1H NMR spectroscopy as a tool to determine accurate photoisomerization quantum yields of stilbene-like ligands coordinated to rhenium(I) polypyridyl complexes

Article abstract of DOI:10.1016/j.ica.2009.10.008

In this work, the use of proton nuclear magnetic resonance, ¹H NMR, was fully described as a powerful tool to follow a photoreaction and to determine accurate quantum yields, so called true quantum yields (Φ_true), when a reactant and photoproduct absorption overlap. For this, Φ_true for the trans-cis photoisomerization process were determined for rhenium(I) polypyridyl complexes, fac-[Re(CO)₃(NN)(trans-L)]⁺ (NN = 1,10-phenanthroline, phen, or 4,7-diphenyl-1,10-phenanthroline, ph₂phen, and L = 1,2-bis(4-pyridyl)ethylene, bpe, or 4-styrylpyridine, stpy). The true values determined at 365 nm irradiation (e.g. Φ_NMR = 0.80 for fac-[Re(CO)₃(phen)(trans-bpe)]⁺) were much higher than those determined by absorption spectral changes (Φ_UV-Vis = 0.39 for fac-[Re(CO)₃(phen)(trans-bpe)]⁺). Φ_NMR are more accurate in these cases due to the distinct proton signals of trans and cis-isomers, which allow the actual determination of each component concentration under given irradiation time. Nevertheless when the photoproduct or reactant contribution at the probe wavelength is negligible, one can determine Φ_true by regular absorption spectral changes. For instance, Φ_{313 nm} for free ligand photoisomerization determined both by absorption and ¹H NMR variation are equal within the experimental error (bpe: Φ_UV-Vis = 0.27, Φ_NMR = 0.26; stpy: Φ_UV-Vis = 0.49, Φ_NMR = 0.49). Moreover, ¹H NMR data combined with electronic spectra allowed molar absorptivity determination of difficult to isolate cis-complexes.

Full text of DOI:10.1016/j.ica.2009.10.008

Inorganica Chimica Acta 363 (2010) 294–300
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
1H NMR spectroscopy as a tool to determine accurate photoisomerization
quantum yields of stilbene-like ligands coordinated to rhenium(I) polypyridyl
complexes
*
Karina Passalacqua Morelli Frin, Melina Kayoko Itokazu, Neyde Yukie Murakami Iha
Laboratory of Photochemistry and Energy Conversion, Instituto de Química, Universidade de São Paulo – USP, Av. Prof. Lineu Prestes, 748, 05508-900 São Paulo, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
In this work, the use of proton nuclear magnetic resonance, 1H NMR, was fully described as a powerful
tool to follow a photoreaction and to determine accurate quantum yields, so called true quantum yields
Article history:
Received 13 August 2009
Accepted 14 October 2009
Available online 20 October 2009
(
Utrue), when a reactant and photoproduct absorption overlap. For this, Utrue for the trans–cis photoiso-
merization process were determined for rhenium(I) polypyridyl complexes, fac-[Re(CO)3(NN)(trans-L)]+
(NN = 1,10-phenanthroline, phen, or 4,7-diphenyl-1,10-phenanthroline, ph2phen, and L = 1,2-bis(4-pyri-
dyl)ethylene, bpe, or 4-styrylpyridine, stpy). The true values determined at 365 nm irradiation (e.g.
UNMR = 0.80 for fac-[Re(CO)3(phen)(trans-bpe)]+) were much higher than those determined by absorption
spectral changes (UUV–Vis = 0.39 for fac-[Re(CO)3(phen)(trans-bpe)]+). UNMR are more accurate in these
cases due to the distinct proton signals of trans and cis-isomers, which allow the actual determination
of each component concentration under given irradiation time. Nevertheless when the photoproduct
or reactant contribution at the probe wavelength is negligible, one can determine Utrue by regular absorp-
tion spectral changes. For instance, U313 nm for free ligand photoisomerization determined both by
absorption and 1H NMR variation are equal within the experimental error (bpe: UUV–Vis = 0.27,
UNMR = 0.26; stpy: UUV–Vis = 0.49, UNMR = 0.49). Moreover, 1H NMR data combined with electronic spectra
allowed molar absorptivity determination of difficult to isolate cis-complexes.
