The cause of absorption and luminescence band shift of disperse Red-13 in silica spheres

Abstract

Optical absorption and luminescence band shifts have been observed for a disperse red-13 (DR-13) attached on silica spheres. A covalent bond is formed between an isocyanatopropyl triethoxysilane (ICPTES) and a DR-13 prior to DR-13 being incorporated inside the spheres. The Stöber synthesis process was performed with the synthesized ICPTES-DR-13 (ICPDR), tetraethoxy orthosilane (TEOS), 2-propanol and NH₄OH solution. The final silica spheres with ICPDR (ICPDRSS) were analyzed with Fourier transform infrared, UV-visible and fluorescence spectrometers. Characteristic absorption peaks at 1700 and 1704 cm⁻¹ representing −C=O stretching vibrations for ICPDR and ICPDRSS indicate the formation of urethane linkages. Although the absorption band at 502 nm did not shift with increasing concentration of DR-13 in methanol, the absorption band for the ICPDRSS shifted 28 nm toward shorter wavelength due to the antiparallel geometry of the azochromophores. A broad luminescence was observed for ICPDRSS and shifted toward the blue with increasing excitation wavelength, which was due to a transformation of the DR-13 in silica spheres from a trans-form to a cis-form.