Khader A. Al-Hassan

Syntheses, characterization, biological activity and fluorescence properties of bis-(salicylaldehyde)-1,3-propylenediimine Schiff base ligand and its lanthanide complexes.

Eight new lanthanide metal complexes [LnL(NO(3))(2)]NO(3) {Ln(III) = Nd, Dy, Sm, Pr, Gd, Tb, La and Er, L = bis-(salicyladehyde)-1,3-propylenediimine Schiff base ligand} were prepared. These complexes were characterized by elemental analysis, thermogravimetric analysis (TGA), molar conductivity measurements and spectral studies ((1)H NMR, FT-IR, UV-vis, and luminescence). The Schiff base ligand coordinates to Ln(III) ion in a tetra-dentate manner through the phenolic oxygen and azomethine nitrogen atoms. The coordination number of eight is achieved by involving two bi-dentate nitrate groups in the coordination sphere. Sm, Tb and Dy complexes exhibit the characteristic luminescence emissions of the central metal ions attributed to efficient energy transfer from the ligand to the metal center. Most of the complexes exhibit antibacterial activity against a number of pathogenic bacteria.

The role of free volume in the twisted intramolecular charge transfer (TICT) emission of dimethylaminobenzonitrile and related compounds in rigid polymer matrices

Abstract The amount of free volume present in a polymer matrix represents a driving force toward twisted intramolecular charge transfer (TICT) emission of p-dimethylaminobenzonitrile (DMABN) and related compounds. The intensity of the TICT band for these compounds in PVC (poly(vinyl chloride), PVA (poly(vinyl alcohol)), PHEMA (poly(hydroxyethyl methacrylate)) and PMMA (poly(methyl methacrylate)) was found to increase in this order, which is consistent with the increased free volume present in the same sequence. This rules out specific solute-solvent interactions as being responsible for the TICT emission in PVA polymer matrices.

Fluorescence decay characteristics of 4-dimethylaminobenzonitrile in different polymer matrices: a time-resolved study in the nanosecond range

Abstract The fluorescence decay curves of 4-dimethylaminobenzonitrile (DMABN) in different polar protic and aprotic polymer matrices are nonexponential. The lifetimes of the twisted intramolecular charge transfer (TICT) band are in the nanosecond range. With nanosecond time-resolved fluorescence spectroscopy dual fluorescence was observed for DMABN in a poly (vinyl alcohol) (PVA) polymer matrix at room temperature. These observations contradict results obtained by Cazeau-Dubroca and coworkers who report lifetimes of the TICT band of DMABN in PVA polymer matrices of the order of 1 s and claim the emission is an α-delayed fluorescence. Free volume effects are shown with 1,1,4,4-tetraphenylbutadiene (TPB) in PVA matrices.

Red edge effect (REE) phenomena of flexible solute molecules as a probe for polymer rigidity and/or free volume

Abstract The fluorescence spectra of the tert-butyl ester of 9-anthroic acid (9TBA) in two PVA (poly(vinyl alcohol)) polymer matrices of different molecular weights are different and indicate media of different rigidity. 9TBA also undergoes different edge excitation red-shifts in these PVA polymer matrices and is attributed to a decrease in the free volume in the higher molecular weight matrix. Comparison of the red edge effect (REE) observed for 9TBA in PVA (molecular weight 88000) polymer matrix with the REE observed in polymethylmethacrylate (PMMA) and in poly(hydroxyethyl methacrylate) (PHEMA) polymer matrices is used to establish that the free volume in PVA (88000) is smaller than in PHEMA or PMMA.

