Optical Properties In Solution Research Articles

Solution‐ and Solid‐State Luminescent Borate Complexes Based on a Substituted π‐Conjugated 2‐(6′‐Hydroxy‐5′‐benzofuryl) Scaffold

AbstractThis paper describes the synthesis of π‐conjugated fluorophores based either on an anil or a benzoxazole scaffold incorporating a rigid 2‐(6′‐hydroxy‐5′‐benzofuryl) fragment. Their subsequent coordination to a BF2 motif led to highly luminescent BIII complexes called boranils or HBBO borate complexes, respectively. All the new compounds were characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. The study of their optical properties in solution revealed two distinct photophysical behaviors depending on the substitution. Complexes bearing a strong electron‐donating p‐nBu2NC6H4 group displayed a marked internal charge transfer (ICT) leading to a pronounced solvatochromism with λem ranging from 507 to 663 nm and quantum yields of up to 87 %. Alternatively, borate complexes functionalized with p‐tBuC6H4 or p‐OMeC6H4 displayed fluorescence in the visible range that is not influenced by the nature of the solvent. Although the emission of the boranils was quenched in the solid state, HBBO borate complexes displayed intense fluorescence from 489 to 567 nm and quantum yields of up to 23 %. Finally, the excited states of a selection of borate complexes were modeled by using time‐dependent DFT, which allowed calculation of the dipole moments of the dyes in their excited states.

Ring-shaped silafluorene derivatives as efficient solid-state UV-fluorophores: synthesis, characterization, and photoluminescent properties.

Four ring-shaped silafluorene-containing compounds (1-4) were synthesized and characterized as potentially promising monomers for fluorescent polymers. Their optical properties in solution and solid state (thin film and powder) were studied. These compounds have low quantum yields in solution (Φ(fl)=0.13-0.15) with fluorescence maxima at about 355 nm, but high quantum yields in the solid state (powder, Φ(fl)=0.35-0.54) with fluorescence maxima at about 377 and 488 nm. Influence of the substituents and the number of silafluorene units in 1-4 on their optical properties was investigated. Extensive study of the X-ray crystal structures of 1-4 was undertaken to analyze and qualitatively estimate the role, extent, and influence of silafluorene moieties' interactions on solid-state fluorescent properties. Excited state UV/Vis and theoretical molecular orbital (MO) calculations were performed to explore possible fluorescence mechanisms and differences in quantum yields among these compounds.

Fluorescence Sensing of Amine Vapors Using a Cationic Conjugated Polymer Combined with Various Anions

AbstractA series of conjugated cationic polymers, differentiated only by their accompanying counter‐anions, was prepared and characterized. The choice of counter‐anion (CA) was found to drastically impact the solubility of the polymers and their optical properties in solution and in the solid state. Fluorescent polymer thin films were found to be instantaneously quenched by volatile amines in the gas phase at low ppm concentrations, and a mini‐array with CAs as variable elements was found to be able to differentiate amines with good fidelity.

Second-Order NLO Switches from Molecules to Polymer Films Based on Photochromic Cyclometalated Platinum(II) Complexes

Novel photochromic dithienylethene-based platinum(II) complexes (C^N^N)Pt(C≡C-DTE-C6H4-D) ((C^N^N) = 4,4'-di(n-hexyl)-6-phenyl-2,2'-bipyridine; D = H, NMe2) were prepared and characterized. Their excellent photochromic properties allow the photoinduced switching of their second-order nonlinear optical properties in solution, as measured by the EFISH technique, due to formation of an extended π-conjugated ligand upon suitable electromagnetic radiation. Insights into the electronic structures of the complexes and the nature of their excited states have been obtained by DFT and TD-DFT calculations. These novel Pt(II) complexes were nanoorganized in polymer films which were poled, affording new materials characterized by a good second-order NLO response that can be easily switched, with an excellent NLO contrast. To the best of our knowledge, our compounds allowed designing the very first examples of switchable NLO polymer films based on metal complexes.

Structure–property relationships for 1,7-diphenoxy-perylene bisimides in solution and in the solid state

