The aggregation effect on the absorption band shift of disperse red-13 attached on the surface of silica spheres

• Two step synthetic processes are employed to attach DR-13 on the silica spheres.
• The UV–visible absorption band shifted toward blue due to the antiparallel geometry.
• The stopband appeared at 788 nm and disappeared when methanol is filled to the space.
• Intense red color appeared when the ICPDRS film exposed in alcohol.

Optical properties of disperse red-13 (DR-13) attached on the surface of the silica spheres have been investigated. Two step synthetic processes have been used to attach the DR-13 on the surface of the silica spheres. The first step is a urethane bond formation between a DR-13 (OH) and a 3-isocyanatopropyl triethoxysilane (ICPTES, NCO) in pyridine at 50 °C. The second step is the hydrolysis and condensation reactions between the resulting compound of the first step reaction (ICPDR) and the silica spheres (ICPDRSS). The absence of a characteristic absorption peak at 2270 cm−1 representing the NCO asymmetric stretching vibration and the existence of a new absorption peat at 1700 cm−1 corresponding the CO stretching vibration indicate the urethane bond formation. The absorption intensity of the DR-13 in methanol, ethanol and 2-propanol linearly increased with the increase of the amount of the DR-13. The ICPDRSS has weak brownish color when it is dried. The field emission scanning electron microscope shows the aggregated ICPDR on the surface of the silica spheres. The average diameter of the spheres is approximately 380 nm. The color of the ICPDRSS changed to intense red when it was wetted in methanol, ethanol and 2-propanol. The absorption peak of the dried ICPDRSS film is at 475 nm. The stopband appears at 788 nm and disappears when the methanol is filled between the spheres due to the low refractive index contrast. New absorption band appears at 718 nm when the methanol is absorbed due to the large aggregation of the ICPDR on the surface of the spheres.