Development of high thermal conductivity polymeric materials for spacecraft use Final report, 1 Jul. 1966 - 31 May 1969

High thermal conductivity polymeric materials for spacecraft applications using phenyl compound

Synthesis of Some Organic Conductive Materials

The primary goal in conducting the experimental work involved in the formulating of this thesis was to synthesize some organic conducting compounds by utilizing the highly electronegative 7,7,8,8-tetracyanoquinodimethan complexed with some completely conjugated benzologs of the quinolizinium ion. The history is divided into three parts, the first part describing the electronic properties of organic conducting polymers, the second part dealing with anion-radical derivatives and complexes of 7,7,8,8-tetracyanoquinodimethan, the third part describing some benzologs of the quinolizinium ion. 1. Electronic Properties of Organic Conducting Polymers One of the most important problems of present-day chemistry is the creation of new substances and materials possessing a series of valuable properties. Particularly great prospects have been opened in the synthesis and study of organic compounds possessing extensively delocalized electrons because of the presence in them of highly conjugated double bonds or the formation of charge transfer complexes. Although in recent years the study of semi conductive properties of organic compounds has made much progress, most of the exact mechanisms involved in the electronic conducting processes are at the present time either not known at all or else poorly understood. Generally, the semi conductive polymers can be classified as follows: (a) covalent organic polymers, (b) charge-transfer complexes, (c) metal organic polymers, (d) H-bonded polymers, and (e) mixed polymers, for example, charge transfer complexes between covalent polymers and low molecular weight donor or acceptor molecules. The main efforts of synthetic chemists working in this field have been devoted to obtaining stable polymers of low resistance. As a working hypothesis, Pohl proposed the idea of eka- and rubi- conjugation. Rubi-conjugation was defined as a type of structure in which various molecular defects and quantum mechanical effects exist which produce a limited, or broken sequence of electronic delocalization. Such conjugation was to be avoided if strong electronic conduction was desired. In eka-conjugation, molecular defects were absent or suppressed, and full interlinking of the chain atom pi orbitals occurred. Long-range electron orbital delocalization was then possible

A Time-Resolved Spectroscopic Study of Photoinitiated Electron Transfer Reactions in Solution

Photoinitiated electron transfer reactions may be considered within the context of two categories: (1) direct electron transfer, as observed in charge transfer molecular complexes. The photoexcitation couples the ground and charge transfer potential surfaces and (2) indirect electron transfer, as observed in covalently bonded donor (D) and acceptor (A) moieties. The optical preparation of an eigenstate of the donor or acceptor is followed by the evolution of the system to the charge transfer state. This thesis presents a study of pico- and subpicosecond polarization and vibrational relaxations accompanying these two classes of condensed phase electron transfer reactions. The thesis presents optical ultrafast pump-probe measurements on the electron donor-acceptor complex tetracyanoethylene-hexamethylbenzene in polar and non-polar solvents. The experimental electron transfer rates are compared with nonadiabatic and adiabatic electron-transfer theories using a previously published analysis of all the vibrational modes active of the reaction. As the experimental electron transfer rates are competitive with and in same cases faster than the polarization relaxation time of the solvent, it is necessary to simulate the Smoluchowski diffusion of the reacting system over an equilibrating reaction coordinate. Regarding the coupling of the reactant and product electronic surfaces, it is shown that the nuclear kinetic operator can give rise to the coupling responsible for the electron transfer reaction. This non-Born-Oppenheimer matrix element is estimated using information obtained from the absorption and Raman spectra. Using this coupling, good agreement is found between the experimentally observed and theoretically predicted rates. This thesis also presents an optical time resolved spectroscopic study of the indirect electron transfer reaction in the model system magnesium triphenylporphyrinquinone in a range of solvent environments. These molecules have long served as model compounds for the ultrafast dynamics in photosynthetic complexes. In view of the recently observed coherent relaxation dynamics of Mg-tetraphenylporphyrin, these multicomponent electron transfer kinetic data are analyzed, focussing on the role of low frequency coherences in electron transfer processes

