A new benzimidazolium receptor for fluorescence sensing of iodide

Article abstract of DOI:10.1080/10610270903469773

A new anthracene-appended benzimidazolium-based receptor 1 has been designed and synthesised. The receptor shows selective recognition of iodide in the excited state by exhibiting quenching of emission of anthracene. In the ground state, receptor 1 shows

Full text of DOI:10.1080/10610270903469773

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Supramolecular Chemistry
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A new benzimidazolium receptor for fluorescence
sensing of iodide
Kumaresh Ghosh a & Indrajit Saha a
a Department of Chemistry , University of Kalyani , Kalyani, Nadia, 741235, West Bengal,
India
Published online: 26 Feb 2010.
To cite this article: Kumaresh Ghosh & Indrajit Saha (2010) A new benzimidazolium receptor for fluorescence sensing of
iodide, Supramolecular Chemistry, 22:5, 311-317, DOI: 10.1080/10610270903469773
To link to this article: http://dx.doi.org/10.1080/10610270903469773
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Supramolecular Chemistry
Vol. 22, No. 5, May 2010, 311–317
A new benzimidazolium receptor for fluorescence sensing of iodide
Kumaresh Ghosh* and Indrajit Saha
Department of Chemistry, University of Kalyani, Kalyani, Nadia 741235, West Bengal, India
(Received 20 September 2009; final version received 5 November 2009)
A new anthracene-appended benzimidazolium-based receptor 1 has been designed and synthesised. The receptor shows
selective recognition of iodide in the excited state by exhibiting quenching of emission of anthracene. In the ground state,
receptor 1 shows different selectivity and prefers to bind bromide with higher binding constant value as established from
NMR titration experiment. Other anions in the study indicated weak or no interaction. Hydrogen bonding and
charge–charge interactions are the forces responsible for strong binding. The interaction properties of the new receptor were
1
evaluated by H NMR, UV–vis and fluorescence spectroscopic methods.
Keywords: benzimidazole-based receptor; fluorometric detection; iodide recognition; photoinduced electron transfer
sensor
Design and synthesis of artificial receptors for selective
recognition and sensing of anion is an interesting topic
O
in supramolecular chemistry. Anions are important as
guest molecules because of their major function in
the environment, industry and importantly, in biology
(1, 2). Over the past few years, significant research on
anion recognition has taken place (3–5). In relation to
this, fluorescent receptors are attractive due to the
simplicity and high detection limit of fluorescence. In
devising this class of receptor, different binding motifs
are attached to the fluorophore either directly or through
a covalent spacer. For effective complexation, different
binding sites such as amide (6), urea/thiourea (7, 8),
guanidinium (9), imidazolium (10), pyrrole (11),
pyridinium (12), etc. are well known. The use of polar
CZH bonds in complexing anions is also well
established (13). Combination of these binding sites
and their synergistic interplay are very crucial in the
design of an effective receptor. In this paper, we wish
to report a new receptor 1, which is built on the
benzimidazolium motif. The hydrogen bonds as
contributed by the polar CZH bond of the benzimida-
zolium motif in combination with amide hydrogens in 1
differentiate the anions with selectivity. In the present
case, receptor 1 fluorometrically recognises iodide
by showing significant quenching of emission of
anthracene.
H
e
O
H
N
H
PF6–
a
N+
H
HN
d
c
H
b
N
Binding cleft
Spacer
Fluorescent probe
1
Iodide is an important halide that plays an important
role in several biological processes such as neurological
activity and thyroid function. The iodide content of urine
and milk is often required to provide information for
nutritional, metabolic and epidemiological studies of
thyroid disorder (14).
In this aspect, there are very few reports on the
fluorescent recognition of iodide (15–17). Recently, we
have reported the fluorescent recognition of iodide by a
charge neutral adenine-based molecular receptor (18).
