Recently, Suzuki et al. [13] have determined the fluorescence quantum yield of DPA in benzene to be 0.88±0.03 by using a time-resolved thermal lensing (TRTL) technique.
To calculate the Φf value, they used the S1 energy (304 kJ mol−1) of DPA instead of the average energy (275 kJ mol−1) dissipated by fluorescence from the S1 state given by Eq III-16. If one use the latter value for calculating Φf based on the TRTL method (Eq 4 in [13]), the fluorescence quantum yield of DPA is found to be 0.97. This is in agreement with the Φf value derived from our measurements based on the integrating sphere.
References
[1] W. H. Melhuish, J. Phys. Chem. 1961, 65, 229.
[2] W. H. Melhuish, New Zealand J. Sci. Tech. 1955, 37, 142.
[3] W. R. Dawson, M. W. Windsor, J. Phys. Chem. 1968, 72, 3251.
[4] B. Gelernt, A. Findeisen, A. Stein, J. A. Poole, J. Chem. Soc., Faraday Trans. II, 1973, 70, 939.
[5] J. Olmsted III, J. Phys. Chem. 1979, 83, 2581.
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[9] M. Mardelli, Olmsted III, J. J. Photochem. 1977, 7, 277.
[10] J. V. Morris, M.A. Mahaney, J. R. Huber, J. Phys. Chem. 1976, 80, 969.
[11] S. R. Meech, D. Phillips, J. Photochem. 1983, 23, 193.
[12] S. Hamai, F. Hirayama, J. Phys. Chem. 1983, 87, 83.
[13] T. Suzuki, M. Nagano, S. Watanabe, T. Ichimura, J. Photochem. Photobiol., A 2000, 136, 7.
[14] W. R. Ware, B. A. Baldwin, J. Chem. Phys. 1965, 43, 1194.
[15] W. R. Ware, W. Rothman, Chem. Phys. Lett. 1976, 39, 449.
[16] N. C. Greenham, I. D. W. Samuel, G. R. Hayes, R. T. Phillips, Y. A. R. R. Kessener, S. C. Moratti, A. B. Holmes, R. H. Friend, Chem. Phys. Lett. 1995, 241, 89.
[17] J. C. de Mello, H. F. Wittmann, R. H. Friend, Adv. Mater. 1997, 9, 230.
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Lumin. 2006, 16, 267.
[23] A. K. Gaigalas, L. Wang, J. Res. Natl. Inst. Stand. Technol. 2008, 113, 17.
[24] A. Endo, K. Suzuki, T. Yoshihara, S. Tobita, M. Yahiro, C. Adachi, Chem. Phy. Lett.
2008, 460, 155.
[25] J. R. Lakowicz, Principles of Fluorescence Spectroscopy, Springer, New York, ed.
3. 2006.
[26] E. Lippert, W. Nägele, I. Seibold-Blankenstein, U. Staiger, W. Voss, Z. Anal. Chem.
1959, 170, 1.
[27] T. -S. Ahn, R. O. Al-Kaysi, A. M. Müller, K. M. Wentz, C. J. Bardeen, Rev. Sci.
Instrum. 2007, 78, 086105.
[28] S. R. Meech, D. V. O’Connor, D. Phillips, J. Chem. Soc. Faraday Trarns. 2, 1983, 79, 1563.
[29] J. N. Demas, G. A. Crosby, J. Phys. Chem. 1971, 75, 991.
[30] D. F. Eaton, Pure Appl. Chem. 1988, 60, 1107.
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[33] B. Valuer, Molecular Fluorescence Wiley-VCH: Weinheim, 2002.
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[35] Bonneau, R.; Carmichael, I.; Hug, G. L. Pure Appl. Chem. 1991, 63, 289.
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Chapter IV
Absolute Measurements of Luminescence
Quantum Yield of Rigid Solutions at 77K
IV-1 Introduction
In Chapter III the reliability of the fluorescence quantum yields obtained by using our integrating sphere instrument was confirmed by comparing our Φf values for fluorescence standard solutions with those reported in the literature. To clarify the relaxation processes of excited singlet and triplet states of molecule, it is necessary to evaluate the phosphorescence quantum yield (Φp) as well as Φf values.
