Fluorescence resonance energy transfer of sulforhodamine B attached on silica spheres

Abstract

Fluorescence resonance energy transfer (FRET) of sulforhodamine B (SRH) has been investigated. The SRH was attached to silica spheres by two step synthetic processes including a urethane bond formation between a 3-isocyanatopropyl triethoxysilane (ICPTES, –NCO) and an SRH (Si–OH) in pyridine at 50 °C and hydrolysis–condensation reaction between synthesized ICPTES/SRH (ICPSRH) and silica spheres. The disappearance of FTIR absorption peak at 2270 cm−1 representing asymmetric stretching vibration of –NCO indicated the progress of the reaction, and a new absorption peak at 1712 cm−1 characterizing –CO stretching vibration implied the formation of the urethane bond. The UV–visible absorption spectra of SRH and the mixture of ICPTES and SRH in methanol showed the same spectral profile. However, the synthesized ICPSRH/silica-spheres (ICPSRHSS) exhibited about 13 nm bathochromic shift. The photoluminescence (PL) peak of the SRH in methanol manifested a hypsochromic shift with the increase of the excitation wavelength. However, the PL peak for the ICPSRH had a bathochromic shift with the increase of the excitation wavelength. Approximately 13 nm Stokes shift was observed for the PL of the SRH in methanol compared with the absorption spectrum. Approximately 43 and 70 nm Stokes shifts were observed for the ICPSRHSS and ICPSRH films, respectively, which might be due to the self-FRET between SRH molecules without significant PL quenching.