الفهرس 
Chapter One: IntroductionOnly 14 pages are availabe for public view
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Abstract
The photophysical properties including singlet-singlet absorption,
molar absorptivity, oscillator strength, dipole moment, energy yield of
fluorescence, fluorescence quantum yields, radiative decay rate constants
(kr), attenuation length, fluorescence lifetimes, absorption and emission
cross sections of three dyes (T1, T2 and T3) from 1,2,4 triazines
derivatives have been measured in different organic solvents of varying
polarity. Both electronic absorption and fluorescence spectra of T1, T2
and T3 are sensitive to solvent polarity. The solvent polarity shows a
slight effect on the positions of the electronic absorption maxima for the
three dyes. The emission spectra are mirror images of the respective
absorption spectra for the three dyes studied in all solvent. It appears that
for the three dyes, the absorption and emission spectra were shifted to
longer wavelengths showing a positive solvatochromism (red shifted) in
most solvents with increasing solvent polarity.
The ground-state (µg) and excited-state (µe) dipole moments were
estimated by using solvatochromic correlations. Further, the
experimentally obtained Δμ values were compared with those using
normalized polarity terms from Reichardt equation. The higher value
of Δµe may refer to the singlet higher excited states of dyes having strong
intramolecular charge transfer character (ICT).
The excitation energy transfer from the oxazole derivative (POP)
as a donor and T1, T2 and T3 dyes as acceptors has been studied in
methanol to improve the emission efficiency. As the concentration of
acceptor increases, the emission intensity of donor decreases with gradual
increase in the acceptor fluorescence. This observation indicates that the
transfer of excitation energy from the POP donor to acceptor T1, T2 and
T3 molecules.
The effect of Ag nanoparticles on the photophysical and
photochemical behaviors of these dyes in traditional solvents have been
studied. As the concentration of the Ag NPs increases, the fluorescence
intensity is reduced and the fluorescence quenching of T1 and T3 occurs.
Ground and excited states as well as electronic geometric
optimizations were performed using density functional theory (DFT) and
time-dependent density functional theory (TDDFT), respectively.
(TDDFT) calculations were carried out at ωB97X-D/6-31G(d) level. The
theoretical absorption and emission spectra of T1 compound were
calculated using TDDFT and compared to experimental results.
The present thesis includes three main chapters: introduction,
experimental, result and discussion as well as references, conclusion,
English and Arabic summaries.
1) The first chapter includes an introduction to dye lasers and their
importance; general properties of these organic dyes and the
special requirements for ideal tunable laser dyes. It also includes
the effect of solvent on the emission spectrum of laser dyes and the
requirements for choosing suitable solvents for laser dyes as well
as fluorescence studies and energy transfer processes. The Chapter
also includes a literature survey on laser dyes and their importance.
2) The experimental part of the thesis ”chapter 2” includes the dyes
structures, their synthesis and the solvents used as well as the
experimental techniques and the different methods of calculation.
3) Chapter 3 includes the results and discussion and contains the
following:
The emission and absorption spectra in different solvents of
different polarities as well as the dipole moments in ground and
excited states of these dyes were calculated by three methods.
The fluorescence quantum yields and fluorescence lifetimes and
the effect of solvents on these dyes were studied.
The excitation energy transfer from an oxazole derivative (POP) as
a donor and the three laser dyes as acceptors has been studied to
improve the emission efficiencies and the rates of the energy
transfer and the critical transfer distances were determined.
Fluorescence quenching by silver nanoparticle (AgNO3) was
studied.
The theoretical absorption and emission spectra of T1 compound
are calculated using TDDFT and compared to experimental results.