Samy A. El-Daly

Spectral, lifetime, fluorescence quenching, energy transfer and photodecomposition of N,N′-bis(2,6-dimethyl phenyl)-3,4:9,10-perylentetracarboxylic diimide (DXP)

Abstract The spectral behavior and fluorescence quantum yield of N,N ′-bis(2,6-dimethyl phenyl)-3,4:9,10-perylentetracarboxylic diimide (DXP) have been measured in different solvents. The role of molecular oxygen and KI in deactivation of excited singlet state DXP have been studied and the second-order quenching rate constant have been determined. The excitation energy transfer from 9,10-diphenylanthracene (DPA) to DXP has also been studied and the value of energy transfer rate constant, k ET , and critical transfer distance, R 0 , indicate a Forster-type energy transfer mechanism. The photochemical reactivity of DXP in carbon tetrachloride has been studied.

Photochemistry of N, Ń-ditridecyl-3,4:9,10-perylenetetracarboxylic diimide in chloromethane solvents

Abstract The spectral behaviour, lifetime and fluorescence quantum yield of N,N-ditridecyl-3,4:9,10-perylenetetracarboxylic diimide (DTPD) have been measured in chloromethane solvents, such as methylene chloride, chloroform and carbon tetrachloride. The excitation energy transfer to DTPD has been studied to improve the laser emission of DTPD. The value of energy transfer rate constant (KET) and critical transfer distance (R0) indicate a Forster type energy transfer mechanism. The photodecomposition of DTPD in chloromethane solvents has been also studied.

1,4-Bis (β-Pyridyl-2-Vinyl)Benzene (P2VB) and2,5-Distyryl-pyrazine (DSP) asBlue Laser Dyes

Solutions of P2VB and DSP in dimethyl-sulphoxide (DMSO) of concentration ca. 10–3 M/l act as laser dyes on pumping with nitrogen laser. P2VB and DSP are lasing in the ranges 390–440 nm (λmax = 416 nm) and 435–465 nm (λmax = 447 nm) respectively. An equimolar mixture of P2VB and DSP behaves as an energy transfer dye laser (ETDL) and is lasing in the range 429–455 nm (λmax = 438 nm). Such ETDL system obeys a long range coulombic energy transfer mechanism with a critical transfer distance R0 = 7.5 nm.

Photophysical Parameters, Excitation Energy Transfer, and Photoreactivity of 1,4-Bis(5-phenyl-2-oxazolyl)benzene (POPOP) Laser Dye

The effect of solvents on the absorption and emission spectra of 1,4-bis(5-phenyl-2-oxazolyl)benzene (POPOP) laser dye has been studied in various solvents at 298 K. A bathochromic shift was observed in absorption and fluorescence spectra upon increase of solvent polarity, which indicates that this transition is π- 𝜋 ∗ . The ground and excited state dipole moments were calculated as 2.23 and 6.34 Debye, respectively. The dye solution in MeOH, n-heptane, and methyl isobutyl ketone gives laser emission in the blue region upon excitation by a 337.1 nm nitrogen pulse; the gain coefficient and emission cross section as well as normalized photostability have been determined. Excitation energy transfer from POPOP to rhodamine B and fluorescine was studied to improve the laser emission from these dyes. Such an energy transfer dye laser system (ETDL) obeys a long range columbic energy transfer mechanism with a critical transfer distance, R0, of 25 and 33 A and kq equal to 1 0 . 4 × 1 0 1 2 and 2 6 . 2 × 1 0 1 2 M − 1 s − 1 for the POPOP/RB and POPOP/fluorescine pair, respectively. The POPOP dye is highly photostable in polar protic and polar aprotic solvents, while it displays photodecomposition in chloromethane solvent via formation of a contact ion pair. The photochemical quantum yield and rate of photodecomposition depend on the electron affinity of solvent.

Fluorescence quenching of N,N-bis(2,5-di-tert- butylphenyl)-3,4:9,10-perylenebis(dicarboximide) (DBPI) by Co2+ ion

Abstract Energy transfer from the singlet excited state of DBPI (N, N -bis(2,5-di-tert-butylphenyl)- 3,4:9,10-perylenebis(dicarboximide)) dye to Co2+ ions as acceptor has been studied in methanol, ethylene glycol and glycerol as well as in anionic and cationic micelles by steady state emission measurements. It was found that the bimolecular quenching rate constant kq is viscosity and temperature dependent. An increase in kq by a factor of 3.4 is observed on using glycerol instead of methanol. This is accompanied by a decrease in the diffusion rate constant kd by a factor of about 1.6×10−3. This is a clear indication of a Forster- type long-range energy transfer mechanism in viscous media. The experimental critical transfer distances R0 have been calculated as 14, 19 and 17 A in methanol, ethylene glycol and glycerol respectively. It was also found that the fluorescence quenching increases with increasing SDS (sodium dodecyl sulphate) concentration but decreases with increasing CTAC (cetyltrimethylammonium chloride) concentration in aqueous media.

