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We demonstrate the application of a commercially available widely tunable continuous-wave external cavity quantum cascade laser as a spectroscopic source for the simultaneous detection of multiple gases. We measured broad absorption features of benzene and toluene between 1012 and 1063 [cm.sup.-1] (9.88 and 9.41 [micro]m) at atmospheric pressure using an astigmatic Herriott multipass cell. Our results show experimental detection limits of 0.26 and 0.41 ppm for benzene and toluene, respectively, with a 100 m path length for these two gases. [c] 2010 Optical Society of America OCIS codes: 140.5965, 280.0280, 300.6260, 300.6340.

Br fragment in photodissociation of o-, m-, and p-bromofluorobenzene at 266 nm is investigated using velocity imaging technique combined with (2!) resonance-enhanced multiphoton ionization (REMPI). The obtained translational energy distributions suggest that the Br fragments are generated through two dissociation channels.

The synthesis and characterization of a new class of highly fluorescent and stable carbazole-based dendrimers that contain the ethynylbenzene and diethynylbenzene cores are presented. The results have indicated the dendrimers potential use as blue-emitting materials in organic light-emitting diodes (OLEDs).

The composition of AMP and concentrations of samples are analyzed to study the inclusion complexes in solution of CD and AMP and the viscosity of these mixtures. The higher concentrations of these solutions show increased viscosity and large cluster formation and a significant response to UV and visible spectra which is not observed in the dilute solutions.

A study on the ground- and excited-state photochemical and photophysical properties of (1-cyclohexenyl)phenyldiazene (CPD) is conducted. CPD is a species formally derived from azobenzene in which one of the phenyl rings is replaced by a 1-cyclohexane substituent.

The synthesis, photochromism, and optical properties of a chiral heliconoid diarylethene that shows a large change in specific optical rotation induced by photochromism is reported. The diarylethene possessing one [4]thiaheterohelicene and one benzothiophene with a chiral methoxymethoxyethyl group on its C-3 position was proved to work as a switch of specific optical rotation at a wavelength at which both colored and colorless forms have no absorption in solution.

Various techniques and methodologies are used to observe the efficiency of the scattering of the light during the laser-assisted holographic grating recording process in films of several azobenzene functionalized polymers. The analysis of the temporal evolution of diffraction efficiency for the same grating formation kinetics suggests that proper and adequate care should be taken during the experiment to get accurate results.

Semiempirical calculations are carried out on model oligomers to investigate the tunable behavior of p-n copolymers with the repeating units constructed by oligothiophenes as the [pi]-excessive type blocks and 1,4-bis(oxadiazolyl) benzene as the [pi]-deficient type block. The analysis has shown that the backbone modification of the p-n copolymer, that is, changing the number of thiophene unit in the p-n diblock copolymer, has modified the optical properties of the polymer.

The synthesis of new type [a] and [b] benzoxanthene dye frameworks is described. It is shown that a type [a]benzofluorone, seminaphtho[a]fluorone (SNAFR-1), displays unique properties, including white light emission as well as excitation over a 400 nm range and the compound can also be used in cellular imaging studies.

The nematic and twisted nematic liquid crystals mixed with azobenzene (AB), spirooxazine (SO) and spiropyran (SP) are investigated by using spectroscopic methods, including birefringence and polarized transmission, to monitor the amplitude of the changes upon phototransformation as well as the dark kinetics. The results have shown SP to be an interesting photochemical probe as it has orientation photochromism and is able to adequately sense the orientation dependent polarity of this anisotropic medium.

The rate constants for the reactions of OH radicals with benzene and toluene are measured directly by a shock tube/ pulsed laser-induced fluorescence imaging method at high temperatures. The direct measurements of the high-temperature rate constants for the reactions of OH radicals with benzene and toluene is extended up to 1740 and 1480 K, respectively, and are in good agreement with the previous measurements.

Novel gold nanoparticles, passivated by monolayers of benzenethiol, biphenylthiol, and similar derivatives, are synthesized and characterized using UV/vis, NMR, and Fourier transform infrared (FTIR) spectroscopies. Femtosecond transient absorption measurements show that the nanoparticles possess optical properties on the boundary between molecular and nanoparticle behavior.

