Theoretical predictions for the development of molecular glasses with quadratic nonlinear optical activity on the basis of azochromophores with various cyano-containing acceptors

Abstract

A computational study of amorphous materials based on various azochromophores with cyano-containing acceptor moieties and bulky substituents in donors and acceptors is presented. The structure of azochromophores is optimized at B3LYP//6-31G(d) computational level in gas and chloroform; molecular static electric properties (dipole moment, average polarizability and first hyperpolarizability) of the chromophores are calculated by DFT at M06-2X//aug-cc-pVDZ level; the effect of the environment is accounted in the framework of PCM approach. The values of chromophores first hyperpolarizability, β_tot, are shown to correlate with the strength of the acceptor moiety; the effect of the solvent results in the 2.7 ÷ 3.2 times enhancement of β_tot, the maximal value is demonstrated by DEA(Et)-AB-TCV (the chromophore with ethyl-substituted diethylaniline donor and tricyanovinyl acceptor) – 1293 ⋅ 10⁻³⁰ esu in chloroform. Atomistic simulation of molecular glasses based on the studied chromophores in amorphous cell is performed with OPLS3e force field modified with ESP charges on chromophore atoms calculated at B3LYP//6-31G(d) level. For molecular materials formed by azochromophores with tricyanofuran (TCF) acceptor the calculated glass transition temperature is 450 and 488 K for DEA-AB-TCF and DEA-AB-TCF(CyPh), respectively. Simulation in the applied electric field at poling temperature 500 K is performed with the field strength 300, 500 and 1000 V/μm; centric, P2, and acentric, <cos³Θ>, order parameters were estimated. The effective chromophores orientation in the material was demonstrated at the field strength 500 V/μm, P2 = 0.15 and <cos³Θ> = 0.25 being estimated for DEA-AB-TCF.