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Ab initio spin-flip configuration interaction (SF-CI) methods with the finite-field (FF) scheme are applied to the calculation of static second hyperpolarizabilities (γ) of several singlet diradical systems, i.e., the model H2 molecule under dissociation, p-quinodimethane, o-quinoid five-membered ring, and 1,4-bis(imidazole-2-ylidene)cyclohexa-2,5-diene (BI2Y) models. The SF-CI method using the UHF reference wave function provides the qualitatively correct diradical character (γ) dependence of γ in a wide range of a diradical character region for H2 under dissociation ahd p-quinodimethane as well as o-quinoid five-membered ring models. For BI2Y, which is a real diradical system, a non-negligible spin contamination is found in the spin-unrestricted Hartree-Fock (UHF) triplet state, which results in overestimations (SF-CIS) or underestimations (SF-CIS(D)) of γ. Such deficiencies are significantly reduced when using the pure spin state, i.e., the restricted open-shell HF (ROHF) triplet wave function as the reference wave function. These results indicate the applicability of the FF-SF-CI method starting with a pure or a nearly pure high-spin state to provide qualitative or semiquantitative γ for large-size diradical systems. For selected systems, these SF-CI results are also compared to the SF equation of motion coupled cluster singles and doubles (SF-EOM-CCSD) and to SF time-dependent density functional theory (SF-TDDFT) schemes. In particular, large amounts of Hartree-Fock exchange in the functional are required to obtain qualitatively correct dependence of γ on y in the case of p-quinodimethane.

Using hybrid density functional theory methods, the static first ( β ) and second ( γ ) hyperpolarizabilities of a donor–acceptor disubstituted singlet diradical system built from phenalenyl radicals linked by an acetylene π-conjugated bridge, DA-BPLE, is investigated and compared to an analogous closed-shell system, DA-BPRY, built from pyrene rings. DA-BPLE presents an intermediate diradical character and exhibits β and γ values about 14 and 7 times larger than those of DA-BPRY having a similar π-conjugation length, respectively. These results suggest the applicability of the structure-property relation in γ of symmetric diradical systems to β and γ of asymmetric diradical systems.

C. K. acknowledges the HPC resources of CINES and of IDRIS under the allocations 2014-[x2014080649] made by GENCI (Grand Equipement National de Calcul Intensif).; International audience; A new chromophore, 2-(4-nitrophenyl)benzofuran (NPBF), was designed for two-photon (TP) uncaging using near-IR light. The TP absorption (TPA) cross-sections of the newly designed NPBF chromophore were determined to be 18 GM at 720 nm and 54 GM at 740 nm in DMSO. The TP uncaging reaction of a caged benzoate with the NPBF chromophore quantitatively produced benzoic acid with an efficiency (δu) of ∼5.0 GM at 740 nm. The TP fragmentation of an EGTA unit was observed with δu = 16 GM. This behavior makes the new chromophore a promising TP photoremovable protecting group for physiological studies.

We investigate the longitudinal static second hyperpolarizabilities ( γ ) of open-shell singlet one-dimensional systems. The intersite interaction effects on the average diradical character and size dependences of γ are examined using hydrogen chain models (H 2 n ) with different chain lengths and bond-length alternations (BLA) by the ab initio MO full-CI and coupled cluster methods. These systems exhibit significant enhancement of γ / n in the small average diradical character region compared to diradical H 2 . The BLA is found to reduce the maximum γ / n and to move the diradical character giving the maximum γ / n to intermediate region. These systems also show remarkable chain-length dependences of γ / n (comparable to those of closed-shell systems) in the small average diradical character region.

We have investigated the structural dependence of static second hyperpolarizabilities (γ) of polycyclic diphenalenyl radicals, i.e., IDPL, as-IDPL and TDPL, using the hybrid density functional theory method. It turns out that the diradical character of as-IDPL (0.923) is larger than that of IDPL (0.770) and is close to 1 (pure diradical state), which supports the fact that the γ of as-IDPL (472 × 103 a.u.) is smaller than that of IDPL (2284 × 103 a.u.). The replacement of a central benzene ring (as-IDPL) by a thiophene ring (TDPL) increases the γ (1375 × 103 a.u.). This is predicted to be caused by the reduction of aromaticity of the central ring and by the hypervalency of the sulfur atom of the thiophene.

