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PubMed2003

Phosphorescence lifetime imaging in turbid media: the forward problem.

An adequate description of the propagation of near-infrared light in highly scattering media is important for imaging hidden luminescent inhomogeneities in tissues. We present an improved approach to modeling of the forward problem based on a telegraph equation. The asymptotic solutions of the telegraph equation are derived and analyzed. The expression for the mean photon path length is also obtained.

Luminescence↗
PubMed2006

Phosphorescence of erythrosin B as a robust probe of molecular mobility in amorphous solid sucrose.

Luminescence from the triplet probe erythrosin B (tetra-iodo fluorescein, Ery B) provides spectroscopic characteristics such as lifetime and emission energy that are sensitive to molecular mobility of the local environment in amorphous solids. This study investigated how variations in the local concentration of Ery B free acid as well as the presence of the dispersing solvent affect the spectroscopic measurements of solid matrix properties (the free acid of Ery B is poorly soluble in water and thus must be introduced via an organic solvent). The emission energy of Ery B from 5 to 100 degrees C in thin films of amorphous sucrose at various probe and solvent (N,N-dimethyl formamide, DMF) concentrations was determined using excitation at 500 nm and emission over the range 520-750 nm. The emission lifetime was determined over the same temperature range using a stretched exponential analysis of intensity decays collected using excitation at 530 nm and emission at 680 nm. Variations in the probe/sucrose mole ratio (concentration) over the range from 0.5 to 10 x 10(-4) and 10-fold variations in the amount of DMF used to disperse the probe did not affect the emission energy, the shape of the emission spectra, or the measured lifetimes of Ery B in amorphous sucrose. These results thus indicate that erythrosin B introduced into amorphous solids can provide a robust measure of the intrinsic mobility of the solid matrix that is relatively insensitive to final probe concentration or presence of residual solvent.

Journal Article↗
PubMed2003

Electrochemical and phosphorescent properties of new mixed-ligand Ir(II) complexes coordinated with both terpyridine and various bipyridine derivatives.

Seven useful mixed-ligand complexes in the form of [Ir(terpy)(L)Cl]2+ were prepared and their spectroscopic and electrochemical properties were investigated. The ligands used were terpy = 2,2':6',2''-terpyridine, L = 2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine, 4,4'-diphenyl-2,2'-bipyridine, 1,10-phenanthroline, 5-phenyl-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, 2,3-bis(2-pyridyl)pyrazine. Synthetic methods were developed by a sequential ligand-replacement which occurred in the reaction vessel using a microwave oven. All complexes showed that LUMOs are based on the pi-system contribution of the terpyridine ligand for [Ir(terpy)(bpy)Cl]2+, [Ir(terpy)(dmbpy)Cl]2+, [Ir(terpy)(dpbpy)Cl]2+, [Ir(terpy)(phen)Cl]2+, [Ir(terpy)(dpphen)Cl]2+ and [Ir(terpy)(phphen)Cl]2+. On the other hand, the LUMO in the [Ir(terpy)(bppz)Cl]2+ complex is localized on the pi-system of the bppz ligand, whereas the HOMOs in the iridium complexes are localized on the terpyridine ligand. It was found that Ir(terpy)(L)Cl emits in a fluid solution at room temperature. The ancillary ligands, such as terpy and bpy, have been explored to extend the lifetime of the triplet 3(pi-pi') excited states of Ir(III) terpyridine complexes. Ir(III) terpyridine units with an electron donor (dmbpy) or electron acceptor substituents (terpy, dpbpy, phphen, dpphen and bppz) are found to decrease the energy of the 3LC states for use as photosensitizer molecular components in supramolecular devices. The spectroscopic and electrochemical details are also reported herein.

Journal Article↗