In continuation, we present here the design, synthesis and
*Corresponding author. Email: ghosh_k2003@yahoo.co.in
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2010 Taylor & Francis
DOI: 10.1080/10610270903469773
http://www.informaworld.com

312
K. Ghosh and I. Saha
N
N
N
(i)
a)
N
H
2
O
O
(i)
Cl
O
(ii)
(iii)
N
H
O
NH2
O
b)
NO2
NH
NH
NO2
NH
Cl
3
4
5
6
O
O
(iv)
N
H
(v)
1
NH
Cl–
N+
H
7
N
Scheme 1. Reagents and conditions: (a) (i) NaH, dry THF, 9-chloromethylanthracene, 10 h (yield: 64%); (b) (i) n-propylamine,
Et3N, dry CH2Cl2, 1 h (yield: 77%); (ii) H2/Pd–C, EtOH, 4 h (yield: 87%); (iii) chloroacetyl chloride, Et3N, dry CH2Cl2, 2 h (yield: 75%);
(iv) 2, dry CH3CN, reflux, 36 h (yield: 79%); (v) MeOH–H2O, NH4PF6 (yield: 92%).
hydrogen bonding interactions of 1 towards I2 against some
anions such as AcO2, H2PO42, HSO42, F2, Cl2 and Br2.
Receptor 1 was synthesised according to Scheme 1.
Initially, diamide 6 was synthesised from m-nitrobenzoyl
chloride 3 after performing a series of reactions as
mentioned in Scheme 1. Diamide 6, on refluxing in
CH3CN with compound 2, which was obtained according to
Scheme 1(a) by the reaction of benzimidazole with 9-
chloromethylanthracene in the presence of NaH in dry THF,
afforded the chloride salt 7. Subsequent anion exchange of
the chloride salt 7 using NH4PF6 gave the desired receptor 1
in appreciable yield (19). All the compounds were
thoroughly characterised by usual spectroscopic techniques.
The amide and benzimidazolium protons in 1 are
suitably oriented for complexation of anionic guests.
Figure 1 illustrates the AM1-optimised geometry of the
complex of 1 with I2 (20). In the complex, the
benzimidazolium (CZH)þ and amide protons fall in
the hydrogen bond distances with iodide.
salts of different anions, the emission at 423 nm was
perturbed to different extents. Figure 2 represents
the change in fluorescence of 1 upon addition of 2
equivalent amounts of a particular anion. Upon addition
The complexation ability of receptor 1 to the different
1
anions in the solution phase was measured by H NMR,
fluorescence and UV–vis titration experiments. Receptor 1
displayed strong fluorescence-structured emission, centred
at 423 nm in CHCl3 containing 0.2% CH3CN solution when
excited at 370 nm. In the presence of tetrabutylammonium
Figure 1. AM1-optimised geometry of the complex of receptor
1 with iodide.

Supramolecular Chemistry
313
0.4
0.3
0.2
0.1
0.0
(g)
(b)
(e)
(a)
700
600
500
400
300
200
100
0
(a) Receptor 1
(b) Acetate
(c) Dihydrogen phosphate
(d) Hydrogen sulphate
(e) Fluoride
(f) Bromide
(g) Chloride
(h) Iodide
700
600
500
400
300
200
100
0
(d)
(f)
(c)
320
340
360
380
400
420
Wavelength (nm)
(h)
390
420
450
480
510
540
400
440
480
520
Wavelength (nm)
Wavelength (nm)
Figure 4. Change in emission of 1 (c ¼ 4.11 £ 1025 M) in the
presence of increasing amounts of H2PO24 in CHCl3 containing
0.2% CH3CN; inset: change in absorption spectra upon
increasing concentrations of H2PO24 .
