Kazuo Kasatani

Photochromic reaction and fluorescence of dithienylethenes in the solid state

Photochromic cyclization reaction efficiency and fluorescence of two dithienylethenes in two solid states, colloidal solutions and amorphous films, were studied. Colloidal solutions of dithienylethenes were prepared by dilution of concentrated methanol solution into hot water. The diameter of particles of the colloidal solutions was about 1 μm according to observation by a scanning electron microscope. Photochromic cyclization reaction efficiency of colloidal solution of cis-1,2-dicyano-1,2-dithienylethene (1) was as high as that of hexane solution of 1. An amorphous film of 1 also shows high efficiency. On the other hand, neither colloidal solution nor polycrystal of 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydride (2) was photochromic; only an amorphous film of 2 was colored very slightly by UV irradiation. For the dithienylethenes in the solid states, long-wavelength fluorescence which can be assigned to the colored closed-ring form was observed, while deeply colored hexane solution did not give any long-wavelength fluorescence. Fluorescence spectra and fluorescence decay curves indicated the existence of efficient energy transfer from the open-ring form to the closed-ring form of dithienylethenes in the solid states.

Photodissociation of molecular beams of halogenated hydrocarbons at 193 nm

Abstract Molecular beams of halogenated hydrocarbons containing chlorine and bromine atoms were photodissociated using an excimer laser at 193 nm. Molecules photodissociated were HCCBr, HCCCH 2 Br, HCCCH 2 Cl, CH 3 Cl, C 2 H 5 Cl and i -C 3 H 7 Cl. The time-of-flight distributions of the photofragments were measured in order to study the primary processes and the dissociation dynamics. Generalizations consistent with the data are that atomic products (RX → R + X) result from direct dissociation of the CX repulsive singlet state, molecular elimination (RX → R′ + HX) is a result of a crossover to the ground state and triplet states are involved in the photodissociation of alkyne compounds.

Photodissociation of molecular beams of SO2 at 193 nm

Abstract A molecular beam of SO 2 has been photodissociated at 193 nm and both the translational energy distribution P ( E T ) and angular distribution f (θ) are reported. The isotropic f (θ) indicates that dissociation is predissociative. P ( E T ) is represented by the prior distribution in phase-space theory, in which a potential barrier is assumed for decomposition.

Doppler spectroscopy of hydrogen atoms from the photodissociation of saturated hydrocarbons and methyl halides at 157 nm

Hydrocarbons (CnH2n+2, n=3, 4, and 6) and methyl halides (CH3X, X=Cl, Br, I) are photodissociated at 157 nm. The hydrogen atom photofragments are detected by a resonance‐enhanced multiphoton ionization technique. The Doppler profiles of the hydrogen atoms from hydrocarbons are well represented by a Gaussian profile, while those from methyl halides by a mixture of a Gaussian and a non‐Gaussian profiles. These Doppler profiles are interpreted assuming that (a) hot ethyl photofragments from hydrocarbons result in the formation of hydrogen atoms and (b) methyl halides undergo both direct and indirect photolytic scissions of the C—H bonds at 157 nm.

Reactions of metal ions and benzene as studied by the laser ablation-molecular beam method. Pressure and kinetic energy dependences of ion-molecule reactions

Abstract Reactions of metal ions with benzene have been studied by the laser ablation-molecular beam method. The 1:1 complex ion, M(C 6 H 6 ) + , has been obtained for transition metals except for Nb by ion-molecule reactions of M + and C 6 H 6 . The kinetic energy (KE) dependence studies have revealed that the slower portions in the wide KE distribution of M + are effective in the reaction. Collision stabilization of nascent complex ions has been shown by the experiments on pressure dependence. Nb gives Nb(C 6 H 4 ) + , which has little KE dependence. The higher reactivity of transition elements as compared to typical elements is attributed to the d-π interaction.