To elucidate the impact of widely employed solubilizing phenoxy substituents on the structural and functional properties of perylene bisimide (PBI) dyes a series of 1,7-diphenoxy-substituted PBIs was prepared from 1,7-dibromo PBI which exhibit hydrogen, methyl, isopropyl or phenyl substituents at one or both ortho positions of the phenoxy substituents. Despite increasing sterical congestion high yields of 74–88% could be obtained for all twofold aromatic nucleophilic substitution reactions. The structural and optical properties in solution and in the solid state were investigated by 1H NMR, UV-Vis absorption and fluorescence spectroscopy, single crystal X-ray analyses (four structures) as well as quantum chemical and force field calculations. For the latter we used an adapted force field which correctly reflects the rigidity of the PBI core. Our studies show that these dyes prefer to accommodate a slightly twisted molecular structure in solution that is supported by CH⋯O hydrogen bonds between the 1,7-oxygen and the 6,12-hydrogen substituents. Because of the rather shallow potential energy surface, however, the molecules may planarize in the crystalline state under the influence of packing forces as revealed by single crystal X-ray analyses for two derivatives bearing methyl or phenyl substituents at all phenoxy ortho-positions. Such substituents are also suited to enwrap the PBI π-scaffold and to prohibit PBI aggregation in the bulk state giving rise to defined vibronic progressions in the solid state UV-Vis absorption and emission spectra, and appreciable fluorescence quantum yields of up to 37%. In dichloromethane solution all of these 1,7-diphenoxy-substituted PBI dyes exhibit fluorescence quantum yields of 98–100% despite significant differences in the shape of the UV-Vis absorption band. The latter was explained in terms of rigidity because the molecules bearing four ortho-substituents at the phenoxy substituents were shown to prevail in much more fixed conformations compared to their more simple counterparts. Our findings underline that the conformational flexibility of bay-substituents can have an important impact on the functional properties of PBI dyes.

Multiple optical properties of a naphthoquinone pigment: 2-methyl-3-(hydroxyphenylthio)-1,4-naphthalenedione.

Naphthoquinone pigments 2-methyl-3-(4- or 2-hydroxyphenylthio)-1,4-naphthalenedione show characteristic optical properties in solution and in the solid state. The position of the OH group in the pigment leads to varied optical properties, including a characteristic colour, in the solid state. The pigment with a 2-OH substituent displays solvatochromism in solution, and that with a 4-OH substituent displays optical chirality in the solid state.

Synthesis and Photoelectrical Properties of Two Potential Solution-Processed Blue Fluorescent Emitters Based on Fluorene-Arylamine Derivatives End-Capped with Anthracene/Pyrene Molecules

Two novel potential solution-processed blue fluorescent emitters composed of a core fluorenediphenylamine unit capped with either anthracene(FAn) or pyrene(FPy) were synthesized and characterized.They were both soluble in common organic solvents and solutions gave smooth films after spin coating. Their optical properties in solution and in the film were investigated by UV-visible and photoluminescence(PL)spectroscopy. The PL emission maximum of FAn and FPy in the film state were found to be 449 and 465 nm,respectively. The electrochemical properties of the as-prepared samples were studied by cyclic voltammetry.The estimated highest occupied molecular orbital(HOMO) energy levels were-5.37 and-5.36 eV for FAn and FPy, respectively. These results indicate that the introduction of diphenylamine effectively prevents plane stacking of the molecules in the solid state, which suppresses the formation of long-wavelength aggregates,and the high HOMO levels enhance the hole-injection ability of the compounds. The results of differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA) indicate that the two materials have excellent thermal stability with the glass transition temperature of FAn reaching 207 ℃ and the thermal decomposition temperature as high as 439 ℃. The good performance of the fluorescent emitters makes them promising candidates as solution-processed blue organic light-emitting diodes.

Reaction of tetrachlorinated perylene bisimide in a strong base to form an asymmetric compound with charge transfer optical properties

A novel perylene oxazine imide (POI) with donor-π-bridge-acceptor (D-π-A) asymmetric structure was synthesized from tetrachlorinated perylene bisimide (PBI) through transformation of one imide group to oxazine, which exhibits significant charge transfer optical properties in solutions.

Synthesis, characterization, and electroluminescence properties of poly(fluorenevinylene benzobisthiazoles)

AbstractA series of vinylene‐linked copolymers based on electron‐deficient benzobisthiazole and electron‐rich fluorene moieties were synthesized via Horner–Wadsworth–Emmons polymerization. Three different polymers P1, P2, and P3, were prepared bearing octyl, 3,7‐dimethyloctyl, and 2‐(2‐ethoxy)ethoxyethyl side chains, respectively. The polymers all possessed moderate molecular weights, good solubility in aprotic organic solvents, and high fluorescence quantum efficiencies in dilute solutions. P2, which bore branched 3,7‐dimethyloctyl side chains, exhibited better solubility than the other polymers, but also exhibited the lowest thermal decomposition temperature of all polymers. Overall, the impact of the side chains on the polymers optical properties in solution was negligible as all three polymers gave similar absorption and emission spectra in both solution and film. Guest‐host light‐emitting diodes using dilute blends of the polymers in a poly(N‐vinylcarbazole) host gave blue‐green emission with P2 exhibiting the highest luminous efficiency, 0.61 Cd/A at ∼500 nm. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Regioregular Polythiophenes with Alkylthiophene Side Chains