Doctor of Philosophy

dissertationSeveral metal-tetracyanoethylene (TCNE) compounds, including the bis(pentamethylcyclopentadienyl)iron(III)]+[tetracyanoethylene]', [FeCp*2][TCNE], family of molecule-based magnets and two cyanide based MBMs were investigated by pressure dependent DC magnetic measurements. The 0-D electron transfer salts: [FeCp*2 ][TCNE], ferromagnetic [FeCp*2 ][TCNQ] (TCNQ = 7,7,8,8- tetracyanoquinodimethane), metamagnetic [FeCp*2][TCNQ], [FeCp*2][HCBD] (HCBD = hexacyanobutadiene), and [FeCp*2][DDQ] (DDQ = 2,3-dichloro-5,6-dicyano-p-benzoquinone) exhibited an array of magnetic behavior both at ambient and applied pressure. [FeCp*2][TCNE] and [FeCp*2][HCBD] exhibited weak ferromagnetism above 4.2 and 3.1 kbar, respectively. The ferromagnetic polymorph of [FeCp*2][TCNQ] displayed linear increase to the critical temperature, Tc, and the bifurcation temperature, Tb, reaching 5.01 and 5.46 K, respectively at 10.3 kbar. The coercive field, Hcr, displayed exponential-like increase, reaching 550 Oe at 10.3 kbar. The metamagnetic polymorph of [FeCp*2][TCNQ] displayed linear increase of the Tc at low applied pressure, reaching 2.90 at 2.9 kbar, then transitioned to a paramagnetic state at further applied pressure. [FeCp*2][HCBD] transitioned from a paramagnetic state at ambient pressure to a weak ferromagnetic state at 3.1 kbar with a Tc, Hcr, and Hc of 2.46 K, 25 Oe, and 2,200 Oe, respectively. The Tc and Hc then increased linearly with further applied pressure to 4.80 K and 10,000 Oe, while the Hcr increased exponentially to 795 Oe, at 11.4 kbar. [FeCp*2][DDQ] exhibited paramagnetic behavior at ambient and applied pressures up to 9.2 kbar. The structurally related 2-D MnII(TCNE)I(H2O) and 3-D Mnn(TCNE)3/2(I3)1/2, showed significant increases to the Tc, Tb, and Hcr with applied pressure. A high- and low-pressure regions were observed for MnII(TCNE)I(H2O). 2-D [R ^ ^ C B u ^ H M tC N ^ ^ O (M = Fe, Cr) displayed suppression of hysteretic properties at high applied pressure and irreversibility of the suppression. A Mean Field (MF) analysis of three structurally related non-cubic Prussian blue analogues (PBA) was performed to assess the intensity of their coupling modes. These values were framed by the reinvestigation of several known cubic PBAs and comparing the coupling intensities, as well as evaluating the MF theory in the context of these structures as several had been evaluated by other means

An investigation of Molecular Magnets Synthesized from Ni(cod)(_2) and the Organic Acceptors TCNQ and TCNQF(_4)

Recently a new molecular magnet, Ni(_2)TCNQ, was reported to be ferromagnetic at room temperatures, with a Curie temperature of 400K(^1) Ni(_2)TCNQ is synthesized through a wet chemical route using the starting materials, Ni(cod)(_2) (bis(1,5-cyclooctactadiene)nickel) and TCNQ (7,7,8,8-tetracyanoquinodimethane). This work focuses on the synthesis of this molecular magnet and subsequent characterisation of the magnetic properties. Several organic acceptor molecules were also examined with the intention of synthesising a new molecular magnet. The chosen organic was TCNQF’(_4), (2,3,5,6- tetrafluoro-7,7,8,8-tetracyanoquinodimethane) due to its small size and magnetic properties. The resulting magnet, Ni(_2)TCNQF(_4), was synthesized following the same procedures as for Ni(_2)TCNQ with the substitution of TCNQ for TCNQF(_4).The magnetic properties for the nickel samples are qualitatively similar and both show ferromagnetic behaviour at room temperature. More specifically the materials exhibit two magnetic phases, in high magnetic fields the materials are paramagnetic and in low magnetic fields exhibit nanoparticulate behaviour. At low temperatures in the paramagnetic phase the materials have been compared to a Brillouin function. This revealed weak ferromagnetic interactions between the spins in Ni(_2)TCNQ and weak antiferromagnetic interactions in Ni(_2)TCNQF(_4).In the nanoparticulate phase the materials are superparamagnetic above the blocking temperature, T(_h), and below exhibit single domain behaviour. The Curie temperature for Ni(_2)TCNQ was found to be much higher than previously reported(^1) at approximately (625±5) K. The Curie temperature for Ni(_2)TCNQF’_4’ was (620±5) K. This suggests that the ferromagnetic phase observed in these materials arises from the nickel nanoparticles present in the material. This conclusion is also supported by XRD and microscopy measurements

