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Time-resolved luminescence lifetime measurements are an important photophysical technique. However, access to this technique at the undergraduate level is limited by the expense of the instrumentat...

Terthiophene dyes were synthesized having a carboxylate or a phosphonate moiety at the 2-position which serves as an anchoring group to zinc oxide nanocrystals (ZnO NCs). Electronic absorption and fluorescence measurements, combined with reduction potentials, provided estimates of -1.81 and -1.86 V vs. NHE for the excited state reduction potential of the carboxylate and phosphonate, respectively. Static quenching was observed when the dyes were bound to the surface of acetate-capped ZnO NCs having a diameter of 2.8 nm. Stern-Volmer studies conducted at several dye concentrations established that a minor fraction of the adsorbed dye remained unquenched even at 1 : 1 dye to NC ratios. Adsorption isotherm measurements established that the phosphonate binds more strongly than the carboxylate and that saturation coverage was ∼1.2 dyes per nm2 for both dyes. Ultrafast transient absorption spectroscopic experiments were used to probe excited state dynamics. In the presence of ZnO NCs, disappearance of the singlet excited state of the dye corresponded to appearance of the spectroscopic signature of the oxidized dye with a time constant of 1.5 ± 0.1 and 6.1 ± 0.2 ps, respectively, for the carboxylate and phosphonate dye. The difference in the electron transfer rates was attributed to a larger electronic coupling for the dye having the carboxylate anchoring group.

A series of heteroleptic bipyridine ruthenium complexes were prepared using known synthetic methods. Each compound incorporated one electron withdrawing 4,4'-dicarboxylic acid-2,2'-bipyridine and two bipyridines each of which had electron donating dialkylamine substituents in the 4 and 4' positions. The electronic absorption spectra exhibited absorptions that moved to lower energy as the donor ability of the amine substituent increased. Density functional calculations established that the HOMO was delocalized over the metal and two pyridine groups located trans to the pyridines of the dicarboxylic acid bipyridine. The LUMO was delocalized over the dicarboxylic acid bipyridine. Cyclic voltammetry of the deprotonated compounds exhibit one quasi-reversible oxidation and three reductions. Coupled with the emission data, the excited state reduction potentials were estimated to range from -0.93 to -1.03 V vs. NHE. Monodispersed 3.2 nm diameter nanocrystals (NCs) of zinc oxide were found to quench partially the excited state of the dyes via a static quenching electron transfer process involving the formation of a dyad of the complex and the NC. The magnitude of the partial quenching of complexed dyes was correlated to the distribution of band gaps for the NCs, which is an inverse function of diameter. Dyes attached to the NCs on the small end of the particle size distribution had electron transfer rates that were uncompetitive with radiative and nonradiative decay mechanisms.

Oleate-capped CdS nanocrystals (NCs) dispersed in dichloromethane were found to quench the excited-state fluorescence of the terthiophene derivative 3′,4′-dibutyl-5″-phenyl-[2,2′:5′,2″-terthiophene]-5-carboxylic acid (1-CO2H). Infrared and 1H NMR spectroscopies provided evidence that 1-CO2H substitutes for oleate on the surface of the CdS NCs. Upon binding, the fluorescence of 1-CO2H is quenched, and the 1H NMR lines from 1-CO2H are broadened. The importance of the carboxylate group in binding to the CdS NC was further established by examining the behavior of a similar fluorophore where the carboxylic acid group was replaced with a bromo substituent (1-Br). The CdS NCs had no influence on the fluorescence intensity or NMR line shapes of 1-Br. For 1-CO2H, Stern–Volmer plots indicated a nearly linear increase in I0/I as the CdS NCs’ concentration was increased, but as the dye/NC ratio reached ∼20/1, I0/I reached a maximum of ∼8 and began to decrease. By a dye/NC ratio of 2/1, the I0/I reached a steady value...

The crystal structures of new red (1) and orange (2) polymorphs of chloro(2,2′:6′2″-terpyridine)-platinum(II) chloride dihydrate, [Pt(terpy)Cl]Cl·2H2O, have been determined by single crystal X-ray diffraction. Compound 1 packs in a one-dimensional stacking structure with two unique intermolecular Pt···Pt distances (3.3278(5) A, 3.4444(5) A). The principal difference between this red polymorph and a previously reported yellow polymorph is in the cation stacking motif. This red polymorph has two alternating short intermolecular Pt···Pt distances while the yellow polymorph has one long and one short Pt···Pt distance. Channels between the cation stacks are occupied by a hydrogen-bonding network of water molecules and chloride anions. This red polymorph has a cation stacking motif similar to those found in a diverse collection of structures with different counterions and solvates of the chloro(2,2′:6′2″-terpyridine)-platinum(II) cation. The orange polymorph 2 possesses a stacking motif with two alternating long intermolecular Pt···Pt distances (4.2169(4) A, 5.1582(4) A). The hydrogen-bonding network involving the chloride counterions and water molecules differs significantly from either the red or yellow polymorphs as well. Structure 1: monoclinic, P 21/c, a = 12.2630(14) A, b = 6.7459(8) A, c = 20.121(2) A, β = 105.018(2)°, V = 1,607.7(3) A3, Z = 4, R 1 = 0.0338, wR 2 = 0.0665. Structure 2: monoclinic, P 21/c, a = 8.0236(7) A, b = 12.9393(1) A, c = 15.847(2) A, β = 101.068(7)°, V = 1,614.6(3) A3, Z = 4, R 1 = 0.0181, wR 2 = 0.0377. The crystal structures of new red (1) and orange (2) polymorphs of chloro(2,2′:6′2″-terpyridine)-platinum(II) chloride dihydrate, [Pt(terpy)Cl]Cl·2H2O show that the red polymorph stacks with two unique intermolecular Pt···Pt distances (3.3278(5) A, 3.4444(5) A) while the orange polymorph has no intermolecular Pt···Pt contacts less than 4.2 A.