Spectral characteristics of 4-(p-N,N-dimethyl-aminophenylmethylene)-2-phenyl-5-oxazolone (DPO) in different media

The absorption and fluorescence characteristics of 4-(p-N,N-dimethyl-aminophenylmethylene)-2-phenyl-5-oxazolone (DPO) have been investigated in different solvents. DPO dye exhibits a large red shift in both absorption and emission spectra as solvent polarity increases, indicating a large change in the dipole moment of dye molecules upon excitation due to an intramolecular charge transfer interaction. The fluorescence quantum yield depends strongly on the properties of the solvents. Crystalline solids of DPO gave strong red emission at 605nm due to the excitation of molecular aggregates. The absorption and fluorescence emission spectral properties of DPO have also been investigated in organized media of aqueous micellar and β-cyclodextrin (β-CD) solutions. The critical micelle concentrations (CMCs) of SDS and CTAB as well as the binding constants of DPO in micellar solution and β-cyclodextrin have been also determined.

Emission characteristics and photostability of 1,4-bis[β-(2-benzoxazolyl) vinyl]benzene (BBVB) laser dye

Abstract The fluorescence efficiencies of (Φf) of 1,4-bis[β-(2-benzonazolyl) vinyl]benzene (BBVB) havebeen measured in various hydrogen bonding and non-hydrogen bonding solvents of different polarities on the π ∗ scale. In hydrogen bonding solvents Φf increases with increasing π ∗ value. The fluorescence has also been studied in other media, including micellar, microemulsion and acidic ones. BBVB solutions exhibit short excited state lifetimes in the range 0.5–0.7 ns. The second-order rate constant of oxygen and rhodamine 6G (R6G) quenching of BBVB fluorescence have been determined from Stern-Volmer relations. The critical transfer distances for the BBVB/R6G system have been determined as R 0 = 46.8 and 48.5 A in ethanol and methanol respectively. The photochemical quantum yields (Φc) have also been determined in various organic solvents.

Synthesis, spectral behaviour and photophysics of donor–acceptor kind of chalcones: Excited state intramolecular charge transfer and fluorescence quenching studies

The spectral and photophysical properties of two chalcones containing electron donating and accepting groups with intramolecular charge transfer characteristics were synthesized and characterized by (1)H NMR, (13)C NMR and X-ray crystallography. Both compounds show very strong solvent polarity dependent changes in their photophysical characteristics, namely, remarkable red shift in the emission spectra with increasing solvent polarity, large change in Stokes shift, significant reduction in the fluorescence quantum yield; indicating that the fluorescence states of these compounds are of intramolecular charge transfer (ICT) character. The solvent effect on the photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of both compounds have been investigated comprehensively. For both dyes, Lippert-Mataga and Reichardts correlations were used to estimate the difference between the excited and ground state dipole moments (Δμ). The interactions of dyes with colloidal silver nanoparticles (Ag NPs) were also studied in ethanol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of dyes by Ag NPs.

Inclusion of Paracetamol into β-cyclodextrin nanocavities in solution and in the solid state

We report on steady-state UV-visible absorption and emission characteristics of Paracetamol, drug used as antipyretic agent, in water and within cyclodextrins (CDs): β-CD, 2-hydroxypropyl-β-CD (HP-β-CD) and 2,6-dimethyl-β-CD (Me-β-CD). The results reveal that Paracetamol forms a 1:1 inclusion complex with CD. Upon encapsulation, the emission intensity enhances, indicating a confinement effect of the nanocages on the photophysical behavior of the drug. Due to its methyl groups, the Me-β-CD shows the largest effect for the drug. The observed binding constant showing the following trend: Me-β-CD>HP-β-CD>β-CD. The less complexing effectiveness of HP-β-CD is due to the steric effect of the hydroxypropyl-substituents, which can hamper the inclusion of the guest molecules. The solid state inclusion complex was prepared by co-precipitation method and its characterization was investigated by Fourier transform infrared spectroscopy, 1H NMR and X-ray diffractometry. These approaches indicated that Paracetamol was able to form an inclusion complex with CDs, and the inclusion compounds exhibited different spectroscopic features and properties from Paracetamol.

UV/Vis, IR and 1H NMR spectroscopic studies of bisazo-dianil compounds based on 5-(2-carboxyphenyl azo)-salicylaldehyde and primary diamines

The electronic absorption and emission spectra of the titled biazo-dianils are studied in organic solvents of different polarity as well as in aqueous buffer solutions of varying pH. The important bands in the IR spectra as well as the main signals of the 1H NMR spectra are assigned. The observed UV/Vis absorption bands are assigned to the corresponding electronic transitions. The fluorescence quantum yield and pK(a)(-) values in the ground and excited states are determined.