FLUORESCENCE DECAY OF THE ACRIDINE ORANGE‐SODIUM DODECYL SULFATE SYSTEM: FORMATION OF DYE‐RICH INDUCED MICELLES IN THE PREMICELLAR REGION*

The fluorescence decay behavior was studied for the acridine orange (AO)‐sodium dodecyl sulfate (SDS) system in order to investigate the nature of the dye‐detergent interaction, especially in the premicellar region, i.e. below the critical micelle concentration (cmc). The fluorescence spectra and decay behavior were found to depend on [AO] and [SDS]. An exponential fluorescence decay with a lifetime of 3‐4 ns was found for large [SDS]s together with a fluorescence band at 545 nm and the monomer‐type absorption spectrum. This can be attributed to the monomer dye associated with micelles. For smaller [SDS]s where the fluorescence band at 640 nm appeared together with a dimer band in absorption spectra, slower fluorescence decays were observed when we probed the long‐wavelength region (λobs > 620 nm). These decays can be attributed to the dimer of the dye associated with micelles. The presence of this slower decay below the cmc directly proves the presence of dye‐rich induced micelles. The distribution of dye molecules among the dye‐rich induced micelles is discussed assuming that the same fluorescence behavior is the consequence of the same distribution of dye molecules among micelles (above the cmc) or among dye‐rich induced micelles (below the cmc).

Photodissociation of molecular beams of N2O4

Abstract A molecular beam of N 2 O 4 molecules was photodissociated by an excimer laser at 193 and 248 nm. The time-of-flight distribution of NO 2 photofragments is consistent with the formation of two electronically excited NO 2* molecules in the Ā( 2 B 2 ) or B( 2 B 1 ) state. Visible emission from NO 2 * was observed in the photolysis at both 193 and 248 nm excitation. The parallel angular distribution of the NO 2 photofragments shows that at.193 nm N 2 O 4 has a transition dipole along the N-N axis and the dissociative lifetime is estimated to be less than 1 ps.

Photodissociation of Cl2SO at 248 and 193 nm in a molecular beam

A pulse molecular beam of Cl2SO was photodissociated at 248 and 193 nm. The time-of-flight distributions were observed for the photofragments, Cl, ClSO and SO. The primary processes are Cl + ClSO (I), 2Cl + SO (II) and Cl2 + SO (III). At 193 nm the measured translational energy distributions imply a vibrationally excited ClSO fragment in process (I), and a simultaneous dissociation in process (II). The relative quantum yield is φI < φII. At 248 nm a radical process (I) is dominant compared to a molecular process (III).

Large Third-Order Optical Nonlinearities of a Croconium Dye in Tetrahydrofuran Solution and in Poly(methyl methacrylate) Coating Films Measured Using Resonant Femtosecond Degenerate Four-Wave Mixing Technique

The third-order optical nonlinearities of a croconium dye in tetrahydrofuran (THF) solution and in poly(methyl methacrylate) (PMMA) coating films were measured using the femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profiles of the DFWM signal of the croconium dye were obtained with a time resolution of 0.3 ps (FWHM), and were found to consist of at least two components, i.e., the coherent instantaneous nonlinear response (electronic response) and the slow response due to the formation of excited molecules for both the THF solution and PMMA coating films. The electronic component of molecular hyperpolarizability, γe, of the croconium dye in the THF solution was determined to be ca. 4.6×10-29 esu at 817 nm. The electronic component of third-order nonlinear optical susceptibility, χ(3)e, of one of the present PMMA coating films containing the croconium dye was ca. 1.3×10-8 esu at 824 nm.

A spectroscopic study of the F(0+u) ion‐pair state of Br2 by the double resonance method

A new ion‐pair state of Br2 has been observed by an optical–optical double resonance technique utilizing ultraviolet fluorescence detection. The OODR excitations proceed in an one‐photon resonant three‐photon absorption through the B3Π (0+u) state. The effects of polarization on their transition strengths are used to determine the symmetry of excited molecular state formed by two‐photon absorption from the B state. The results indicate that the new state has the 0+u symmetry with Te=53 899.6(7) cm−1, ωe=155.8(2) cm−1, and re=3.276(8) A for 79Br2. This state is expected to correlate with Br+(3P0)+Br−(1S) and named F (0+u) after the well‐defined I2 molecule. The single rovibronic fluorescence spectra of the F(0+u) state show several transitions terminating on low‐lying valence states.