Luminol Chemoluminescence

1
Luminol Chemoluminescence
www.wikipedia.org
2
Fluorescence or Phosphorescence?
Both molecular structure and chemical environment
determines if a molecule will or will not
luminescence
p p transitions are most favorable for
fluorescence.

• e is high (100 1000 times greater than n
  p)
• kF is also high (absorption and spontaneous
  emission are related).
• Fluorescence lifetime is short (10-7 10-9 s
  for p p vs. 10-5 10-7 s for n p).

3
Nonaromatic Unsaturated Hydrocarbons
Luminescence is rare in nonaromatic hydrocarbons.
Possible if highly conjugated due to p p
transitions.
Seyhan Ege, Organic Chemistry, D.C. Heath and
Company, Lexington, MA, 1989.
4
Aromatic Hydrocarbons
Most intense fluorescence is found in compounds
with aromatic groups
Low lying p p singlet state
Phosphorescence is weak because there are no n
electrons
Ingle and Crouch, Spectrochemical Analysis
5
Heterocyclic Aromatics
Aromatics containing carbonyl or heteroatoms are
more likely to phosphoresce
n p promotes intersystem crossing.
Fluorescence is often weaker.
Skoog, Hollar, Nieman, Principles of Instrumental
Analysis, Saunders College Publishing,
Philadelphia, 1998.
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Aromatic Substituents

• Electron donating groups usually increase fF.
• Electron withdrawing groups usually decrease fF.

Ingle and Crouch, Spectrochemical Analysis
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Halogen Substituents
Internal Heavy Atom Effect
Promotes intersystem crossing. fF decreases as MW
increases. fP increases as MW increases. tP
decreases as MW increases.
Ingle and Crouch, Spectrochemical Analysis
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Increased Conjugation
fF increases as conjugation increases. fP
decreases as conjugation increases. Hypsochromic
effect and bathochromic shift.
Ingle and Crouch, Spectrochemical Analysis
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Rigid Planar Structure
fF 1.0
fF 0.2
fF 0.8
not fluorescent
Ingle and Crouch, Spectrochemical Analysis
Skoog, Hollar, Nieman, Principles of Instrumental
Analysis, Saunders College Publishing,
Philadelphia, 1998.
10
Metals
Metals other than certain lanthanides and
actinides (with f-f transitions) are usually not
themselves fluorescent.
A number of organometallic complexes are
fluorescent.
Skoog, Hollar, Nieman, Principles of Instrumental
Analysis, Saunders College Publishing,
Philadelphia, 1998.
11
Solvent Polarity
Increasing solvent polarity usually causes a
red-shift in fluorescence.
http//micro.magnet.fsu.edu/primer/techniques/fluo
rescence/fluorescenceintro.html
12
Solvent Polarity
Joseph Lakowicz, Principles of Fluorescence
Spectroscopy, Kluwer Academic / Plenum
Publishers, New York, 1999.
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Temperature
Increasing temperature increases frequency of
collisions (probability of external conversion).
Decreasing temperature can induce a blue-shift in
fluorescence.
Joseph Lakowicz, Principles of Fluorescence
Spectroscopy, Kluwer Academic / Plenum
Publishers, New York, 1999.
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Fluorescence and Phosphorescence
Which effect is used more regularly?
SciFinder Scholar Citations 2009
Fluorescence Phosphorescence
Labels/Tags 4399 13 Dyes
4424 31
www.wikipedia.org
15
Fluorescence or Phosphorescence?Publications in
Analytical Chemistry

• Fluorescence Phosphorescence
• 10847 7927
• Advantages
• Phosphorescence is rarer than fluorescence gt
  Higher selectivity.
• Phosphorescence Analysis of aromatic compounds
  in environmental samples.
• Disadvantages
• Long timescale
• Less intensity

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Shpolskii Spectroscopy

• Analytical potential of fluorescence spectroscopy
  often limited by unresolved band structure (5-50
  nm)
• homogeneous band broadening depends directly on
  radiative deactivation properties of the excited
  state (usually 10-3 nm)
• inhomogeneous band broadening various analyte
  microenvironments yields continuum of bands
  (usually few nm)
• Solution Incorporate molecules in rigid matrix
  at low temperature to minimize broadening
• Result Very narrow luminescence spectra with
  each band representing different substitution
  sites in the host crystalline matrix

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Shpolskii Spectroscopy

• Requirements
• T lt 77K with rapid freezing rate
• Matrix with dimension match
• Low analyte concentration

• Instrumentation
• Xe lamp excitation
• Cryogenerator with sample cell
• High resolution monochromator with PMT

Analytes polycyclic aromatic compounds in
environmental, toxicological, or geochemical
systems
Garrigues and Budzinski, Trends in Analytical
Chemistry, 14 (5), 1995, pages 231-239.
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Shpolskii Spectroscopy
Garrigues and Budzinski, Trends in Analytical
Chemistry, 14 (5), 1995, pages 231-239.
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Epi-Fluorescence Microscopy

• Light Source - Mercury or xenon lamp (external
  to reduce thermal effects)
• Dichroic mirror reflects one range of
  wavelengths and allows another range to pass.
• Barrier filter eliminates all but fluorescent
  light.

http//micro.magnet.fsu.edu/primer/techniques/fluo
rescence/fluorosources.html
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Fluorescence Microscopy
Need 3 filters Exciter Filters Barrier
Filters Dichromatic Beamsplitters
http//microscope.fsu.edu/primer/techniques/fluore
scence/filters.html
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Are you getting the concept?
You plan to excite catecholamine with the 406 nm
line from a Hg lamp and measure fluorescence
emitted at 470 15 nm. Choose the filter cube
you would buy to do this. Sketch the transmission
profiles for the three optics.
http//microscope.fsu.edu/primer/techniques/fluore
scence/fluorotable3.html
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Fluorescence Microscopy Objectives
Image intensity is a function of the objective
numerical aperture and magnification
Fabricated with low fluorescence glass/quartz
with anti- reflection coatings
http//micro.magnet.fsu.edu/primer/techniques/fluo
rescence/anatomy/fluoromicroanatomy.html
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Fluorescence Microscopy Detectors
No spatial resolution required PMT or
photodiode Spatial resolution required CCD
http//micro.magnet.fsu.edu/primer/digitalimaging/
digitalimagingdetectors.html
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Fluorescence Resonance Energy Transfer (FRET)
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Special Fluorescence Techniques
LIF
TIRF
http//microscopy.fsu.edu/primer/techniques/fluore
scence/tirf/tirfintro.html