Figure 2. Change in fluorescence emission of
1
(c ¼ 4.11 £ 1025 M) in the presence of 2 equivalents of the
tetrabutylammonium salt of different guests in CHCl3 containing
0.2% CH3CN.
of 2 equivalent amounts of tetrabutylammonium salts of I2,
Br2, H2PO42 and HSO24 , the emission of 1 was quenched by
82, 34, 60 and 24%, respectively. The addition of I2 caused
a significant quenching in fluorescence intensity, whereas
much smaller change in emission was observed for other
anions except H2PO24 and Br2. Figure 3 illustrates the
change in emission of 1 upon gradual addition of
tetrabutylammonium iodide. On the contrary, emission of
1 at 423 nm in Figure 4 decreased up to the addition of 2
equivalent amounts of H2PO24 . Further addition caused an
increase in emission with a minor blue shift. Such
characteristic change in emission of 1 in the presence of
excess H2PO24 is presumably attributed to
the deprotonation of the bound dihydrogen phosphate
with the resultant formation of the monohydrogen
phosphate receptor complex, as described by Gale et al.
(21). In the process, partial decomplexation of H2PO42
cannot be neglected. In the presence of tetrabutylammo-
nium salts of AcO2, F2 and Cl2, the emission of 1 was
negligibly changed as evidenced from titration curves in
Figure 5. Thus, the large quenching of emission in the
presence of I2 is the characteristic feature of 1 for the
fluorometric identification of I2 among the other anions in
the present study. This quenching of emission is attributed
to the (i) complementarity in size of iodide with the
pseudocavity formed by the receptor-binding site and
(ii) heavy atom effect of iodide, which is true for Br2 also.
The Stern–Volmer plot in Figure 6 illustrates the
0.4
(a)
700
500
0.3
(a) Iodide
(b) Bromide
(c) Hydrogensulphate
(d) Dihydrogen phosphate
(e) Chloride
(f) Acetate
(g) Fluoride
(b)
600
400
0.2
500
0.1
400
300
0.0
300
320
340
360
380
400
420
Wavelength (nm)
200
(c)
200
100
0
(d)
100
(e)
(f)
0
400
440
480
520
(g)
Wavelength (nm)
0
2
4
6
8
10
Figure 3. Change in emission of 1 (c ¼ 4.11 £ 1025 M) in the
presence of increasing amounts of I2 in CHCl3 containing 0.2%
CH3CN; inset: change in absorption spectra upon increasing
concentrations of I2.
[G]/[H]
Figure 5. Plot of the change in emission of 1 at 423 nm vs. the
ratio of guest-to-host concentration.

314
K. Ghosh and I. Saha
In order to establish the nature of interaction of 1 with the
anions in the ground state, we performed UV–vis and NMR
titration experiments. Receptor 1 showed minor change in
absorbanceuponaddingalltheguests, andtherebysuggested
weak interaction. In most of the cases, the change in
absorption was irregular (see Supporting Information).
The minor change in absorbance of 1 with I2 (inset of
Figure 3) indicated poor interaction. Such minor change in
absorption spectra of 1 reveals that it is perfectly a PET
system, the different components of which are highlighted in
structure 1 (23). In the presence of H2PO24 , the absorption of
1 at 373 nm decreased up to the addition of 2 equivalent
amounts of guest. Further addition caused an initial increase
and then decreased in absorption accompanying a blue shift
of ,2 nm (inset of Figure 4). Again, this may be due to the
complexation of H2PO24 (up to the addition of 2 equivalent
amounts) in the cleft followed by a conformational change
(after the addition of 2 equivalent amounts).
10
8
Iodide
6
4
Bromide
2
0
1.0×10–4 2.0×10–4 3.0×10–4 4.0×10–4 5.0×10–4 6.0×10–4
[G] in M
0.0
Figure 6. Stern–Volmer plots for 1 with Br2 and I2 at 423 nm.