Linear (one-photon) and nonlinear (two-photon) spectral properties of 4-N,N-dimethylamino-4′-aminoazobenzene have been investigated under protonation in DMSO/water solvent mixtures. Observed spectral changes have been discussed in terms of ammonium–azonium tautomerism. The corresponding tautomeric constants have been determined for the first time for such kind of tautomeric equilibria. The process of protonation leads to changes of the two-photon absorption properties, suggesting that such process could be used as a tool for change of third-order nonlinear optical activity in solution.

The static second hyperpolarizability (γ) of a singlet diradical system involving phenalenyl radicals linked with acetylene π-conjugated bridge, BPLE, is investigated as well as reference closed-shell systems, BPRY1 and BPRY2, by the hybrid density functional theory method. The γ value of BPLE with intermediate diradical character is shown to be about four times as large as that of BPRY1 with similar π-conjugation length and to be about twice as large as that of BPRY2 with longer π-conjugation length. This feature is in agreement with our prediction that the molecules with intermediate diradical characters enhance γ values compared to the closed-shell molecules.

Supramolecular porphyrin self-assemblies have been prepared from butadiyne-linked bis(imidazolylporphyrin) by complementary coordination of imidazole to zinc, and their two-photon absorption (2PA) and higher-order nonlinear absorption properties were investigated over femtosecond time scales using an open-aperture Z-scan method. The self-assembled porphyrin dimer of the conjugated monozinc bisporphyrin 7D was shown to have a large 2PA cross section (7.6 x 10(3) GM, where 1 GM = 10(-50) cm(4) s molecule(-1) photon(-1)) at 887 nm. By comparison of this result with that for a meso-meso-linked porphyrin array without the butadiyne connection (3.7 x 10(2) GM at 964 nm), it was demonstrated that the predominant factor in this significant enhancement of the cross section was the expansion of porphyrin-porphyrin pi-conjugation. Self-coordination and monozinc metalation were also found to be contributing factors. Furthermore, a novel self-assembled porphyrin polymer 8P consisting of a biszinc complex with a mean molecular weight of M(n) = 1.5 x 10(5) Da was shown to exhibit an extraordinarily large two-photon absorption cross section (4.4 x 10(5) GM at 873 nm). Nanosecond Z-scan experiments for 7D and 8P were also undertaken and resulted in the measurement of large effective 2PA cross sections, including the excited-state absorption (2.1 x 10(5) GM for 7D and 2.2 x 10(7) GM for 8P, respectively). Finally, three-photon absorption was observed by femtosecond Z-scan experiments at 1188 nm (7.1 x 10(-89) m(6) s(2)) and 1282 nm (1.8 x 10(-89) m(6) s(2)), an observation which is the first of its kind in porphyrin chemistry.

We have found that large area multiple color changes can be created in soda-lime silicate glass with Ag particles, prepared by ion-exchange and heat treatment, by femtosecond laser (λ = 400 nm) irradiation. The original yellow color in the glass resulting from surface plasmon resonance (SPR) of the Ag particles changed to a reddish color, then purple and finally blue with increasing irradiation time. Optical microprobe examination of the absorption spectrum of the laser irradiated regions revealed an apparent bleach of the original band of SPR at 412 nm and the consequent appearance of two new bands around 450 nm and 490 nm with irradiation time.

Two-photon absorption (TPA) properties of symmetric molecular systems composed of charged groups linked with a π -conjugated bridge are investigated using the time-dependent perturbation theory with the single and double excitation CI method in the INDO/S approximation in order to clarify the effect of introducing charges on the TPA property. It turns out that the introduction of charges causes the red shift and significant enhancement of TPA cross section in the first peak position as compared to that in the neutral molecule with a similar framework. This is primarily ascribed to be the increase of transition moment between the one-photon-allowed, first excited state and the two-photon allowed, higher excited state for the charged molecules because of the localization of contributing MOs in the both-end regions.

