Manifestations of Light-Matter
Interactions
• Reflection
• Refraction
• Scattering
• Absorption
Absorption
Theory and Applications of Ultraviolet Spectroscopy,
by H. H. Jaffe and M. Qrchin
•Absorption spectrum of a red textile
tf— ,-
Wavelength/nm
•Transmission spectrum of the same
Beer-Lambert Law
Absorption
Io	c	It
		
	l	
		
A = -log^ = -log7 = ec / [-]
c molar concentration [mol H]
I optical pathlength [an]
£ molar decodk extinction coefficient
Example: c = 10"3M, c = 104 moH • I • cm-'
=> 7=0.01, A = 2=> 99% of the light is
absorbed within the first 2 mm of the solution
MM. M IttSH
höhere optik
Al    IH II K
. i . i ... • vt,.-.
Iii»
August Beer (1825-1863)
OD ~ 2:       1% transmission
,        .... .  . OD can be adjusted with
OD ~ 1:       10% transmission
^on/ .  . concentration
OD -0.01:   98% transmission
Absorption Spectra: Why the s and ^vary with the band?
t
X (in nm or A) —> <— v (in cm"1 or s"1)
Electronic structures for various states are generated assuming the molecule is stationary and it is in its lowest energy state
R* _ ^2 *2-
hv
R -► *R
lu - —
ho _!_
(ho)2 (ho)1(lu)1
R _ ^! Ov
Electron jump between orbitals generally takes ~ 10"15 to 10"16 s Nuclear vibrations take ~ 10"13 to 10"14 s
Spin frequency even at very high magnetic field occurs in ~ 10"12 s
Light as an oscillating electric field
(a)
(b) o
1 x
Finish
Oscillating electric wave
Hydrogen atom
A / c		? o\ t   \ H		H h	h ■	
-	■	■ h	\ c I	3 c	\ 1	) / 1
V2X
+
Repulsion
Attraction
OX
(0 O      Qt    O      0* O
O
Hydrogen atom
Electronic oscillation of the hydrogen atom
Start
Ŕv(X = 1002 A) +H2(ls^)2 '-*- H2(l«ffg;2p7r(,)
Rules for absorption and emission are the same
Absorption
t
CD i_
CD
C
LU
Excited level
AE -	= hv
	r
Ground level
Emission
t
a3
LU
Excited level
▼ Ground level
Probability of light absorption and emission
Fermi's Golden Rule
¥1^1-2 ^
2
0.3c. s
OBS
l->2
p2jr[<^1|P1^2|^2>]2 -fi
Enrico Fermi Nobel Prize. 1938
R + hv-> *R *R-> R + hv
^2(*R)>2
-OBS
P
allowedness of absorption or emission
density of states
perturbing Hamiltonian
^bock
Oscillator Strength-Absorption
Probability of light absorption and emission are related to the oscillator strength /
A perfectly allowed transition has /= 1
Electronic (<X>)
fe
Orbital Overlap Orbital Symmetry
Vibronic (%) Nuclear position fv
Spin (S) Electron Spin fs
How probable (<D. %. S)2 would 'look like' (<D. %. S^?
Electronic transitions: Overlap and symmetry of orbitals involved
The electronic factor fe may be subclassified in terms of different kinds of forbiddenness:
(1) Orbital overlap forbiddenness, which results from poor spatial overlap of the orbitals involved in the electronic transition, example, the n,7i* transition in ketones, for which the HO and LU are orthogonal to one another and the overlap integral <n 71 *> is close to zero.
(2) Orbital symmetry forbiddenness, which results from orbital wavefunctions (involved in the transition) that overlap in space but have their overlap integral canceled because of the symmetry of the wave functions. Examples transitions in benzene, naphthalene, and pyrene.