Usually the phosphorescence of organic molecules in solution at room temperature is quenched appreciably by collisional deactivation processes. Hence the phosphorescence of organic solutions is generally observed only under low-temperature rigid glass states.
For such a rigid glass state, polarization effects and effects of refractive index influence greatly the quantum yield measurements even in the case of using the relative method.
This seems to be the reason for difficulty of determining Φp as compared with Φf and for the lack of suitable standards for Φp measurements.
In this chapter, our integrating sphere instrument is modified for the quantum yield measurements of rigid solutions at 77K. Using this apparatus the fluorescence and phosphorescence quantum yields of 1-halonaphthalenes and 4-halobenzophenones in rigid solutions at 77K are measured to reveal the heavy atom effects of halogen substituent on the spin-forbidden radiative and nonradiative transitions.
IV-2 Experimental Material
Figure IV-1 shows the sample molecules used in this chapter. Benzopheneone (BP;
Kishida), 4-Fluorobenzopheneone (BP4F; Tokyo Kasei), 4-Chlorobenzopheneone
n-hexane and by vacuum sublimation. Naphthalene (Kanto) was purified by vacuum sublimation. 1-Fluoronaphthlene (Nap1F; wako), 1-chloronaphthalene (Nap1Cl; Tokyo Kasei), 1-bromonaphthalene (Nap1Br; Tokyo Kasei) and 1-iodonaphthalene (Nap1I;
Kanto) were purified by distillation under reduced pressure. Ethanol (Tokyo Kasei, spectrophotometric grade), was used without further purification.
Apparatus
A schematic diagram of the modified integrating sphere instrument is illustrated in Figure IV-2. A quartz tube with an inner diameter of 6mm was used as the sample cell, and situated in a quartz liquid nitrogen dewar. In the case of room temperature solutions, the sample cuvette in the integrating sphere was excited directly by incident light, while in the quantum yield measurements of 77K rigid solutions, monochromatized light was introduced into the integrating sphere so as to hit the internal surface coated with high reflectance material (Spectralon). After multiple reflections on the internal surface, much of the optical anisotropy was eliminated. The detector first monitored the excitation light profile when a quartz tube without sample solution was set at the position above the center of the IS, and then recorded the excitation light profile and the luminescence spectrum when a quartz tube with sample solution was set at the same position. From these spectral data, the luminescence quantum yield was calculated according to Eq II-1. The whole system was fully calibrated for spectral sensitivity using deuterium and halogen standard light sources.
Benzophenone (BP)
O
Benzophenone (BP)
O
4-Fluorobenzophenone (4F-BP)
O
F 4-Fluorobenzophenone
(4F-BP) O
F
4-Chlorobenzophenone (4Cl-BP)
O
Cl 4-Chlorobenzophenone
(4Cl-BP) O
Cl
4-Bromobenzophenone (4Br-BP)
O
Br 4-Bromobenzophenone
(4Br-BP) O
Br
4-Iodobenzophenone (4I-BP)
O
I 4-Iodobenzophenone
(4I-BP) O
I
Naphthalene (NA) Naphthalene
(NA) F
1-Fluoronaphthalene (1F-NA)
F
1-Fluoronaphthalene (1F-NA)
Cl
1-Chloronaphthalene (1Cl-NA)
Cl
1-Chloronaphthalene (1Cl-NA)
Br
1-Bromonaphthalene (1Br-NA)
Br
1-Bromonaphthalene (1Br-NA)
I
1-Iodonaphthalene (1I-NA)
I
1-Iodonaphthalene (1I-NA)
Integrating sphere Dewar
Detector
Light source
Sample tube
Figure IV-2 Schematic diagram of integrating sphere with quartz
dewar for measuring absolute luminescence quantum
yields of rigid solutions at 77K
IV-3 Results and Discussion
IV-3-1 Luminescence quantum yields of 9,10-diphenylanthracene and benzophenone at 77K
In order to evaluate the reliability of the luminescence quantum yield obtained by the modified apparatus, we first measured the fluorescence quantum yield of 9,10-diphenylanthracene in ethanol at 296K and 77K. The Φf value of 9,10-diphenylanthracene in solution is known to be close to unity and almost insensitive to temperature between room temperature and 77K [ 1 ]. Figure IV-3 shows the fluorescence spectra of DPA in ethanol at room temperature and 77K. In the rigid solution at 77K, vibrational structures in the fluorescence spectrum are found to become prominent. Even at 77K, phosphorescence was not observed under the present experimental conditions. This observation is in consistent with the nearly unity Φf value of DPA. Based on the measurements using the apparatus in Figure IV-2, the Φf values of 9,10-diphenylanthracene in ethanol at 296 and 77K were obtained to be 0.95 and 0.97, respectively. These values are in good agreement with the values determined by Huber et al [1]. They measured the fluorescence quantum yield based on the relative method, taking into account the corrections for the temperature dependence of the refractive index and absorbance of the sample solutions.
