Distance Effects of Phenylpiperazine-Containing Methacrylic Polymers on Optical and Structural Properties

New materials based on methacrylic polymers modified with 1-(4-nitrophenyl)piperazine side chains, differing in the distance of the chromophore from the polymer main chain and/or the separation between the chromophoric units in the chain, are obtained and characterized in terms of their potential applications in optoelectronic devices. The surface, structural, and optical properties of the investigated materials are determined using atomic force microscopy, spectroscopic ellipsometry combined with transmission measurements, Raman and Fourier transform infrared spectroscopy, as well as cyclic voltammetry. The relevant model systems are additionally analyzed with quantum chemical density functional theory calculations in order to enable the generalization of the structure-photophysical property relationships for the optimization of the material features. It is found that the structural modification of the material, relying on the transit of the piperazine moiety away from the main polymer chain, leads to the hypsochromic shift of the absorption spectrum. Moreover, the lowest refractive index values are obtained for the polymer with a distant ethylene group in the side-chains and increased separation between the piperazine units. It was shown that the optical energy band gaps of the investigated piperazine-containing polymers are in the range from 2.73 to 2.81 eV, which reveals their promising potential for the advances in photovoltaics, field effect transistors, or electrochromic devices as an alternative for other widely applied polymer materials.