Keywords:
1H NMR spectroscopy
True quantum yield
Rhenium(I) complexes
Trans to cis photoisomerization
Stilbene-like ligands
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
terparts, and more suitable to be exploited in the development of
molecular devices.
The trans to cis photoisomerization reaction of trans stilbene-
like compounds (trans-L) has been extensively investigated.
Although the mechanisms are still under investigation, it has been
reported that both singlet and triplet pathways are involved in the
photoisomerization process [1–8]. When trans-1,2-bis(4-pyri-
dyl)ethylene (bpe) is coordinated to a heavy atom, such as rhe-
nium(I) in fac-[Re(CO)3(phen)(trans-bpe)]+, the coupling between
the singlet and triplet manifolds is enhanced [9]. The complex acts
as a sensitizer through an energy transfer from the 3MLCT excited
state to the 3IL one, which is the only pathway to reach the excited
state responsible for the isomerization. On the other hand, for the
coordinated trans-4-styrylpyridine (stpy), a contribution of the sin-
glet pathway is also considered in the photoisomerization process
[10].
The photoinduced isomerization quantum yields for the coordi-
nated trans-L to rhenium(I) complexes have been usually deter-
mined by the variation of absorbance [10–21]. However, when
both the reactant and photoproduct absorb in the same spectral re-
gion, quantum yields obtained by absorption spectral changes are
only apparent. Therefore, another technique is required to follow
the trans to cis photoisomerization reaction and to determine true
quantum yields. The best approach in these cases is the proton nu-
clear resonance spectroscopy, 1H NMR, since both the chemical
shifts and coupling constants, especially for the olefinic protons,
are fairly different for the two isomers. Previously, this technique
has only been employed to demonstrate the occurrence of the
photoisomerization processes in these complexes [13,15,22],
although it can provide accurate quantum yields for the isomeriza-
tion process of coordinated trans-L ligands. Moreover, the use of
NMR spectroscopy is not limited to follow only photoreactions;
this technique is as good for any reaction kinetics wherein a prod-
uct and a reactant absorb in the same spectral region.
Another interesting feature of the trans to cis photoisomeriza-
tion of stilbene-like ligands coordinated to fac-[Re(CO)3(NN)
(trans-L)]+ (NN = polypyridyl ligands) is their sensitization to visi-
ble region, which can be an advantage over their free organic coun-
In this work, the use of proton nuclear magnetic resonance, 1H
NMR, is fully described and showed as a powerful tool to follow the
photoprocess and to determine accurate photoisomerization
* Corresponding author: Tel.: +55 11 3091 2151; fax: +55 11 3915 5571.
E-mail address: neydeiha@iq.usp.br (N.Y. Murakami Iha).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.10.008

K.P.M. Frin et al. / Inorganica Chimica Acta 363 (2010) 294–300
295
quantum yields. Moreover, the molar absorptivities of difficult to
isolate photoproducts can be obtained by association of 1H NMR
and absorption variation measurements. Therefore, the true quan-
tum yields can be determined without the use of further NMR
experiments. This approach has been exploited by determining
true quantum yields for the fac-[Re(CO)3(NN)(trans-L)]+ complexes
(NN = 1,10-phenanthroline, phen, or 4,7-diphenyl-1,10-phenan-
throline, ph2phen, and L = 1,2-bis(4-pyridyl)ethylene, bpe, or 4-
styrylpyridine, stpy) and were compared with the ones determined
only by absorption variations.
True quantum yields (average of at least two independent
experiments at each irradiation wavelength) were determined
based on the area of photoproduct and reactant proton signals.
Apparent photoisomerization quantum yields (average of at least
three independent experiments at each irradiation wavelength)
were determined by using variation in absorption spectra (follow-
ing the absorption decay in the 320–340 nm region, where the con-
tribution of cis-complexes was considered as low as possible) as
reported elsewhere [10,16–20].
