Synthesis and chemistry of highly distorted polycyclic aromatic hydrocarbons

A significant feature of smaller cyclophanes and buckminsterfullerenes is the presence of nonplanar aromatic rings. Such compounds are of considerable interest due to both the synthetic challenge they pose and to their unusual conformational, spectroscopic, and chemical behavior. A great deal of work has focussed on determining the extent to which an aromatic ring can be distorted from planarity while remaining isolable under ambient conditions. Although this question has been examined in detail for isolated benzene rings (for example, through investigations of [n]paracyclophanes), analogous studies of polycyclic aromatic hydrocarbon (PAH) frameworks have never been pursued. -- Here the first systematic examination of the distortion from planarity of a PAH moiety is reported. The synthesis of a number of [n](2,7)pyrenophanes from [3.3]dithiacyclophane precursors is described. Some physical, spectroscopic, and chemical properties of these molecules are also described, and a number of X-ray structures of markedly nonplanar aromatic moieties are reported. From this data, it is concluded that the end-to-end bend of the most strained pyrenophane prepared is greater than the average end-to-end bend of the pyrene moiety. However, POAV analysis of the pyramidalization of pyrenophane sp² carbon atoms reveals markedly lower pyramidalizations than are observed in D₅h C₇₀. Attempts at the functionalization of [n](2,7)pyrenophanes in the hope of using them as precursors for larger nonplanar PAHs were made. However, suitable conditions for functionalization of pyrenophanes were not found. A synthetic approach to a C₂-chiral 1,6-[n]pyrenophane is also described. -- An attempted synthesis of a derivative of the buckybowl pinakene using a tandem Bergman cycloaromatization/free radical conjugate addition is presented. -- The experimental work is preceded by reviews of the literature concerning the concept of aromaticity, nonplanar aromatic molecules (especially [n]paracyclophanes) and fullerene fragments

Light-Activated Compounds

The presently-disclosed subject matter includes light-activated ruthenium compounds. In some embodiments the compounds release one or more ligands when exposed to light, and in specific embodiments the light includes a wavelength of about 500 nm to about 1000 nm. The present compounds can also comprise an overall charge, wherein the overall charge can be a positive overall charge or a negative overall charge. Further still, embodiments include methods of treating cancer in a subject by administering a compound and then exposing a site of the subject to light

Strained Macrocycles and Photomagnetic Switches

Das Ziel dieser Arbeit war die Synthese eindimensionaler Nanoröhren basierend auf leichten Elementen. Inspiriert von Kohlenstoff Nanoröhren werden Interessante Eigenschafte für diese Materialien erwartet. Aktuell ist die Synthese solcher Kohlenstoff Nanorohren nur mit vergleichsweise aufwendigen Methoden möglich. Hierbei stellt besonders die uniforme Synthese von Röhren mit exakt gleichen Durchmessern und Symmetrien ein noch ungelöstes Problem dar. Durch diese Arbeit erhofften wir uns eine völlig neue Arte der Synthese für solche 1D Nanomaterialien zu etablieren. Dazu wurden in Kapitel 2 und 3 zwei verschiedene Typen von gespannten aromatischen Makrozyklen synthetisiert. Die synthetisierten Makrozyklen zeichnen sich durch einen hohen Grad an Funktionalisierung aus, welcher zukünftig dazu genutzt werden soll die Prinzipien der dynamisch kovalenten Chemie in der finalen Materialsynthese anzuwenden. Der durch die Funktionalisierung erzeugte innere Hohlraum dieser zyklischen Verbindungen lässt sich nutzen, um verschiedene molekulare Gäste zu binden. Die Erkenntnisse in Bezug auf die Synthese solcher Makrozyklen, die hierbei erzielt wurden, werden entscheidend dazu beitragen, dass anfänglich beschriebene Ziel der nasschemischen Synthese 1D organischer Nanoröhren in Zukunft zu erreichen. Die Methoden, der Makrozyklisierung sollten in Kapitel 4 dazu genutzt werden einen chiralen aromatischen Makrozyklus auf Basis von [5]Helicen-Untereinheiten zu synthetisieren, allerdings ohne Erfolg. Stattdessen wurde ein Nebenprodukt isoliert, dass sich als bisher unbekannter molekulare Schalter erwies. Dieser Schalter erlaubt es durch Bestrahlung bei tiefen Temperaturen reversibel ein paramagnetisches Isomer zu erzeugen. Dadurch eröffnet sich eine völlig neue Klasse an molekularen Schaltern, deren Anwendungspotential den Rahmen dieser Arbeit überschreitet.The aim of this work was the synthesis of one-dimensional nanotubes based on light elements. Inspired by carbon nanotubes, interesting properties for these materials are expected. Currently, the synthesis of such carbon nanotubes is only possible with comparatively complex methods. Especially the uniform synthesis of tubes with exactly the same diameters and symmetries is still an unsolved problem. Through this work we hoped to establish a completely new way of synthesis for such 1D nanomaterials. To this end, two different types of strained aromatic macrocycles were synthesized in Chapters 2 and 3. The synthesized macrocycles are characterized by a high degree of functionalization, which will be used in the future to apply the principles of dynamic covalent chemistry in the final material synthesis. The internal cavity of these cyclic compounds created by functionalization can be used to bind various molecular guests. The knowledge regarding the synthesis of such macrocycles obtained here will be instrumental in achieving the initially described goal of wet chemical synthesis of 1D organic nanotubes in the future. The methods of macrocyclization were to be used in Chapter 4 to synthesize a chiral aromatic macrocycle based on [5]helicene subunits, but without success. Instead, a byproduct was isolated that proved to be a previously unknown molecular switch. This switch allows reversible generation of a paramagnetic isomer by irradiation at low temperatures. This opens up a completely new class of molecular switches whose potential applications are beyond the scope of this work

