Quantitative evaluation of thermodynamic parameters for thermal back-reaction after mechanically induced fluorescence change

Kinetics of the thermal back-reaction of beta-diketonate boron difluoride complexes after mechanical perturbation were evaluated by fluorescence intensity changes for the first time, suggesting that the activation parameters of the reaction intermediates governed intermolecular interactions such as hydrogen bonding assisted by substituent groups.ArticleRSC ADVANCES. 3(43):19785-19788 (2013)journal articl

Concentration-Dependent Fluorescence Color Tuning of the Difluoroboron Avobenzone Complex in Polymer Films

We have investigated concentration-dependent fluorescence color tuning of BF2AVB in a poly(methyl methacrylate) film. BF2AVB exhibits a color change from purple-blue to orange via green, and then crystals segregate from the polymer matrix. We analyzed the fluorescence and fluorescence excitation spectral change as a function of the BF2AVB concentration in the film. We also obtained fluorescence microscope images to confirm the miscibility and crystallization properties in the films. This originates from the aggregated state formed in the polymer matrix depending on the stacking structure of the parallel (B-phase), antiparallel (G-phase), and amorphous states. The emissive species change with increasing BF2AVB concentration. The polymer matrix isolation method enables not only directly visualization of the dynamics of the crystal formation process and Ostwald’s rule of stages by fluorescence changes, but it also enables device fabrication, such as fabrication of organic light-emitting diodes and luminescent solar concentrators.ArticleBulletin of the Chemical Society of Japan.90(6):709-713(2017)journal articl

Fluorescence visualization of the molecular assembly processes during solvent evaporation via aggregation-induced emission in a cyanostilbene derivative

The initial stage of organic crystal formation during solvent evaporation was observed using aggregation-induced enhanced emission, indicating that the fluorescence from the J-aggregates was established prior to the increase in total intensity at the assembly process. This suggests that the kinetics of the transformation of J-aggregates into embryonic nuclei, and subsequently into crystals, can be visualized using fluorescence.ArticleCRYSTENGCOMM. 16(42):9779-9782 (2014)journal articl

Fluorescence properties of nanoaggregates of pyrene ammonium derivative and its photoinduced dissolution and reaction in tetrahydrofuran/aqueous solutions

We studied the fluorescence properties of nanoaggregates of pyrene ammonium derivative (PyAm) and their photoinduced dissolution and reaction in tetrahydrofuran (THF)/aqueous solution. The final concentration (dye concentration after reprecipitation) dependence of the fluorescence peak was measured. The fluorescence peak of PyAm that originated from the excimer is shifted to the long wavelength side increasing with the final concentration, which is ascribable to the characteristic fluorescence spectral changes depending on their size. The size-dependent fluorescence change in the nanoaggregates is related to some molecular conformation, packing, and elastic properties of the nanoparticles at the surface. To understand the fluorescence properties of the intermediates from aggregates to crystals is important for the studies of organic nanocrystals/aggregates prepared by the reprecipitation methods. We also determined the fluorescence spectra of the PyAm nanoaggregates in a THF/aqueous solution by photoinduced dissolution and reaction. It originated from the photochemical reaction between PyAm and THF. Changes in the perpendicular light scattering intensity by photoirradiation supports the photoinduced dissolution of PyAm in the THF/aqueous solution. These findings are important in the research field of photochemical reactions in organic nanocrystals.ArticleRESEARCH ON CHEMICAL INTERMEDIATES. 41(9):6897-6906 (2015)journal articl

Fluorescence Enhancement of a Dicyanostilbene Derivative Film Casted from an Alcoholic Solution Triggered by UV-light Irradiation

The films of a dicyanostilbene derivative (DBDCS) cast from an alcoholic solution show aggregation-induced emission enhancement by UV light irradiation and a fluorescence color change from green to blue upon heating. The former can be attributed to the planarization by rotational motion around the olefin moieties due to elevation in the local temperature via the excited state by UV irradiation. The latter originates from the phase transformation of DBDCS with cooperative alcoholic desorption and molecular reorganization.ArticleChemistry Letters.45(4):421-423(2016)journal articl

Fluorescence properties of pyrene derivative aggregates formed in polymer matrix depending on concentration

