure and serves to push the steady-state composition in favor of the spiropyran form.
    The Journal of Organic Chemistry 03/2007; 72(3):888-97. · 4.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Structural solid-phase and solution-phase properties of two pyrene-spiropyran molecular dyads are described. Each dyad comprises a 1,1′-[indole-4,6-diylbis(ethyne-2,1-diyl)]bis(pyrene) backbone, with the bis(pyrene) and spiropyran units adopting a T-shaped arrangement. The strength of the Cspiro–O bond is altered by replacement of H by NO2 in the terminal aryl group of the spiropyran unit. X-ray crystal structure determinations carried out for two of the dyads (H and NO2) reveal the pyrene groups to be aligned anti to each other. The crystal packing diagrams are different; both contain pyrene π-stacked centro-symmetric dimers, but in one structure this is the total extent of the π stacking whereas the other structure has pyrene dimers interleaved to generate infinite parallel stacks. Detailed 1H NOE experiments are consistent with a solution-phase structure that differs markedly from the solid-state structure, and in which the pyrene groups are syn to one another but orientated away from the spiropyran group. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
    Annalen der Chemie und Pharmacie 02/2007; 2007(10):1653 - 1658. · 3.10 Impact Factor
  • Angewandte Chemie International Edition 02/2007; 46(27):5175-7. · 11.34 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Langmuir and Langmuir−Blodgett films of a nitrile-terminated tolan, namely 4-[4‘-decyloxyphenylethynyl]benzonitrile, have been fabricated and characterized at various surface pressures, with surface pressure and surface potential isotherms together with Brewster angle microscopy being used to map the different phases of the tolan monolayer at the air−water interface. The Langmuir films have been characterized by UV−vis spectroscopy, with quantitative analysis of the reflection spectra supporting an organizational model in which compression of the film leads to change in the tilt angle of the tolan molecules from an initial value of ca. 35° to one of ca. 60° before collapse of the monolayer. Moreover, a blue shift in the reflection spectrum of the Langmuir film of 30 nm with respect to the spectrum of a chloroform solution of the nitrile tolan indicates that two-dimensional H-aggregates are formed at the air−water interface. These structures represent a minimum free-energy conformation for the system, as they are observed even before the compression process starts. The monolayers are transferred undisturbed onto solid substrates, with atomic force microscopy revealing well-ordered films without three-dimensional defects.
    Chemistry of Materials - CHEM MATER. 01/2007; 19(4).
  • Synfacts 01/2007; 2007(10):1042-1042.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The torsional motions of jet-cooled 1,4-bis(phenylethynyl)benzene (BPEB), a prototype molecular wire, were studied using cavity ring-down spectroscopy in the first UV absorption band (316-321 nm). The torsional spectrum of 1,4-bis(phenylethynyl)-2,3,5,6-tetradeuteriobenzene was also recorded in the gas phase. Both spectra were successfully simulated using simple cosine potentials to describe the torsional motions. The ground-state barrier to rotation was estimated to be 220-235 cm(-1), which is similar to that of diphenylacetylene (tolane). Complementary DFT calculations were found to overestimate the torsional barrier.
    The Journal of Physical Chemistry A 03/2006; 110(6):2114-21. · 2.77 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The gold complexes Au(C≡CC6H4C≡CC6H4Me)(PPh3) (3) and {Au(PPh3)}2(μ-C≡CC6H4C≡CC6H4C≡CC6H4C≡C) (6), prepared from the reaction of AuCl(PPh3) with the corresponding terminal or trimethylsilyl protected alkynes, react readily with Ru3(CO)10(μ-dppm) to afford phenylene ethynylene derivatives featuring the Ru3(μ-AuPPh3)(μ-C2R)(CO)7 cluster “end-caps”. The hydrido cluster Ru3(μ-H)(μ-C2C6H4C≡CC6H4Me)(CO)7 (4a) has also been obtained. There are significant differences in the absorption spectra of the organic precursors, the gold complexes and the clusters indicate a mixing of electronic states between the cluster and phenylene ethynylene moieties, while the presence of the Ru3 and in particular Ru3(μ-AuPPh3) cluster end-caps leads to a quenching of the phenylene ethynylene centred emission. The crystallographically determined structures of 3, 4a and Ru3(μ-AuPPh3) (μ-C2C6H4C≡CC6H4Me)(CO)7 (4b) are reported.
    Journal of Cluster Science 02/2006; 17(1):65-85. · 1.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Chemical Communications 07/2005; · 6.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    New Journal of Chemistry 01/2005; 29(7). · 2.97 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Journal of Materials Chemistry 01/2004; 14(15). · 5.97 Impact Factor
  • R. Giménez, D.P. Lydon, J.L. Serrano
    [Show abstract] [Hide abstract]
    ABSTRACT: The discipline of metallomesogens has been actively investigated in the past decade. Recent research has focused mainly on building up basic knowledge by exploring new shapes. The interest comprises both the molecular and supramolecular level. Important results are the generation of helical superstructures or the discovery of a McMillan phase. Different approaches include lanthanide complexes, specially designed ligands and polymeric compounds. Applications have been proposed on the basis of the optical, mechanical and electronic properties of these materials. Up to now, the only true application is in solid state chemistry where some lyotropic metallomesogens are used as templates for mesoporous materials.
    Current Opinion in Solid State and Materials Science 01/2002; · 5.44 Impact Factor

Publication Stats

74 Citations
57.32 Total Impact Points

Institutions

  • 2004–2009
    • Durham University
      • Department of Chemistry
      Durham, ENG, United Kingdom
  • 2007
    • University of Newcastle
      Newcastle, New South Wales, Australia
    • Newcastle University
      • School of Chemistry
      Newcastle upon Tyne, ENG, United Kingdom