Concentration effect on the optical absorption and luminescence properties of disperse red-13 in silica spheres

Optical properties of disperse red-13 (DR-13) covalently attached in the silica spheres have been investigated with the two step synthetic processes including a urethane bond formation between a 3-isocyanatopropyl triethoxysilane (ICPTES, -N=C=O) and DR-13 (-OH) with different ratios (3:14, 13:14 and 23:14) of the ICPTES and the DR-13 in pyridine and hydrolysis-condensation reactions between synthesized ICPTES/DR-13 (ICPDR) and tetraethoxyorthosilicate (TEOS) in NH4OH. The absorption peak at 1704 cm-1 representing the -C=O stretching vibration of the spheres attached ICPDR (ICPDRSS) indicates the formation of the urethane bond. Several other absorption peaks originated from ICPDR appeared in the FTIR spectra. The UV-visible absorption peak of the ICPDRSS shifted toward blue with respect to that of DR-13 in methanol, which indicated the antiparallel structure of the DR-13. The photoluminescence peak shifted toward red with the increase of the ratio of DR-13 with respect to ICPTES. This result implies the increase of the intermolecular interaction between DR-13 molecules with the increase of the DR-13 concentration.