Molar absorptivities of fac-[Re(CO)3(NN)(cis-L)]+ complexes
were obtained by photolysis of a corresponding trans-isomer com-
plex in CD3CN of appropriate concentration (ca. 10ꢀ4 mol Lꢀ1).
Photolysis percentages and, consequently, concentrations of the
trans and cis species were determined using the absorption spectra
and 1H NMR spectroscopy.
2. Experimental
2.1. Materials
All chemicals, Aldrich, were reagent grade, except deuterated
grade solvent, Aldrich or Cambridge, for photochemical measure-
ments. [ClRe(CO)5], Strem, 1,10-phenanthroline (phen), QM, and
4,7-diphenyl-1,10-phenanthroline (ph2phen), trifluoromethane-
sulfonic acid (tfms) and trans-1,2-bis(4-pyridyl)ethylene (trans-
bpe), Aldrich, were used as received. Potassium tris(oxalate)
ferrate(III) was prepared and purified according to the literature
procedure [23]. trans-4-styrylpyridine (trans-stpy) was prepared
as previously reported [18]. 1H NMR (CD3CN, d/ppm): 8.53
(d, 2H); 7.62 (d, 2H); 7.47 (d, 2H); 7.41 (d, 1H); 7.41 (t, 2H); 7.34
(t, 1H); 7.17 (d, 1H).
3. Results and discussion
1H NMR spectral changes observed at 365 nm irradiation of fac-
[Re(CO)3(ph2phen)(trans-bpe)]+ are shown in Fig. 1. Irradiation of
trans-isomer complexes, fac-[Re(CO)3(NN)(trans-L)]+, results in de-
crease of trans-isomer proton signals while the cis-isomer signals
build up in intensity due to the isomerization process of the coor-
dinated stilbene-like ligands, Eq. (1).
2.2. Syntheses of rhenium(I) complexes
fac-[ClRe(CO)3(NN)] complexes (NN = phen or ph2phen) were
prepared according to the literature procedure [17,18,20,24].
[ClRe(CO)5] and an excess of the NN ligand were suspended in xy-
lene and heated to reflux for several hours. The crude product was
recrystallized from dichloromethane by slow addition of n-pen-
tane. These fac-[ClRe(CO)3(NN)] complexes were converted to
fac-[(tfms)Re(CO)3(NN)] as previously described [17,18,20] by add-
ing trifluoromethanesulfonic acid to fac-[ClRe(CO)3(NN)] sus-
pended in dichloromethane and precipitated by addition of
diethyl ether.
fac-[Re(CO)3(NN)(trans-L)]+ complexes were synthesized fol-
lowing the procedure previously described [18,20,25] by refluxing
fac-[(tfms)Re(CO)3(NN)] with an excess of trans-L in methanol and
precipitated with NH4PF6.
Proton signals in the 7.4–7.0 ppm region correspond to the ole-
finic ones (Hc and Hc0) on a trans configuration and display a char-
acteristic coupling constant of 16 Hz. Under 313, 365 or 404 nm
irradiation, new peaks are clearly observed as a result of the photo-
process. Shifts of the cis-isomer signals to lower frequencies and
2.3. Methods
Electronic absorption spectra were recorded on a Hewlett Pack-
ard 8453 spectrophotometer with quartz cuvets of 1.000 or
0.100 cm optical length.
*
*
the coupling constant decrease of olefinic protons (Hc and Hc0 )
from 16 to 12 Hz are the main differences observed for the fac-
[Re(CO)3(ph2phen)(trans-bpe)]+ complex in comparison with the
fac-[Re(CO)3(ph2phen)(cis-bpe)]+ one.
1H NMR spectra were recorded on a Bruker AC-200 (200 MHz), a
DPX-300 (300 MHz) or a DRX-500 (500 MHz) spectrometers at
298 K using CD3CN as a solvent. The signals of residual CH3CN were
used as an internal standard.
