Design and synthesis of organic chromophores for imaging, lithography and organic electronics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011Cataloged from PDF version of thesis.Includes bibliographical references.The absorption and emission maxima, photostabilities and photoreactivities of small-molecule organic chromophores can be tailored by (a) the choice of an appropriate parent structure and (b) the deliberate introduction of substituents that predictably alter the optical properties and photochemistry of this parent structure. Suitably-designed chromophores can be used in a variety of applications, such as imaging (for example, as fluorescent labeling agents or as indicators for specific analytes), optical lithography and as active components in organic electronic devices. In Chapter 1, a fluorogenic chemosensor to detect saturated nitramine and nitrate ester explosives was devised based on a photochemical reduction reaction. 10-Methyl-9,10- dihydroacridine (AcrH2) was found to transfer a hydride ion equivalent to the high explosives RDX and PETN upon irradiation at 313 nm in degassed acetonitrile solutions. Mechanistic photophysical studies indicated that the photoreduction of RDX proceeded via a two-step electron-hydrogen atom transfer reaction, whereas PETN photoreduction proceeded via a threestep electron-proton-electron transfer sequence. A zinc analog was synthesized and found to display an 80- or 25-fold increase in 480 nm emission intensity upon reaction with RDX or PETN, respectively; moreover, the Zn analog was found to be unresponsive to TNT and other common contaminants, in addition to being photostable under ambient conditions. In Chapter 2, the nitramine-containing explosive RDX and the nitroester-containing explosive PETN were shown to be susceptible to photodegradation upon exposure to sunlight. The products of this photodegradation were identified as reactive, electrophilic NOx species, such as nitrous and nitric acid, nitric oxide, and nitrogen dioxide. NN-Dimethylaniline was capable of being nitrated by the reactive, electrophilic NOx photodegradation products of RDX and PETN. A series of 9,9-disubstituted 9,10-dihydroacridines (DHAs) were synthesized from either N-phenylanthranilic acid methyl ester or a diphenylamine derivative and were similarly shown to be rapidly nitrated by the photodegradation products of RDX and PETN. An increase in the emission signal at 550 nm was observed upon nitration of DHAs due to the generation of fluorescent donor-acceptor chromophores. Using fluorescence spectroscopy, the presence of ca. 1.2 ng of RDX and 320 pg of PETN could be detected by DHA indicators in the solid state upon exposure to sunlight. In Chapter 3, optical lithography with organic photochromes is demonstrated. In the past, the formation of microscale patterns in the far field by light has been diffractively limited in resolution to roughly half the wavelength of the radiation used. We demonstrated lines with an -4- average width of 36 nm, about one-tenth the illuminating wavelength ( 11 = 325 nm), made by applying a film of thermally-stable photochromic molecules above the photoresist. Simultaneous irradiation of a second wavelength (k= 633 nm) rendered the film opaque to the writing beam except at nodal sites, which let through a spatially constrained segment of incident 1 light, allowing subdiffractional patterning. In Chapter 4, rylene dyes functionalized with varying numbers of phenyl trifluorovinylether (TFVE) moieties were subjected to a thermal emulsion polymerization to yield shape-persistent, water-soluble chromophore nanoparticles. Perylene and terrylene diimide derivatives containing either two or four phenyl TFVE functional groups were synthesized and subjected to thermal emulsion polymerization in tetraglyme. Dynamic light scattering measurements indicated that particles with sizes ranging from 70 - 100 nm were obtained in tetraglyme, depending on monomer concentration. The photophysical properties of individual monomers were preserved in the nanoemulsions and emission colors could be tuned between yellow, orange, red, and deep red. The nanoparticles retained their shape upon dissolution into water and the resulting water suspensions displayed moderate to high fluorescence quantum yield, thus making them attractive candidates for bioimaging applications. In Chapter 5, a series of substituted 6,6-dicyanofulvenes (DCFs) were synthesized starting from masked, dimeric or monomeric cyclopentadienones. DCFs lacking sufficient steric bulk around the fulvene core tended to reversibly undergo a [4+2] dimerization. In addition to being highly crystalline, DCFs were darkly-colored compounds due to the presence of weak electronic transitions in the visible region of the electromagnetic spectrum. DCFs displayed two distinct, reversible one-electron reductions by cyclic voltammetry. Based on their high crystallinity and suitable electron affinities, and buoyed by their relatively cheap and straightforward synthesis, DCFs are interesting candidates for organic electron-transport materials.by Trisha Lionel Andrew.Ph.D

The Synthesis of Azaperylene-9,10-dicarboximides

The syntheses of two azaperylene 9,10-dicarboximides are presented. 1-Aza- and 1,6-diazaperylene 9,10-dicarboximides containing a 2,6-diisopropylphenyl substituent at the N-imide position were synthesized in two steps starting from naphthalene and isoquinoline derivatives

Photoluminescent Energy Transfer from Poly(phenyleneethynylene)s to Near-Infrared Emitting Fluorophores

Photoluminescent energy transfer was investigated in conjugated polymer-fluorophore blended thin films. A pentiptycene-containing poly(phenyleneethynylene) was used as the energy donor, and 13 fluorophores were used as energy acceptors. The efficiency of energy transfer was measured by monitoring both the quenching of the polymer emission and the enhancement of the fluorophore emission. Near-infrared emitting squaraines and terrylenes were identified as excellent energy acceptors. These results, where a new fluorescent signal occurs in the near-infrared region on a completely dark background, offer substantial possibilities for designing highly sensitive turn-on sensors.National Institute of General Medical Sciences (U.S.) (F32GM086044)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (DAAD-19-02-0002