The crystal structures of a related series of isosteric compounds, namely tritylnitrile 1, tritylisonitrile 2, and a solid solution of tritylnitrile/tritylisonitrile 3 have been determined by single crystal X-ray diffraction. The bond lengths, angles, and intermolecular interactions do not deviate significantly from previously reported nitriles and isonitriles. These isosteric compounds pack in nonisomorphous but very similar structures. Subtle differences between the packing of 1 and 2 are detailed. The solid solution of tritylnitrile/tritylisonitrile 3 is isomorphous with the structure of tritylnitrile 1. This solid solution possesses substitutional disorder involving the nitrile and isonitrile groups (Z′ = 2, nitrile/isonitrile occupancy ratios 53.7/46.3 and 54.6/45.4). The structure of tritylisonitrile 2 possesses positional disorder over two sites (Z′ = 2, occupancy ratio of 93.1/6.9). A comparison with previously reported nearly isosteric structures reveals that other chemically dissimilar compounds crystallize in each of the two molecular packing arrangements described in this report. Structure 1: monoclinic, P21/c, a = 18.049(11) A, b = 9.583(6) A, c = 17.824(11) A, β = 108.680(10)°, V = 2921(3) A3, Z = 8, R 1 = 0.0467, wR 2 = 0.1491. Structure 2: triclinic, P $$ \overline{1} $$ , a = 9.5877(13) A, b = 10.7479(14) A, c = 14.809(2) A, α = 88.457(2)°, β = 80.303(2)°, γ = 77.128(2)°, V = 1466.4(3) A3, Z = 4, R 1 = 0.0423, wR 2 = 0.1151. Structure 3: monoclinic, P21/c, a = 18.03464(15) A, b = 9.5739(8) A, c = 17.8251(11) A, β = 108.5920(10)°, V = 2917.4(4) A3, Z = 8, R 1 = 0.0587, wR 2 = 0.1734. The crystal structures of the isosteric pair tritylnitrile 1 and tritylisonitrile 2 are nonisomorphous while the structure of a solid solution of tritylnitrile/tritylisonitrile 3 is isomorphous with the structure of tritylnitrile 1.

We report crystalline mixed-ligand copper complexes with phenanthroline and isocyanides with almost millesecond emission lifetimes that are efficient dioxygen sensors. The oxygen sensitivity of the prototype ([Cu(CN-xylyl)(2)(dmp)]tfpb, dmp = 2,9-dimethyl-1,10-phenanthroline; CN-xylyl = 2,6-dimethylphenylisocyanide; tfpb = tetrakis(bis-3,5-trifluoromethylphenylborate) is 38 times better than that of [Ru(phen)(3)]tfpb(2) (phen = 1,10-phenanthroline).

Photophysical data for solution phase mixtures of a new terthiophene based organic dye, 3′,4′-dibutyl-2-phenyl-2,2′:5′,2′′-terthiophene-5′′-carboxylic acid, and size selected, well-dispersed zinc oxide nanocrystals are reported. Time-resolved fluorescence and time- and frequency-resolved pump−probe spectroscopy confirm and characterize electron injection from the dye to the semiconductor nanocrystals (NCs) in room temperature ethanol dispersions at a series of dye:ZnO NC concentration ratios. The spectrum of the oxidized dye was determined by spectroelectrochemistry. The singlet excited state of the dye (190 ps lifetime in ethanol) is quenched almost exclusively by electron transfer to the ZnO NC, and the electron transfer dynamics exhibit a single time scale of 3.5 ± 0.5 ps at all concentration ratios. In the measured transient responses at different dye:ZnO NC ratios, gain in the amplitude of the electron injection component is anticorrelated with loss of amplitude from unperturbed excited state dye mol...

The synthesis of 3′,4′-dibutyl-2-phenyl-2,2′:5′,2′′-terthiophene-5′′-carboxylic acid and its behavior with monodispersed ZnO having diameters from 2.7 to 3.2 nm are reported. The excited state of the dye (E0* = −1.61 V vs NHE) was quenched upon binding to ZnO nanocrystals. Adsorption isotherms were measured for the terthiophene dye in ethanol and fit with a Langmuir model, which gave a size-independent Kads of 2.3 ± 1.0 × 105 M−1. The maximum number of attached dyes per nanocrystal depended on the diameter and was consistent with each dye occupying 0.5 ± 0.1 nm2 at maximum coverage. Deviation from the Langmuir model observed at low dye concentrations was attributed to a small amount of free zinc ion present in solution that binds the carboxylate ions more strongly than do ZnO nanocrystals. Incorporation of the equilibrium expression between zinc ion and free carboxylate into the model provided a satisfactory fit for both the adsorption isotherm experiments and the complex shape of the Stern−Volmer graphs....