The dependence of the second hyperpolarizability (gamma) on the diradical character (y) for singlet diradical systems is investigated using a model compound, the p-quinodimethane (PQM) molecule with different both-end carbon-carbon (C-C) bond lengths, by several ab initio molecular orbital and density functional theory methods. The diradical character based on UHF calculations indicates that at equilibrium geometry PQM is in a singlet ground state and primarily exhibits a quinoid structure, whereas the diradical character increases when increasing both-end C-C bond lengths. At the highest level of approximation, that is, using the UCCSD(T) method with the 6-31G+diffuse p (zeta = 0.0523) basis set, the longitudinal static gamma of PQM presents a maximum value for intermediate diradical character (y approximately 0.5) while the gamma values are larger for intermediate and large diradical character (y approximately 0.5-0.7) than for small diradical character (y0.2). This feature suggests that the gamma values of singlet diradical systems in the intermediate and somewhat strong correlation regimes are significantly enhanced as compared to those in the weak correlation regime. These results are substantiated by a complementary study of the variation in gamma upon twisted ethylene.

Third-order nonlinear optical properties of multinuclear organometallic complexes consisting of metal–metal multiple bonds previously studied by picosecond degenerate four-wave mixing (DFWM) are reexamined by femtosecond optical heterodyned optical Kerr effect (OHD-OKE) and femtosecond Z-scan techniques. The real part of off-resonant second hyperpolarizabilities are obtained at a wavelength of 1280 nm to be +3.0 ± 10−33 esu for a Pt–Mo–Mo–Pt tetranuclear complex and less than 10−33 esu for a Mo–Mo dinuclear complex. The present results clarify that the previously reported values are not off-resonant values and the off-resonant property of the tetranuclear complex is superior to that of the dinuclear one.

The effect of introducing charges on the two-photon absorption (TPA) is examined using the models involving the dicationic styrylpyridine units linked with a diphenyl diacetylene bridge. It turns out that the introduction of charges causes the red shift and drastic enhancement of TPA cross-section as compared to that in the neutral molecule. This is primarily ascribed to be the enhancement of transition moment between the first and second excited states, the feature of which is associated with the decrease of orbital interaction among the LUMOs of both-end dicationic styrylpyridines and the HOMO and LUMO of the central diphenyl diacetylene bridge.

Two-photon absorption(TPA)properties of several linear molecules were experimentally studied and discussed in terms of theirπ-bridge. Asymmetric molecules containing C = C, N = N, and N = Cπ-bridges were examined and found that molecular planarity along theπ-bridge plays an important role on TPA activity. Also symmetric bis(styrylpyridines)derivatives containing a diacetyleneπ-bridge were examined and found to exhibits stronger TPA than the aromaticπ-bridge molecule with similar extent ofπ-conjugation. Drastic enhancement of TPA cross section due to resonance enhancement was also found for one of the diacetylene compounds in visible wavelength region.

Two-photon absorption (TPA) spectra are presented for newly synthesized bis(pyridylstyryl)-substituted diacetylene and related methyl triflate derivatives. The TPA cross section of a derivative (MPPBT) was found to increase drastically with decreasing the incident wavelength below 650 nm and to reach (2.42±0.46)×10 −47 cm 4 s molecule −1 photon −1 at 571 nm, in addition to the weaker, lowest energy TPA peak centered at 764 nm. A four-state model was needed to account for the observed spectral shape, suggesting that the drastic enhancement is due to one-photon resonance enhancement not only of the lowest energy TPA transition but also of a higher energy two-photon transition.

The two-photon absorption (2PA) properties of a series of dyes containing donor and acceptor groups connected via a π-electronic bridge were studied by using a femtosecond Z-scan technique. It was found that the nature of the π-electronic bridge does not substantially affect the measured 2PA intensities. In the case of the substituted azobenzenes the decrease of the strength of the donor and/or acceptor groups leads to decrease of the 2PA intensity, the effect of the acceptor strength being greater.