Electronic factor - Orbital overlap
Long-Wavelength Absorption Bands (Corresponding to HO -» LU Transitions) of Some Typical Organic Chromophores
Chromophore A,max(nm)
C-C
c=c
c=c-c=c
c=c-c=c-c=c
c=o
c=c-c=o c=c-c=o
Benzene
Pyrene
Anthracene
<180 180 220 260 280 350 280 260 350 380
'max
Transition type
1000
10,000
20,000
40,000
20
30
10,000 200 510 10,000
g,ct
71,71
7T,7t
7t,7T
n,7t
n,7i
71,71
71,71
71,71'
71,71'
Zero Order to First Order Through Vibronic Coupling
(a)
Planar
All angles 120°
Vibronic interaction has a small effect
(b)
Bent
Two atoms move down, plane destroyed
J
Vibronic interaction significant
CH vibration
<
H
Pure p T= pure 7i,7i*
sp"
T = (it, 7t*-<—*- 7i, a*)
«... Q
Strictly planar
no = Po <n0lTc) = 0
Variations
Nonplanar n0 = sp" <n0l7x>^0
Vibrational mixing could change the shape of the zero-order orbital and lead to slight overlap between perpendicular orbitals (e.g., V , a and V and '71*')
Vibronic mixing results in state mixing
Due to vibration an n, n* S1 state is no longer pure but contains a finite amount of n, n* character mixed in so the zero order wavefunction is not valid and the first order wavefunction may in fact be:
first order n, 7i*
-> = v|/(n, Ti*) + X\\j(n, 71*)
zero order zero order
n, 7i
71, 71'
Mixing coefficient
X =
<v|/a I H I v|/b>
In general, X is the result of vibrational mixing (break down of
Bonn-Oppenheimer approximation)
Result of vibrational - electronic mixing (vibronic coupling)
T
n^jt*1
n^jt*1
nn* transition forbidden
n2jt2 Jt*°
As per Bonn-Oppenheimer approximation
I
n7C* transition becomes weakly allowed
n2jx2 jx*°
Vibration mixes the states, no longer pure states
Absorption and emission spectra Vibrational structure due to vibrational mixing
av ~ 0.001
i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—f 350        400        450        500        550        600 650
A. (nm)
Symmetry based selection rules
g
g
The absorption spectra of conjugated diencs in Intensities of Electronic Transitions in Molecular Spectra
the vacuum ultra-violet (1) TTT rt     . _, ,   .     ... _       _   ,   _       t . _.
v ' III. Organic Molecules with Double Bonds. Conjugated Dienes
By W. C. Price and A. D. Walsh robert s mulliken
Physical Chemistry Laboratory, Cambridge Ryerson Physical Laboratory, University of Chicago, Chicago, Illinois
(Received December 9, 1938)
(Communicated by Ii. G. W. Norrish, F.R.8.—Received 14 August 1939)
Selection Rules (Electronic part)
Orbital Symmetry (717c*, e.g., benzene, pyrene)
The two orbitals involved in the transition can't have the same symmetry, i.e., g to g or u to u transition is forbidden
Symmetry can be destroyed by vibration and these symmetry forbidden transitions can become weakly allowed due to vibrational mixing.
Probability of Absorption and Emission
Probability of light absorption is related to the oscillator strength/
Theoretical oscillator . Experimental
strength / ~ ^.oXlU Js CIV absorption
Area under s vs. wavenumber plot
Emission follows the same rules as absorption
Relationship between absorption intensity (and fluorescence lifeti
Strickler and Berg "Relationship between Absorption Intensity and Fluorescence Lifetime of Molecules" J. Chem. Phys. 1962, 37, 814.
