J. Vandendriessche

Investigation of the mobility of polybutadienes: 1. Excimer fluorescence technique

Abstract Intramolecular excimer formation of meso-2,4-di( N -carbazolyl)pentane dissolved in polybutadienes of molecular weight 500 and 1000 has been investigated. The probe dynamics, which follow the WLF equation, are not similar in the two matrices. The effect cannot be ascribed to the difference between the glass transition temperatures of the two polymers but to a variation of their microstructures.

Intramolecular exciplex formation in 1-(1-pyrenyl)-3-(N-skatolyl)propane☆

Abstract The photophysical properties of 1-(1-pyrenyl)-3-( N -skatolyl)propane were investigated. Excitation of the pyrene chromophore leads to the formation of an intramolecular exciplex. This complex has a larger dipole moment than that of the corresponding intermolecular complex. The kinetics of exciplex formation are analysed in solvents of various polarities. The binding energy of the complex increases with solvent polarity. The decay pattern of the pyrene fluorescence indicates fast equilibration between the various conformers in comparison with the rate of exciplex formation.

Excimer formation in poly(N-vinylcarbazole) and its model compounds as revealed by picosecond time-resolved absorption spectroscopy

Abstract The absorption spectra of N-ethylcarbazole, 1,3-di(N-carbazolyl) propane, meso (d¢)-2,4-di(N-carbazolyl) pentane and poly(N-vinylcarbazole) in the excited singlet state were measured in solution by a picosecond Nd 3+ : YAG laser photolysis method. Analyzing the absorption rise curve, the formation time constant of the sandwich excimer at room temperature is determined and discussed.

Studies of the mobility of probes in poly(propylene oxide): 2. Excimer fluorescence technique

Abstract Intramolecular excimer formation of meso -2,4-di( N -carbazolyl)pentane dissolved in two poly(propylene oxides) of molecular weights 425 and 4000 as well as in 1,2-propanediol (monomer) has been investigated. The intramolecular conformational change required for the excimer sampling process is shown to be controlled by the segmental motions of the polymer matrices involved in the glass transition phenomenon. The data obtained in 1,2-propanediol have been fitted by a Vogel-type WLF equation. The results show that intermolecular interactions in the monomer lead to a thermal expansion coefficient of the free volume smaller by a factor of about 2 than that of the polymer.

Relation between excimer formation in small probes and free-volume theory in polymer melts

Abstract Intramolecular excimer formation of meso-2,4-di( N -carbazolyl)pentane dissolved in different elastomers has been investigated. The intramolecular conformational change required for the excimer sampling process is shown to be controlled by the segmental motions of the polymer matrix involved in the glass transition phenomenon. The results show that, at a fixed frequency of the probe motion, the fractional free volume as well as the free volume per atomic group vary from one polymer to another.

An interpretation of the photophysical properties of poly(N-vinylcarbazole) based on bichromophoric model systems and the conformational analysis of the polymer

Abstract The photophysical properties of poly(N-vinylcarbazole) are interpreted, based on the photophysical properties of the diastereomers of 2,4-di(N-carbazolyl)pentane and a theoretical study of the conformational distribution in the dyads of poly(N-vinylcarbazole). From the conformational distribution in the polymer it is derived that more than 95% of the excitation will occur on a chromophore belonging to an excimer site. Since excimer formation at these excimer sites is very rapid (>10 10 s −1 ), it is concluded that, if energy migration is to be important, the rate constant of energy migration from one chromophore to another should be ⪢10 10 s −1 .

Studies of cyclic and linear poly(dimethylsiloxanes): 26. An investigation of the mobility of cyclic poly(dimethylsiloxane) in the melt through the excimer emission of small probes

Abstract Intramolecular excimer formation of 10,10′-diphenyl-bis-9-anthrylmethyl oxide as well as of meso-2,4-di( N -carbazolyl)pentane in a cyclic poly(dimethylsiloxane) has been investigated. It is shown that the rate of conformational change of the probes contains an intramolecular component in addition to that of the local chain dynamics.

Polymer photophysics: A model approach

Abstract The study of the excited state behaviour of 2,4-diarylpentanes and 1,1′-diaryl diethyl ethers illustrates the importance of configurational and conformational aspects in the intramolecular excimer formation of di- and poly-chromophoric systems. This model approach is a first step in the understanding of complex polymer photophysics.

Fluorescence Probing of the Local Dynamics of Polymers: A Model Approach

The importance of the ground state configurational distribution of a polymer chain in solution in relation to its physical properties has been well recognized. Differences in the photophysical properties of polymers with different tacticity have been noted in the past. However, an in depth study of the relation between the configurational distribution and polymer photophysics is still, in view of the complexity of the possible relaxation pathways in a polymer system, a difficult task.