The photochemical properties of a series of newly synthesized dendrimers, having a 2-(2'-hydroxyphenyl)-benzoxazole (HBO) core, are studied in benzene. The results of the dendrimer effect on the fluorescence quantum yield of the excited-state intermediate are the evidence of an efficiency increase with relation to the deactivation process of (E)-keto form (super 1)K(sub E) by isomerization to give the ground-state (Z)-keto form (super 1)K(sub z).

A novel thermodynamic approach is proposed that explains a number of experimental findings including the light-induced deformation of free-standing films and the formation of surface relief gratings for main inscription geometries. The magnitude of the elastic stress, estimated by taking the derivative of the free energy over the sample deformation, is shown to be sufficient to induce plastic deformation of the polymer film.

Photoinduced intramolecular charge separation (CS) and charge recombination (CR) processes of the tetrathiophene-substituted benzene dyads with an amide spacer in solvents of different polarities were investigated using various fast spectroscopies. It was revealed that the CR rates in the dyads were fast because of the enhanced superexchange interaction through the amide spacer.

The photoinduced change in refractive index of poly(methyl methacrylate) films doped with an azobenzene liquid crystal is measured by the prism-coupling method. The coupling angles shifted and then recovered to the initial position by turning off the light on irradiation of the film with a high-pressure mercury lamp at 366 nm.

A theoretical characterization of the potential energy surfaces of the singlet benzene excimer states derived from the B(sub 2u) monomer excited state is performed using time-dependent density functional theory. The calculated values are found to be in semiquantitative agreement when compared to experimentally determined values for the benzene excimer energetics.

The energy dissipation mechanism from photoexcited azobenzene is studied by femtosecond time-resolved UV absorption spectroscopy using 7-amino-4-trifluoromethylcoumarin (ATC) as a probe. Three major components are observed in the transient kinetics of Az-Pro-ATC vibrational cooling.

The ultrafast dynamics of solutions of phenol and two phenol derivatives namely hydroquinone (1,4-benzenediol) and pyrocatechol (1,2-benzenediol) are studied with Optically Heterodyne-Detected Optical Kerr-Effect (OHD-OKE) spectroscopy. The solvents, methanol and acetonitrile, were selected to provide strong and weak solvent-solute hydrogen-bonding interactions, respectively while pyrocatechol features an intramolecular hydrogen bond.

A study examined efficient monomer and excimer emission from various donor-acceptor substituted phenylethynes (PE) with time-resolved fluorescence measurement during the pulse radiolysis in benzene. The formation of PE in the singlet excited state and the excimer state could be interpreted by the charge recombination between the PE radical cation and the PE radical anion, which are generated initially from the radiolytic reaction in benzene.

Synthesis of thieno[2,3-f:5,4-f]bis-[1]benzothiophene and thieno[3,2-f:4,5-f]bis[1]benzothiophene, the anti and syn isomers of a pentacyclic compound consisting of alternating thiophene and benzene rings is reported. It is found that the anti isomer, the ribbon like embedding of three thiophenes units leads to a near-planar molecule with favorable pi-pi stacking behavior in the solid state.

An investigation of the photochemical properties of photoinduced omega-bond dissociation in p-benzoylbenzyl phenyl sulfide (BBPS) in solution is conducted by time-resolved EPR and laser flash photolysis techniques. BBPS is demonstrated to undergo photoinduced omega-bond cleavage to yield the p-benzoylbenyl radical (BBR) and phenyl thiyl radical (PTR) at room temperature.

A correlation function formalism is applied to compute the two-photon absorption spectrum of benzene and an expression for the average vibrational energy in the excited state is derived. Using harmonic Hamiltonians for the ground and excited electronic states, it is found that the theory agrees quantitatively with the experimentally observed sparsity of the thermal two-photon absorption spectrum as compared with the single-photon absorption spectrum.

The electronic structure of benzene adsorbed on single-domain Ge(100-(2*1) and on a single-domain Ge monolayer grown on SDi(100)-(2*1) is investigated by angle-resolved ultraviolet photoemission spectroscopy (ARUPS). The weekly bound benzene species can only be observed on Ge(100) but not on Si(100) or Ge/Si(100) and the reason for this bonding is because it is based on kinetic hindrance of saturation of the chemisorbed species.