Strickler-Berg relation
The relation of the radiative lifetime of the molecule and the absorption coefficient over the spectrum
n: refractive index of medium
v: position of the absorption maxima in wavenumbers [cm-1] S : absorption coefficient
Tn : radiative lifetime
Same Rules for Excitation <& De-excitation
I
Us-1
)
+hv
AE = *E - E0 = hv -E0
■hv
Example
Transition type
i
max
109	p-Terpheny]	S^tt.tt*) -	-S0	3 x 104	1	
108	Perylene	Sj^tt*) -	-S0	4 x 104	10"	-1
107	1,4-Di methyl-benzene	Sj(7r,7r*) -	-S0	7 x 102	io-	-2
106	Pyrene	Si(n,7T*) -	-S0	5 x 102	10"	-3
105	Acetone	Si(n,7r*) -	-S0	10	10"	-4
Radiative        0 _9_2     _ _2
rate constant    £e = 3 x 10 v0j£dv*v0f
1/T° = ke° ~smaxAv2 ~104emax
Experimental and Calculated Radiative Lifetimes for Singlet-Singlet Transitions
Compound	t° (Xl09)	t(x109)
Anthracene	13.5	16.7
Perylenec	4.1	4.6
9,10-Diphenylanthracene	8.9	8.8
Acridone	14.9	14.1
Fluorescein	4.7	4.0
9-Aminoacridine	14.6	14.3
Rhodamine B	6.0	6.0
Acetone	10,000	1,000
Perfluoroacetone	10,000	5,000
Benzene	140	600
Electronic spectra of larger molecules
An atom A diatomic (or other /\ |arge molecule
small) molecule
Distance R
Shapes of Absorption Spectra: medium dependent
u
C
i-i O
(c) Aqueous solution
450
500 550 Wavelength, nm
600
N
Franck-Condon principle and vertical transitions
Franck-Condon Principle: Vibronic Transitions
J. Franck E. Condon
1882-1964 1902-1974 Nobel Prize, 1925
The ground state (E0) supports a large number of vibrational energy levels. At room temperature, only the lowest vibrational level is populated, and electronic transitions originate from the v=0 vibrational level.
Franck-Condon principle is based on the fact that electrons move faster than nuclei that are heavier.
Internuclear Distance
Franck-Condon principle
An electronic transition occurs without changes in the positions of the nuclei in the
molecules and its environment
QM harmonic oscillator QM anharmonic oscillator
Vibrational overlap integral decides the intensity of absorption
Relative position of energy surfaces and Franck-Condon principle control the shape of the absorption
and emission spectra
Relative position of energy surfaces and Franck-Condon principle control the shape of the absorption and emission spectra
co
(D C LU
Vertical or Franck-Condon allowed transitions
'XY
0^0 The most probable Franck-Condon transition
v (cm )
Spectrum broadened by solvent interactions
CD C LU
Compressed excited state
'XY
0 -> 2 The most probable Franck-Condon transition
0^2
0^3
0^0
Spectrum broadened by solvent interactions
o)
B -*■ X + Y dissociation
*R
'XY
Continuum of absorption (0->6, 0^7, etc.)
v (cm 1)
Photoablation & Lasik use this part of the spectrum
v (cm )
v (cm )
Stoke's shift: Absorption and Emission Spectra
(a)
Absorption
Characteristic of upper state
Fluorescence
Characteristic of lower state
• The shortest wavelength in the fluorescence spectrum is the longest wavelength in the absorption spectrum
i_
CD C
CD
Wavelength
G.G. Stokes (1819-1903)
Electronic excited state
Electronic ground state
Owing to a decrease in bonding of the molecule in its excited state compared to that of the ground state, the energy difference between S0 and St is lowered prior to fluorescence emission. This is known as Stoke's shift.
Absorption and Emission Spectra
Mirror Image Rule, Franck-Condon Principle, and Stoke's sh
Nuclear Coordinates
	Iaaaaaaaa/^	t
1	I	
v=10
v=4
XY
https: //www, yo utube.com / wa tc h ? v=U LCTTxe H160 &t=0s
Absorption
Absorption Emission
Excitation
500
~\—I—I—I—f—I—r 300 350
X (nm)
50 0
Vavilov's rule
The quantum yield of fluorescence (and the quantum yield of phosphorescence) are independent of initial excitation energy. Emission originates from the lowest vibrational level.