As one of representative values for the quantum yield of low-temperature rigid solutions, the phosphorescence quantum yield of benzophenone in EPA (ether:isopentane:alcohol = 5:5:2 by volume) at 77K has been reported by Gilmore et al to be 0.85 [2]. They measured the Φp value on the basis of the absolute method including complex corrections for index of refraction of rigid EPA at 77K, window
400 500 R.T.
77K
Wavelength (nm) Φ
f= 0.95 Φ
f= 0.97
In te n si ty / a rb . u n it
Figure IV-3 Fluorescence spectra of DPA in ethanol at R.T.
(black) and 77K (red)
benzophenone in ethanol at 77K without such complex corrections, and obtained the value to be 0.88. This Φp value is very close to that (0.85) reported by Gilmore et al.
From these results we could confirm that our integrating sphere instrument gives reliable luminescence quantum yield not only for room temperature solutions but also for rigid solutions at77K.
IV-3-2 Fluorescence and phosphorescence quantum yields of naphthalene and 1-halonaphthalenes at 77K
Using the modified apparatus in Fig IV-2 we measured the Φf and Φp of naphthalene (NA) and 1-halonaphthalenes in ethanol at 77K to examine quantitatively the internal heavy atom effects of halogens on spin-forbidden transitions. Figure IV-4 shows the fluorescence and phosphorescence spectra of naphthalene and its 1-halogenated derivatives in ethanol at 77K, together with their absorption spectra at room temperature.
It is apparent from Figure IV-4 that the relative phosphorescence intensity increases rapidly in the sequence of fluoro- (1F-NA), chloro- (1Cl-NA), bromo- (1Br-NA) and iodonaphthalenes (1I-NA). In the luminescence spectra of 1I-NA, the relative fluorescence intensity becomes negligibly small, and the emission spectrum at 77K is dominated by phosphorescence. Our integrating sphere instrument enables us to measure simultaneously the absolute fluorescence and phosphorescence quantum yields as well as the corrected luminescence spectra. In Table IV-1, the Φf and Φp values of NA and its 1-haloganated derivatives in ethanol at 77K obtained by using our apparatus are presented together with the quantum yields reported by Ermolaev and Svitashev [3-5].45 They determined the Φ and Φ values in Table 1 based on the relative method in which
300 400 500 600 700
Figure IV-4 Room temperature absorption, 77K fluorescence (blue) and 77K phosphorescence (red) spectra of naphthalene and 1-halonaphthalenes in ethanol
NA
1F-NA
1Cl-NA
1Br-NA
1I-NA x 50
x 20 x 20
x 50
Wavelength (nm)
A b so rb an ce / a rb . u n it In te n si ty / ar b . u n it
Table IV-1 Photophysical parameters of naphthalene and 1-halonaphthalenes (2×10-4M) in ethanol at 77K (Eλ= 270 nm)
NA 0.38 (0.55)a 0.024 (0.051)b 0.62 1.3 0.030 0.74
1F-NA 0.41 (0.84)b 0.026 (0.056)b 0.59 0.8 0.055 1.2 1Cl-NA 0.023 (0.058)b 0.09 (0.30)b 0.98 0.31 0.30 2.9 1Br-NA 0.0034 (0.0016)b 0.14 (0.27)b 1.0 0.02 7.0
1I-NA 0.14 (0.38)b 1.0 0.0026 3.3 × 102
43
<0.0022 (<0.0005)b 54
/ s-1 Compounds
77K
Φf Φp Φisc τp kp kisc' / s / s-1
aIn an E. P. A. from ref. 2. bIn an ethanol/ether glass at 77K, from ref. 4.
