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

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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
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Outline

• Introduction
• Aim of this study
• General kinetics scheme of 1,8-DAN
• Proposed kinetics scheme of 1,8-DAN

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• 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

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• 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

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4-hydroxy-1-naphalenesulphonate
1-Aminonaphthalene
1,8-diaminonaphthalene
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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

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General Scheme of 1,8-DAN Proton Transfer
1,8-DAN has two amino groups that could be
protonated
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Absorption Spectra of 1,8-DAN by Paul et al.
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Absorption Spectra Of The Three Forms 1,8-DAN At
8.010-5 M
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Only One Transition, Earlier Suggested by Paul et
al. for DANH
Absorption spectra disprove this structure
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Two Different Transitions For DANH
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Dissociation Constants
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Dissociation Constants in the Ground State
pH pKa log A- / HA When A-
equals HA pH pKa pKa1 4.0
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Dissociation Constants in the Ground State
pKa2 -0.1
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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

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Absorption and fluorescence spectra of the
neutral of 1,8-DAN
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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
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Fluorescence Spectra
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Fluorescence Spectra of 1,8-DAN by Paul et al.
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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
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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

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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

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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

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Neutral Form Quencher
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Intermediate Emission
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Protonated Form Quencher
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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

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Stern-Volmer plot

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

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Proposed Scheme for Proton transfer reactions of
1,8-DAN
Diabatic process in the excited state
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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.

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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

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Fluorescence Decay Profile Of The Three Forms Of
1,8-DAN
Decay emission of the neutral and pH 2 are similar
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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
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Energy Surface for the Mono-cation Form
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Energy Surface for the Di-cation Form
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Zeolite Y Sieves

• Zeolite Y has a major channel of 12 member Oxygen
  ring .
• Its pours diameters
• d1 12 Å
• d2 7.4 Å

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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)

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Protonation Process
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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

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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

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Emission Spectra of NaY
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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

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Emission Spectra of HY 34
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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.

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Proposed Scheme of 1,8-DAN
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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.

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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.

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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

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Thank You All
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