Singlet-Tri
plet Crossing and Phosphorescence
Triplet State and Phosphorescence
&. N. Lewis
Kasha
	
•	
S. Vavilov
A. Terenin
Porter
Pioneering Publications
[Contribution from the Chemical Laboratoř v of the University of California)
Reversible Photochemical Processes in Rigid Media.   A Study of the Phosphorescent
State
By Gilbert N. Lewis, David Lipkin and Theodore T. Magel
paramagnetism  of the phosphorescent state
Chemical Laboratories of the University of California Berkblkv, California
Gilbert X. Lewis m. Calvin Received June 16, 1945
{Contribution from the Chemical Laboratory of the University of California]
Phosphorescence and the Triplet State
By Gilbert N. Lewis and M. Kasha
'Contribution from the Chemical Laboratory of the University of California!
Phosphorescence in Fluid Media and the Reverse Process of Singlet-Triplet
Absorption
By Gilbert N. Lewis and M. Kasha
Photomagnetism. Determination of the Paramagnetic Susceptibility of a Dye in Its Phosphorescent State*
G. n. Lewis, Iff. Calvin, and m. Kasha! Department of Chemistry, University of California, Berkeley, California
(Received December 16, 1948)
photomagnetism of triplet states of organic molecules
Paramagnetic Resonance Absorption in Naphthalene in Its Phosphorescent State*
Clyde A. Hutchison, Jr., and Billy W. Mangum!
Enrico Fermi Institute for Nuclear Studies and Department of Chemistry, University of Chicago, Chicago, Illinois
(Received August 8, 1958)
Triplet States in Solution
George Porter and Maurice W. Windsor Department of Physical Chemistry, University of Cambridge, Cambridge, England (Received August 19, 1953)
sensitized phosphorescence in organic solutions at low temperature
ENERGY TRANSFER BETWEEN TRIPLET STATES
By A. Terenin and V. Ermolaev Photochemical Laboratory, Section of Chemical Sciences, Academy of Science of U.S.S.R.
Received 2\st March, 1956
By Dr. D. F. EVANS
Physical Chemistry Laboratory, Oxford
Classic references on triplet state and heavy atom effect
1.	JACS., 63,3005,(1941).	1.	J. Chem. Phys., 29, 952 (1958)
2.	JACS., 64, 1916,(1942).	2.	JACS, 82, 5966 (1960)
3.	JACS., 66,2100,(1944).	3.	J. Chem. Phys, 32, 1261 (1960)
4.	JACS., 66, 1579,(1944).	4.	J. Mol. Spectroscopy, 6, 58 (1961)
5.	JACS., 67, 994,(1945).	5.	J. Phys. Chem, 66, 2499 (1962)
6.	JACS., 67, 1232, (1945).	6.	J. Chem. Phys, 39, 675 (1963)
7.	Chem. Rev., 47, 401 (1947)	7.	J. Chem. Phys, 40, 507 (1964)
8.	J. Chem. Phys., 17, 905 (1949)	8.	Photochem. Photobiology, 3, 269 (1964)
9.	J. Chem. Phys., 17, 1182 (1949)	9.	J. Chim. Phys, 61, 1147 (1964)
10. J. Chem. Phys, 17, 804 (1949)		10.	Trans. Faraday Soc, 62, 3393 (1966)
11. J. Chem. Phys., 20, 71 (1952)		11. Chem. Rev., 66, 199(1966)	
12. Nature, 176, 777,(1955).		12. J. Chem. Ed., 46, 2(1969)	
13. J. Chem. Soc., 1351,(1957).		13. JACS, 114, 3883 (1992)	
Singlet-Triplet Transitions Role of Spin-Orbit Coupling
T
V-'
Si
Spin-Orbit coupling mixes the states, no longer pure states
Observed Zero-point Motion- . _
