Photophysical Behavior of 1,8-Diaminonaphthalene in Acidic Solutions and in Zeolite Sieves - PowerPoint PPT Presentation

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Photophysical Behavior of 1,8-Diaminonaphthalene in Acidic Solutions and in Zeolite Sieves

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Title: Photophysical Behavior of 1,8-Diaminonaphthalene in Acidic Solutions and in Zeolite Sieves


1
Photophysical Behavior of 1,8-Diaminonaphthalene
in Acidic Solutions and in Zeolite Sieves
Master Thesis By Abdul-Rahman Al-Betar Appointed
Committee Prof. Uwe K. A. Klein Thesis
Advisor Prof. Shaikh A. Ali Member Dr. Than
Htun Member May 2004
2
Outline
  • Introduction
  • Aim of this study
  • General kinetics scheme of 1,8-DAN
  • Proposed kinetics scheme of 1,8-DAN

3
  • General Overview of Proton-Transfer
  • 1950s
  • Kinetics of Proton-transfer reactions became the
    subject of many studies
  • Eigen
  • Was the first to measure the fast recombination
    of H and OH- using relaxation method
  • Forster and Weller
  • Were the first to explain the difference between
    the ground and the excited states of the
    dissociation constants

4
  • Short Pulse
  • It becomes possible to directly measure
    proton- transfer of excited molecules
  • 4-H-1-NS and 1-AN
  • Have been studied by means of laser-induced
    picosecond spectroscopy
  • 1,8-DAN
  • Is the subject of this research

5
4-hydroxy-1-naphalenesulphonate
1-Aminonaphthalene
1,8-diaminonaphthalene
6
Aim of this Study
  • Paul et al. have studied 1,8-DAN in sulphuric
    acid solutions. However, there is no complete
    analysis of the overall reaction scheme.
  • To set up the complete behavior scheme of 1,8-DAN
    in the ground and excited state with varying
    acidity.
  • Photochemical characterizations of zeolite, based
    on fluorescence properties.
  • Which is a new insight for industry using
    spectroscopic measurements

7
General Scheme of 1,8-DAN Proton Transfer
1,8-DAN has two amino groups that could be
protonated
8
Absorption Spectra of 1,8-DAN by Paul et al.
9
Absorption Spectra Of The Three Forms 1,8-DAN At
8.010-5 M
10
Only One Transition, Earlier Suggested by Paul et
al. for DANH
Absorption spectra disprove this structure
11
Two Different Transitions For DANH
12
Dissociation Constants
13
Dissociation Constants in the Ground State
pH pKa log A- / HA When A-
equals HA pH pKa pKa1 4.0
14
Dissociation Constants in the Ground State
pKa2 -0.1
15
Dissociation Constants in the Excited State
  • pK was determined by Forster-Cycle
  • pKa pKa - h C NA (l -1 HA - l-1A- ) /
    2.303 R T
  • Where
  • l is the wavelength taken at the 0-0
    transition between absorption and emission
    spectra

16
Absorption and fluorescence spectra of the
neutral of 1,8-DAN
17
Acidity constants in the ground and first excited
states
Equilibrium pKa Paul et al. Our work pKa Paul et al. Our work
DANH ? DAN H 4.2 4.0 --- -9.7
DANH22 ? DANH H -0.1 -0.1 -6.5 -10.7
Where pKa is theoretical values obtained from
Forster-Cycle
18
Fluorescence Spectra
19
Fluorescence Spectra of 1,8-DAN by Paul et al.
20
Fluorescence Spectra Of The Three Forms 1,8-DAN
Emission of the neutral and pH 2, show the same
emission peak at lEX 340 nm
21
Fluorescence Spectra Of The Three Forms 1,8-DAN
  • Emission of the neutral and pH 2,
  • at lEX 300 nm
  • Red shift due to solvent relaxation

22
Solvent Relaxation Process
  • Due to changes of dipole moment on excitation,
    shifting of energy levels occur with lower energy
    gap
  • Which cause a red shift in the fluorescence
    spectrum

23
Quenching Constant, kq
  • proton-induced fluorescence quenching has been
    observed for mono-cation form prior to the
    formation of di-cation
  • The quencher for the neutral form emission is
    H
  • Whereas, the quencher for the protonated form
    emission is H2Ofree i.e. the proton acceptor

24
Neutral Form Quencher
25
Intermediate Emission
26
Protonated Form Quencher
27
Quenching Constant, kq
  • Plotting 1/h Vs. H, gives slope kq t0 /h0
  • kq 1.26 x 109 M-1s-1
  • With good agreement to the finding by
    Stern-Volmer plot using lifetime ( kq 1.29 x
    109 M-1s-1)
  • Which is within 2 error

28
Stern-Volmer plot
  • Plotting t0/t Vs. H, gives slope kq t0
  • kq 1.29 x 109 M-1S-1

29
Proposed Scheme for Proton transfer reactions of
1,8-DAN
Diabatic process in the excited state
30
Quenching Constant, kq
  • Plotting h0/h Vs. gH2Ofree
  • kq 3.12 108 M-1s-1
  • gH2O Vs. gHClO4, was taken from earlier work
    by El-Rayyes et al. and then was applied to our
    concentration in this work.

