Photophysical Properties of Dye-Doped Silica Nanoparticles Bearing Different Types of Dye-Silica Interactions

Photophysical properties of three types of dye-doped silica nanoparticles (NTs) with different dye-silica interactions have been investigated. In two cases the dye-silica interactions are noncovalent, where tris(2,2'-bipyridine)ruthenium(II) chloride (Rubpy) is attracted to the silica network electrostatically and tetramethylrhodamine-dextran (TMR-Dex) is trapped inside the silica matrix through spatial/steric hindrance. In the third case, tetramethylrhodamine-5-isothiocyanate (TRITC) modified with 3-aminopropyltriethoxysilane (APTES) to form TMR-APTES is bound to the silica matrix covalently. Although in all three types of architectures absorption, excitation, and emission spectra show only small red-shifts (<5 nm) as compared with free dye in water, excited state emission lifetimes, quantum yields, and anisotropies vary significantly and in quite different ways between the three architectures. All three types of interactions facilitate effective encapsulation of dye within a silica network. However, covalent bonding possesses a notable advantage over the other two types of interactions as it results in a large reduction of a nonradiative relaxation rate of the embedded dye (TMR-APTES) and, thus, a large (similar to 3.55-fold) increase of its quantum yield.