New direct syntheses of [Pt(trpy)(NCCH3)](CF3SO3)2 2 (where trpy = 2,2′:6′,2′′-terpyridine) and [Pt(tBu3-trpy)(NCCH3)](CF3SO3)2 3 (where tBu3-trpy = 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine) via the displacement of acetonitrile from [Pt(NCCH3)4](CF3SO3)2 have been developed. The synthetic utility of 2 was investigated in reactions with triphenylphosphine (PPh3), 2,6-dimethylphenyl isocyanide (CN-Xyl), 2,5-dimethyl-2,5-diisocyanohexane (TM4), and tert-butyl isocyanide (CN-tBu). Whereas the expected substitution products were observed for reactions with PPh3, CN-Xyl, and CN-tBu, dealkylation of TM4 occurred to afford [Pt(trpy)(CN)](CF3SO3) 6. The structures of [Pt(trpy)L]2+ dications show little intermolecular interactions in the solid state, with the exception of the tBu3-trpy complex 3 which exists as head-to-tail dimers with a Pt–Pt distance of 3.29 A. The cyano product 6 was found to stack in infinite chains of cations with a Pt–Pt distance of 3.45 A.

The double salt materials platinum(II)tetrakis-R-β-methylphenethylisocyanide tetracyanoplatinate(II) ( R-1 ) and platinum(II)tetrakis-S-β-methylphenethylisocyanide tetracyanoplatinate(II) ( S-1 ) have been synthesized with highly enantiomerically pure isocyanide ligands. The vapochromic behavior of R-1 and S-1 has been studied in the presence of a chiral probe vapor to determine if enantiomerically selective sensing is possible with these materials. The wavelength of maximum emission values ( λ max ) for solid-state vapoluminescence spectra of R-1 and S-1 in the presence of enriched R- and S-2-butanol vapor differ by approximately 10 nm while the λ max values for R-1 and S-1 under nitrogen are nearly identical. Principal component analysis has been performed on datasets that consist of a series of vapoluminescence spectra of R-1 and S-1 as a function of the R/S-2-butanol ratio. Plots of principal component one versus R/S-2-butanol ratio show mirror image trends for R-1 relative to S-1 . While care must be taken to control water vapor and monitor R-1 and S-1 for possible decomposition, the reported results nevertheless show that R-1 and S-1 are capable of enantiomerically selective vapochromic sensing.

We have shown that crystals of a number of emissive copper compounds of the form [Cu(NN)2]X (X = BF4−, tfpb−) (where NN = 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (dmp), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bdmp), 2,9-diisopropyl-1,10-phenanthroline (dipp), 2,9-ditert-butyl-1,10-phenanthroline (dbp); tfpb− = tetrakis(bis-3,5-trifluoromethylphenylborate) are oxygen sensors, if they contain void space. All of the tfpb− salts were found to be oxygen sensors reinforcing the idea that bulky counterions can produce void space and obviate the need for a support material in solid-state photoluminescent oxygen sensors. The reponse time for the X = tfpb− and NN = dipp complex was measured to be fast (280 ms (95% of final value)). The first solid-state quantum yields and lifetimes are reported for the [Cu(NN)2]X systems and are found to be approximately 10 times larger than those observed in solution-state measurements. The linear Stern−Volmer plots with highly reproducible Ksv constant...

Photophysical data for a series of end substitued 3',4'-dibutyl-2,2':5',2''-terthiophenes are reported. Static absorption and fluorescence, quantum yields, time-resolved fluorescence, and time- and frequency-resolved pump-probe spectra are applied to investigate excited state relaxation in bromo, nitro, and tricyanovinyl substituted species in a variety of solvents. The effect of solvent polarizability and end-group substitution is discussed in the context of charge transfer in the excited state and its impact on nonradiative decay rates. In solution at room temperature, both symmetric and asymmetric addition of electron withdrawing end groups generate an excited state with substantial charge transfer character. Solvent polarizability has a significant influence on the excited state dynamics in the charge transfer compounds. Examples include a 20-fold reduction in the intersystem crossing rate going from hexane to toluene and an order of magnitude increase in the internal conversion rate between toluene and acetone. The results demonstrate that the impact of the substituents on intramolecular charge transfer, and the resulting amplification of the interactions between the excited state(s) and the local molecular environment, can dramatically change the excited state relaxation dynamics in substituted terthiophenes.

cis-Bis(isopropyl isocyanide)dicyanoplatinum(II), PtII(CN-i-C3H7)2(CN)2, has been synthesized, and its solid-state characteristics have been investigated. X-ray crystallographic data show that PtII...

Carbon dioxide gas sensors have been fabricated by self-assembling single-wall nanotube films on a surface acoustic wave delay line operating at 286 MHz. Polymer functionalization was used to enhance the sensitivity of the carbon nanotubes to carbon dioxide. A pulse radar-type interrogation system was used to monitor the conductivity of the nanotube film by measuring the attenuation of the surface acoustic wave due to film-conductivity changes. The conductivity of the film was found to decrease with carbon dioxide concentration. The effect of varying the sheet conductivity of the nanotube film was examined. Both analytical and experimental results show that controlling the conductivity of the CNT film within a specific range highly enhances the sensitivity to carbon dioxide. Experimental results show that the sensor tracks carbon dioxide concentration changes between 0% and 10%. The final sensor is sensitive, small and wirelessly interrogable, thus making it potentially useful for respiratory monitoring.

We report the synthesis and characterization of trans-Pt(p-CN−C6H4−C2H5)2(CN)2 and compare the properties to the previously reported cis isomer, cis-Pt(p-CN−C6H4−C2H5)2(CN)2. These geometric isomer...