The electronic second hyperpolarizability γ of the carbon tetrachloride molecule is calculated by the ab initio molecular orbital method considering electron correlation with large basis sets. The static electronic γ value with the CCSD(T) method is 1.65 times the Hartree-Fock value, indicating a considerable electron correlation effect. Taking account of the frequency dispersion and vibrational effects, we estimate the most probable theoretical γ value at 800 nm to be around 17900au (9.0 × 10−36 esu). On the other hand, the experimental value recently observed by optical Kerr effect method is 10.6 × 10−36 esu at 800nm. It is concluded that the major part of the experimental χ(3) value of carbon tetrachloride can account for the static electronic hyperpolarizability.

Static molecular second hyperpolarizabilities γ of several donor-π-acceptor molecules have been examined using an ab initio molecular orbital (MO) method to evaluate the effects of substituents and molecular distortion on γ. It was found that γ values of the donor-π-acceptor compounds are affected by the degree of π electron delocalization more than the donor or acceptor strength of the substituents. Also it was found that contributions from higher order excitation process are not negligible for γ values of the donor-π-acceptor molecules.

The nonlinear refractive index, as well as the two-photon absorption (TPA), has been investigated by the femtosecond Z-scan method for push–pull molecules, in which a primary donor group is weakened by conversion into a pyrrole or related heterocycle. The results at the fast response time show that, contrary to what had been expected from a previous work, there is a little decrease in the nonlinear refractive index change by introduction of the weaker donor groups. Although the measured TPA spectra showed that the observed nonlinear refractive index change was regarded to be off-resonant; difference in the frequency dispersion among the molecules considerably contributes to the decrease, in addition to difference in the intrinsic static nonlinearity. This shows that there is some future in the development of these non-resonant materials.

A novel series of isopolydiacetylene oligomers have been characterized on the basis of their electronic absorption, emission and nonlinear optical properties. The ultraviolet?visible spectra indicate only a small shift to lower energy as a function of increasing oligomer length. To evaluate the third-order nonlinear susceptibilities, ?(3), and second hyperpolarizabilities, ?, of these oligomeric samples a new Kerr gate technique, differential optical Kerr effect detection, has been employed. A linear relationship between ? and the number of repeat units is found, suggesting that the fixed-length linearly conjugated segments dominate the electronic polarizability. The largest nonlinearity was observed in the heptamer sample, displaying a second hyperpolarizability relative to the tetrahydrofuran solvent of ?heptamer /?THF = 181 ? 9.

The linear and nonlinear optical properties for a series of thienyl- and bithienyl(aryl)iodonium triflate salts 1–4 have been determined. The energy of the linear absorption maxima for salts 2–4 experiences only a minor shift to lower energy as the aryl group is made more electron deficient. In contrast, the real parts of the second hyperpolarizabilities, γR, experience a 10-fold increase. Open-aperture Z-scan data for all three bithienyl iodonium salts 2–4 demonstrate the presence of three-photon absorption under irradiation at 650 nm.

We present a study on the ultrafast third-order nonlinearities of a novel series of iso-polydiacetylene oligomers (iso-PDAs). Unlike polydiacetylenes that contain a linearly-conjugated backbone, iso-PDAs have a backbone that is cross-conjugated. A new Kerr-gate technique, differential optical Kerr effect (DOKE) detection, is used to measure third-order nonlinear susceptibilities, χ(3), and second hyperpolarizabilities, γ, of monomer, dimer, trimer, pentamer, and heptamer samples in tetrahydrofuran (THF) solutions. A linear increase in γ as a function of the number of repeat units is observed for all samples except the monomer, suggesting that the fixed-length linearly conjugated segments dominate the electronic polarizability. An added increase to the oligomer nonlinearities due to communication along the cross-conjugated path is not observed. The largest nonlinearity was observed in the heptamer sample, displaying a second hyperpolarizability relative to the THF solvent of γheptamer/γTHF=181±9. In additi...

