Novel pendant azobenzene/polymer systems for second harmonic generation and optical data storage

Mitica Cezar Spiridon,Konstantinos Iliopoulos,Florica Adriana Jerca,Valentin Victor Jerca,Dumitru Mircea Vuluga,Dan Sorin Vasilescu,Denis Gindre,Bouchta Sahraoui

doi:10.1016/j.dyepig.2014.10.010

Abstract

New poly(methyl methacrylate)s bearing push–pull azo-moieties, with the azo-dye content ranging from 31 wt% to 100 wt%, are synthesized by (co)polymerization of a methacrylamide-based azo-monomer. The high reactivity of the colored monomer allowed well-balanced structures to be achieved, characterized by a suitable thermal stability. The second harmonic generation efficiency of the poled samples is investigated by means of the SHG Maker fringes setup. Features that hinder the translation of the azo-moiety optical nonlinearity in the material at the macroscopic level are debated. The results underline the role of chromophore–chromophore and chromophore–polymer interactions on the alignment of the azo-moieties. The polarity of the polymer matrix is proven to influence the chromophore–chromophore interactions. Two-photon absorption is employed for gray scale encoding of second harmonic signals on poled thin films, thus pointing out the possibility to employ these new materials for optical data storage applications.

Highlights

Nowadays, there is an increasing research interest in organic materials which exhibit significant nonlinearities, as they can be used in a diversity of photonic applications [1e6]
We obtained two dimensional Second HarmonicGeneration (SHG) images of the samples by employing SHG microscopy and we show that optical data storage can be successfully achieved in these structures
The nonlinear optical first-order hyperpolarizability (b) includes two parts in a donor-p-acceptor molecule: one is the hyperpolarizability resulting from charge separation induced by the high field, and the other part is the hyperpolarizability from the contribution of charge transfer state

Summary

Introduction

There is an increasing research interest in organic materials which exhibit significant nonlinearities, as they can be used in a diversity of photonic applications [1e6]. Intense research activity is ongoing to find optical data storage materials, as well as suitable processes, for surpassing the capacity limits of the currently utilized storage media [7] In this direction we have recently demonstrated the possibility to store information in coumarin-based copolymer thin films by using photo-induced dimerization [8,9]. Higher SHG is achieved only after a noncentrosymmetric polar ordering of the chromophores [29] This requirement is attained using various methods, i.e. corona poling [30]. In this framework, we designed a series of new poly(methyl methacrylate)s bearing a pushepull type azo-moieties (Scheme 1), covalently attached from the acceptor site. We obtained two dimensional SHG images of the samples by employing SHG microscopy and we show that optical data storage can be successfully achieved in these structures

First-order hyperpolarizability determination using the solvatochromic method

Instrumentation

Synthesis and poled thin films preparation

Results and discussion

Molecular weights of the azo-polymers

Copolymer composition and monomer reactivity ratios

Thermal properties

Nonlinear optical properties of azo-polymers

Conclusions