We present the synthesis of regioregular polythiophenes with alkylthiophene side chains P3TC16 prepared by Ni-catalyzed polymerization from the branched, thiophene-based monomer 5-bromo-5″-hexadecyl-[2,2′;3′,2″]terthiophene. The optical properties in solution and thin films of the polymer were investigated in situ as a function of temperature and compared to the low regioregularity analogue FeP3TC6 synthesized by Fe(III) mediated oxidative polymerization of 5″-hexyl-[2,2′;3′,2″]terthiophene. It was found that due to the regioregular structure, P3TC16 tends to strong aggregation in solution, which is ascribed to π–π interactions. The bandgap in thin films of 1.88 eV is slightly smaller than the bandgap of the reference polymer poly(3-hexylthiophene) (P3HT, 1.91 eV). Interestingly, it was found that the HOMO and LUMO levels of P3TC16 are shifted to significantly lower values as compared to P3HT. First results regarding the application of P3TC16 in FETs are shown and mobilities of up to 3.1 × 10–2 cm2/(V s) ...

Effects of Alkoxy Substitution on the Optical Properties of 9,10-Anthraquinone and Anthracene: 2,3,6,7-Tetrapropoxy-substituted vs. 2,6-Dipropoxy-substituted Derivatives

Abstract 2,3,6,7-Tetrapropoxy- and 2,6-dipropoxy-substituted 9,10-anthraquinone (AQ) and anthracene (ANT) derivatives were synthesized, and their optical properties in solution and in the solid state were investigated. In AQs, the tetrapropoxy derivative exhibited a red shift of absorption in comparison with the dipropoxy derivative and ANT. In contrast, in ANTs, the dipropoxy derivative exhibited a red shift of absorption and fluorescence in comparison with the tetrapropoxy derivative and ANT. The electronic effects of alkoxy substitution could be explained by TD-DFT calculations.

Effect of textured seeds on the morphology and optical properties of solution- and vapor-grown ZnO nanorod arrays

This paper examines the growth of aligned ZnO nanorod arrays through chemical deposition from solution and the vapor phase. The nanorod alignment is ensured primarily by a thin layer of seeds—zinc oxide nanoparticles produced by decomposing zinc acetate directly on the substrate and aligned with their c axes normal to the substrate surface. The acetate route was used to produce nanorod arrays 1 × 1 mm in dimensions on substrates with photoresist.

Ion‐Specific Self‐Assembly of Low‐Dimension Aggregate Structures of Conjugated Polymer at Two‐Phase Interface

A novel and facile approach to manipulate the morphology of Cu(2+)-ion-specific assembly of conjugated polymer by coordinative interaction at an oil-water two-phase interface is present. The application of increasing importance is the use of π-conjugated polymers as receptors, exploiting their ability to selectively form complexes, which can obviously change the optical properties in solution and induce the formation of varied solid nano/microstructures. By this method, microtubes are formed through self-rolling of a strained ionic bilayer film at the oil/water interface.

(Z)-3-Methyl-N-(7-nitroacridin-3-yl)-2,3-dihydro-1,3-benzothiazol-2-imine from laboratory powder diffraction data

The title compound, C(21)H(14)N(4)O(2)S, belongs to a family of molecules possessing nonlinear optical properties in solution. Its structure has been solved from laboratory X-ray powder diffraction data using a new direct-space structure solution method, where the atomic coordinates are directly used as parameters and the molecular geometry is described by restraints. The molecular packing is controlled by two systems of π-π interactions and one weak edge-to-face interaction.

Nonlinear optical properties of solutions of heavy fullerenes in the near-ultraviolet region

Nonlinear optical properties (particularly optical limiting) are determined for solutions of heavy fullerenes C76 + C78 + C84 + C90 + …, in the near-ultraviolet region (λ ≈ 280 ± 7 nm). It is shown that no optical limiting is observed in solutions of light fullerenes (C60 and C70), but found in solutions of water-soluble fullerenol-d (a mixture of oxypolyalcohols of fullerene C60-C60(OH)n1On2, with their sodium salts) based on light fullerenes.

Hydrogen Reactivity of Palladium Nanoparticles Coated with Mixed Monolayers of Alkyl Thiols and Alkyl Amines for Sensing and Catalysis Applications

