ABSTRACT
Novel solid-emissive indeno[1,2-b]benzo[4,5-e]pyran-11-one-type fluorophores having non-planar structures with sterically hindered substituents (R = butyl, phenyl, and thienyl) have been designed and conveniently synthesized. The fluorescence quantum yields of in 1,4-dioxane were (Phi = 0.053) >> (Phi = 0.013) > (Phi = 0.003). On the other hand, the solid-state fluorescence quantum yields of the fluorophores were (Phi = 0.39) > (Phi = 0.15) > (Phi = 0.06). To elucidate the large differences in the quantum yields in solution and in the solid state and among the fluorophores , we performed time-resolved fluorescence spectroscopic measurements, semi-empirical molecular orbital calculations (AM1 and INDO/S), and X-ray crystallographic analyses of . The comparison of the values of the radiative and non-radiative rate constants determined by the time-resolved spectroscopic measurements in solution and in the crystalline state supported that non-radiative decay is reduced by restriction of the rotation of the phenyl and thienyl rings in the solid state. In addition, the X-ray crystal structures demonstrated that, in and , the non-planar structure with sterically hindered substituents prevents the fluorophores from forming short pi-pi contacts and produces strong solid-state fluorescence. On the other hand, in the crystal of , the formation of continuous intermolecular CH[dot dot dot]S bonding between neighboring fluorophores was found to increase short pi-pi contacts and reduce the fluorescence intensity.
Subject(s)
Benzopyrans/chemistry , Fluorescent Dyes/chemistry , Fluorescent Dyes/chemical synthesis , Indans/chemistry , Computer Simulation , Crystallography, X-Ray , Models, Chemical , Models, Molecular , Molecular Structure , Quantum Theory , Sensitivity and Specificity , Spectrometry, Fluorescence/methodsABSTRACT
Novel indeno[1,2-b]benzo[4,5-e]pyran-11-one-type fluorophores exhibiting intense solid-state fluorescence were conveniently synthesized and the relation between their solid-state photophysical properties and the X-ray crystal structures were investigated, which demonstrates that non-planar structures with sterical hindered substituents prevent the fluorophores from forming short pi-pi contacts causing fluorescence quenching in the solid state.
ABSTRACT
Novel heterocyclic quinol-type fluorophores (4 a-c) and (5 a-c) that contain substituents (R = Me, Bu, Ph) with nonconjugated linkages to the chromophore skeleton have been synthesized and their photophysical properties have been investigated in solution and in the solid state. Considerable differences in the absorption and fluorescence spectra were observed between the two states. Quinols 4 a-c and 5 a-c exhibited almost the same absorption and fluorescence spectra in solution; however, their solid-state fluorescence excitation and emission spectra in the crystalline state were quite different. We performed X-ray crystallographic analyses to elucidate the dramatic effect of the substituents of the nonconjugated linkage on the solid-state fluorescence excitation and emission spectra. The relationships between the solid-state photophysical properties and the chemical and crystal structures of 4 a-c and 5 a-c are discussed on the basis of the X-ray crystal structures.
ABSTRACT
A gold nanoparticle surface-modified with amide ligands shows enhanced optical sensing of anions: the detection limit is increased by about three orders of magnitude higher than that originally expected from the anion binding ability of neutral amide ligands.