Controlling pairing of pi-conjugated electrons in 2D covalent organic radical frameworks via in-plane strain

Controlling the electronic states of molecules is a fundamental challenge for future sub-nanoscale device technologies. π-conjugated bi-radicals are very attractive systems in this respect as they possess two energetically close, but optically and magnetically distinct, electronic states: the open-shell antiferromagnetic/paramagnetic and the closed-shell quinoidal diamagnetic states. While it has been shown that it is possible to statically induce one electronic ground state or the other by chemical design, the external dynamical control of these states in a rapid and reproducible manner still awaits experimental realization. Here, via quantum chemical calculations, we demonstrate that in-plane uniaxial strain of 2D covalently linked arrays of radical units leads to smooth and reversible conformational changes at the molecular scale that, in turn, induce robust transitions between the two kinds of electronic distributions. Our results pave a general route towards the external control, and thus technological exploitation, of molecular-scale electronic states in organic 2D materials

Controlling pairing of π-conjugated electrons in 2D covalent organic radical frameworks via in-plane strain

Controlling the electronic states of molecules is a fundamental challenge for future sub-nanoscale device technologies. -conjugated bi-radicals are very attractive systems in this respect as they possess two energetically close, but optically and magnetically distinct, electronic states: the open-shell antiferromagnetic/paramagnetic and the closed-shell quinoidal diamagnetic states. While it has been shown that it is possible to statically induce one electronic ground state or the other by chemical design, the external dynamical control of these states in a rapid and reproducible manner still awaits experimental realization. Here, via quantum chemical calculations, we demonstrate that in-plane uniaxial strain of 2D covalently linked arrays of radical units leads to smooth and reversible conformational changes at the molecular scale that, in turn, induce robust transitions between the two kinds of electronic distributions. Our results pave a general route towards the external control, and thus technological exploitation, of molecular-scale electronic states in organic 2D materials. Controlling the electronic states of molecules is a fundamental challenge for future sub-nanoscale device technologies but the external dynamical control of these states still awaits experimental realization. Here, via quantum chemical calculations, the authors demonstrate that in-plane uniaxial strain of 2D covalently linked arrays of radical units induces controlled pairing of pi -conjugated electrons in a reversible way