their Φf value (0.55) of the reference sample (NA) was larger than our value (0.38). In a subsequent paper [6], however, Ermolaev used 9,10-di-n-propylanthracene in ethanol / ether rigid solution at 77K as the standard in the quantum yield measurements of NA, 1Cl-NA, 1Br-NA, and 1I-NA and reported the Φf and Φp values being much smaller than those given in ref. 4.
It can be seen from Table IV-1 that in the 1-halonaphthalenes the fluorescence quantum yield decreases and the phosphorescence quantum yield increases as the atomic number of the halogens increases. Assuming that the quantum yield of intersystem crossing (Φisc) of these compounds is given by (1- Φf) at 77K, one can derive the values for the T1→S0 radiative (kp) and nonradiative (kisc’) rate constants by substituting the Φp, Φisc and the phosphorescence lifetime (τp) into the following equations:
p isc
p
p Φ τ
= Φ
k (IV-1)
p p isc
' 1 k k = −
τ (IV-2)
Table IV-1 clearly indicates that both kp and kisc’ increases as the atomic number of the substituent increases because of the enhancement in spin-orbit coupling. It would appear that the internal heavy atom effect is more prominent in the nonradiative transitions.
First we consider the effects of spin-orbit coupling on the T1→S0 radiative transition of 1-halonaphthalenes. The probability of T1←S0 absorption at unit density is given by
2
r
1 2 0
3
3 r
8πh
∑
S e Tr (IV-3)where S0 and T1r are the ground state wavefunction and perturbed triplet state wavefunctions, er is the electric dipole moment operator and r is the value of the Ms, i.e.
0, ±1. Because the rate of T1→S0 phosphorescence is much smaller than the rate of thermal re-equilibration of triplet multiplet populations, the intrinsic rate constant for T1→S0 phosphorescence is given by
2
r
1 3 0
3 4
p r
3
64
∑
= S e Tr
k πhcν
(IV-4)
where ν is the frequency of the emitted light, probably best taken to be the Franck-Condon maximum of the T1→S0 phosphorescence emission. According to the first order perturbation theory, the perturbed triplet wave function is
p p 1
r 1 SO r p
1 r '
1 (T) (S )S
E E
T H T S
T = + − (IV-5)
where Sp is the perturbing singlet wave function. From Eqs IV-4 and IV-5, kp is written as
r 2
ν π
Thus it can be seen that the intensity of the T1→S0 transition is borrowed from the Sp→S0 transition. The part Sp HSO T1r is proportional to ζnl, the spin orbit coupling factor which for hydrogenic-like atoms is equal to
( )
+
+
l l l n
Z a
c m
h e
2 1 1
2 3
4 3
0 2 2
2 2
(IV-7)
where Z is the atomic number of the atom and n and l are the principal and orbital angular momentum quantum numbers respectively of the electron of concern. Since the transition probability is proportional to Sp HSOT1r 2, the S↔T probability is dependent on Z8.