Narrowed spectra at 452 nm from a thin platelike crystal of distyrylbenzene derivative, 2,5-diphenyl 1,4-distyrylbenzene with two trans double bonds (trans-DPDSB) grown by vapor deposition, are observed. The trans-DPDSB crystal is irradiated by the third harmonic (355 nm) of a Nd:YAG laser. The FWHM of the narrowed spectra can reach 6 nm for the crystal when the pumping energy is 400 [micro]J/pulse. The threshold value for an optically pumped laser is approximately 350 [micro]J/pulse. OCIS codes: 160.3380, 160.4890, 140.5960.

A series of oligomers consisting of ethynyl-linked azobenzene units was prepared using Pd-catalyzed cross coupling and the linear and nonlinear optical properties of the oligomers were investigated. The results suggested that the incorporation of azobenzene functional groups and alkynyl linkages into organic optical materials resulted in dramatically improved performance in nonlinear optical applications.

The various photoresponsive current-voltage characteristics of the organic thin film transistors (OTFTs) are analyzed. An increase in the incident light power is shown to lead to a significant reduction in the photosensitivity of the devices.

The photochemistry of a series of 9,10-anthraquinones with multiple benzyloxy substituents is examined. The results have shown the importance of considering the medium and photoredox behavior in anthraquinone photochemistry.

The composition of layered alkali titanates ([M.sub.x][Ti.sub.2-x/3][Li.sub.x/3][O.sub.4]; M = K(+), Li(+), Na(+)) was tuned to control the swelling of the titanates in water and subsequently achieve molecular-sieve-like molecular recognitive photocatalytic decomposition of aqueous organic compounds on the titanates. The efficiency of the molecular recognitive photocatalytic benzene decomposition was related to the degree in the swelling of the titanates in water.

The new organic gelator LMWG, featuring electroactive tetrathiafulvalene (TTF) and photoresponsive azobenzene groups, is designed and analyzed for developing multistimuli responsive organogels. The studies have shown that the photoisomerization of the azobenzene groups in LMWG has triggered the gel-sol transition and hence organogels with LMWG has responded not only to thermal stimuli but also to redox reactions and light irradiation.

Optical properties and the geometric structure of self-assembled monolayers of azobenzene-functionalized alkanethiols are examined by UV/visible and near edge X-ray absorption fine structure spectroscopy and density functional theory. The analysis of the energetic shifts has substantiated sizable excitonic coupling among the azobenzene chromophores as a vital mechanism that hinders trans to cis isomerization in densely packed self-assembled monolayers.

The synchrotron radiation photoemission technique is employed to explain the interfacial electronic structure of copper phthalocyanine deposited on a gold surface. The adsorption taking place in the system is shown to affect only the carbon atoms present in the benzene ring.

A method is described for improving femtomole-level trace detection by using large-area surface-enhanced Raman scattering (SERS) substrates. Multiphoton-induced exposure of a commercial photoresist is used for physically limiting the available molecular adsorption sites to only the electromagnetic hot spots on the substrate.

The reversible Z-E photoswitching properties of the (Z) and (E) isomers of the severely constrained bridged azobenzene derivative 5,6-dihydrodibenzo[c,g][1,2]diazocine are examined by ultraviolet (UV)/visible (vis) absorption spectroscopy in solution in n-hexane. The photochromic and photoswitching properties more favorable than those for normal azobenzene (AB) and the severe constraints by the ethylene bridge have favored the Z-E photoisomerization reactions.

A pincer-like benzene-bridged sensor with a pyrene excimer as a signal source and imidazolium as a phosphate anion receptor is prepared and examined for ATP sensing. The results have shown that the sensor is a useful fluorescence sensor for examining the ATP-relevant biological processes.

The optical diffraction in two- and three-dimensional vector holograms is studied and the reconstruction of polarized optical images recorded in azobenzene-containing amorphous polymers (AP) and polymer-dissolved liquid-crystalline composites (PDLCC) is demonstrated. The studies have shown that the information of the polarized optical image is recorded as the polarization induced anisotropy in the AP and PDLCC medium and is reconstructed as the polarized optical images.

A newly discovered soliton-like electrogenerated chemiluminescence (ECL) waves in the electrochemical oxidation of thin films of the semiconducting conjugated polymer poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) are reported. The results obtained from exploration of several model systems with spatially distributed reaction 'triggers' demonstrated the mechanistic details of observed complex oxidation process in polymer films.