Fluorescence Probes for Cyclodextrin Interiors

Abstract6-Propionyl-2-(dimethylamino)naphthalene (PRODAN) emits two fluorescence bands, at ∼510 and ∼435 run, when dissolved in γ-cyclodextrin (CD) aqueous solutions. The relative contributions of these two bands were found to depend on time and temperature. These emissions are attributed to the inclusion of PRODAN with the dimethylamino group toward the larger and smaller rims inside the γ-CD cavities, respectively. The first position corresponds to a slightly polar and slightly rigid environment, while the second corresponds to a hydrophobic and rigid environment relative to the aqueous polar bulk. In contrast, PRODAN in either α-CD or β-CD aqueous solutions emits a single fluorescence band at 525 and 510 nm, respectively. The emission of PRODAN in α-CD is similar to that in water and indicates no inclusion at all. In β-CD, only one kind of inclusion is possible with the dimethylamino group of PRODAN toward the larger rims of β-cavities. These results are supported by fluorescence decay lifetime measurements and are consistent with our previous observations made for 4-dimethylaminobenzonitrile (DMABN) and 4-diethylaminobenzonitrile (DEABN) in α- and β-CD aqueous solutions [23,24]. Therefore the possibility of twisted intramolecular charge transfer (TICT) state formation in PRODAN in terms of environmental polarity and local free volume of CD cavities is discussed. These observations put PRODAN, DMABN, and other TICT compounds as fluorescence probes for CD interiors.

The red edge effect as a tool for investigating the origin of the anomalous fluorescence band of 9,9′-bianthryl in rigid polar polymer matrices

Abstract The excitation wavelength dependence of the fluorescence of 9,9′-bianthryl (BA) in polar polymer matrices at room temperature is attributed to the presence of different conformers (angular distribution of the two anthryl moieties) trapped in sites with different solvation and absorbing at different energies. The broadening of the fluorescence at the red edge excitation of BA in polar polymer matrices is due to a twisted intramolecular charge transfer (TICT) band. This case of the red edge effect (REE) exhibited by BA represents a converse example to the REE observed for flexible molecules with one fluorescence band and a sharpening of the fluorescence.

The role of the angle of pretwist of some molecules forming twisted intramolecular charge transfer (TICT) states in polymer matrices

Abstract It is shown that the relative intensity of the twisted intramolecular charge transfer band of ester and benzonitrile derivatives of dialkylaniline in non-hydrogen-bonding polymers increases with increasing size of the donor (dialkylamino) group and is sensitive to both the local polarity and local free volume of polymer sites.

Edge-excitation red-shift of the fluorescence of flexible solute molecules that may assume different geometries

Abstract An excitation wavelength dependence of the fluorescence of tert-butyl and methyl esters of 9-anthroic acid and tetraphenyl-butadiene in rigid media is explained in terms of the presence of conformers that assume different geometries and absorb at different energies.

Fluorescence Probes as Molecular Weight Detectors of Polymers

It is shown that the relative intensity of the twisted intramolecular charge transfer (TICT) band of ester and benzonitrile derivatives of dialkylaniline in polymethylmethacrylate polymer matrices of different molecular weights (MW) to increase with increasing MW of the polymer. Our results emphasis the role of local free volumes (mobility in the matrix cage) and focus attention on the role of the MW of the polymer on the fluorescence of various TICT probes. These observations are confirmed by the red edge effect and fluorescence decay results.

FLUORESCENCE DECAY CHARACTERISTICS OF 9,9'-BIANTHRYL (BA) IN NON-POLAR VERSUS POLAR POLYMER MATRICES AT ROOM TEMPERATURE

Abstract The fluorescence decay curves and lifetimes of 9,9′-bianthryl (BA) in polystyrene (PS) polymer matrix are compared with the corresponding ones in poly(vinyl alcohol) (PVA) and poly(hydroxyethylmethacrylate) (PHEMA) polymer matrices at room temperature. The decay curves are mono-exponential in PS with a lifetime of ≈ 6.4 ns and non-exponential in the case of PVA and/or PHEMA with lifetimes of ≈ 1.7 and 10 ns when fitted to a bi-exponential model. This is consistent with the red edge effect (REE results made here and before.