Photoluminescence in small isotactic, atactic and syndiotactic PVA polymer molecules in water

Polyvinyl alcohol (PVA) dispersed in small polymer molecules in water (similar to4.0 g/dl) has photoluminescence (PL) in three distinct bands at 415. 437. and 465 nm. This occurs in a resonance excitation with vibronic level of O-H stretching vibration v(1) (or overtone) at lambda(ex) = 400 or 350 nm wavelength of excitation. Relative band intensities, which lie in the 100:94:45 order in three bands in lambda(ex) = 350 nm excitation.. vary depending on the excitation process with a function of the value of lambda(ex) and PVA concentration in the solution. A single band occurs of the absorption spectrum at 196 nm in an altogether different pi - pi* electronic transition. The three PL bands thus attribute to pi - pi* electronic transition in non-bonding 2p(2) (O) electrons in free OH groups in three syndiotactic (s), atactic (a), and isotactic (i) conformers of PVA polymer molecules. v, band appears in a resonance Raman transition at similar to3215, 3475, or 3560 cm(-1) in the respective conformers. Solvent interaction with H2O molecules (destabilizes s- and i-PVA to convert into a-PVA) quenches the PL progressively in dilute solutions so that it no longer occurs in concentrations below 1.0 g/dl. The results are analyzed and modeled in terms of the localized n-electrons in small polymer molecules. (C) 2004 Elsevier B.V. All rights reserved.