Utilization of K-region oxidation for the synthesis of functional materials

Pyrene with its long fluorescence lifetime, large Stokes shift and proclivity towards excimer formation has become the gold standard in the sensing of microenvironments using fluorescence spectroscopy. Derivatives of pyrene find applications in a broad range of fields. However, the design of more complex systems is hampered by the lack of selectivity one encounters when working with pyrene. Alkylation, halogenation and nitration produce practically inseparable isomers. Methods that desymmetrize pyrene are currently of high value. Known methods have recently been improved and applied to a number of systems within the Bodwell group. The optimization of a K-region oxidation reaction and utilization of desymmetrized pyrene in the synthesis of redox-active molecules and progress towards a 2,7-pyrenylene-ethynylene macrocycle is investigated in this thesis work. References [1] R. Rieger, K. Müllen, J. Phys. Org. Chem., 2010, 23, 315-325. [2] J. Andréasson, U. Pischel, Chem. Soc. Rev., 2015, 44, 1053-1069. [3] P. Conlon, C. J. Yang, Y. Wu, Y. Chen, K. Martinez, Y. Kim, N. Stevens, A. A. Marti, S. Jockusch, N. J. Turro, W. Tan, J. Am. Chem. Soc., 2008, 130, 336-342

I Asymmetric photochemistry II Exploratory and mechanistic studies on the triplet sensitized vapor phase photochemistry of allenes III Developments in the synthesis of strained cyclic cumulenes

The development and implementation of a new chiral triplet sensitizer derived from 1,1\sp\prime-binaphthol is described. Irradiation of 1,3-diphenylallene (16) in the presence of 4,5,6,7-tetrahydro-dinaphtho(2,1-g:1\sp\prime,2\sp\prime-i) (1,6) dioxecine (10) resulted in 0.66% optical induction. Irradiation of 1,3-cyclooctadiene (17) in the presence of 10 resulted in 11.3% optical induction. The singlet state of 10 could be effectively quenched by higher diene concentration, substantially reducing the optical yield. Irradiation of trans-1,2-diphenyl-cyclopropane (1) in the presence of 10 resulted in very low optical yields. The mechanism by which triplet excited state allenes react in the vapor phase is investigated through both theory and experiment. Benzene sensitized vapor phase irradiation of cyclohexylallene (63) yields cis and trans-1,3,8-nonatriene (82) as the primary products. Triene 82 undergoes triplet sensitized (4+2) cycloaddition reactions yielding bicyclic alkenes 45 and 83. Additionally, 82 undergoes a series of triplet sensitized (2+2) cycloadditions, yielding bicyclic alkenes 84-86. The absence of any observed tricyclics argues for the intermediacy of planar triplet allene 89, instead of triplet cyclopropylidene 88. Benzene sensitized vapor phase irradiation of vinylidenecycloheptane (64) yielded only starting material. Models indicated that neither intermediate, triplet cyclopropylidene 99 or planar triplet allene 100, was particularly well suited for hydrogen abstraction to occur. Benzene sensitized solution phase irradiation of either 63 or 64 yielded only starting material. Ab initio calculations at the UMP3/6-31G*//UHF/3-21G level are reported for hydrogen abstraction from methane by triplet cyclopropylidene (52), and planar triplet allene (61). The calculations predict E\sb{\rm a} = 16.7 and 18.8 kcal/mol for hydrogen abstraction by 52 and 61, respectively. The syntheses and trapping of 1-phenyl-1,2-cyclohexadiene (137) is described. Several pathways directed toward the synthesis of 1,2-cyclopentadiene (131) are also described. Additionally, the development of a new, and presumably general route to cyclic allenes is presented. The syntheses and trapping of 1,2,3-cyclohexatriene (199) and cyclohexen-3-yne (240) are described. Both are prepared by introduction of the strained $\pi$ bond through fluoride induced elimination of vicinal trimethylsilyl, and triflate or halide groups. Both syntheses are general and should be applicable to different ring sizes

Generation and reactivity studies of dehydrotropylium -cobalt hexa(carbon monoxide)complex: Aromaticity of tropyne-cobalt hexa(carbon monoxide) complexes