We investigated the fluorescence properties of dye aggregates formed in a poly(vinylalcohol) (PVA) matrix by phase separation. Trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide (PyAm) was used as a fluorescent dye molecule. The size of PyAm aggregates in the PVA thin films were increased with increasing dye concentration, which was confirmed by atomic force microscope (AFM) measurements. The fluorescence spectra of PyAm in the PVA film at a lower concentration of 0.001 mol% only showed the monomer emission. The fluorescence peak shifted to the red with increasing dye concentration, which was assigned to a dimer or excimer-like emission. Changes in the fluorescence spectra relate to the formation of aggregates in the films. The fluorescence anisotropy decay time constant increases with increasing PyAm concentration up to the order of 100 ps. It is suggested that the exciton efficiently diffuses within the aggregates, and then was trapped at the dimer sites. We also demonstrated the application for gas sensing of nitroaromatics: 2,4-dinitrotoulene (DNT) based on the fluorescence quenching by the photoinduced electron transfer. The quenching efficiency of PyAm fluorescence reached about 43% under concentration of 2.0 mol%. The fluorescence intensity efficiently quenched at the dimer or excimer-like band. These results indicated that the efficient fluorescence quenching increases the reaction probability between PyAm and DNT by the exciton diffusion in the aggregates, called "amplified quenching''. The nano-sized aggregates of PyAm formed in the PVA films are responsible for high sensitivity as an artificial fluorescent chemosensor for vapors of the nitroaromatics.ArticlePHYSICAL CHEMISTRY CHEMICAL PHYSICS. 12(36):10923-10927 (2010)journal articl

Properties and evolution of emission in molecular aggregates of a perylene ammonium derivative in polymer matrices

Accepted 27 Jul 2015Size-dependent fluorescent properties of aggregates of a perylene ammonium derivative (PeryAm) were studied by steady-state and time-resolved spectroscopic methods. Quantitative analyses of aggregated states in aqueous solution indicated that the aggregation proceeded through dimer units of PeryAm. The fluorescence of the aggregate in the PVA film prepared from the aqueous solution continuously redshifted with an increase in the concentration of PeryAm in the mother liquor while keeping the absorption spectra in almost the same band shapes. Fluorescence anisotropy values of aggregates in the PVA film were dependent on the monitoring wavelength, and time profiles of the fluorescence at longer wavelengths showed a rapid increase just after the pulsed excitation. These results indicated efficient energy transfer to the stable sites in aggregates. Fluorescence microscopy images showed that aggregates were segregated in the PVA film and the color of the emission was dependent on the size of the aggregate. Under the steady-state irradiation, the emission color of the aggregates changed from green to yellow, which was attributable to the association of a small cluster of PeryAm with the green emission resulting in the formation of yellow-colored aggregates. On the basis of these results, we have discussed the mechanisms and dynamics of the aggregation and size-dependent emission in aggregates.ArticlePHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES. 14(10):1896-1902 (2015)journal articl

Fluorescence properties of aromatic amine adsorbed on metallic and semiconducting single-walled carbon nanotubes

Semiconducting single-walled carbon nanotubes (SWNTs) have been enriched by 1-aminopyrene treatment of the mildly oxidized SWNTs due to removal of metallic SWNTs having a higher affinity for 1-aminopyrene. The enrichment was caused by the differences in the adsorption properties of 1-aminopyrene on the metallic and semiconducting SWNTs. The fluorescence properties of 1-aminopyrene adsorbed on the metallic and semiconducting SWNTs have been investigated in order to clarify its adsorption mechanism. 1-Aminopyrene was adsorbed on the metallic SWNTs through the interaction of the amino group with the graphene surface and through a hydrogen bonding interaction between the amino group and the carboxyl group on the graphene surface. On the other hand, in the case of semiconducting SWNTs, 1-aminopyrene was adsorbed through a pi-pi interaction on the graphene surface in addition to the hydrogen bonding interaction with the carboxyl groups.ArticleJOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY. 218(2-3):226-230 (2011)journal articl

Fluorescence visualization of the molecular assembly processes during solvent evaporation via aggregation-induced emission in a cyanostilbene derivative

The initial stage of organic crystal formation during solvent evaporation was observed using aggregation-induced enhanced emission, indicating that the fluorescence from the J-aggregates was established prior to the increase in total intensity at the assembly process. This suggests that the kinetics of the transformation of J-aggregates into embryonic nuclei, and subsequently into crystals, can be visualized using fluorescence.ArticleCRYSTENGCOMM. 16(42):9779-9782 (2014)journal articl