The binding of anions was also realised from 1H NMR
titrations of 1 in CDCl3 containing 6% CD3CN (due to
solubility problem of 1). During titration, amide proton
(Ha), benzimidazolium proton (Hb) and the peri proton
(Hc) moved to the downfield directions upon complexa-
tion. The amide proton (Hd) of 1 underwent less
downfield shift (Dd ¼ 0.20–0.28 in 1:1 complexes)
during complexation, indicating its poor involvement
in the binding process. The peri proton Hc of 1 showed
a change in chemical shift of 0.03–0.46 ppm in its 1:1
complexes with the anions. Figure 8 shows the changes in
chemical shift of Ha and Hb of 1 on progression of
titrations with the anions. Importantly, during NMR
titrations of 1 (c ¼ 3.19 £ 1023 M) with the tetrabutyl-
ammonium salts of H2PO24 and HSO42, precipitation
appeared, and therefore it was difficult to continue the
titration experiments. Even the titration of 1 with F2 was
difficult to complete due to disappearance of the
interacting protons after the addition of 1 equivalent
amount of tetrabutylammonium fluoride to the receptor
solution. The sharp break of the titration curves at
[G]/[H] ¼ 1 in Figure 8 further illustrates the 1:1
stoichiometry of the complexes of 1 with Cl2, Br2, I2
and AcO2 in the ground state. This perfectly matches
with the results of fluorescence titration.
quenching phenomena. The nonlinear nature of the curves
(Figure 6) indicates that both static (hydrogen bonding
effect) and dynamic quenching (bimolecular collision) take
place during the binding of Br2 and I2. Assignment of
HOMO and LUMOs in the complex of 1 with iodide
additionally demonstrates the photoinduced electron
transfer (PET)-mediated quenching of emission of
anthracene in 1 (Supporting Information).
In the binding, the stoichiometry of the complex of 1
with I2 was determined by fluorescence Job’s plot (22),
which was found to be 1:1 (Figure 7). This was also true
for Cl2 and Br2 ions. In contrast, receptor 1 formed 2:1
(guest:host) complexes with H2PO24 and HSO42 ions
(Supporting Information). Furthermore, the break of the
titration curves in Figure 5 corroborated the stoichiometry
of the complexes. All the curves, except for H2PO24 and
HSO24 in Figure 5, show the break at [G]/[H] ¼ 1 and
confirm the 1:1 stoichiometry of the complexes.
1.5×10–5
1.2×10–5
9.0×10–6
6.0×10–6
3.0×10–6
0.0
However, to learn about the binding potencies of 1 in
the ground and excited states, we measured the binding
constant values (Table 1) by NMR (24) and fluorescence
methods (25). From the values in Table 1, it is clear that
receptor 1 shows different selectivities in the ground and
excited states. While, in the ground state, receptor 1
prefers to bind Br2, in the excited state, it shows a higher
affinity for I2. Usually, halides tend to bind in the order of
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
XH
F
2 . Cl2 . Br2 . I2 on the basis of their basicity (26).
However, the binding constants obtained from NMR
titration data analysis show that Br2 is bound more
strongly in the ground state, with binding constant being
Figure 7. Job’s plot between complex 1 and iodide. The
concentration of [HG] was calculated by the equation
[HG] ¼ DI/I0 £ [H].

Supramolecular Chemistry
315
Acetate
Chloride
(a) 4.0
3.5
(b)
1.4
1.2
1.0
0.8
3.0
Acetate
2.5
Bromide
Bromide
2.0
Chloride
0.6
0.4
0.2
0.0
1.5
Iodide
Iodide
1.0
0.5
0.0
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
[G]/[H]
[G]/[H]
Figure 8. Titration curves for 1 from NMR considering the change in chemical shifts of (a) NHa and (b) CþZHb.