The influence of metal ion interaction with crowned spirobenzopyrans on the photoisomerization behavior was investigated through the use of various solvents, crowned spirobenzopyrans, and metal ions. Studies on the photoisomerization behavior of crowned spirobenzopyrans in various solvents revealed that solvation of the phenolate anion moiety in the merocyanine form induced photoisomerization back to the spiropyran form, giving rise to negative photochromism. Metal ion interaction with the phenolate anion moiety similarly caused photoisomerization back to the spiropyran form, while that with the crown ether moiety just produced a polar environment and its influence on photoisomerization behavior was dependent on the affinity of the metal ion captured by the crown ether moiety for the phenolate anion. Therefore, photochromic switching of crowned spirobenzopyrans between positive and negative to control the metal ion interaction with the phenolate anion moiety through the crown ether moiety is possible. This finding suggests a molecular design method for crowned spirobenzopyrans showing desired ion-responsive photochromism.

1-(4′-Substituted phenyl)-4-(4′-methylpyridinium)butadiyne triflate (5ab), which was prepared by the reaction of 1-(4′-Substituted phenyl)-4-(4′-pyridyl) butadiyne (4ab) with methyl trifluoromethanesulfonate, was found to be grown into the large crystal due to the quaternized structure. The uv irradiation and thermal treatment of 5ab gave rise to 1,4-addition polymerization to yield the polydiacetylene. The third-order nonlinear optical susceptibility (χ (3)) of the polymer was determined by the Z-Scan method to exhibit the remarkable high value of 1.65×10−11esu at 650 nm.

CdSe microcryssals with various sizes was successfully embedded in SiO2 glass matrix by magnetron rf-sputtering technique. The mean size of microcrystals was controllable by changing the relative surface area ratio of the CdSe chips to the matrix in the target, and increased with increasing the relative area. The negative real part of the third-order optical susceptibility was seen for all of the present films, and the magnitude of the absolute value of real part increased with increasing concentration of CdSe. The imaginary part due to two photon absorption also increased with the CdSe concentration. After normalized with respect to the concentration, it was revealed that actual optical third-order nonlinearity of the CdSe microcrystals increased as the mean size decreased, in other words as the quantum confinement effect increased.

International audience; A great number of studies focus their interest on the photophysical properties of fluorescent hybrid gold nanoparticles for potential applications in biotechnologies such as imaging and/or treatment. Spherical gold nanoparticles are known to quench a chromophore fluorescent signal, when moieties are located in their close vicinity. The use of a polymer spacer on such a system allowed only partial recovery of the dye emission by controlling the surface to dye distance. Gold-based anisotropic sharp nanostructures appear to exhibit more interesting features due to the strong electric field generated at their edges and tips. In this paper, a complete study of hybrid fluorescent bipyramidal-like gold nanostructures is presented. We describe the chemical synthesis of gold bipyramids functionalized with fluorescent water-soluble polymers and their photophysics both in solution and on a single object. We show that the use of a bipyramidal shape instead of a spherical one leads to total recovery of the fluorescence and even to an enhancement of the emission of the dyes by a factor of 1.4.

A large photoinduced anisotropy ratio was observed in the push−pull azo dyes bonded covalently to polyurethane by polarized UV−vis spectroscopy. During irradiation with an Ar+ laser, the absorbance perpendicular to the polarization direction of the laser light increases gradually even when the photoisomerization rate of trans to cis forms is equal to the reisomerization rate of cis to trans forms. The trans molecules are considered to reorient during the trans−cis−trans isomerization cycles. The process of photoinduced reorientation was also observed by polarized FT-IR spectroscopy. The dynamic behavior of trans and cis isomers is discussed in terms of orientation factors evaluated using the absorbance of some IR vibrational bands. The values of orientation factors for the trans and the cis isomers vary with irradiation time due to the reorientation. The reorientation process for the cis molecules was found to be essential to the reorientation for the trans molecules. On the other hand, according to the r...