The fac-[Re(CO)3(NN)(cis-L)]+ (NN = phen or ph2phen and
L = bpe or stpy) proton signals, although without having isolated
products, are now assigned, Table 1, and are presented along with
the data for the trans-isomer complexes [17–20] for comparison.
In this work, the photoprocess was monitored using the highest
The photolysis system (Oriel) has been described in detail else-
where [17,20]. Light intensities for each irradiation wavelength
were determined by actinometry using tris(oxalate)ferrate(III) be-
fore and after each photolysis experiment [26].
All irradiations were carried out in a system especially designed
for this purpose with a 1.000 cm optical length quartz cuvet (pho-
tolysis compartment) directly connected to another one
(0.100 cm), where absorption changes were measured. The con-
centration of complexes was adjusted to yield absorbances around
2 at the irradiation wavelength in the 1.000 cm cuvet. The 1H NMR
spectrum was registered after each photolysis time and changes in
both chemical shift and coupling constant were monitored.
*
signals for each isomer, Ha0 and Ha0 (9.65–9.55 ppm region), to
obtain the most accurate values, although any cis–trans proton sig-
nal pair can be used. True quantum yields, Utrue, determined based
on the 1H NMR spectral changes were obtained by the proton sig-
nal area of cis-isomer and by using the Eq. (2), where nR is the num-
R
R
ber of initial reactant, P and R are the area of the photoproduct
and reactant signals, respectively, I0 is the incident light intensity
and tirr is the irradiation time:

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K.P.M. Frin et al. / Inorganica Chimica Acta 363 (2010) 294–300
Fig. 1. 1H NMR spectra of fac-[Re(CO)3(ph2phen)(trans-bpe)]+ in CD3CN upon photolysis at 365 nm. (500 MHz, 3.5 ꢂ 10ꢀ4 mol Lꢀ1, T = 298 K).
R
nR ꢁ
P
Fig. 3, by using Eq. (3) and trans and cis-isomer concentrations ob-
R
R
Utrue
¼
ð2Þ
tained by 1H NMR data:
I0tirr
ð
R þ PÞ
A ꢀ etransðkÞ ꢁ b ꢁ Ctrans
ecisðkÞ ¼
ð3Þ
Spectral changes during trans to cis photoisomerization, Fig. 2,
show a decrease of the trans complex contribution in 270–
400 nm and the appearance of the cis photoproduct (200–
270 nm), but there is no region to monitor the contribution of each
isomer itself (see inset Fig. 2). Therefore, even measuring at three
different wavelengths, selected where the absorption of the cis-iso-
mer is as low as possible (320–340 nm), quantum yields so deter-
Ccis ꢁ b
A = absorbance of irradiated solution;
etransðkÞ = trans-isomer molar absorptivities;
b = optical length;
Ctrans = molar concentration of the trans-isomer;
Ccis = molar concentration of the cis-isomer.
mined are still apparent, Uapp
.
Quantum yields determined by 1H NMR, Utrue, are much higher
than the values determined by absorption changes, Uapp, Table 2,
for fac-[Re(CO)3(NN)(trans-L)]+ in CD3CN, under 313, 365 or
404 nm irradiation.
Once molar absorptivities of cis-complex isomers are obtained,
the molar concentration of cis-isomer in the irradiated solution can
be determined by Eq. (3) and the number of the cis photoproduct,
ncis, is obtained by Eq. (4):
One can observe that 1H NMR measurements give more accu-
rate quantum yields, which can be considered the true ones since
the trans and cis-isomers proton signals appear in fairly different
frequencies. Thus, the use of 1H NMR spectroscopy has been suc-
cessfully employed to determine the trans to cis photoisomeriza-
tion quantum yields of coordinated stilbene-like ligands.
Additionally, this technique, when combined with absorption
spectroscopy, allows the determination of molar absorptivities of
ncis ¼ Ccis ꢁ V ꢁ 6:023 ꢂ 1023
ð4Þ
Ccis = molar concentration of the cis-isomer;
V = irradiated volume (L).