Oligothiophene sulfones of up to six rings can be conveniently prepared by the direct oxidation of butyl-substituted thiophene oligomers with m-CPBA in dichloromethane. Reverse selectivity of oxidized rings is observed relative to previously reported systems without beta-substitution. The selectivity in the trimer and hexamer is confirmed with single-crystal X-ray structure data. The sulfones possess red-shifted absorptions and increased electron affinities relative to the parent oligomers.

A convenient synthetic scheme was developed to access a series of square-planar Pt(II) complexes of the form (TBA)[Pt(CN)3(CNR)] (TBA = tetra-n-butyl ammonium cation, R = CH3, c-C6H11, p-(C2H5)-C6H4). These heteroleptic complexes were characterized by combustion analyses, single-crystal X-ray structure determinations, HRFAB-MS, (1)H NMR, ATR-IR, solution UV-Vis, and solid-state emission spectroscopies. Surprisingly, each of these complexes exhibit low energy room temperature solid-state luminescence in the absence of intermolecular Pt-Pt interactions. Additionally, the polymorphic behavior of (TBA)[Pt(CN)3(CN-c-C6H11)] was elucidated through a combination of single-crystal X-ray structure determinations, X-ray powder diffraction, and mass uptake experiments. Vapoluminescence and polymorphic transformations of (TBA)[Pt(CN)3(CN-c-C6H11)] were concomitant with water vapor absorption. A new double-salt complex [Pt(terpy)Cl] [Pt(CN)3(CNCH3)] (terpy = 2,2',6',2''-terpyridine) was also synthesized and characterized by combustion analysis, ATR-IR, HRFAB-MS, and solid-state UV-Vis and emission spectroscopies. The vapoluminescent properties of this salt in response to water were examined by mass uptake experiments, ATR-IR, and solid-state emission spectroscopy. A principal component analysis (PCA) of the solid-state emission changes induced by water vapor confirmed the presence of an intermediate emissive species.

We report the structural and electrical characterization of thin films of organic semiconductor molecules consisting of an oligothiophene core capped with electron-withdrawing tricyanovinyl (TCV) groups. X-ray diffraction and atomic force microscopy of evaporated films of three different TCV-capped oligothiophenes showed that the films were highly crystalline. Electrical transport was measured in thin film transistors employing silver source and drain contacts and channel probes to correct for contact resistance. Three compounds exhibited n-channel (electron) conduction consistent with cyclic voltametry data that indicated they undergo facile reduction. Maximum electron mobilities were 0.02 cm2/V.s with an on/off current ratio of 10(6). A fourth end-capped molecule, TCV-6T-TCV, which had six thiophene rings, exhibited both p- and n-channel transport. Overall, these results confirm that substitution of oligothiophene cores with electron-withdrawing groups is a useful strategy to achieve electron-transporting materials.

A new tricyanovinyl-substituted quaterthiophene compound has been synthesized and characterized by X-ray crystallography, cyclic voltammetry, spectroelectrochemistry, and theoretical analysis. The tricyanovinyl group provides a dramatic change in the physical properties of the quaterthiophene. The molecule has been tested as the semiconducting layer in an n-type thin-film transistor. The device properties correlate well with the solid-state packing, spectroelectrochemical results, and theoretical modeling.

We report structural and electrical transport properties of a family of π-stacking soluble organic semiconductors, N,N‘-dialkyl-3,4,9,10-perylene tetracarboxylic diimides (alkyl − pentyl [1], octyl [2], and dodecyl [3]). The structures of evaporated polycrystalline films of 1−3 were studied using X-ray diffraction and atomic force microscopy. Films of 1−3 pack similarly with the direction of π−π overlap in the substrate plane. Organic thin film transistors (OTFTs) based on 1−3 deposited on SiO2 gate dielectric showed linear regime electron mobilities of 0.1, 0.6, and 0.2 cm2/(V s), respectively, corrected for contact resistance. OTFTs of 2 had saturation electron mobilities as high as 1.7 cm2/(V s) with on-to-off current ratios of 107. Variable temperature measurements were used to examine the charge transport kinetics in the range 80−300 K and revealed (1) thermally activated electron mobilities with activation energies dependent on gate voltage and (2) the presence of well-defined isokinetic points, i.e...

A series of new quinodimethane-substituted terthiophene and quaterthiophene oligomers has been investigated for comparison with a previously studied quinoid oligothiophene that has demonstrated high mobilities and ambipolar transport behavior in thin-film transistor devices. Each new quinoidal thiophene derivative shows a reversible one-electron oxidation between 0.85 and 1.32 V, a quasi-reversible one-electron second oxidation between 1.37 and 1.96 V, and a reversible two-electron reduction between -0.05 and -0.23 V. The solution UV-vis-NIR spectrum of each compound is dominated by an intense (epsilon congruent with 100 000 M(-1) cm(-1)) low energy pi-pi transition that has a lambda(max) ranging between 648 and 790 nm. All X-ray crystal structures exhibit very planar quinoidal backbones and short intermolecular pi-stacking distances (3.335-3.492 A). Structures exhibit a single pi-stacking distance with parallel cofacial stacking (sulfur atoms of equivalent rings pointed in the same direction) or with alternating distances and antiparallel cofacial stacking (sulfur atoms of equivalent rings pointed in the opposite direction). Examples of the layered and herringbone-packing motifs are observed for both the parallel and the antiparallel cofacial stacking. Analysis of the X-ray structures and molecular orbital calculations indicates that all of these compounds have one-dimensional electronic band structures as a result of the pi-stacking. For structures with a unique pi-stacking distance, a simple geometric overlap parameter calculated from the shape of the molecule and the slip from perfect registry in the pi-stack correlates well with the transfer integrals (t) calculated using molecular orbital theory. The calculated valence (633 meV) and conduction (834 meV) bandwidths for a quinoid quaterthiophene structure are similar to those calculated for the benchmark pentacene and indicate that both hole and electron mobilities could be significant.

