The Effect of ω-Substituted Acceptors in 4-Dimethylamino-trans-Styrenes on the Polarity in the Ground and Excited Singlet State
ABSTRACT The electric dipole moment in the ground (μg) and in the first excited singlet state (μe) of co-substituted acceptors in 4-dimethylamino-trans-styrenes (Z = P(S)Ph2 , P(O)Ph2 , SO2CH3 ) were determined by solvatochromic and thermochromic methods. The obtained values of μe and μg and the values for Z = CN and Z = NO 2 known from the literature [2] fulfill the linear relation between the dipole moments (μe or μg and the Hammett constants σp of the substituents. On pincreasing the electron-acceptor power of Z, μe grows faster than μg
Viscosity independence of the ratio of fluorescence lifetimes and quantum yields of ω-substituted 4- dimethylamino-trans-styrenes
Abstract The fluorescence lifetimes τ and quantum yields φ F of 4-dimethylamino-ω-diphenylphosphinyl- trans -styrene ( 2a ) and 4-dimethylamino-ω-methylsulphonyl- trans -styrene ( 3a ) were measured in n -paraffins ( n = 6 to n = 16) at 293 K. The ratio τ/φ F was found to be viscosity independent and equal to the radiative lifetime τ 0 ′ calculated from the integrated absorption spectrum. The strong fluorescence quenching and the shortening of the lifetime τ when reducing the viscosity are due to twisting around the double bond, resulting in trans-cis isomerization.
Viscoelastic Measurements of Poly(dimethylsiloxanes) and a Polystyrene Solution Using the Layered Waveguide Technique
An experimental system is developed to measure the high frequency (1 MHz to 7 MHz) viscoelastic constants of liquids and deformable solids using a layered waveguide geometry consisting of an aluminum strip delay line upon which coatings are applied. A piezoelectric transducer mounted at one end is used to generate and receive pulses of radio frequency shear waves that reflect back and forth in the line. The change in attenuation and the phase shift of the wave in the line produced when the sample coating is applied are measured by a calibrated attenuator method and an echo superposition technique, respecively. From these measurements the viscoelastic constants of the sample are calculated using the layered waveguide equations developed earlier. The conditions under which these equations can be applied to the delay line are discussed in detail. Tests were made with a series of four poly(dimethylsiloxane) samples having static viscosities ranging from 100 to 100,000 centistokes. The measure changes are calc...