Rate Constant   Limited Rate Constant   "Fully Allowed Rate"      ( ' '
^obs, = *max X /c x /v x /s
Prohibition to maximal Prohibition factors due to changes in
caused by "selection rules" electronic, nuclear, or spin configuration
Absorption and Emission
SlNGIET
(a) Absorption       (b) Re-cmission      (c) Fluorescence       id) Phosphorescence
cm
Phosphorescence
T,--So 0-0 Band
MnglW-tnptel spliRing
1	1 III Anthracene	
		S0    T1     T1 ~* so
£max~104 S    } I		
		
		£max~10-4
		
'» «        i 'I ! 1 i •■III		/': «\  ill / \
/           " 1 '■ Vi U'                1      / '.	i i	\ i/      r- / -i   i \
300
(0,4)
(0,2)
400
(0,0)
(0,2)
500      600 700
X (nm) —>-
(0,4)
(0,3)
(0,1)
(0,1)
(0,3)
v=4 v=3 v=2 i/=1 v=0
(0,0)
tl (0,0)
sj
v=4 v=3 v=2 i/=1 v=0
v=4 v=3 v=2 v=-\ v=Q
v=4 v=3 v=2
v=^
v=0
• Precursor state (Si) has short lifetime
• Generally not susceptible to quenching
Phosphorescence:
• Low radiative rate constant, 10-6 to 10 S"
• Precursor state (Ti) has long lifetime
• Very much susceptible to quenching
• Emission quantum yield depends on Si to Tj crossing
Organic Glass for Phosphorescence
VISCOSITY OF LOW TEMPERATURE GLASSES
(Adapted from Greenspan and Fischer m)
Solvent Approximate viscosity
in poise at - 180°C
l-Propanol/2-propanol (2:3)	6 x 1012
Ethanol/methanol	2 x 1012
Ethanol/methanol 4- 4.5 % water	—
Ethanol/methanol + 9% water	—
Iso-octane/isononane	3 x 1010
Methylcyclohexane/cis/trans-decalin	1 x 10"
Methylcyclohexane/toluene	7 x 109
Methylcyclohexane-isohexanes (3:2)	3 x 106
Methylcyclohexane/methylcyclopentane	2 x 105
Methylcyclohexane/iso-pentane	—
Methylcyclohexane-iso-pentane (1:3)	1 x 103
2-Methylpentane	7 x 104
2-Methyl tetrahydrofuran	4 x 107
Ether/iso-pentane/ethanol (5:5:2)	9 x 103
• Be chemically inert
• Have no absorption in the region of optical pumping
• Have a large solubility for the studied material
• Be stable (don't crack) to the action of light
• Have a good optical quality
Emission Quantum Yield
Source
Detector
Sample
Emission Quantum Yield (O)
# of photons emitted
# of photons absorbed
Ground State (S0)
Singlet Excited State (SJ
hv ^
Competition with fluorescence
S0 + hv
i
ahz.
Si
k
L
0
k
k
ML
0
'1 -f
*f>*.c £(So^Ti)
/cp S/cTS
©@©
©®@
0/ =
(^/+^c+^c+-)[^l]
1
Lifetime
1/x     ke      8maxAv      10 £max
Radiative lifetime
Excited State Decay
phosphorescence
Radiative Decay
intersystem crossing A
delayed fluorescence
Excitation
Non-emissive Decay Non-radiative Decay
0 =
# of photons emitted
# of photons absorbed
Factors Controlling Quantum Yield of Fluorescence
Rigid vs non-rigid molecules
Kasha's rule
"The emitting level of a given multiplicity is the lowest excited level of that multiplicity"
Kasha, Characterization of Electronic Transitions in Complex Molecules, Faraday Soc. Discussion 9, 14-19 (1950)
Michael Kasha
(1920-2013).
Fluorescence occurs only from Si to S0;
Phosphorescence occurs only from Tj to S0;
Sn and Tn emissions are extremely rare.