Therefore, each isomer contribution in absorption spectra dur-
ing photolysis is determined and, consequently, the true quantum
fac-[Re(CO)3(NN)(cis-L)]+ complexes,
ecis(k), in all spectral region,

K.P.M. Frin et al. / Inorganica Chimica Acta 363 (2010) 294–300
297
Table 1
1H NMR spectral data for fac-[Re(CO)3(NN)(cis-L)]+ and fac-[Re(CO)3(NN)(trans-L)]+ in CD3CN (500 MHz).
Compounds
Proton
*
d (ppm)
J (Hz)
Remarks
H
a0 (d, 2H)
9.58
8.02
8.09
7.63
8.33
6.96
6.82
8.14
6.94
6.57
5.3
5.3
*
Hb0 (d, 2H)
*
H
H
c0 (m, 10H)
*
r0 (s, 2H)
*
Ha (d, 2H)
6.8
6.8
12
5.5
5.5
12
*
Hb (d, 2H)
*
Hc (d, 1H)
γ
β
β
*
Ha0 (d, 2H)
*
α
α
Hb0 (d, 2H)
*
Hc0 (d, 1H)
σ
σ
γ
H
a0 (d, 2H)
9.64
8.06
7.63
8.08
8.55
7.40
7.34
8.31
7.36
7.23
5.4
5.4
[19,20]
Hb0 (d, 2H)
H
H
c0 (m, 10H)
r0 (s, 2H)
Ha (d, 2H)
Hb (d, 2H)
Hc (d, 1H)
Ha0 (d, 2H)
Hb0 (d, 2H)
Hc0 (d, 1H)
6.3
6.3
16
6.7
6.7
16
γ
β
α
σ
σ
α
γ
β
*
H
a0 (d, 2H)
9.59
8.04
8.09
7.65
8.13
6.99
6.39
6.89
7.05
7.18
7.25
5.4
5.4
*
Hb0 (d, 2H)
*
H
r0 (s, 2H)
*
Hd0 (m, 10H)
*
Ha0 (d, 2H)
1.4; 5.4;
*
Hb0 (d, 2H)
*
Hc0 (d, 1H)
12
12
γ
β
β
*
Hd0 (d, 1H)
*
He0 (dd, 2H)
α
*
Hf0 (dd, 2H)
σ
σ
*
Hg0 (dd, 1H)
α
γ
H
a0 (d, 2H)
Hb0 (d, 2H)
9.64
8.06
8.08
7.64
8.26
7.02
7.41
7.54
7.36
5.4
5.4
[19]
H
r0 (s, 2H)
Hd0 (m, 10H)
Ha0 (d, 2H)
6.8
16
16
1.7; 7.8
Hc0 (d, 1H)
Hd0 (d, 1H)
He0 (dd, 2H)
Hb0, Hf0, Hg0 (m, 5H)
β
β
γ
γ
α
σ
σ
α
(continued on next page)

298
K.P.M. Frin et al. / Inorganica Chimica Acta 363 (2010) 294–300
Table 1 (continued)
Compounds
Proton
*
d (ppm)
J (Hz)
Remarks
H
a0 (dd, 2H)
9.55
8.08
8.83
8.17
8.25
6.88
6.79
8.05
6.52
1.4; 5.1
5.1; 8.3
8.3
*
Hb0 (dd, 2H)
*
H
c0 (dd, 2H)
*
Hd0 (s, 2H)
*
Ha (dd, 2H)
*
*
Hb , Hb0 (m, 4H)
*
Hc (dd, 1H)
12
5.3; 1.6
12
β
β
*
Ha0 (dd, 2H)
γ
α
*
Hc0 (dd, 1H)
δ
δ
γ
α
H
a0 (dd, 2H)
Hb0 (dd, 2H)
9.62
8.12
8.84
8.17
8.54
7.39
7.30
8.22
7.30
7.18
1.3; 5.2
5.2; 8.3
1.3; 8.3
[17,19]
H
c0 (dd, 2H)
Hd0 (s, 2H)
Ha (dd, 2H)
Hb (dd, 2H)
Hc (dd, 1H)
Ha0 (dd, 2H)
Hb0 (dd, 2H)
Hc0 (dd, 1H)
4.6
4.6
16
5.4
4.0
16
β
β
γ
α
δ
δ
γ
α
*
H
a0 (dd, 2H)
9.56
8.08
8.83
8.17
8.02
6.91
6.35
6.87
7.16
6.98
7.25
1.5; 5.0
5.0; 8.3
1.5; 4.0
*
Hb0 (dd, 2H)
*
H
c0 (dd, 2H)
*