,10 times larger than that with Cl2 and I2. It is thought
that bromide selectivity of 1 arises from the size difference
[ionic radii (27) of F2, Cl2, Br2 and I2 are 1.19, 1.67, 1.82
determined in CHCl3 containing 0.2% CH3CN, although
the selectivity trend is found to be unaltered. The binding
constant values obtained by the NMR method in Table 1
are less in magnitude compared to the values determined
by the fluorescence method. The higher value of binding
constant in the excited state is also presumed to be due to
more polar character of the excited state of 1 compared to
2
˚
and 2.06 A, respectively]. Binding constant values for Br
and I2 as calculated from the emission intensity data of
anthracene at 423 nm follow a reverse order to that of the
NMR titration results. This is due to the nature of
interactions of those halides in the excited state. We
believe that in the excited state, the flexible receptor 1,
which can assume different conformations in solution,
provides hydrogen bonding cavity that sterically fits I2
rather than Br2 for which a marginal increase in binding
constant value for I2 is observed.
1
its ground state. Thus, the H NMR study underlines the
fact that the binding site of 1 has an affinity for halides and
particularly, for Br2 in the ground state and I2 in the
excited state, involving hydrogen bonding interaction
according to the mode in Figure 1.
Receptor 1 was further tested to realise its sensitivity for
I2 in the presence of F2 and Cl2 ions. Figure 9 demonstrates
the iodide-induced change in emission of 1 containing 1
equivalent as well as 5 equivalent amounts of F2 and Cl2
ions. It is evident from Figure 9 that a decrease in emission of
1 upon titration with iodide is dramatically less in the
It is quite reasonable that the polar solvent CH3CN
reduces the strength of interaction between the host and
the guest. This is reflected in the results given in Table 1.
The binding constant values as determined by the
fluorescence method in CHCl3 containing 6% CH3CN
are found to be less in magnitude compared to the values
Table 1. Binding constants of 1 with the guests by NMR and fluorescence methods.
Guestsa
Ka (M21)b from fluorescence
Ka (M21)c from fluorescence
Ka (M21)d from NMR
2.15 £ 103
e
e
Acetate
–
–
g
Dihydrogen phosphate
Hydrogen sulphate
Fluoride
Chloride
Bromide
Iodide
7.25 £ 103f
5.75 £ 103f
–
2.62 £ 103f
–
–
–
–
–
e
g
e
e
h
–
–
e
e
7.22 £ 103
1.59 £ 104
3.09 £ 103
2.81 £ 105
4.39 £ 104
4.80 £ 105
1.02 £ 105
a Tetrabutylammonium salts were taken.
b In CHCl3 containing 0.2% CH3CN.
c In CHCl3 containing 6% CH3CN.
d In CDCl3 containing 6% CD3CN.
e Due to minor change, binding constant values were not determined.
f Considering K11 (see Supporting Information).
g Not determined due to precipitation.
h Not determined due to broadening of amide signals and also deprotonation.

316
K. Ghosh and I. Saha
(2) Martinez-Manez, R.; Sancenon, F. Chem. Rev. 2003, 13,
4419–4476.
In the presence of 5 equiv. F–
In the presence of 5 equiv. Cl–
750
600
450
300
150
0
´
(3) Gale, P.A.; Garcıa-Garrido, S.E.; Garric, J. Chem. Soc. Rev.
2008, 37, 151–190.
(4) Sessler, J.L.; Barkey, N.M.; Pantos, G.D.; Lynch, V.M. New
J. Chem. 2007, 31, 646–654.
(5) Caltagirone, C.; Gale, P.A. Chem. Soc. Rev. 2009, 38, 520–
563.
(6) Caltagirone, C.; Gale, P.A.; Hiscock, J.R.; Hursthouse,
M.B.; Light, M.E.; Tizzard, G.J. Supramol. Chem. 2009, 21,
125–130 and references cited therein.
(7) Blondean, P.; Benet-Buchholz, J.; de Mendoza, J. New
J. Chem. 2007, 31, 736–740 and references cited therein.
(8) Ghosh, K.; Adhikari, S. Tetrahedron Lett. 2006, 47,
8165–8169 and references cited therein.
(9) Schmuck, C.; Machon, U. Eur. J. Org. Chem. 2006,
4385–4392.
