Molecular Modeling Of Methacrylic Composite Materials Doped With Nonlinear Optical Azochromophores With Various Acceptor Fragments

The methacrylate-based composite polymer materials with various weight content of azochromophores-guests - aminoazobenzenes with various acceptor moieties: AAB-NO2, AAB-DCV, AAB-TCV, and AAB-TCP, - are studied by atomistic modeling. Polymer matrices are PMMA, copolymer of methyl methacrylate and methacrylic acid, MMA-MAA, and copolymer MMA-MAZ, MAZ unit containing azochromophore, covalently attached to the side chain via spacer. The realization of various non-covalent interactions (hydrogen and pi-pi interactions) is considered, special emphasis is given to the role of chromophore structure and polymer matrix nature. It is shown that rather uniform distribution of chromophores in composite materials is retained even at 30 wt% content. In all composites with chromophore content growth both the number of non-covalently bound chromophores and the proportion of chromophores bound inter se increase, while the proportion of chromophores, bound with polymer matrix, decreases. The number of hydrogen bonds (HBs) between chromophores-guests is determined mostly by the nature of the acceptor group of the chromophore, maximum number of HBs being formed by AAB-TCP. The MMA-MAA matrix allows realization of greater number of inter-chain HBs compared to MMA-MAZ matrix, while such bonds are absent in PMMA. Azochromophores in MAZ units of MMA-MAZ matrix form pi-pi-stacking structures with mostly codirected chromophore dipole moments, besides AAB-TCV guests form such stacking structures with host matrix chromophores. Chromophores in MAZ units more easily interact with guests than with each other via pi-pi stacking. The studied matrices could be considered promising to be used as hosts at developing composite materials with quadratic nonlinear optical response.