Energy Gap Law
Exceptions
|Afcsof>tion Emsaon
CO
Azuftene
MVV
Absorption
T
T
300 tM X(nm)
500
S2 (80.9 kcoi/molt) kc(S2-SO
S, (40.9 kcol/mote)
Hie(SrS0)
So
M W « 1.4 x 10 7 k|{8i-S0) = 1.3 OO6
k(C(s2-s, ; « ? * io8
k(C!SrS0) = 1.2 MO
M. Kasha; G. Viswanath, Confirmation of the anomalous fluorescence of azulene. J. Chem. Phys. 1956, 24, 51A.
Ordering of excited states depends on chain length
tat*
rat*.
7t** .
rat*-
JtJt* . Jt**
JUT*. Jt**.
2500 3000 3500 4000 4500
R. L. Christensen et. al., J. Phys. Chem. 1990, 94, 7429
Exceptions
R. L. Christensen et. al., J. Phys. Chem. 1990, 94, 7429
T. Gilbro, R. S. H. Liu, et. al., J. Luminescence, 1992, 57, 11
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The effect of wavelength on organic photoreactions in solution. Reactions from upper excited states
N. J. Turro, V. Ramamurthy, W. Cherry, and W. Farneth
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Fluorescence and Phosphorescence from Higher Excited States of Organic Molecules
Takao Itoh
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© CK« this: Chem. Rev. 2012.112,8.4541 -4568 Publication Date: May 16, 2012 « https://doi.org/10.1021/cr200166m Copyright © 2012 American Chemical Society
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Breaking the Kasha Rule for More Efficient Photochemistry
Alexander P. Demchenko/ Vladimir I. Tomin,* and Pi-Tai Chou*'
Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, 9 Leontovicha Street, Kyiv 01030, Ukraine 'institute of Physics, Pomeranian University in Slupsk, ul. Arciszcwskicgo, 22b, Slupsk 76-200, Poland sDcpartment of Chemistry, National Taiwan University, 1 Roosevelt Road Section 4, Taipei 106, Taiwan
REVIEWS
Pyrene as an exemplar of excimer formation
56
Why excited state complexes are more stable?
Collisional separation
N N
One electron stabilized (+)
One electron destabilized (-)
Two electrons stabilized (2+)
Net stabilization = one electron
Two electrons destabilized (2-)
71
N
Two electrons stabilized (2+)
Net stabilization - 0
© ®
Discrete vibrations of excited monomer
AE
Discrete vibrations of ground-state
monomer
00
X
I
Monomer absorption
Monomer emission
Exciplex absorption (absent)
■ex
Exciplex emission
1.5
c
CD
■| 1.0
CD o
CD
o w
CD
o
"O CD N
"CO
E
0.5
0.0
Excited state complexes: Exciplexes
Pyrene
Monomer fluorescence
12mM
350
400
450
N'
Pyrene diethylaniline exciplex
Exciplex fluorescence
In methylcyclohexane solution
500
550
—f
600
c o "w
E
CD
Albert F. Weiler
Pulse
Py DMA-*— DMA+ Py*«—excitation
of Py
(b)
20.0
22.5
25.0
X (nm)
v(x103cm"1)
TICT Emission
LE state (S-|, planar, partial CT)
Adiabatic -►
photoreaction
TICT state (S.,, twisted, full CT)
c o
CO
E
CD
c
III
N
3      -..n^ 3
c
III
N
TICT
300
400 500 Wavelength (nm) -
H
N=C-
-N
N
uuu
'SCH,
N = C
NC
CH, SCHS
(349 nm)
(413 n
Delayed Fluorescence
Intersystem crossing
Delayed thermal fluorescence
Thermal equilibration
Fig. 1.11 Illustrating production of delayed thermal fluorescence (DTF).