The development of new organic semiconductors with improved performance in organic thin film transistors (OTFTs) is a major challenge for materials chemists. There is a particular need to develop air-stable n-channel (electron-conducting) organic semiconductors with performance comparable to that of p-channel (hole-conducting) materials, for organic electronics to realize the benefits of complementary circuit design, i.e., the ability to switch transistors with either positive or negative gate voltages. There have been significant advancements in the past five years. In terms of standard OTFT metrics such as the field effect mobility (μFET) and on-to-off current ratio (ION/IOFF), n-channel OTFTs have achieved performance comparable both to that of n-channel amorphous silicon TFTs and to that of the best reported p-channel (hole-conducting) OTFTs; however, issues of device stability linger. This review provides a detailed introduction to OTFTs, summarizes recent progress in the development of new n-channel...

A new synthesis of RuII(bpy)(sal)2 (1) (bpy=2,2′-bipyridyl, sal=salicylaldehyde) has been developed and the separation and characterization of all three geometric isomers have been completed. The isomers are denoted 1a (phenolic oxygens trans), 1b, (aldehyde oxygens trans), and 1c (aldehyde oxygen trans to phenolic oxygen). All three isomers have been characterized by 1H NMR, high resolution FAB-MS, UV–Vis, and cyclic voltammetry. Additionally, 1a has been characterized by solid-state UV–Vis and a single-crystal X-ray structural study. The solid-state packing of the RuII(bpy)(sal)2 molecules in the structure of 1a displays intermolecular π–π interactions between bpy ligands of adjacent molecules. The bpy interactions form infinite π-stacks with alternating short stacking distances of 3.437 and 3.402 A.

A series of radial thiophene-based structures consisting of a central benzene or thiophene ring surrounded by acetylene-bridged terthienyl arms has been investigated by physical and theoretical methods. Fourier transform Raman spectroscopy of the neutral solids shows that the terthiophene arms are weakly coupled across the core (benzene plus acetylene groups) likely due to cross-conjugation or meta-conjugation effects that may prevent full delocalization. By increasing the number of arms around the central ring, the electronic structure of the molecules seems to be affected only at the core, whereas the outer terthiophene arms remain almost unaltered. Raman spectroelectrochemistry and quantum chemical calculations provide further insight into the charge delocalization of the oxidized species. There is no evidence to suggest that these oxidized forms, obtained upon electrochemical doping of the molecules, show charge delocalization across the core.

A series of quaternized poly(2-vinylpyridine) (PVP) polymers has been synthesized with the general formula [(PVP) R ]I, where R =H, Me, Bu. Addition of AgI to the polymers results in new silver ion conducting solid polymer materials. Conductivities as high as 6×10 −3 S/cm have been observed for the 3:1 AgI/[(PVP)Me]I composition. Analogous materials with a 3:1 composition for the protonated and butyl-substituted polymers display lower conductivities near 2×10 −4 S/cm. Conductivity studies, as a function of temperature, show these materials to be thermodynamically stable with a low activation energy for ion conduction. Differential scanning calorimetry experiments suggest that a new phase with the general formula (PVP) R Ag 3 I 4 forms with silver ions in a new amorphous state.

The vapoluminescent characteristics of platinum(II) double salt materials in the presence of varying levels of relative humidity (RH) have been investigated. Luminescence spectra for three different platinum(II) double salt materials showed that the intensity and the wavelength maximum depend on the concentration of water vapor surrounding the material. Partial least squares (PLS) analysis of the data demonstrated that two of the double salts responded linearly to changes in RH. A single-channel dip probe sensor was constructed and used to evaluate changes in RH. Different methods for attaching the platinum(II) double salt material to the dip probe were also investigated. Simple adsorption of the material onto the probe produced a sensor with superior performance compared to a Teflon AF support matrix. The PLS analysis of simultaneous three-channel cross-reactive sensor array data from three different platinum(II) double salt materials yielded a much more reproducible RH sensor. In addition, the three-channel cross-reactive array produced a more linear PLS model compared to a single-channel sensor composed of a simulated mixture of the same three platinum(II) double salt materials.

A quinoid-type oligothiophene, 3 0 ,4 0 -dibutyl-5,5 00 -bis(dicyanomethylene)-5,5 00 -dihidro-2,2 0 :5 0 ,2 00 -terthiophene, which can be viewed as an analog of TCNQ, has been investigated by spectroelectrochemistry and density functional theory calculations, in its neutral and dianionic states. Electrochemical data show that the molecule can be both reduced and oxidized at relatively low potentials. Upon reduction, both experiments and theory agree well with the generation of a dianionic charged species. The model shows that the electronic structure of the dianion is consistent with two anionic dicyanomethylene groups attached to a central terthienyl spine having an aromatic structure. The two negatively charged dicyanomethylene groups conjugate with the terthiophene allowing for the extension of the p-delocalized system over the whole molecule. The stability of the dianionic species, due to its aromatic character, gives support to the low value for the electrochemical two-electron reduction process. Infrared spectra of the neutral and of the dianion species have been assigned and correlated. q 2003 Elsevier Science B.V. All rights reserved.