Hd0 (s, 2H)
*
Ha0 (dd, 2H)
1.5; 5.0
1.5; 5.0
12
*
Hb0 (dd, 2H)
β
β
*
Hc0 (d, 1H)
γ
α
*
Hd0 (d, 1H)
12
*
He0 (m, 2H)
δ
δ
*
Hf0 (m, 2H)
*
Hg0 (m, 1H)
γ
α
H
a0 (dd, 2H)
Hb0 (dd, 2H)
9.62
8.12
8.17
8.84
8.16
7.26
6.97
7.37
7.52
7.35
1.5; 5.0
5.0; 8.4
1.5; 8.4
[18,19]
H
c0 (dd, 2H)
Hd0 (s, 2H)
Ha0 (d, 2H)
Hb0 (d, 2H)
Hc0 (d, 1H)
Hd0 (d, 1H)
He0 (dd, 2H)
Hf0, Hg (m, 3H)
5.5
7.0
16
16
β
β
γ
α
1.5; 8.0
δ
δ
γ
α
yields can be obtained. Thus, when the 1H NMR spectroscopy is
properly employed along with absorption spectrum variation, the
apparent quantum yields once obtained by absorption changes
can be corrected to the true values without further NMR experi-
ments. For instance, the true quantum yields for fac-[Re(CO)3-
(phen)(trans-bpe)]+ under 404 nm irradiation and for fac-[Re-
(CO)3(phen)(trans-stpy)]+ under 313 nm irradiation, Table 2, were
determined using this correction for apparent quantum yields,
Uapp, previously reported [10,18].
In the region employed for the quantum yield determination
(320–340 nm), molar absorptivities of fac-[Re(CO)3(ph2phen)(cis-
bpe)]+ are lower than for trans-isomer complexes but the contribu-
tion of cis-complex are in the same order of magnitude
(104 L molꢀ1 cmꢀ1) and can not be neglected. Consequently, the

K.P.M. Frin et al. / Inorganica Chimica Acta 363 (2010) 294–300
299
Fig. 3. Molar absorptivities of fac-[Re(CO)3(ph2phen)(cis-bpe)]+ (- - -) in compar-
33
Fig. 2. Difference absorption spectra of fac-[Re(CO)3(ph2phen)(trans-bpe)]+ in
ison with fac-[Re(CO)3(ph2phen)(trans-bpe)]+
(
).
CH3CN (3.5 ꢂ 10ꢀ4 mol Lꢀ1
, Dt = 4 s, kirr = 365 nm). Inset: absorption spectra of
fac-[Re(CO)3(ph2phen)(trans-bpe)]+
[Re(CO)3(ph2phen)(cis-bpe)]+ (- - -).
(
33
) and of a solution having 25% of fac-
true quantum yields are higher than those determined by absorp-
tion changes (apparent).
Gray and co-workers [27] reported similar values for molar
absorptivities of fac-[Re(CO)3(NN)(cis-bpe)]+ complexes, NN =
phen, bpy, Me2bpy, Me4phen, although the trans–cis photoisomer-
ization quantum yields determined by absorption changes are
equal to the values determined by changes in 1H NMR spectra.
