Fluorescence dynamics of dye-dye and dye-nanostructures interactions

Abstract

The decay dynamics of (Boradiazaindacene) BODIPY dye molecules embedded in Porous silicon (PSi) nanostructures produced by electrochemical anodization of p-type silicon wafers in an HF solution are investigated using time-resolved lifetime measurements. Illumination light and resistivity effects on the growth mechanism of the PSi are studied. Coherence is observed to be the foundation of regularity in obtaining conical shapes and the pillar size is almost linearly proportional to the illumination wavelength. Moreover, high resistivity of silicon wafer considerably changes the surface topography of the PSi and silicon nanospheres are obtained instead of nanopillars. The decay rate of the BODIPY embedded in the vicinity of various size pillar tips is affected due to different apex angles of the conical nature. Interaction between BODIPY and nanospheres is explained using confocal FLIM technique. It is observed that there is an efficient energy transfer mechanism between BODIPY and PSi. Energy transfer efficiency strongly depends on the thickness of the silicon dioxide layer covering the PSi. As oxidation increases, energy transfer rate decreases. This change in energy transfer rate seems to obey NSET mechanism, which allows us to obtain a three dimensional topographic map of the developed oxide layer on the rough and complicated surface of a PSi nanostructure. Finally, interaction between BODIPY dye molecules, which are covalently bound to a PEG based hydrogel is also studied. Since the hydrogel structure is capable of absorbing a large amount of water, without dissolving and losing its shape, upon swelling, the distance between the BODIPY dyes is controllably changed; it is observed that the fuorescence lifetime of BODIPY increases. The decay dynamics of the BODIPY dye molecules confined within a hydrogel cluster obeys FRET rather than self (or contact) quenching.