Substances possessing substituted phenyl groups which are capable of internal rotation increase their fluorescence with increasing viscosity of the medium.of auramine 0, a substituted diphenylmethane dye, measured in glycerol a t various temperatures and in dextrose-glycerol-water mixtures a t room temperature followed the relation @ = ( ? / T ) / [ m + @ ( 7 / T ) ] where CY and ( 3 are constants, 7 is the viscosity and T is absolute temperature. The results are interpreted as being due to one of the fluorescence quenching steps passing via a rotational diffusion process. We calculate that this steD takes place if during the period of excitation of the light-excited dye the groups on the molecule have rotatedThe fluorescence yield relative to one another by more than i".
The general theory of moir6 patterns obtained from parallel rulings and concentric circles is presented. Near superposition of a regular ruling on to parallel rulings of variable spacings results in a curved moire pattern which is functionally related to the deviation in spacings. When two figures consisting of uniformly spaced concentric circles are overlapped, the resulting moir6 patterns are hyperbolas defined by the centerto-center distance of the figures and the interring spacing. Since very small relative displacements of the figures result in large changes in the moire pattern, this technique can be a sensitive detector of minute changes in refractive index and in refractive index gradient which bring about apparent relative displacement of the figures. The technique is demonstrated for the case of a constant refractive index gradient and for a variable refractive index gradient as encountered in diffusion measurements. Birefringence and dispersion can also be determined utilizing the moire method. Demonstration of the use of the moire technique for the evaluation of lenses is also presented.
SYNOPSISVarious aspects of the application of fluorescence characteristics in the field of polymer research are described. The polarization characteristics of fluorescence, that is, the angular distribution of the intensity of the polarized component, are indicative of the distribution patterns of fluorescent molecules in the medium. This principle can be utilized for the investigation of molecular orientation behavior in polymer solids. Examples are given for the molecular orientation behaviors during the deformation of poly(viny1 alcohol) and polypropylene films. The phenomenon of rotational depolarization of fluorescence is applied to the measurement of micro-Brownian motions of polymer chains and the local viscosity of polymer solutions and melts. The internal structure of concentrated poly(styrene) solutions and the molecular motions in the melts of n-paraffins and polyethylene homologs are discussed. Rotational relaxation time ranging from 1 0-l2 to lo-' sec can be measured by this method by using the lifetime of excitation of fluorescent groups as the reference time scale. The phenomenon of the excimer fluorescence emitted from the excited dimer provides a new method for studying molecular configuration and conformation of polymer molecules. Examples are given for the case of naphthalenecontaining polymers. The sequence of monomeric units in copolymers of vinylnaphthalene and styrene are studied from the intensity of excimer fluorescence relative to that of ordinary fluorescence from the naphthalene groups. The intramolecular excimer formations of polymer molecules are also discussed in relation to molecular motions.
Absolute rate constants for electron-transfer reactions of aromatic molecules in solution at room temperature have been studied by the nanosecond laser photolysis method. Holes or electrons of photochemically produced radical cations or anions were transferred to second aromatic compounds. The decay of the ion radical donor and the rise in the amount of the ion radical acceptor for each donor and acceptor pair were observed at their absorption maxima, and the simulation of this rise and decay gave electron transfer rate constants. The relationship between these rate constants and the reaction free energy change showed that the electron transfer of highly exothermic reactions proceeds with a diffusion-controlled rate constant, which suggests that electron transfer occurs through some loose complex in solution.
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