Size-Tunable Emission from 1,3-Diphenyl-5-(2-anthryl)-2-pyrazoline Nanoparticles

Abstract

Organic nanoparticles of 1,3-diphenyl-5-(2-anthryl)-2- pyrazoline (DAP) ranging in average diameters from 40 to 160 nm were prepared through the reprecipitation method. The average diameters of the particles were controlled by variation of the aging time. We found that DAP nanoparticles exhibit the size-dependent optical properties. The absorption transitions of the nanoparticles at the lower-energy side experience a bathochromic shift with an increase in the particle size as a result of the increased intermolecular interactions, while the higher-energy bands of anthracene split possibly due to the electronic coupling between the pyrazoline ring of one molecule and the anthracene moiety of the neighboring molecule. Most interestingly, the nanoparticle emission in the blue light region from pyrazoline chromophore shifts to shorter wavelengths with an increase in the particle size, accompanied with a relatively gradual dominance of the emission at about 540 nm from an exciplex between the pyrazoline ring of one molecule and the anthracene moiety of the neighboring molecule. The hypsochromic shift in the emission of DAP nanoparticles was identified as originating from the pronounced decrease in the Stokes shift due to the restraint of vibronic relaxation and the configuration reorganization induced by the increased intermolecular interaction.

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

“…Yao et al reported the size dependence of emission spectra for pyrazoline nanoparticles. 11 The fluorescence peaks shift to red increasing the particle size. They concluded that the 55 effects originated from the formation of charge transfer excitons, depending on the particle size.…”

“…The size-dependent optical properties have been widely studies by several groups. [5][6][7][8][9][10][11][12][13][14][15][16] Asahi and Masuhara et al precisely studied the relation between the optical properties and crystal size by using single particle fluorescence spectroscopy coupled with atomic force 50 microscopy (AFM). 7,8 It is found that the size dependence is correlated well to the surface-to-volume ratio of nanocrystals.…”

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

“…Kasai and Nakanishi et al first reported that the fluorescence spectra of perylene nanocrystals, which were prepared by the reprecipitation method, depended on their size, and the fluorescence spectra of the nanoparticles differ from that of the bulk crystals [2,3]. There are many reports about organic nanoparticles in the past decade [4][5][6][7]. They proposed lattice softening of the nanoparticles as a cause of the size-dependent optical properties.…”

“…They proposed lattice softening of the nanoparticles as a cause of the size-dependent optical properties. Yao et al reported the size dependence of the emission spectra for pyrazoline nanoparticles, which originated from the formation of charge transfer excitons due to the flexibility and various inter-and intramolecular overlapping structures in the nanoparticles [5].…”

“…They proposed lattice softening of the nanoparticles as a cause of the size-dependent optical properties. Yao et al reported the size dependence of the emission spectra for pyrazoline nanoparticles, which originated from the formation of charge transfer excitons due to the flexibility and various inter-and intramolecular overlapping structures in the nanoparticles [5].We have investigated the fluorescence properties of pyrene ammonium derivative (PyAm, Figure 1) in poly(vinylalcohol) (PVA) thin films [8]. The fluorescence spectra of PyAm in the PVA film at a lower concentration showed only a monomer emission.…”