(10) Kim, S.K.; Moon, B.-S.; Park, J.H.; Seo, Y.; Koh, H.S.;
Yoon, Y.J.; Lee, K.D.; Yoon, J. Tetrahedron Lett. 2005, 46,
6617–6620.
In the presence of 1 equiv. Cl–
In the presence of 1 equiv. F–
With iodide
0.0
1.0×10–4
2.0×10–4
[I–] in M
3.0×10–4
Figure 9. Change in emission of 1 (c ¼ 4.07 £ 1025 M) upon
titration with I2 in the presence of F2 and Cl2 in CHCl3
containing 0.2% CH3CN.
(11) Schmuck, C.; Hernandez-Folgado, L. Org. Biomol. Chem.
2007, 5, 2390–2394.
(12) Ghosh, K.; Sarkar, A.R. Tetrahedron Lett. 2009, 50, 85–88.
(13) Lee, H.N.; Singh, J.; Kim, S.K.; Kwon, J.Y.; Kim, Y.Y.;
Kim, K.S.; Yoon, J. Tetrahedron Lett. 2007, 48, 169–172;
Wong, W.M.H.; Vickers, M.S.; Cowley, A.R.; Paul, R.L.;
Beer, P.D. Org. Biomol. Chem. 2005, 3, 4201–4208;
Wallace, K.J.; Belcher, W.J.; Turner, D.R.; Syed, K.F.;
Steed, J.W. J. Am. Chem. Soc. 2003, 125, 9699–9715;
Sato, K.; Arai, S.; Yamagishi, T. Tetrahedron Lett. 1999, 40,
5219–5222; Steed, J.W. Chem. Soc. Rev. 2009, 38,
506–519; Ilioudis, C.A.; Steed, J.W. Org. Biomol. Chem.
2005, 3, 2935–2945; Maeda, H.; Kusunose, Y. Chem. Eur.
J. 2005, 11, 5661–5666; Bai, Y.; Zhang, B.-G.; Xu, J.;
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J. Chem. 2005, 29, 777–779; Dickson, S.J.; Wallace,
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32, 786–789.
presence of F2 and Cl2 ions, and thereby indicates their
significant interference in the binding process.
In conclusion, we have designed and synthesised an
easy-to-make fluorescent benzimidazolium-based receptor
1, which shows selective recognition of I2 in the excited
state by exhibiting quenching of emission of anthracene.
The large quenching of emission in the presence of I2 is
the characteristic feature of 1 for the fluorometric
identification of I2 among the other anions in the present
study, although receptor 1 binds Br2 more strongly in the
ground state. It is also of note that F2 and Cl2 ions
interfere in the sensing of I2. To our belief, steric fit,
hydrogen bonding (both conventional and unconventional
in nature) and charge–charge interactions are the possible
factors responsible for selectivity in binding of Br2 and I2
at two different states. Further work along this direction is
underway in the laboratory.
(14) Haldimann, M.; Zimmerli, B.; Als, C.; Gerber, H. Clin.
Chem. 1998, 44, 817–824 and references therein.
(15) Kim, H.; Kang, J. Tetrahedron Lett. 2005, 46, 5443–5445.
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references cited therein.
(17) Singh, N.; Jung, H.J.; Jang, D.O. Tetrahedron Lett. 2009,
50, 71–74.
Acknowledgements
(18) Ghosh, K.; Sen, T. Tetrahedron Lett. 2008, 49, 7204–7208.
