Environment effect on the electronic absorption spectra of crystal violet

Solvent polarizability and anisotropy effects on the photophysical behavior of oxazine 1: an appropriate polarizability indicator dye

The spectroscopic features of a laser dye, oxazine 1 (OX1), were investigated in liquid and in liquid crystalline solutions as a function of the solvent polarity and polarizability. The nature of spectral shift was investigated by studying the absorption spectra of the dye in different solvents. The spectral shifts were correlated by the solvent polarity and polarizability. As a result, the solvent polarity has no large and regular effect on the spectral behavior of the dye, and thus it might be considered as a poor solvatochromic dye. In contrast, an excellent linear correlation was observed between the solvent polarizability and the spectral properties of the dye, and therefore, this dye might be considered as a good indicator for measuring the solvent polarizability. The absorption and fluorescence spectra of the dye were investigated in nematic solvents with high birefringence. In nematic solvents, anisotropy of polarizability has a major contribution to the shaping of the absorbance and emission spectra of OX1.

Solid phase adsorption of crystal violet lactone on silica nanoparticles to probe mechanochemical surface modification

The solid phase adsorption of crystal violet lactone (CVL) on five types of Stober silica nanopowders with BET specific surface areas in the range of 50-800 m2/g under dry milling conditions was described for the first time. The hydrogen bonding between surface silanol and the carboxylate of the ring-opened triphenylmethane dye (CVL+) led to the formation of monolayers of CVL+ in a flat-laid configuration. The lambda max of CVL+ in diffusive reflection visible spectra was influenced by the particle size of silica powders, suggesting that the microenvironmental polarity of adsorbed CVL+ is considerably reduced along with the decrease of the particle size. The solid phase adsorption of CVL obeyed Langmuir adsorption isotherms to give a saturated amount of CVL+ for every silica nanoparticle. The surface concentration of CVL+ on nanoparticles at the saturation was estimated to be 0.31 mg/m2 on average, disclosing that about 52% of the surface can be covered by CVL+ under the assumption that the BET-specific surface areas are equivalent to the real surfaces active for the CVL adsorption. The generation of the blue color of CVL provided a convenient means to estimate qualitative and quantitative analysis of the surface coverage with surface-active reagents, which conceal surface silanols. Subsequently, silica nanoparticles were milled with a surface modifier, followed by milling with CVL to observe the intensity of the blue color in order to disclose that the surface coverage with oligo- and polyethylene glycols as well as with nonionic surfactants by dry milling was specifically determined by the number of repeating oxyethylene units. Although the surface-active reagents were easily desorbed in water, the desorption was notably suppressed by milling with CVL, suggesting that the surface-modified particles with the surface-active reagents are covered with ultrathin films of CVL.