Detection of Explosives via Photolytic Cleavage of Nitroesters and Nitramines

The nitramine-containing explosive RDX and the nitroester-containing explosive PETN are shown to be susceptible to photofragmentation upon exposure to sunlight. Model compounds containing nitroester and nitramine moieties are also shown to fragment upon exposure to UV irradiation. The products of this photofragmentation are reactive, electrophilic NO[subscript x] species, such as nitrous and nitric acid, nitric oxide, and nitrogen dioxide. N,N-Dimethylaniline is capable of being nitrated by the reactive, electrophilic NO[subscript x] photofragmentation products of RDX and PETN. A series of 9,9-disubstituted 9,10-dihydroacridines (DHAs) are synthesized from either N-phenylanthranilic acid methyl ester or a diphenylamine derivative and are similarly shown to be rapidly nitrated by the photofragmentation products of RDX and PETN. A new (turn-on) emission signal at 550 nm is observed upon nitration of DHAs due to the generation of fluorescent donor−acceptor chromophores. Using fluorescence spectroscopy, the presence of ca. 1.2 ng of RDX and 320 pg of PETN can be detected by DHA indicators in the solid state upon exposure to sunlight. The nitration of aromatic amines by the photofragmentation products of RDX and PETN is presented as a unique, highly selective detection mechanism for nitroester- and nitramine-containing explosives and DHAs are presented as inexpensive and impermanent fluorogenic indicators for the selective, standoff/remote identification of RDX and PETN.United States. Army Research OfficeNational Science Foundation (U.S.) (ECCS-0731100

Synthesis, Reactivity, and Electronic Properties of 6,6-Dicyanofulvenes

A series of 6,6-dicyanofulvene derivatives are synthesized starting from masked, dimeric, or monomeric cyclopentadienones. The reactivities of 6,6-dicyanofulvenes relative to their parent cyclopentadienones are discussed. 6,6-Dicyanofulvenes are capable of undergoing two consecutive, reversible, one-electron reductions and are presented as potential n-type small molecules.Chesonis Family FoundationMassachusetts Institute of Technology. Institute for Soldier NanotechnologiesUnited States. Air Force Office of Scientific Researc

Breaking the Far-Field Diffraction Limit in Optical Nanopatterning via Repeated Photochemical and Electrochemical Transitions in Photochromic Molecules

By saturating a photochromic transition with a nodal illumination (wavelength, λ), one isomeric form of a small molecule is spatially localized to a region smaller than the far-field diffraction limit. A selective oxidation step effectively locks this pattern allowing repeated patterning. Using this approach and a two-beam interferometer, we demonstrate isolated lines as narrow as λ/8 (78 nm) and spacing between features as narrow as λ/4 (153 nm). This is considerably smaller than the minimum far-field diffraction limit of λ/2. Most significantly, nanopatterning is achieved via single-photon reactions and at low light levels, which in turn allow for high throughput.Utah Science Technology and Research (USTAR) InitiativeUnited States. Defense Advanced Research Projects Agency (Contract No. N66001-10-1-4065)National Science Foundation (U.S.

Near-infrared photodetector consisting of J-aggregating cyanine dye and metal oxide thin films

We demonstrate a near-infrared photodetector that consists of a thin film of the J-aggregating cyanine dye, U3, and transparent metal-oxide charge transport layers. The high absorption coefficient of the U3 film, combined with the use of a reflective anode and optical spacer layer, results in a zero-bias external quantum efficiency of 16.1 ± 0.1% (λ = 756 nm) for a device containing an 8.1 ± 0.3 nm-thick U3 film. The specific detectivity (D*) and response speed (f [subscript 3 dB]) of a fully optimized device are measured to be (4.3 ± 0.1) × 10[superscript 11] cm Hz[superscript 1/2] W[superscript −1] and 92 kHz, respectively.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-07-D-0004)National Science Foundation (U.S.). Graduate Research Fellowship ProgramLink FoundationHertz Foundation (Fellowship

QLEDs for displays and solid-state lighting

The mainstream commercialization of colloidal quantum dots (QDs) for light-emitting applications has begun: Sony televisions emitting QD-enhanced colors are now on sale. The bright and uniquely size-tunable colors of solution-processable semiconducting QDs highlight the potential of electroluminescent QD light-emitting devices (QLEDs) for use in energy-efficient, high-color-quality thin-film display and solid-state lighting applications. Indeed, this year’s report of record-efficiency electrically driven QLEDs rivaling the most efficient molecular organic LEDs, together with the emergence of full-color QLED displays, foreshadow QD technologies that will transcend the optically excited QD-enhanced products already available. In this article, we discuss the key advantages of using QDs as luminophores in LEDs and outline the 19-year evolution of four types of QLEDs that have seen efficiencies rise from less than 0.01% to 18%. With an emphasis on the latest advances, we identify the key scientific and technological challenges facing the commercialization of QLEDs. A quantitative analysis, based on published small-scale synthetic procedures, allows us to estimate the material costs of QDs typical in light-emitting applications when produced in large quantities and to assess their commercial viability.National Science Foundation (U.S.) (Graduate Research Fellowship)United States. Dept. of Energy (Center for Excitonics, an Energy Frontier Research Center funded by the Office of Basic Energy Sciences, under Award Number DE-SC0001088