Next we consider the effects of spin-orbit coupling on the nonradiative transitions between excited singlet and triplet states of 1-halonaphthalenes. The total wavefunction ψ for a system can be written as
i i
i φχ
ψ = (IV-8)
where φi is the electronic wavefunction and χiis the vibration wavefunction of a state i. Then the rate of spin-forbidden nonradiative transitions (intersystem crossing) from state n to m can be written as Eq IV-9 according to the Fermi’s Golden rule.
ρ χ χ φ π φ
π ρ 2 2
SO 2
SO isc
2 2
m n m
n H
m H n
k = h = h (IV-9)
where ρis the state density of the final state and χn χm 2 is the Franck-Condon factor (vibrational overlap factor).
The Φf and Φp of 1-halonaphthalenes in Table IV-1 suggest that the rate of S1→T1
intersystem crossing (kisc) is also enhanced by internal heavy atom effects due to halogen substitution. The kisc at room temperature (RT) can be determined from the fluorescence lifetime (τf) and Φisc as
f isc
isc τ
=Φ
k (IV-10)
where the Φisc values of NA and 1-halonaphthalenes were obtained by PA measurements described below, and τf was determined by nanosecond and picosecond fluorescence lifetime measurements. The PA signals of naphthalene and the photocalorimetric reference 2-hydroxybenzophenone in ethanol at 293 K are displayed in Figure IV-5 (a).
The difference between the first maximum and minimum in the PA signal was taken as the signal amplitude H. The signal amplitude HS of naphthalene is related to the incident laser energy E0S by
(
1 10 S)
S 0
S A
E K
H = α − − (IV-11)
where K is a constant that depends on the geometry of the experimental set-up and the thermoelastic quantities of the medium and AS is the absorbance of the sample solution at the excitation wavelength. The signal amplitude HR of the photocalorimetric
(
1 10 R)
R 0
R A
KE
H = − − (IV-12)
where the thermal conversion efficiency α of the photocalorimetric reference 2-hydroxybenzophenone is assumed to be unity. From Eqs IV-11 and IV-12, the value of α of the sample solution can be obtained as follows.
( )
(
S)
R
10 1
10 1
S 0 R
R 0 S
A A
E H
E H
−
−
−
= −
α (IV-13)
The relationship between the PA signal amplitude and the laser energy was linear for naphthalene and 1-halonaphthalenes in ethanol within the energy range studied as shown in Figure IV-5 (b).
With the exception of the decay of the excited triplet state, all other decay processes occur within the heat integration time (about 340 ns), so that the quantum yield of intersystem crossing (Φisc) can be obtained from the following relation.
λ
λ E E αE
E =Φf S +Φisc T + (IV-14)
where Eλ is the excitation photon energy (= 450 kJ mol-1 at 266 nm), Φf is the fluorescence quantum yield, ET is the triplet energy (254 kJ mol-1), and Es is the average energy dissipated by fluorescence from the S1 state, which is given by
( )
∫ ( )
=
∫
ν ν
ν ν ν
d I
d E I
f f
S (IV-15)
where If
( )
ν is the spectral distribution of fluorescence as a function of wavenumber( )
ν . The magnitude of Es was calculated to be 357 kJ mol-1. By substituting these quantities into Eq IV-14, the Φisc of naphthalene was determined to be 0.83. The Φiscvalues of 1-halonaphthalenes in Table IV-2 were determined in a similar manner.
As shown in Table IV-2, the kisc values of NA and 1-halonaphthalenes calculated from the fluorescence lifetime (τf) and the quantum yield of intersystem crossing (Φisc) at RT significantly increase by heavy atom substitution. Our results (see Figure IV-6) suggest that in 1-halonaphthalenes kisc is more sensitive to spin-orbit coupling than are kp and kisc’.
7
Table IV-2 Photophysical parameters of naphthalene and 1-halonaphthalenes (2×10-4M) in ethanol at room temperature (Eλ= 270 nm)
kf
/ 106 s-1
NA 0.20 0.83 2.1 0.86
1F-NA 0.20 0.84 5.0 2.1
1Cl-NA 0.014 0.98 2.7 5.2
1Br-NA 0.0005a 0.97 0.078 6.3 1.2 × 103
1I-NAb - - - -
-aDetermined by the relative method using Φf of 1Cl-NA bThe quantum yields and τf
of 1I-NA could not be determined by occurrence of photodecompositions (ref.7).