Single- and multi-energy O and Cu ions were implanted into silica glass (or sapphire) changing the ratios of O and Cu doses as like Cu only (0:1), 1/2O+Cu (0.5:1) and O+Cu (1:1). Optical property changes induced by the ion implantations and successive heat treatments have been studied. Specific optical absorption was clearly observed at about 570 nm, which attributed to Cu nano-particles for the samples of Cu, 1/2O+Cu and Cu+1/2O implantations. Multi-energy implantation at 300 K enhanced the absorption. With the increase of annealing temperature, the size and concentration of Cu particles are increased. The sequence of ion implantation between Cu and O affects the optical absorption and nano-particle formation. Third-order non-linear optical susceptibility, χ(3), has been measured for sapphire samples. The values of χ(3) were 6.5×10−9 esu and 4.0×10−9 esu for Cu and 1/2O+Cu implantation, respectively.

Spirobenzopyran derivatives carrying an oxymethylcrown ether moiety were synthesized, and their photochromism was studied in the presence of various metal ions in acetonitrile. The metal ion complexing ability of the crown ether moiety in crowned spirobenzopyrans affects both thermal isomerization and photoisomerization of their spirobenzopyran moiety to a great extent. When the interaction of the crown ether moiety with a metal ion was strong enough to cause thermal isomerization of the spirobenzopyran moiety to its corresponding merocyanine form and to suppress UV-induced isomerization to the merocyanine form, a negative photochromism appears. On the other hand, a relatively weak interaction of the crown ether moiety with a metal ion affords a positive photochromism. This phenomenon enables us to switch the photochromic behavior between positive and negative photochromisms.

1,4-Bis(4-alkylpyridinium)butadiyne triflate (2a and 2b) that was prepared by the reaction of 1,4-bis(4-pyridyl)butadiyne (1) with alkyl trifluoro-methanesulfonate, was found to grow into a large crystal as a result of the quaternized structure. The thermal treatment of 2a and 2b gave rise to 1,4-addition polymerization to yield the polydiacetylene. The third-order nonlinear optical susceptibility [X (3) ] of the polymer was determined by the femto-second Z-scan method to exhibit the remarkable high value of 1.1 × 10 -11 esu at 650 nm.

1,4-Bis(4-methylpyridinium)butadiyne triflate (1), which was prepared from the reaction of 1,4-bis(4-pyridyl)butadiyne with methyl trifluoromethanesulfonate, was found to be piled up along the c axis with two triflates as counter anions. The UV irradiation and thermal treatment of 1 gave rise to 1,4-topochemical polymerization to yield poly[1,4-bis(4-methylpyridinium) butadiyne triflate)]. The third-order nonlinear optical susceptibility (X (3) ) of the polymer was determined by the degenerate four wave mixing (DFWM) method to exhibit the remarkable high value of 2.2 x 10 -10 esu.

Frequency dispersion of second hyperpolarizability of furan homologues is calculated by the time-dependent Hartree–Fock (TDHF) method. Using the calculated results, the most reliable theoretical values for the second hyperpolarizability are estimated including both effects of electron correlation and frequency dispersion with the comparison of several approximation methods. The estimated values are compared with the observed values measured by the optical Kerr effect (OKE) method. It is found that by inclusion of the effect of frequency dispersion the calculated results approach more closely to the observed values especially for the molecules with heavier hetero atoms like thiophene, selenophene or tellurophene.

Polarized light-induced anisotropy of 4-dimethylamino-4′-nitroazobenzene (DMANA; NO2–C6H4–NN–C6H4–N(CH3)2) in PMMA is investigated by polarized spectroscopy and compared with the anisotropy of Disperse Orange 3 (DO3; NO2–C6H4–NN–C6H4–NH2) studied previously. The orientation factors evaluated from spectroscopic results show that the trans isomers of DMANA isomerize to cis forms by motion of the p-NO2–C6H4 group easily compared with motion of the p-N(CH3)2–C6H4 group. This result is different from the result of DO3 in PMMA where the trans forms tend to isomerize to cis forms by motion of the amino group side than that of nitro group side. We consider that this difference is due to the volume effect of the substituent at the para position of a phenyl group. This study clearly indicates that the motion of push–pull azo-dyes in the isomerization processes strongly depends on the relative volume of the p-substituent.

