Positron annihilation studies on chalcone chromophore doped PVA

Abstract

AbstractA novel organic non‐linear optical material 1‐(4‐methylphenyl)‐3‐(4‐ N, N dimethyl amino phenyl)‐2‐propen‐1‐one (MPDMAPP) chalcone chromophore has been synthesized by standard method. Pure and MPDMAPP doped Poly(vinyl alcohol) films are prepared using solution casting method and characterized using UV‐Visible absorption and Positron Annihilation Lifetime Spectroscopy. The optical spectroscopic study shows three absorption bands, 196‐202 nm assigned to localized n →π * transitions, 205‐320 nm to n →π * inter‐band and 385‐428 nm assigned to π →π * transition and arises due to the charge transfer complex. Using observed UV‐Vis spectra, three optical energy gaps, Eg1 (4.96–4.25 eV), Eg2 (3.47–3.32 eV) and Eg3 (2.33–2.24 eV) have been estimated. The observed change in Eg upon doping is understood based on the formation of charge transfer complex arising from the –HC=CH– structure present in the composite and due to the interactions of dopant and OH group of PVA. The PALS results shows that the o‐Ps lifetime decreases continuously as doping concentration increases and I3 initially increases (from 18.82% to 20.95%) from 0 wt% to 0.05 wt% and then decreases gradually up to 16.76% for higher dopant concentrations with decrease in optical band gaps. The variation of positron data with Eg is understood by correlating the probability of Ps formation with the complex. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)