Palladium monolayer-protected clusters (MPCs) coated with octylamines (C8NH(2)), hexanethiolates (C6S), and mixed monolayers of C8NH(2) and C6S exhibit significantly different reactivities with hydrogen gas, depending on the relative amounts of the two ligands coating the Pd nanoparticle surface, as determined by UV-vis spectroscopy of Pd MPCs in solution and electronic measurements of films of Pd MPCs as a function of exposure time to hydrogen. The average estimated composition of the ~3.0 nm diameter Pd MPCs was Pd(919)(C6S)(192) or Pd(919)(C8NH(2))(177-x)(C6S)(x), where x was varied to be 0, 3, 10, 16, 32, or 81 by the synthesis of pure C8NH(2) Pd MPCs and subsequent liquid-phase place exchange with a varied amount of C6SH. When x = 0-10, the Pd MPCs react strongly with H(2), leading to aggregated particles in solution and large irreversible changes in the morphology of films accompanied by an increase in film conductivity by 2-5 orders of magnitude. Pd(919)(C6S)(192) MPCs are stable against significant aggregation in solution and do not exhibit large film morphology changes, but they are also not highly reactive to H(2), as determined by minimal changes in the optical properties of solutions and the small, irreversible changes in the conductivity of films in the presence of H(2). Finally, when x is 32 and 81, the Pd MPCs are fairly stable, exhibit minimal aggregation or morphology changes, and readily react with H(2) based on the significant, reversible changes in film conductivity in the presence of H(2). Pd MPCs with mixed monolayers have the benefit of high H(2) reactivity while maintaining the structural stability necessary for sensing and catalysis applications.

A colorimetric CO sensor for fire detection

We report on a colorimetric carbon monoxide (CO) sensor based on a rhodium complex. The sensor relies on changes in the light absorption properties of the chemochromic reagent when exposed to the gas. Its optical properties in solution and in a polymeric matrix were investigated by spectrophotometry. A strong color change from purple to yellow was obtained when exposed to CO. For its implementation in a sensor configuration, the complex embedded in a PVC-based matrix was spin-coated onto a glass waveguide. The sensor was tested in a gas cell and with standardized test fires. It showed a high sensitivity to low concentrations of CO, a fast reaction time and complete reversibility. The device may find applications in the field of fire detection and indoor air quality monitoring.

Synthesis and Crystallochromy of 1,4,7,10‐Tetraalkyltetracenes: Tuning of Solid‐State Optical Properties of Tetracenes by Alkyl Side‐Chain Length

We synthesized a series of 1,4,7,10-tetraalkyltetracenes using a new 2,6-naphthodiyne precursor and 2,5-dialkylfurans as starting materials (alkyl=methyl to hexyl). Surprisingly, the solid-state color of the tetracenes ranges through yellow, orange, and red. Both yellow and red solids are obtained for the butyl derivative. Optical properties in solution show no marked differences; however, those in the solid state show characteristics that vary with alkyl side-chain length: methyl, propyl, and pentyl derivatives are orange; ethyl and butyl derivatives are yellow; and another butyl and hexyl derivative are red. X-ray analyses reveal that the molecular structures are planar, semi-chair, or chair forms; the chair form takes a herringbone-like arrangement and the other forms take slipped parallel arrangements. The mechanism of crystallochromy is discussed in terms of molecular structure, crystal packing, and calculations that take account of exciton coupling.

Fullerene Dimers (C60/C70) for Energy Harvesting

A new family of fullerene-based compounds, namely, soluble [60]- and [70]fullerene homodimers and the [60]/[70]heterodimer linked through 2-pyrazolino-pyrrolidino bridges, has been synthesised by simple procedures and in high yield. Electrochemical studies confirm their suitability to act as electron acceptors in combination with poly(3-hexylthiophene-2,5-diyl) (P3HT). Their optical properties in solution and in the solid state were studied. A significantly stronger absorption in [70]fullerene-containing dimers relative to [60]homodimer in solution in the visible range was observed. Furthermore, in all donor-acceptor blends studied an efficient charge transfer was observed by means of photoluminescence (PL), photoinduced absorption and light-induced electron spin resonance spectroscopy. The [70]homodimer was found to be a distinctive species, being the strongest PL quencher and most efficient acceptor with the longest lifetime of the charge-separated (polaron) states. As a consequence, bulk-heterojunction solar cells based on this novel [70]homodimer blended with P3HT demonstrated the highest quantum and power conversion efficiencies of 37 and 1 %, respectively, compared to those of [60]fullerene dimers.

Synthesis and Optical Nonlinearities of a 2-Amino-1,2,3-triazolquinone Derivative

We report on the synthesis and nonlinear optical characterization of a novel 2-amino-1,2,3-triazolquinone derivative, namely, 2-(yliminopropylphenyl-N,N′-dimethylamino)naphto-1,2,3-triazole-4,9-dione (ATZQ). The second-order nonlinear optical properties in solution were characterized using the hyper-Rayleigh scattering (HRS) technique, while the third-order nonlinearities of ATZQ-doped polymer films were measured through the use of the THG-Maker fringes technique. These experiments showed that this compound exhibits large second- and third-order nonlinear effects at the molecular level, with a first hyperpolarizability constant of β∼834 × 10−30 esu at 1064 nm and a second hyperpolarizability constant of γ∼3.5 × 10−33 esu at the telecommunication wavelength range of 1200–1700 nm.