Tunable Optoelectronic Properties of Polydimethylsiloxane-Arylazopyrazole Flexible Composite

Growing interest in flexible electronic platforms spurs introduction of guest structures into polymeric materials to achieve composites with novel optical and electronic properties. In this work, optoelectronic composites were realized by incorporation of novel derivative of arylazopyrazole (AAP) in polydimethylsiloxane matrix. The composites were investigated before and after irradiation with 365 nm UV source through optical spectroscopy. The responses at UV - Vis region, revealed significant regulation of properties by the presence and photoisomerization of embedded AAP, as well as a strong dependence on concentration. The refractive indices ranged from 1.83 - 2.38 in pristine state and 1.59 - 1.71 upon UV irradiation; and associated dielectric constants were 3.5 - 5.5 and 3.0 - 4.0, respectively. The impact of concentration manifested in increasing magnitude of properties as AAP concentration increased. In pristine state, composites absorbance spectra showed maxima centered at 340 nm that was typical of π→ π
^*
transition in the AAP. After exposure to UV, the maxima shifted to ~ 310 nm with secondary peak occurring at 450 nm due to n→π
^*
transition because of conformal change of the AAP to cis structure. Analyses of absorbance spectra showed that the secondary n→π
^*
transition was indirect and assisted by phonons due to rotation of AAP molecules during photo-isomerization, while primary π→π
^*
excitation was direct with gap values 3.1- 3.5 eV.