In these cases, the absorbance difference, commonly used to
determine quantum yields, does give only apparent values. If the
contribution of the photoproduct or reactant at the probe wave-
length is negligible, the determined value is the true quantum
yield, otherwise it gives a value, which is lower than a true quan-
tum yield obtained using an actual concentration of the photo-
product and/or remaining concentration of the reactant. For
instance, the absorbance of the free cis-L is negligible in the region
(300–325 nm) employed to determine quantum yields, Fig. 4, and
therefore photoisomerization quantum yields for free trans-L
determined by absorption and 1H NMR changes, Fig. 5, are similar,
Table 3.
Fig. 4. Absorption spectra of 3.2 ꢂ 10ꢀ4 mol Lꢀ1 trans-bpe (
33
) and 84% cis-bpe
solution (- - -).
Trans to cis photoisomerization quantum yields of the free
ligands determined by absorption and NMR changes are equal
within the experimental error and are in accord with the literature
[3–5,8]. Thus, in these cases, the ordinary spectral absorption
variation provides the true quantum yields for the photoprocess.
Otherwise, 1H NMR spectroscopy proved to be a powerful and effi-
cient technique to determine accurate quantum yields, although
some experimental conditions have to be considered. One of them
is a good signal to noise ratio requirement at a lower acquisition
time, which can be achieved by using high frequency equipments
such as a 500 MHz one. Sample concentration has to be adjusted
to an absorbance not much higher than 2 at the irradiation wave-
length to prevent the inner filter effect. Usually, this is a diluted
solution for NMR experiments and consequently a longer acquisi-
tion time is needed to obtain a better signal to noise ratio.
Fig. 5. 1H NMR spectra of trans-bpe in CD3CN upon photolysis at 313 nm.
(300 MHz, T = 298 K.)
Table 2
Trans–cis photoisomerization quantum yields of fac-[Re(CO)3(NN)(trans-L)]+ in CD3CN.
NN
L
313 nm
365 nm
404 nm
a
a
Uapp
Utrue
Uapp
Utrue
Uapp
Utrue
phen
bpe
stpy
bpe
stpy
0.41 0.02
0.35 0.02
0.21 0.02
0.30 0.02
0.81 0.07
0.59 0.05b
0.43 0.03
0.60 0.05
0.39 0.02
0.31 0.02
0.17 0.01
0.32 0.05
0.80 0.07
0.60 0.06
0.44 0.02
0.64 0.09
0.38 0.04
0.29 0.03
0.19 0.01
0.20 0.02
0.77 0.09b
0.43 0.02
0.43 0.02
0.42 0.03
ph2phen
a
[19].
b
Obtained by using molar absorptivities for cis-complexes.

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K.P.M. Frin et al. / Inorganica Chimica Acta 363 (2010) 294–300
Table 3
Desenvolvimento Científico e Tecnológico (CNPq) for the financial
support.
Trans–cis isomerization quantum yields for uncoordinated trans-bpe and trans-stpy in
CD3CN solution. (kirr = 313 nm).
Compound
U
(UV–Vis)
U
(1H NMR)
trans-bpe
0.27 0.04
0.25a
0.26 0.04
References
trans-stpy
0.49 0.03
0.49 0.04
[1] A.R. Olson, Trans. Faraday Soc. 27 (1931) 69.
0.46b
[2] D.G. Whitten, M.T. McCall, J. Am. Chem. Soc. 91 (1969) 5097.
[3] D.G. Whitten, Y.J. Lee, J. Am. Chem. Soc. 92 (1970) 415.
[4] Y.J. Lee, D.G. Whitten, L. Pedersen, J. Am. Chem. Soc. 93 (1971) 6330.
[5] G. Bartocci, P. Bortolus, U. Mazzucato, J. Phys. Chem. 77 (1973) 605.
[6] M.S. Wrighton, D.L. Morse, L. Pdungsap, J. Am. Chem. Soc. 97 (1975) 2073.
[7] J. Saltiel, A.S. Waller, D.F. Sears Jr., J. Photochem. Photobiol., A 65 (1992) 29.
[8] H. Görner, H.J. Kuhn, Adv. Photochem. 19 (1995).