31
Fluorescence Decay Measurements
  • The decay of the neutral and the mono-cation form
    have very similar decays,
  • Both are single-exponential and nicely fit the
    equation
  • I(t) I0 e-t/t
  • Whereas the decay for the di-cation form shows
    bi-exponential decay and nicely fit the
    equation
  • I(t) A1 e-t/t1 A2 e-t/t2

32
Fluorescence Decay Profile Of The Three Forms Of
1,8-DAN
Decay emission of the neutral and pH 2 are similar
33
Lifetime Measurements t
1,8-DAN t1 /ns Paul et al. Our work t2 /ns Paul et al. Our work
Neutral 1.6 7.7 ---
Mono-cation 7.4 8.3 ---
Di-cation --- 1.6 --- 22.2
34
Energy Surface for the Mono-cation Form
35
Energy Surface for the Di-cation Form
36
Zeolite Y Sieves
  • Zeolite Y has a major channel of 12 member Oxygen
    ring .
  • Its pours diameters
  • d1 12 Å
  • d2 7.4 Å

37
Calcination Process
  • Three forms of zeolite Y were used
  • NaY, HY 34 and HY96
  • NaY can be changed to HY of different
    concentrations by ion exchange with NH4NO3
  • NH4NO3 NaY NH4Y 500 C HY NH3(g)

38
Protonation Process
39
Why 1,8-DAN inside Zeolite Sieves ?
  • To do acidity characterization of solid acids
  • e.g. Zeolite Y
  • Acidity characterization can be done by
  • 1. Temperature-programmed desorption (TPD)
    Qualitative
  • 2. Calorimetric methods Qualitative
  • 3. Fourier transformation infrared (FTIR)
    Qualitative
  • 4. Laser-induced spectroscopy (LI)
  • Introduced by El-Rayyes et al.
    Quantitative

40
Emission Spectra of DAN /Zeolite Y
  • DAN/NaY shows the neutral band of 1,8-DAN.
  • However, under higher energy excitation it shows
    the protonated band even there is no proton
  • Some interesting effects with Na ion
  • i.e. the lone pairs interact with Na to give
    the higher energy band

41
Emission Spectra of NaY
42
Emission Spectra of DAN /Zeolite Y
  • DAN/HY 34 shows both neural band and the
    protonated band of 1,8-DAN.
  • DAN/HY 96 shows both the neural band and the
    protonated band of 1,8-DAN.
  • However, under higher energy excitation it gives
    low energy band.
  • Which need further studies

43
Emission Spectra of HY 34
44
Conclusion
  • 1,8-DAN shows a Diabatic Reaction Process
  • i.e. the reaction of the excited neutral form
    with H does not lead to the excited
    mono-protonated form, rather it goes to the
    ground state.
  • There are three different forms of 1,8-DAN in the
    ground state. Whereas, there are only two forms
    in the excited state.

45
Proposed Scheme of 1,8-DAN
46
Conclusion
  • The Mono-cation form has two transitions band,
    rather than one transition as believed before,
    which is supported by absorption spectra.
  • The Di-cation form has a bi-exponential decay
    which suggest the existence of a new form X. i.e.
    an adduct between the solvent molecules and the
    fluorophore molecules as shown for 1-AN.

47
Conclusion
  • The excited state reactions is very sensitive to
    the presence or absence of water molecules and
    protons, which makes 1,8-DAN possibly a good
    indicator for zeolite acidity.
  • i.e. 1,8-DAN may be used as a probe molecule to
    assess zeolite acidity.

48
Acknowledgement
  • All praise be to Allah for his limitless help and
    guidance. Peace pleasing of Allah be upon his
    prophet Mohammed.
  • To my advisor Prof. Uwe Klein
  • To other members Prof. A. Ali and Dr. Than Htun
  • To helpful discussion Dr. El-Rayyes
  • To helpful consultation Dr. Fettouhi
  • To technicians help M. Arab and Mr. Mazhar
  • To graduate advisor, chemistry chairman and dean
    of science college
  • To all faculty, staff and students

49
Thank You All
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