A spirobenzothiapyran derivative bearing a monoaza-12-crown-4 moiety shows remarkable stabilization of its photoinduced colored isomer (merocyanine form) by complexation of a metal ion, especially Li+ and Ag+. Comparison of the crowned spirobenzothiapyran with its corresponding spirobenzopyran derivative indicates that the stabilization of the merocyanine form in the presence of Li+ and Ag+ are derived mainly from the metal-ion complexing ability of its crown ether moiety and the metal-ion affinity of its merocyanine thiophenolate anion, respectively.

Static polarizabilities and hyperpolarizabilities have been calculated for the furan homologues including furan (C4H4O), thiophene (C4H4S), selenophene (C4H4Se), and tellurophene (C4H4Te), at the Hartree−Fock and various correlation levels by ab initio molecular orbital methods. The influence of substitution with heavy atoms on the molecular properties of the homologues was examined theoretically. In the calculations for molecules with Se and Te atoms, the contribution of core electrons in the atoms was estimated using effective core potential (ECP) methods. With the calculation for the thiophene molecule, effectiveness of the use of the ECP method was examined, and the ECP method was found to give the (hyper)polarizability values similar to those obtained considering all electrons for the molecule. The calculated results show that substitution of the heteroatom with heavy atoms systematically increases the individual components of the polarizability, α, and second hyperpolarizability, γ. On the other han...

We investigated the mechanism of the third-order nonlinear optical (NLO) response of liquid CS2 by molecular dynamics simulation from both qualitative and quantitative aspects. The time-dependent relative importance of the orientational and collision-induced dynamics of the molecules to the fluctuation of polarizability was analyzed in order to understand the relation between the dynamics of the molecules and the third-order NLO response. Our analysis shows that the fluctuation of polarizability associated with the orientational dynamics of the molecules is responsible for 81% of the total NLO response. We calculated the values of the third-order NLO coefficients and they were found to be in semiquantitative agreement with the experimental values. We discuss the validity of fitting semiempirical theoretical models to the experimental signals as a means to analyze the mechanism of the NLO response.

Polymer matrix dependence of polarized light-induced anisotropy of the push–pull azo dye, Disperse Orange 3 (DO3; NO2–C6H4–NN–C6H4–NH2), was investigated by UV–Vis and polarized FTIR spectroscopies. The orientation factors obtained by these spectroscopic methods helped us to understand the dynamics of DO3 in polymers. In methacrylate polymers and polystyrene (PS), the trans forms of DO3 are apt to isomerize to cis forms by the motion of p-NH2–C6H4 group side, because the relative volume of the p-NH2–C6H4 group is considered to be small compared with that of the p-NO2–C6H4 group. The large photoinduced anisotropy of DO3 (trans and cis isomers) was found in poly(methyl methacrylate) (PMMA). The small free volume in PMMA is considered to inhibit the rapid rotational motion of DO3 molecules. The free volume provides the primary effect on the polarized light-induced anisotropy, but the local polarity effect of matrices cannot be ignored for the anisotropy of DO3. In the less polar PS with the larger free volume, the anisotropy for cis isomers depends on the motion of NH2 groups, which do not interact with polymers so much.

The third-order nonlinear optical properties of 1,3-and 1,4-disituted poly (phenyleneethynylene)s containing electron-donor and accpetor groups were investigated in terms of the local polirization effect. The electron-donor and acceptor groups being set apart in the benzene ring adjacent to the triple bond in 1,4-disusbstituted poly (phenyleneethynylene)s was found to increase the X (3) value, together with the shift of the maximum absorption to longer wavelengths, while no significant effect was observed in the X (3) value for 1,3-disubstituted poly (phenyleneethynylene)s having both electron-donor and acceptor groups present in a benzene ring, in accordance with the fact that the maximum absorption remains at shorter wavelength.

Second hyperpolarizability γ of tellurophene (C 4 H 4 Te), a tellurium-containing homologue of thiophene, was measured by optically heterodyne-detected optical Kerr effect (OHD–OKE) experiments. We found that the γ of tellurophene was +6.3×10 −36 esu and was larger than twice of that for selenophene and almost three times that for thiophene. The large γ for tellurophene as the homologue was discussed in terms of the symmetry species of the two lowest excited states and their transition energies from the ground state under the 3-state approximation. Low-lying excited A 1 state is presented as the plausible cause of the large γ .