(19) Receptor 1: Mp 1208C; 1H NMR (400 MHz, CDCl3
containing 2% DMSO-d6): d 9.84 (s, 1H, ZNHZ), 8.77 (s,
1H), 8.64 (s, 1H), 8.12–8.06 (m, 4H), 7.76–7.70 (m, 3H),
7.61–7.44 (m, 8H), 7.23 (t, 1H, J¼8 Hz), 6.49 (br t, 1H,
ZNHZ), 6.48 (s, 2H), 5.20 (s, 2H), 3.25 (q, 2H, J¼8 Hz),
1.53–1.50 (m, 2H), 0.87 (t, 3H, J¼8 Hz); 13C NMR
(100 MHz, DMSO-d6): d 166.4, 164.0, 142.7, 138.6, 136.0,
132.6, 131.6, 131.4, 131.0, 129.9, 129.3, 128.4, 127.6,
127.2, 126.1, 123.7, 122.6, 122.0, 118.9, 114.6, 114.3,
49.5, 43.8, 41.4, 22.7, 11.8 (two carbons in aromatic region
are not resolved); FTIR (KBr): 3390, 2965, 2934, 17þ03,
We thank CSIR, Government of India for the financial support.
I.S. thanks CSIR for a fellowship. K.G. thanks DST, Government
of India for providing facilities in the department under FIST
programme.
Supporting Information
Figures showing the change in absorption and fluorescence
spectra of 1 in the presence of anions, fluorescence Job’s plot of
receptor 1 in the presence of HSO24 and H2PO42, binding constant
curves, assignments of HOMO and LUMOs of the complex of 1
with iodide are available online.
1644, 1591, 1561 cm21
;
Mass (LCMS, ES ):
C34H31N4O2.PF6 requires 527.2 for (M 2 PF6), found
527.2.
(20) AM1 calculation was done using CS Chem 3D version 7.0.
(21) Gale, P.A.; Hiscock, J.R.; Moore, S.J.; Caltagirone, C.;
Hursthouse, M.B.; Light, M.E. Chem. Asian J. 2009, DOI:
10.1002/asia.200900230.
References
(1) Spichiger-Keller, U.S., Ed.; Chemical Sensors and
Biosensors for Medical and Biological Applications;
Wiley: Weinheim, Germany, 1998.

Supramolecular Chemistry
317
(22) Job, P. Ann. Chim. 1928, 9, 113–203.
Valeur, B. J. Phys. Chem. 1993, 97, 4552–4555. (c) For the
determination of binding constant values for H2PO24 and
HSO24 ions: Chou, P.T.; Wu, G.R.; Wei, C.Y.; Cheng, C.C.;
Chang, C.P.; Hung, F.T. J. Phys. Chem. B 2000, 104,
7818–7829.
(23) Bissel, R.A.; de Silva, A.P.; Gunaratne, H.Q.N.; Lynch,
P.L.M.; Maguire, G.E.M.; Sandanayake, K.R.A.S. Chem.
Soc. Rev. 1992, 187–195.
(24) Fielding, L. Tetrahedron 2000, 56, 6151–6170 (dObs¼(dC2
dH)({(1 þ [G]/[H] þ 1/Ka[H])/2}
(26) Amendola, V.; Esteban-Gomez, D.; Fabbrizzi, L.; Licchelli,
M. Acc. Chem. Res. 2006, 39, 343–353 and references cited
therein.
{(1 þ [G]/[H] þ 1/Ka[H])2/4 2 [G]/[H]}1/2) þ dH.
(25) For determination of binding constant values for Br2 and I2
working formula used I¼I0 þ (Ilim 2 I0)/2CH{CH þ CG
þ
(27) (a) Cotton, F.A.; Wilkinson, G.; Murillo, C.A.; Bochman,
M. Advanced Inorganic Chemistry, 6th ed.; John Wiley and
Sons: New York, 1999. (b) Turner, D.R.; Paterson, M.J.;
Steed, J.W. J. Org. Chem. 2006, 71, 1598–1608.
1/Ka 2 [(CH þ CG þ 1/Ka)2 2 4CHCG]1/2}. (a) Valeur, B.;
Pouget, J.; Bourson, J.; Kaschke, M.; Eensting, N.P. J. Phys.
Chem. 1992, 96, 6545–6549. (b) Bourson, J.; Pouget, J.;