Fluorescence resonance energy transfer and arrangements of fluorophores in integrated coumarin/cyanine systems within solid-state two-dimensional nanospace

Abstract

Two functional dyes, coumarin and 3,3′-diethyloxacarbocyanine (DOC), are integrated with a wide range of DOC contents by intercalating DOC into the solid-state two-dimensional nanospace of a coumarin/phyllosilicate hybrid, wherein the coumarin moiety is anchored covalently to the phyllosilicate moiety. Ultraviolet–visible spectroscopy and X-ray diffraction analysis show that the mole ratios of DOC to coumarin moiety ([DOC]/[Coum]) range from 0.004 to 40 mol/mol, thus providing a series of systems with a variety of fluorescence properties and arrangements of fluorophores. Fluorescence spectroscopy reveals that both the coumarin moieties and DOC molecules fluoresce and that DOC even emits by excitation at 320 nm due to energy transfers within the integrated coumarin/DOC systems. The extent of the energy transfers and fluorescence intensities depend on [DOC]/[Coum]. The proposed models of the arrangements of the fluorophores for the integrated systems consist of coumarin moieties located on both close to and far from the DOC molecules in the same two-dimensional nanospace with the DOC molecules always in close proximity to a coumarin moiety. These unique arrangements of fluorophores allow two types of fluorescence behavior: (1) fluorescence resonance energy transfer (FRET) from the excited coumarin moiety located close to DOC and (2) emission by coumarin for the excited coumarin moiety located far from DOC.