Despite a large amount of information on the application of Nicholas reactions in organic syntheses, little attention has been paid to the structural variation of cationic intermediates and the factors that may influence reactivities and stabilities of these species. The primary focus of this project was to design and generate a new type of Nicholas carbocation that possesses multiple sources of stabilization. For this matter, nominally aromatic cation 99 was chosen as the target compound. The effects of resonance stabilization on the stability and reactivity of the cation 99 were investigated both experimentally and by means of computational calculations. From reactivity studies of cation 99, a sharp switching of reaction pathway from electrophilic addition to dimerization was observed for the nucleophiles with N \u3c1. Non-aromatic, highly conjugated acyclic cation 127, was prepared as structural model and its reactivities in Nicholas reactions were investigated for comparison purposes. From experimental and computational studies cation 99 was found to be weakly aromatic with its NICS (1) value approximately 28% of tropylium ion.* Preliminary attempts were made to prepare the precursor to the benzo-fused derivative of dehydrotropylium cation (100). This has led to the formation of phosphonate substituted benzo-fused dehydrotropone ( 151). The scope and limitations of the method for synthesis of other Co2(CO)6-complexes of substituted benzo-fused dehydrotropone (152 and 153) were further investigated.* *Please refer to dissertation for diagrams

Las excepcionales propiedades de los [n]CPPs: ¿por qué importa tanto el tamaño y la estructura molecular?

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Química Física I, leída el 15/04/2016. Tesis formato europeo (compendio de artículos)Cycloparaphenylenes ([n]CPPs from now on), were firstly synthesized in 2008, and promptly joined the fascinating world of carbon nano-materials in their own right. These systems are formed by cyclic molecules with n phenyl units connected each other in their para-position, a configuration that resembles an ultra-short armchair single-wall carbon nanotube (SWCNT). In this Ph. D. Thesis we put forward a systematic study on the electronic properties of [n]CPPs, providing a thoroughly link between [n]CPPs, SWCNTs and their linear analogues ([n]LPPs). Curvature, strain and electronic π‒conjugation are the main characteristics of [n]CPPs that we will systematically study to examine their unexplored properties, and eventually their potential applications. In addition, we shall use [n]CPPs as models to realize the concept of radial cyclic electronic π‒conjugation, which has been only theoretically considered so far. Let us emphasize that we shall take advantage of the success of Raman spectroscopy for characterizing carbon-based materials. Raman spectroscopy is also among the most suitable tools to probe the electronic properties of such materials due to the high susceptibility of the π-electrons polarizability. In this Ph. D. Thesis we present a systematic study of a series of [n]CPPs considering all the geometrical parameters involved in their vibrational modes. We shall examine the influence of size on the Raman spectra of [n]CPPs, together with the effect of oxidation and mechanical compression on their molecular structures. Finally, we will explore the hosting capabilities of [n]CPPs as well as their mechanical properties relative to those of SWCNTs...Esta tesis doctoral tiene como eje fundamental el análisis exhaustivo de diversas propiedades de los compuestos denominados [n]ciclo-parafenilenos (desde ahora [n]CPPs). Estas moléculas cíclicas están formadas por fenilenos unidos en posición para mediante enlaces sencillos. Como consecuencia de la configuración cíclica, los [n]CPPs poseen un alto grado de tensión interna, dado que sus unidades fenilénicas se ven forzadas a doblarse parcialmente para poder cerrar el ciclo. Asimismo, esta configuración fenilénica cíclica hace que los [n]CPPs se hayan considerado como la mínima unidad de nanotubos de carbono con quiralidad única de tipo armchair. El aspecto esencial de la tesis ha sido el estudio experimental y teórico de la espectroscopía Raman de los [n]CPPs, con un análisis de la dependencia de la misma con el tamaño, curvatura, tensión y conjugación electrónica. Por otro lado, también se ha estudiado la influencia de la temperatura, presión y la oxidación de los [n]CPPs en las variables espectroscópicas. Esto nos ha permitido explorar otras propiedades de los [n]CPPs como son: la conjugación electrónica, su deformabilidad y otras propiedades mecánicas, comparando el comportamiento observado en las mismas para los oligoparafenilenos lineales y los nanotubos de carbono. Por último, también se ha comprobado que los [n]CPPs y los nanotubos de carbono comparten propiedades relacionadas con su configuración tubular como son su habilidad para hospedar sistemas del tamaño apropiado...Depto. de Química FísicaFac. de Ciencias QuímicasTRUEunpu