[structure: see text] A series of thiophene-based homologues with an aromatic core surrounded by terthiophene "arms" with acetylene linkages has been synthesized by using Sonogashira coupling methods. The homologues were investigated spectroscopically in solution and in the solid state. They display extended pi-conjugation through the aromatic core that affects the strong emission and redox properties.

Two new oligothiophenes, the dinitro compound 3',4'-dibutyl-5,5' '-dinitro-2,2':5',2' '-terthiophene (1) and the quinodimethane 3',4'-dibutyl-5,5' '-bis(dicyanomethylene)-5,5' '-dihydro-2,2':5',2' '-terthiophene (2), have been synthesized and studied with electrochemistry, UV-vis-NIR-IR spectroscopy, ESR, and X-ray crystallography. These compounds, designed to be both electron and hole carriers, show redox properties that are unusual for oligothiophenes. Cyclic voltammetry and spectroelectrochemistry demonstrated that each compound could be oxidized to a cation radical and reduced to an anion radical and dianion. The spectra of 2 and its three redox partners were analyzed in terms of a limiting structure in which the neutral 2 has orbitals corresponding to those of a substituted-terthiophene dication. Compound 1 crystallizes with the thiophene rings held in an unusual nonplanar, cisoid configuration in face-to-face pi-stacks, with a spacing between molecules of 3.65 A. The C-C bond lengths of the outer nitro-substituted rings have quinoid character. Compound 2 crystallizes with the thiophene rings in a planar, transoid configuration. The molecules are held in pi-stacks formed from pi-dimers with a spacing between molecules of 3.47 and 3.63 A. The C-C bond distances of the thiophene rings of 1 and 2 and other oligomers were analyzed by a principal component analysis. The analysis found that 93% of the structural variance resided in one principal component related to the quinoid structure of the oligothiophene moiety. The analysis reliably demonstrated a quinoid contribution to the structure of 1. This method should be applicable to understanding the structure of other conjugated molecules in which quinoid structures contribute.

The reaction of the [Ru(bpy)(NO(2))(4)](2-) (bpy = 2,2'-bipyridine) ion in aqueous solutions produces two different nitrosyl complexes, depending on the pH of the solution. At acidic pH, complex cis,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) was isolated. At neutral or basic pH, [Ru(bpy)(NO(2))(4)](2-) reacts to give cis,trans-Ru(bpy)(NO(2))(2)(NO)(OH). Both new complexes were fully characterized by elemental analysis and UV-vis, IR, (1)H NMR, and (15)N NMR spectroscopy. A single-crystal X-ray structure of cis,trans-Ru(bpy)(NO(2))(2)(NO)(OH) was also obtained. cis,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) isomerizes in acetone or water solution to give a mixture of the trans,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) and cis,cis-Ru(bpy)(ONO)(2)(NO(2))(NO) linkage isomers as determined by (1)H and (15)N NMR spectroscopy. A single-crystal X-ray structure of a solid solution of cis,cis-Ru(bpy)(ONO)(2)(NO(2))(NO)/trans,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) was also obtained. This pair of isomers is the first crystallographically characterized compound with nitro, nitrito, and nitrosyl ligands. The kinetic studies of the Ru-NO(2) --Ru-NO conversion reactions of [Ru(bpy)(NO(2))(4)](2)(-) in buffered solutions from pH 3 to pH 9 complement previous studies of the reverse reaction. The reactions are first order in [Ru(bpy)(NO(2))(4)](2-). At high pH, the reaction is independent of the concentration of H(+) while, at low pH, the reaction is first order in the concentration of H(+). The rate determining step of the high pH reaction involves breakage of the Ru-NO(2) bond while, at low pH, the mechanism involves a rapid reversible protonation of a NO(2) ligand followed by the rate determining loss of hydroxide to produce a nitrosyl ligand.

A three-channel cross-reactive sensor array based on vapoluminescent platinum(II) double salt materials has been characterized. Two arrays were studied, one consisting of [Pt(CN-cyclododecyl)4][Pt(CN)4] (1), [(phen)Pt(CN-cyclohexyl)2][Pt(CN)4] (2), and [Pt(CN-n-tetradecyl)4][Pt-(CN)4] (3) materials, where phen = 1,10-phenanthroline, and a second array that has compound 3 replaced by the mixed double salt material [(phen)Pt(CN-cyclododecyl)Cl)]2[(phen)Pt(CN-cyclododecyl)2]2[Pt(CN)4]3 (4). Compounds 2, 3 and 4 are characterized here for the first time. Inclusion of solvent vapors into these materials often leads to dramatic shifts in their solid-state absorption and luminescence spectra. In these studies the arrays were exposed to a set of 10 test solvent vapors to determine the ability of each cross-reactive array to give reproducible vapoluminescent spectra characteristic of each solvent vapor. It was discovered that temperature programming between solvent vapor exposures greatly improved the reproducibility of the luminescence spectra obtained. A statistical analysis of three-dimensional resolution factors between pairs of solvent clusters in principal component space supported this assertion. The success of the temperature programming protocol was limited by the thermal stability and the sensitivity to low background water vapor levels of some platinum(II) double salt materials. The ability of the cross-reactive sensor array to differentiate between two different solvent vapors over a large concentration range was also investigated. Acetone and methanol were found to occupy two distinct regions of the three-dimensional principal component space. Detection limits for acetone and methanol were estimated from the principal component analysis as 75 and 6 g/m3, respectively.

