Department of Physics
Permanent URI for this collectionhttp://localhost:4000/handle/123456789/1932
Browse
3 results
Search Results
Item Photophysics of protonated 6-methoxyquinoline: steady state and time-dependent fluorescence(Elsevier, 1990-11) Pant, Debi D.Nanosecond time-resolved emission spectroscopy was used to investigate the excited state solute—solvent interaction in 6-methoxyquinoline. A red shift in the emission maximum is observed on excitation at the red edge of the absorpton band which depends on the temperature and viscosity of the medium. The fluorescence lifetime is dependent on the emission and excitation wavelengths. A significant change in the energy of emission is observed on the nanosecond time scale. The room temperature data can be explained using the Bakhshiev formulation of solvent relaxation. However, transient and steady state fluorescence studies from 80 to 290 K reveal that, at 160 K, a rapid relaxation process occurs (not solvent relaxation). The photophysics of 6-methoxyquinoline are similar to those of the quinine dication which exhibits two relaxation processes (from 80 to 290 K) — a charge-transfer process around 160 K and a solvent relaxation process at ambient temperature.Item Photophysics of doubly-charged quinine: Steady state and time-dependent fluorescence(Elsevier, 1990-04) Pant, Debi D.The quinine dication in aqueous solution (1 N H2SO4) gives two fluorescence lifetimes (τ1 = 2.80 ns and τ2 = 19.36 ns) at ambient temperature. τ2 shows a small increase with an increase in acid concentration between 0.1 N and 15 N. Quenching by Cl− shows that τ1 and τ2 are differentially quenched. The Stern—Volmer quenching constant KSV for τ1 is 10 M−1 and for τ2 is 75 M−1. In addition, KSV is dependent on emission wavelength. In acidified solution, τ2 increases with an increase in emission wavelength, whereas τ1 exhibits a behaviour which resembles a two-state mechanism with a negative amplitude in the region of longer emission wavelength. However, the two-state theory does not give an entirely satisfactory mechanism for the time-dependent emission. Time-resolved emission spectroscopy (TRES) shows a spectral relaxation which partially explains the dependence of τ2 on emission wavelength in accordance with Bakhshiev formulation. Transient and steady state fluorescence studies from 80 to 290 K show that at 160 K there is a rapid relaxation process resulting in an increase in τ2 and a sudden spectral shift. We propose that the complex behaviour of quinine decay consists of two major relaxation processes: a charge-transfer process which occurs around 160 K and a solvent reorientation process which occurs in the fluid medium.Item Structure and Intermolecular Dynamics of Liquids: Femtosecond Optical Kerr Effect Measurements in Nonpolar Fluorinated Benzenes(Elsevier, 1998-07) Pant, Debi D.Polar solvation dynamics of a 95:5% (v/v) water/acetone mixture have been measured at the ZrO2 nanoparticle surface by time-resolved fluorescence of a probe molecule adsorbed to the particle surface. The interfacial solvent response displays two sub-picosecond diffusive components with the same time constants as bulk solution. However, the relative amplitudes for the individual relaxation components are significantly different, leading to a faster average solvation response for molecules at the ZrO2 surface. Furthermore, the overall fluorescence Stokes shift is approximately three times smaller for dye molecules adsorbed to the nanoparticle surface. Implications for electron injection into semiconductor nanoparticles are discussed.