Synthesis and study of conjugated polymers containing di- or triphenylamine

Incorporation of hole transporting moieties such as diphenylamine or carbazole into conjugated polymers was achieved. Palladium catalyzed polymerization afforded a series of N-interrupted polyphenyleneethynylenes. Oxidative coupling of 4,4\u27e-diethynyl-N-hexyldiphenylamine also afforded a high molecular weight diacetylene polymer. These polymers can form flexible free standing film from solution casting. Triphenylaine-based dendrimers were synthesized through Pd-coupling using a repetitive convergent scheme. Electronic properties and photophysics of these polymers were studied. Studies of electron donor-acceptor complexes of these polymers lead to the discovery of a reaction of tetracyanoethylene (TCNE) with electron-rich acetylenes. The reaction is extremely efficient in conversion of electron rich acetylenes to highly polarized donor-acceptor chromophores containing the 1,1,4,4-tetracyanobutadiene-2-yl (TCBD) group as an acceptor. Electronic absorption spectra of these TCBD derivatives imply high molecular polarizabilities as would be expected for such chromophores

Extending the Scope of the Density Overlap Region Indicator

In this thesis, original applications of the Density Overlap Region Indicator (DORI), a density dependent bonding descriptor capable of simultaneously capturing covalent and noncovalent interactions, are discussed. The use of scalar fields, such as DORI, were generally restricted to visualizing bonding situations in static gas phase molecules. Here, DORI is pushed out of its comfort zone and used to probe systems prone to electronic and geometric fluctuations, or those constrained by their condensed phase environments. The applications to challenging chemical systems highlighted within demonstrate the capabilities of DORI as a formidable tool that can be beneficial in many facets of chemistry. Molecules in the excited state are difficult to analyze using popular bonding descriptors, primarily because the required information (orbitals) are not given by standard computational methodologies. DORI, which relies exclusively on the electron density and its derivatives, overcomes previous limitations and permits the characterization of excitation processes (charge transfer, excimer, Rydberg, ...) through visual and numerical signatures. Using DORI, the evolution of covalent and non-covalent excited state interactions where used to rationalize photoemission in BODIPY-derivatives. Certain BODIPY substituents formnon-covalent intramolecular interactions in the excited state, which are crucial for stabilizing the Sx - S0 intersection and prompting nonradiative decay. This application demonstrates that DORI is ideally suited for characterizing excited state phenomena. Dynamical fluctuations represent another domain beyond the standard usage of bonding descriptors. Highly fluxionalmolecules, such as molecular machines or proteins, have complex multi-dimensional conformational spaces that are generally explored using a handful of geometrical collective variables (bond lengths, angles, etc.), or dimensionality reduction algorithms. DORIâs covalent and non-covalent patterns are exploited as alternative sets of descriptors, which are simpler than geometrical parameters because electronic and geometrical fluctuations can be captured by a single-dimensional variable. DORI is also synergistically used alongside dimensionality reduction algorithms to reveal enhanced descriptions of the conformational spaces of a molecular rotor and a photoswitch. Thus, cost effective bonding descriptors are well adapted and beneficial in analyzing electronic and geometrical fluctuations requiring extended mapping of conformational spaces. Finally, DORI allows for simultaneous visualization of covalent and non-covalent interactions, and is thus particularly suited to investigate their interplay, notably present in dense environments of high-pressure crystals and in protein-ligand cavities. Using actual experimental electron densities of an organic crystal, DORI exposes pressure-induced disruptions of intramolecular delocalization and identifies the directional non-covalent interactions that cause these perturbations. Similarly, the scalar field pinpoints the specific non-covalent proteinligand interactions which modify the covalent regions of the ligand and facilitate the reactive process. Overall, the examples presented in this thesis demonstrate the versatility of DORI in translating complex chemical behavior into intuitive representations, greatly extending the range of applications that benefit from visual bonding descriptors