[9] D.M. Dattelbaum, M.K. Itokazu, N.Y. Murakami Iha, T.J. Meyer, Phys. Chem. A
107 (2003) 4092.
a
70% Acetonitrile/30% water [3,4,19].
Acetonitrile irr = 320 nm [8,19].
b
4. Conclusion
[10] A.O.T. Patrocínio, N.Y. Murakami, Inorg. Chem. 47 (2008) 10851.
[11] M. Wrighton, D.L. Morse, J. Am. Chem. Soc. 96 (1974) 998.
[12] V.W.W. Yam, V.C.Y. Lau, K.K. Cheung, J. Chem. Soc., Chem. Commun. (1995)
259–261.
[13] V.W.W. Yam, V.C.Y. Lau, L.X. Wu, J. Chem. Soc., Dalton Trans. (1998) 1461–
1468.
[14] S.S. Sun, A.J. Lees, J. Am. Chem. Soc. 122 (2000) 8956.
[15] V.W.W. Yam, Y. Yang, J. Zhang, B.W.K. Chu, N. Zhu, Organometallics 20 (2001)
4911.
[16] R. Argazzi, E. Bertolasi, C. Chiorboli, C.A. Bignozzi, M.K. Itokazu, N.Y. Murakami,
Inorg. Chem. 40 (2001) 6885.
[17] M.K. Itokazu, A.S. Polo, D.L.A. De Faria, C.A. Bignozzi, N.Y. Murakamiha, Inorg.
Chim. Acta 313 (2001) 149.
[18] A.S. Polo, M.K. Itokazu, N.Y. Murakami, J. Photochem. Photobiol., A: Chem. 181
(2006) 73.
[19] A.S. Polo, M.K. Itokazu, K.M. Frin, Coord. Chem. Rev. 250 (2006) 1669.
[20] K.M. Frin, N.Y. Murakami, J. Braz. Chem. Soc. 17 (2006) 1664.
[21] M. Busby, P. Matousek, M. Towrie, A. Vlcek Jr., J. Phys. Chem. A 109 (2005)
3000.
[22] O.S. Wenger, L.M. Henling, M.W. Day, J.R. Winkler, H.B. Gray, Polyhedron 23
(2004) 2955.
Absorption spectral change is an accessible and readily avail-
able technique widely employed to determine quantum yields.
When both the photoproduct and the reactant absorb in the same
spectral region, e.g. the photoisomerization of trans-L in fac-[Re-
(CO)3(NN)(trans-L)]+ complexes, the use of this technique itself
does not provide true quantum yields. In these cases, the 1H
NMR spectroscopy has been successfully employed and proved to
be an important tool to determine accurate quantum yields since
the proton signals for photoproduct and reactant appear in differ-
ent regions. As a consequence, quantum yields so determined are
the true ones while those determined by variations in absorption
spectra are apparent. Besides the true quantum yield determina-
tion, the 1H NMR technique, when combined with the absorption
spectroscopy, allows the determination of photoproducts molar
absorptivities. Then, the determination of true quantum yields
can be provided by the use of the faster and low-cost absorption
spectrum experiment.
[23] C.A. Parker, C.G. Hatchard, J. Phys. Chem. 63 (1959) 22.
[24] N. Murakami Iha, G. Ferraudi, J. Chem. Soc., Dalton Trans. (1994) 2565–2571.
[25] M.K. Itokazu, A.S. Polo, N.Y. Murakami, J. Photochem. Photobiol., A: Chem. 160
(2003) 27.
[26] H.J. Kuhn, S.E. Braslavsky, R. Schmidt, Pure Appl. Chem. 76 (2004) 2105.
[27] O.S. Wenger, L.M. Henling, M.W. Day, J.R. Winkler, H.B. Gray, Inorg. Chem. 43
(2004) 2043.
Acknowledgements
The authors are grateful to the Fundação de Amparo à Pesquisa
do Estado de São Paulo (FAPESP) and the Conselho Nacional de