Photophysical studies of molecular mobility in polymer films and bulk polymers. 2. Quenching of pyrene fluorescence by phthalic anhydride in bulk poly(dimethylsiloxanes)
- Univ. of Notre Dame, IN (USA)
Molecular mobility in bulk poly(dimethylsiloxanes), PDMS, has been monitored by measuring the quenching rate constant k{sub q} of pyrene fluorescence by phthalic anhydride, PA. Increasing PDMS molecular weight resulted in a marked change in viscosity but did not impose significant restriction on solute mobility in PDMS at room temperature and at viscosities > 50 cP. The simple relationship k{sub q} {proportional to} ({eta}){sup {minus}0.04} is obeyed. However, a relationship k{sub q} {proportional to} ({eta}){sup {minus}0.04} holds in PDMS at low viscosity from 1 to 50 cP. Diffusion coefficients of reactants in PDMS are 1.4 {times} 10{sup {minus}5} to 2.2 {times} 10{sup {minus}6} cm{sup 2} s{sup {minus}1} and are larger than those in squalane, the room temperature viscosity of which is only 35.4 cP. It is concluded that no simple relationship between k{sub q} and {eta} can be applied for all viscous systems. A significant effect of temperature on the quenching rates was observed, and an empirical relation between k{sub q}, T, {eta}, and activation energy, k{sub q} {proportional to} (T/{eta}){sup E{sub a}/2.3+E{sub {eta}}} was derived in agreement with the experimental data, where E{sub a} and E{sub {eta}} are the activation energies of quenching and viscous flow, respectively. The data are explained by utilizing concepts of macroviscosity, microviscosity, chemical structure of the polymer chains, and also free volume theory. High yields of excited pyrene triplets were observed in the laser photolysis of pyrene-phthalic anhydride in bulk PDMS and in cyclohexane, while the yield in acetonitrile was reduced. This is attributed to a fast back electron transfer process from the product anion to the pyrene cation which yields excited triplets of pyrene in alkane solution but not in polar solvents.
- OSTI ID:
- 7073254
- Journal Information:
- Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 93:16; ISSN 0022-3654; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360603* -- Materials-- Properties
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400000 -- Chemistry
400201 -- Chemical & Physicochemical Properties
AROMATICS
CONDENSED AROMATICS
DATA
DATA ANALYSIS
EXPERIMENTAL DATA
FILMS
FLUORESCENCE
HYDROCARBONS
INFORMATION
LUMINESCENCE
MATHEMATICAL MODELS
MEASURING INSTRUMENTS
MEASURING METHODS
MOLECULAR MODELS
NUMERICAL DATA
ORGANIC COMPOUNDS
POLYMERS
PYRENE
QUENCHING
SURFACE PROPERTIES