Compounds
RT Φf Φisc
τf kisc
/ ns / 107 s-1
97 40
36
Figure IV-5 (a) Laser fluence dependence of PA signals for Naphthalene and 2HBP in EtOH (b) PA signal amplitude as a function of laser fluence for Naphthalene and 2HBP in EtOH (E
λ= 355 nm)
0 20 40
0 0.1
Time (µs)
Laser fluence (µJ)
P A s ig n al ( ar b . u n it ) P A s ig n al a m p li tu d e
0 5 10
0 0.2
(a)
(b)
10
010
110
210
010
110
210
3Figure IV-6 Spin orbit coupling constants dependence for normalized rate constants of 1-halonaphthalenes in ethanol
k
pk
isc’ k
iscζ
nlX2/ ζ
nlF2k
X/ k
FIV-3-3 Phosphorescence quantum yields of benzophenone and 4-halobenzophenones at 77K
Using the modified apparatus in Figure IV-2 we measured the Φp of benzophenone (BP) and 4-halobenzophenones in ethanol at 77K to examine quantitatively the internal heavy atom effects of halogens on spin-forbidden transitions of aromatic carbonyl compounds. Figure IV-7 shows the phosphorescence spectra of BP and its 1-halogenated derivatives in ethanol at 77K, together with their absorption spectra at room temperature. The emission spectrum of BP in ethanol at 77K is dominated by phosphorescence, and the fluorescence is not observed even at 77K. This is due to extremely fast S1→T1 intersystem crossing. The BP, 4-fluorobenzophenone (4F-BP), 4-chlorobenzophenone (4Cl-BP) and 4-bromobenzophenone (4Br-BP) exhibit almost identical phosphorescence spectra, although 4-iodobenzophenone (4I-BP) shows enhancement in the 0-0 band intensity.
In Table IV-3, the Φp values of BP and its 4-haloganated derivatives in ethanol at 77K obtained by using the apparatus shown in Figure IV-2 are presented together with the phosphorescence (τp). Because the rate of S1→T1 intersystem crossing of BP at RT is known to be very fast and the observed Φp values of BP and 4-halobenzophenones are close to unity, one can assume that the Φisc of the BP and the 4-halobenzophenones at 77K would be unity. Therefore, the values for the kp and kisc’ can be obtained by substituting the Φp and the phosphorescence lifetime (τp) into the following equations:
p p
p τ
=Φ
k (IV-16)
Table IV-3 shows that the kp and kisc’ values of BP and 4-halobenzophenones are much larger than those of NP and 1-halonaphthalenes (see Table IV-1), because the spin-orbit interaction between a 1(n,π*) and a 3(π,π*) state for carbonyl compounds is much larger than that in aromatic hydrocarbons (the El-Sayed rule [ 8 ]). In the case of 1-halonaphthalenes, remarkable heavy atom effects were found for the rates of T1→S0 radiative and nonradiative transitions as well as S1→T1 intersystem crossing because of intrinsic spin-forbidden nature of these transitions. It can be found, however, that in the case of 4-halobenzophenones the heavy atom effect is not observed for 4F-BP, 4Cl-BP and 4Br-BP and is found only in the case of 4I-BP.