20
Fluo
Delayed Fluorescence
Eosin Y
More Fluo
0O3O
High Temp
■OC3b
i/r
■Q040
Low Temp
Types of emissions
□ Fluorescence
□ Phosphorescence
□ Emission from upper excited states
□ Excimer emission
□ Exciplex emission
□ TTCT emission
□ Delayed emission
Photoluminescence of Solutions: With Applications to Photochemistry and Analytical Chemistry
C A: Parker
1968
Third Edition
Principles of
Fluorescence Spectroscopy
Joseph R.Lakowicz
Bernard VaWvr arxJ ( WIUY-VCH
Mirio N. Bcb<'<Jn $jn!ot ^^^^^^m
Molecular Fluorescence
Intrinsic f luorophore and extrinsic f luorophore
Intrinsic fluorophores are those which occur naturally Extrinsic fluorophores, fluorescence probes
♦ Intrinsic and Extrinsic Fluorophores
• Intrinsic or Natural Fluorophores
Proteins: Tryptophan, Tyrosine Protein Fluorescence Spectroscopy: Binding of ligands Protein-protein association Denature
Cofactors: NADH—NAD, FMN, FAD Extrinsic Fluorophores
Flg.l. Fluorescent probe represents t molecular reporter in the biological sample.
Pyrene Emission at Room Temperature
Vibrational Pattern
nm
Comparison of Pyrene Emission in Different Solvents:
I1/I3 as Polarity Probe
94 Solvents have been tested, showing ratios from 0.41 to 1.95. Can. J. Chem. 62,1984
Solvent Polarity Probe
Solvent Polarity: The emission wavelength generally increases with solvent polarity.
Solvent Reorganization: The energy of Si after solvent reorganization generally decrease with solvent polarity.
EA Bu
I
f _
Me2N
Absorption
Fluorescence
400 500 600
WAVELENGTH (nm)
700
H = Hexane
CH = Cyclohexane T = Toluene EA = Ethyl acetate Bu = Butanol
Solvation Dynamics
NONPOLAR SOLUTE RANDOM SOLVENT
UNSOLVATED HIGH ENERGY
SOLVATED LOW ENERGY
Dynamic Stokes shift
-1 -3 -1 -3 -1
Wavenumber (cm )X10 Wavenumber (cm )X10 Wavenumber (cm )X10
Ol
Viscosity Probes
Viscosity Probes = An increase in the viscosity of the medium surrounding a fluorophore can restrict conformational freedom and alter the quantum yield
Supramolecular Sensors: Proton
hv.
	
Fluor	Spacer
	
Cation
Receptor j._
o
Nonf luorescent
Fluor
Spacer
Cation
Receptor
©
Fluorescent
Non Fluorescent
Fluorescent
Mechanism of PET Signaling
LUMO
U
HOMO
HOMO
LUMO
HOMO
Excited Free Fluorophore Receptor
HOMO
Excited Fluorophore
Bound Receptor
nonfluorescent
Metal ion sensing
2 ZnCI2
Non-fluorescent
Fluorescent
Anion sensing
H-jN ■
NH3 ©
Low fluorescence
+
o
pin-
Nonfluorescent
©
H->N-
M    © /
.-IS)
•*NH 3©
Low fluorescence
©
H-iN-
/3N7 © 0?
©Vh ©
§N©>
High fluorescence
Use of Excimer Emission in Ca2+ Sensing
Xakamura et al. J. Phys. Chem. B> 2001,i 05, 2923
+ A fluorescent host with anthracene moiety at each end of a linearpolyether chain
4> Upon addition of Ca2+fluorescence spectrum changes from monomer emission to excimer emission
Chalfie, Shimomura and Tsien
The Nobel Prize in Chemistry 2008 was awarded for the discovery and development of the
Martin Chalfie Osamu Shimomura Roger Y. Tsien
Columbia University Marine Biological Laboratory University of California,
and Boston University Medical School San Diego
The Nobel Prize in Chemistry 2008 www.nobelprize.org
Fluorescent Protiens
□ Green fluorescent proteins can be expressed in living organisms
Rabbit expressing GFP
Modifications of Green Fluorescent Protein
Mutants = Mutations in the amino acid sequence can be exploited to regulate the absorption and emission properties of the chromophore
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