Polarized-light induced anisotropy of Disperse Orange 3 (DO3) depending on the polymer matrices was investigated by polarized FTIR spectroscopy. The dynamic behavior of the azo dyes doped in a series of methacrylate polymers was analyzed in terms of the orientation factors. Two factors, the free volume and the local polarity of matrices, are found to govern the dynamic behavior of DO3. It was found that induced anisotropy for trans and cis isomers varies depending on Tg of polymer matrix. Further, the thermal isomerization rate depend on the isomerization mode which is governed by the matrix polarity. The branched-alkyl chains are considered to block the interaction between ester groups and DO3 and introduce the DO3 molecules into the less polar environment.

We present the results of femtosecond optical heterodyn detected optical Kerr effect (OHD-OKE) spectroscopy and low frequency Raman scattering spectroscopy for three thiophene homologues (C4H4X, X=O, S, and Se). The observed OHD-OKE transients were analyzed both in time and frequency domains. Fourier transformed OHD-OKE data were directly compared with the corresponding spontaneous Raman scattering spectra. The reorientation lifetimes for furan (O), thiophene (S) and selenophene (Se) were determined to be 0.9, 2.0 and 3.2 ps, respectively, and were fairly explained in terms of the Stokes-Einstein-Debye relation. Their subpicosecond dynamics was analyzed with an antisymmetric Gaussian function and a skewed function developed by Bucaro and Litoviz, which gave good curve fits to observed data. Librational and translational dynamics of the molecules was discussed in terms of microscopic environments formed by neighboring molecules and the results of intermolecular interaction energy calculations by an ab init...

Laser oscillation from dye-doped microparticles of organic polymers was investigated. Spectral shift in peak wavelengths of laser oscillation depending on pumping intensity was observed in the microparticles of poly(cyclohexylmethylsilane) (PCHMSi). The shift observed for PCHMSi microparticles was discussed in terms of the third-order non-linear optical (NLO) effect. It was concluded that the effective power density of light just inside the microparticle’s surface was about 30 times larger than that of the pump pulse.

Static second hyperpolarizabilities were calculated for molecules including tetrahydrofuran homologs by ab initio molecular orbital methods at the Hartree–Fock and various correlation levels. Substitution of the heteroatom with a heavier atom is found to be effective for increase of the second hyperpolarizability of these homologs. Comparison between the present results and previous results for furan homologs shows that π-conjugation is not effective for the increase of second hyperpolarizability of the molecules when the heteroatom is heavier. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 737–743, 1998

The second hyperpolarizability (γ) of the carbon disulfide molecule is calculated by the ab initio molecular orbital method considering basis set dependence, electron correlation and frequency dispersion. The quality of the basis set is found to influence strongly the correlation correction. The 6-31G basis set augmented with diffuse p and d functions (6-31G + pd overestimates the correlation effect on the second hyperpolarizability. The 6-31G + pdd basis set, made by augmenting the 6-31G + pd basis set with one more semi-diffuse d function, gives γ values similar to those with a more accurate 6-31G(3 d ) + pd basis set at both the Hartree-Fock and correlated levels.

Two-photon-excitation release of nitric oxide (NO) from our recently synthesized photolabile NO donor, Flu-DNB, was confirmed to allow fine spatial and temporal control of NO release at the subcellular level in vitro. We then evaluated in vivo applications. Femtosecond near-infrared pulse laser irradiation of predefined regions of interest in living mouse brain treated with Flu-DNB induced NO-release-dependent, transient vasodilation specifically at the irradiated site. Photoirradiation in the absence of Flu-DNB had no effect. Further, NO release from Flu-DNB by pulse laser irradiation was shown to cause chemoattraction of microglial processes to the irradiated area in living mouse brain. To our knowledge, this is the first demonstration of induction of biological responses in vitro and in vivo by means of precisely controlled, two-photon-mediated release of NO.