τ
pk
pk
isc '/ ms / s
-1/ s
-1BP 0.88 5.57 158 21
4F-BP 0.87 6.02 145 21
4Cl-BP 0.87 6.24 140 20
4Br-BP 0.87 5.39 161 25
4I-BP 0.90 1.69 534 58
Φ
pTable IV-3 Phosphorescence quantum yield and lifetime of benzophenone and 4-halobenzophenone (5×10-3M) in ethanol at 77K (Eλ= 355 nm)
300 400 500 600 BP
4F-BP
4Cl-BP
4Br-BP
4I-BP
Figure IV-7 Room-temperature absorption and 77K phosphorescence spectra of benzophenone and 4-halobenzophenones in ethanol
Wavelength (nm)
A b so rb an ce / a rb . u n it In te n si ty / ar b . u n it
IV-4 Conclusions
An instrument for measuring the absolute luminescence quantum yield of rigid solutions at low temperature has been developed by using an integrating sphere as a sample chamber. We could confirm that our integrating sphere instrument gives reliable luminescence quantum yield not only for room temperature solutions but also for rigid solutions at low temperature by measuring 9,10-diphenylanthracene in ethanol. Our integrating sphere instrument enables us to measure simultaneously the absolute fluorescence and phosphorescence quantum yields as well as the corrected luminescence spectra.
The Φf and Φp of 1-halonaphthalenes suggest that the rate of S1→T1 intersystem crossing (kisc) is enhanced by internal heavy atom effects due to halogen substitution.
Our results suggest that in 1-halonaphthalenes kisc is more sensitive to spin-orbit coupling than are kp and kisc’
References
1 J. R. Huber, M. M. Mahany, W. W. Mantulin, J. Photochem., 1973-4, 2, 67
2 E. H. Gilmore, George E. Gibson, Donald S. McClure, J. Chem. Phys. 1952, 20, 829;
J. Chem. Phys. 1955, 23, 399.
3 B. Valuer, Molecular Fluorescence, Wiley-VCH, Weinheim, 2002.
4 V. L. Ermolaev, K. K. Svitashev, Optics and Spec. 1959, 7, 399.
5 F. Wilkinson, in Organic Molecular Photophysics, Vol. 2, J. B. Birks, Ed., Wiley, New York, 1975, Chapter 3.
6 V. L. Ermolaev, Opt. Spectrosc. (USSR), 1962, 13, 49; S. L. Murov, I. Carmiohael, G.
L. Hug, Handbook of Photochemistry, Marcel Dekker, New York, 1993.
7 E. Haselbach, Y. Rohner, P. Suppan, Helv. Chim. Acta, 1990, 73, 1644.
8 M. A. El-Sayed, J. Chem. Phys., 1963, 38, 2834.
Chapter V
Summary
In the present thesis the absolute fluorescence and phosphorescence quantum yields of some standard solutions were reevaluated by using a new instrument developed for measuring the absolute emission quantum yields of solutions. The instrument consisted of an integrating sphere equipped with a monochromatized Xe arc lamp as the light source and a multichannel spectrometer. By using a back-thinned CCD (BT-CCD) as the detector, the sensitivity for spectral detection in both the short and long wavelength regions was greatly improved compared with that of an optical detection system that uses a conventional photodetector. Using this instrument, the absolute fluorescence quantum yields (Φf) of some commonly used fluorescence standard solutions were measured by taking into account the effect of reabsorption/reemission. The value of Φf
for 5 × 10–3 M quinine bisulfate in 1 N H2SO4 was measured to be 0.52, which is in good agreement with the value (0.508) obtained by Melhuish by using a modified Vavilov method. In contrast, the value of Φf for 1.0 × 10–5 M quinine bisulfate in 1 N H2SO4, which is one of the most commonly used standards in quantum yield measurements based on the relative method, was measured to be 0.60. This value was significantly larger than Melhuish’s value (0.546), which was estimated by extrapolating the value of Φf for 5 × 10–3 M quinine bisulfate solution to infinite dilution using the self-quenching constant. The fluorescence quantum yield of 9,10-diphenylanthracene in cyclohexane was measured to be 0.97.
The integrating sphere instrument was modified to determine the absolute luminescence quantum yield of rigid solutions at 77K. Using the modified apparatus the fluorescence and phosphorescence quantum yields of 1-halonaphthalenes and 4-halobenzophenones in ethanol at 77K were measured to clarify quantitatively the internal heavy atom effects of halogens on the spin forbidden transitions in aromatic hydrocarbons and aromatic carbonyl compounds.