Spectroscopy of Hexamethyldipyrromethene Anion: Interactions With Metal Ions.

This work includes: (1) a search for charge transfer interaction involving hexamethyldipyrromethene (HL) as a donor; (2) a spectroscopic study of hexamethyldipyrromethene anion (L\sp-), and, (3) an investigation of the spectroscopic characteristic of the copper chelate CuL\sb2. There are presented reactions in which HL may react with some electron acceptors. It is reported that TCNE interacts with HL to form a 1:1 complex that has an equilibrium constant of (2.5 0.9) $\times$ 10\sp{15}. Spectroscopic results indicate that haloacetones also interact with HL. Hexamethyldipyrromethene is a molecule that consists of two methyl substituted pyrrole rings joined by means of a vinyl bridge. Its anion has been obtained by means of different reagents in various solvents and has been studied by using several instrumental techniques. Spectroscopic features such as visible absorption band maxima and \sp1H NMR chemical shifts depend on the counter ion (an alkali metal ion, Y\sp{+}). A study of the novel Y\sp{+}L\sp{-} species allows a characterization of the L\sp{-} moiety free from interligand peturbation or other orbitals that are present in the transition metal complexes (ML\sb2). In this study; characterization of the Y\sp{+}\rm L\sp{-} species by means of visible absorption, FT-IR, luminescence, and high resolution NMR techniques is presented. It is concluded that the Y\sp{+}L\sp{-} species constitute bridged complexes. In particular, a \sp7Li NMR downfield chemical shift of 1.66 ppm showed that the cation in Li \sp{+}L\sp{-} is indeed coordinated to the nitrogens. An equilibrium between two Y\sp{+}L\sp{-} species has been clearly demonstrated by means of NMR and visible absorption spectra. A spectroscopic study of the CuL\sb2 complex is also included. This species may display a unique visible absorption band or two bands; the absorption depends on the method of synthesis. Qualitative experiments which seem to indicate that both spectra arise from a single molecule in two different geometries are presented

UNHINDERED TRIANGULENE SALT PAIRS: SUBSTITUTION-DEPENDENT CONTACT ION PAIRING AND COMPLEX SOLVENT-SEPARATED DISCOTIC IONS IN SOLUTION

This work sought to enforce aromatic interactions between compatible π-molecular orbital systems with ionic bonding. In this case the interacting partners are oppositely charged discotic triangulene derivatives. The observed properties of the heterodimeric ion-pairs likely arise due to a hypothetical synergy between electrostatics and π-interactions. The work presented here describes investigation of putative covalency arising from this hypothetical synergy in the electrostatics driven π-stacking. In order to probe this, various hypotheses were made and experiments were designed to test their validity. The results from the experiments show existence of contact ion-pairs and complex solvent-separated discotic ions in solution. The formation of complex ion-pairs arise due to the fact that the electrostatic interaction that brings the discotic ions together is strong, but does not neutralize when the contact is made. So, the dipole created by the monopoles in a dimeric contact ion-pair can attract ions at both termini forming oligomers. This process apparently continues towards highly aggregated states and then to nanometric species and at some point the material precipitates. The propensity to aggregate and form complex-ions limited our approach to the measurement of the energetics of the ion-pairing for two reasons: (1) the observables had a complex dependence on temperature, solvent, concentration and ionic strength; and (2) the mass in solution was undergoing kinetic evolution towards solid states. The turbidimetric effects arising due to aggregate formation further complicated the extraction of weak interactions between the ions and hence effects determination of ion-pairing constants