The electronic and the Fourier transform Raman (FT-Raman) spectra of a novel well−barrier−well vinylene-bridged sexithiophene in neutral and in doped states have been recorded. The samples were oxidized chemically, with trifluoroacetic acid or ferric chloride, and electrochemically in dichloromethane solutions. The evolution of the Raman spectral pattern upon oxidation at different anodic potentials has been analyzed for a thin solid film of the material. Experimental observations are explained by the initial generation of a radical cation species followed by the generation of a dication species. A comprehensive assignment of the electronic and Raman spectroscopic features observed in both neutral and oxidized states has been performed on the basis of density functional theory (DFT) calculations. Time-dependent DFT calculations have been performed to calculate the electronic excitation energies. The experimental data and theoretical results give a clear picture of the structure and electronic properties o...

The infrared absorption and Raman scattering spectra recorded during the electrochemical oxidation of two sexithiophenes are reported. Using in situ spectroelectrochemical methods five oxidation states, neutral, radical cation, dication, radical trication, and tetracation of an α,α‘-diphenyl sexithiophene, were studied. The experimental spectra are in agreement with the predictions of the effective conjugation coordinate theory and are in good accordance with theoretical density functional theory calculations.

We report the synthesis and characterization of a new vapochromic platinum compound, [Pt(CN−cyclododecyl)4][Pt(CN)4]. This compound is stable to 120 °C and reversibly sorbs three water molecules per formula unit at room temperature when it is exposed to 100% relative humidity. Dramatic changes in absorption and emission spectra are observed in response to water uptake. The vapor response characteristics of this material were further investigated by simultaneous optical reflectance and quartz crystal microbalance (QCM) measurements, using water as the test vapor. The sensing film on the QCM consisted of a mixture of the solid vapochromic powder dispersed in a hydrophobic vapor permeable polymer. The polymer was incorporated as a binder to adhere the sensing material to the QCM surface. Reflectance measurements were taken from the film on the QCM surface using a bifurcated fiber optic bundle incorporated into the flow cell. The vapor sorption characteristics of the vapochromic compound as determined by the ...

A series of half- and mixed-sandwich (Cp⧧ = 1-trifluoromethyl-2,3,4,5-tetramethylcyclopentadienide) ruthenium compounds have been synthesized from a new Cp⧧Ru synthon, [Cp⧧Ru(NCCH3)3](PF6). [Cp⧧Ru(NCCH3)3](PF6) is efficiently generated by photolysis of [Cp⧧RuBz](PF6) in acetonitrile with a quantum yield of approximately 0.34. The methods described here should be useful for the synthesis of other compounds that contain the Cp⧧Ru group.

Using a modification of a recently reported convenient synthesis of the isobutyl ester form of the bis(isothiocyanato) ruthenium dye (N3), we report the isolation and spectroscopic characterization of the minor isomer in which one NCS− is N-bound and the other is S-bound. The synthesis involves the reaction of Ru(iBu2dcbpy)2Cl2, where iBu2dcbpy is the diisobutyl ester of 4,4′-dicarboxy-2,2′-bipyridine, with a source of thiocyanate. The impact of the isocyanate salt, solvent, and temperature on the yield of the linkage isomers is presented. In addition to the two linkage isomers 1 and 2, the partially substituted chloroisothiocyanato complex 3, Ru(iBu2dcbpy)2Cl(NCS), was also isolated. Selective removal of the chloride using silver triflate provided a path to [Ru(iBu2dcbpy)2(pyridine)(NCS)]OTf, 4, in high yield. The complexes were characterized by 1H and 13C NMR, IR, and electronic absorption spectroscopies and mass spectrometry. At 80 °C in DMSO-d6, the isomerization of 2 to 1 is complete and exhibits first-order kinetics with a rate constant of 0.00014 s−1. Room temperature hydrolysis of the isobutyl ester groups of 2 using [nBu4 N]OH in acetonitrile produced a mixture of the two linkage isomers.

We report a convenient synthesis of K(2)[Ru(bpy)(NO(2))(4)] via the thermal displacement of benzene from [(Bz)Ru(bpy)Cl]Cl (Bz = eta(6)-C(6)H(6); bpy = 2,2'-bipyridine) by nitrite ion in methanol solution. K(2)[Ru(bpy)(NO(2))(4)] has been fully characterized by elemental analysis, X-ray crystallography, and (1)H NMR, IR, UV-vis, and emission spectroscopy. Reaction of K(2)[Ru(bpy)(NO(2))(4)] with pyridine under mild or forcing conditions produces fac-K[Ru(bpy)(NO(2))(3)(py)] and cis-[Ru(NO(2))(2)(bpy)(py)(2)] (py = pyridine), respectively. We report full characterization data for these compounds, including crystal structures. The d pi(Ru) --pi*(bpy) charge-transfer band in the electronic spectra of K(2)[Ru(bpy)(NO(2))(4)] and fac-[Ru(bpy)(NO(2))(3)(py)] displays a significant solvent dependence. The energy of the absorption band correlates linearly with the Gutmann solvent acceptor number. The solvatochromic response of these nitro complexes is essentially identical to that of the analogous cyanide complexes, indicating that the mechanism previously proposed to explain the solvatochromism of the cyanide complexes may need to be reexamined.

A convenient synthesis of tris-heteroleptic polypyridyl [Ru(pp)(pp‘)(pp‘ ‘)]2+ complexes is reported (where pp, pp‘, and pp‘ ‘ represent three different polypyridyl ligands). Photolysis of [BzRu(pp)Cl]Cl (Bz = η6-C6H6) gives a mixture of Ru(pp)(CH3CN)2Cl2 and [Ru(pp)(CH3CN)3Cl]Cl. Refluxing this mixture with pp‘ yields Ru(pp)(pp‘)Cl2. Finally, refluxing Ru(pp)(pp‘)Cl2 with pp‘ ‘ in a 75% ethanol/water solution gives [Ru(pp)(pp‘)(pp‘ ‘)]2+. No ligand scrambling is observed. The complexes are characterized by 1H NMR, elemental analysis, FAB-MB, UV−vis and emission spectroscopy, and cyclic voltammetry.

The first structure report of trichlorido[4'-(p-tolyl)-2,2':6',2''-terpyridine]iridium(III) dimethyl sulfoxide solvate, [IrCl(3)(C(22)H(17)N(3))] x C(2)H(6)OS, (I), is presented, along with a higher-symmetry setting of previously reported bis[4'-(p-tolyl)-2,2':6',2''-terpyridine]iridium(III) tris(hexafluoridophosphate) acetonitrile disolvate, [Ir(C(22)H(17)N(3))(2)](PF(6))(3) x 2 C(2)H(3)N, (II) [Yoshikawa, Yamabe, Kanehisa, Kai, Takashima & Tsukahara (2007). Eur. J. Inorg. Chem. pp. 1911-1919]. For (I), the data were collected with synchrotron radiation and the dimethyl sulfoxide solvent molecule is disordered over three positions, one of which is an inversion center. The previously reported structure of (II) is presented in the more appropriate C2/c space group. The iridium complex and one PF(6)(-) anion lie on twofold axes in this structure, making half of the molecule unique.

We have prepared a new salt of the solvatochromic [Ru(bpy)(CN)4]2- anion bis(triphenylphosphine)iminium 2,2‘-bipyridyltetracyanoruthenate, ((PPN)2[Ru(bpy)(CN)4]), that reversibly sorbs water and changes color from purple to yellow when it is exposed to humid air. Solid samples of anhydrous (PPN)2[Ru(bpy)(CN)4] reversibly hydrate in humid air, first to (PPN)2[Ru(bpy)(CN)4]·H2O and then to (PPN)2[Ru(bpy)(CN)4]·15H2O. A single-crystal X-ray study of (PPN)2[Ru(bpy)(CN)4]·2CH3CN·2(CH3CH2)2O·2H2O shows that this novel humidity sensor has large channels in the structure that allows sorbed water molecules to reversibly interact with the cyanide ligands of the chromophore. The hydration changes that result from exposure of the solid in the 0 to 66% relative humidity range cause the MLCT visible absorption bands to shift dramatically to higher energy. These hydration changes also result in large shifts in the ν(CN) region of the infrared spectrum; these changes indicate significant H-bonding interactions between so...

We have developed an isolated flow MAS NMR probe to enable simultaneous observation of events occurring on a catalytic surface with characterization of the effluent gas using an external analytical instrument. The probe design is unique in that it uses ceramic ball bearings to support the rotor. The spinning and spectroscopic capabilities of the probe were proven by obtaining a 13 C CP/MAS NMR spectrum of hexamethylbenzene at MAS rates of 2 kHz. The flow capabilities of the probe were demonstrated by observing methanol adsorption onto zeolite HZSM-5 and by studying conformational changes of a vapochromic sensor material when it was exposed to volatile organic compounds. The variable-temperature capabilities were shown by monitoring the change in the 207 Pb chemical shift of Pb(NO 3 ) 2 as a function of temperature. Temperatures >300°C were achieved for the probe. The reaction of methanol to dimethyl ether on zeolite HZSM-5 was used to demonstrate the ability of the probe to study heterogeneous catalysis reactions in situ. The observed products varied depending on whether flow vs. batch conditions were used. Under flow conditions only dimethyl ether was observed. In previous studies under sealed (i.e. batch) conditions, an equilibrium was observed between methanol and dimethyl ether.

We have synthesized [Pt(CN-iso-C3H7)4][M(CN)4] (M = Pt, Pd) and studied their reversible hydration and sorption properties with UV−vis, FT-IR spectroscopy, and X-ray diffraction. Powder diffraction studies show that anhydrous [Pt(CN-iso-C3H7)4][Pt(CN)4] and [Pt(CN-iso-C3H7)4][Pd(CN)4] crystallize in a tetragonal space group with nearly identical lattice constants. Gravimetric studies reveal that variable guest−host stoichiometries occur when solid [Pt(CN-iso-C3H7)4][Pt(CN)4] sorbs the guest at room temperature from the gas phase [water, 12.1(1) molecules per formula unit, chloroform 6.0(1), methanol 8.0(1), and trifluoroethanol 4.1(1)]; these sorption processes are reversible. The unit cell distances in the tetragonal ab-plane expand dramatically when the solvent guests are sorbed, but changes along the c-axis (the M−M direction) are minimal. Crystallization of [Pt(CN-iso-C3H7)4][Pt(CN)4] from water gives monoclinic crystals of a hexadecahydrate [Pt(CN-iso-C3H7)4][Pt(CN)4]·16H2O. This salt consists of alt...

We have studied the sorption of volatile organic compounds (VOCs) by [(n-C4H9)4N]2[Pt(CN)4] and [Pt(p-CN-C6H4-C10H21)4][Pt(CN)4] with FTIR spectroscopy. The data indicate a strong correlation exist...