Cooperative effect of spacer and Lewis base on highly reversible spectral changes of the octaethylporphyrin chromatic system in sensitivity, stability, and visibility to trifluoroacetic acid

Article abstract of DOI:10.1246/bcsj.20160176

The diacetylene-group connected chromatic system of [octaethylporphyrin]-[spacer]-[Lewis base] triads (OEP-SPC-LB) was conclusively studied, in which a trigger-like interaction of the terminal LB with trifluoroacetic acid (TFA) dramatically affects the inherent electronic properties of OEP. The ¹HNMR, IR, and electronic absorption spectral properties of these OEP derivatives were examined, and were contemplated in view of a cooperative effect of SPC and LB on their OEP nucleus. Based on the results from this study, the structural elements for molecular design will be proposed in order to improve their reversible spectral changes between neutral and acidic media in terms of sensitivity, stability, and visibility to TFA.

Full text of DOI:10.1246/bcsj.20160176

Advance Publication Cover Page
Cooperative Effect of Spacer and Lewis Base on Highly Reversible Spectral
Changes of the Octaethylporphyrin Chromatic System in Sensitivity,
Stability, and Visibility to Trifluoroacetic Acid
Hideto Kempe, Junya Yamamoto, Miki Ishida, Nobutomo Takahashi, Junro Yoshino, Naoto Hayashi,
and Hiroyuki Higuchi*
Advance Publication on the web July 15, 2016 by J-STAGE
doi:10.1246/bcsj.20160176
© 2016 The Chemical Society of Japan

Cooperative Effect of Spacer and Lewis Base on
Highly Reversible Spectral Changes of The Octaethylporphyrin Chromatic System
in Sensitivity, Stability, and Visibility to Trifluoroacetic Acid
Hideto KEMPE,1 Junya YAMAMOTO,2 Miki ISHIDA,2 Nobutomo TAKAHASHI,2 Junro YOSHINO,2
Naoto HAYASHI,2 and Hiroyuki HIGUCHI1,2*
1Graduate School of Innovative Life Science, University of Toyama,
2Graduate School of Science and Engineering, University of Toyama,
3190 Gofuku, Toyama, Toyama 930-8555, Japan
*E-mail address: higuchi@sci.u-toyama.ac.jp (H. Higuchi)
Abstract
The diacetylene-group connected chromatic system of
three OEP, DHBTh, and LB components are connected with
the diacetylene linkage, the skeletal features such as
conformation and geometry are almost the same in each
DHBTh set of derivatives, regardless of LB, due to no steric
hindrance between them (wide infra). Therefore, the
OEP-DHBTh-LB system would be placed in a well-defined
structural system, suitable for analysis and evaluation of the
effect from each component DHBTh or LB on the
spectrum-property relationships of these OEP derivatives
between neutral and acidic conditions.
[octaethylporphyrin]-[spacer]-[Lewis base] triads (OEP-SPC-
LB) was conclusively studied, in which a trigger-like inter-
action of the terminal LB with trifluoroacetic acid (TFA)
dramatically affects the inherent electronic properties of OEP.
1
The H NMR, IR, and electronic absorption spectral properties
of these OEP derivatives were examined, and were
contemplated in view of a cooperative effect of SPC and LB on
their OEP nucleus. Based on the results from this study, the
structural elements for molecular design will be proposed in
order to improve their reversible spectral changes between
neutral and acidic media in terms of sensitivity, stability, and
visibility to TFA.
R
R
R
S
S
S
SPC
S
S
S
R
R
R
R=C6H13
HH-DHBTh
HT-DHBTh
TT-DHBTh
Phen
Anth
NMe2
NMe2
NMe2
LB
N
1. Introduction
NMe2
Py
DMAB (4-yl)
DMAB (3-yl)
BisDMAB
Porphyrin nucleus is a natural pigment of particularly great
interests in not only photo-sensitized reactions1 but also in
redox respiratory system,2 duly to possess its high sensitivity to
the trigger-like stimuli such as light and oxygen, swiftly to
transform itself to a meta-stable state in response to those
stimuli, and readily to recover its original state by release from
those outside stimuli. In those sequential reversible processes
between these transitory states, chemically oxidative-reductive
reactions are smoothly performed in the living bodies regularly
and repeatedly. Modeling on such a sustainable mechanism
taken in the natural world, in recent years, the artificially
functional porphyrin-based materials of various types sensitive
to pH,3 metal-ions,4 temperature,5 light,1, 6 and so forth, have
been vastly demonstrated, by connecting those electronic and
structural properties with particular spectral changes at each
state. In relation with such drastic development of organic
functional materials science, we have been also engaged in the
study of various unique octaethylporphyrin (OEP) derivatives,
aiming at the highly performable system especially sensing to
organic acids and/or to electrochemical operations.7
Chart 1. Abbreviation of SPC and LB in OEP-SPC-LB.
R
R
N
N
N
N
N
N
S
S
Ni
Ni
N
N
1
S
S
N
N
R
R
R=C6H13
HH-isomer
TT-isomer
R
R
N
N
N
N
N
N
S
S
Ni
Ni
NMe2
NMe2
2
S
S
R
N
N
R
R
R
NMe2
NMe2
R
N
N
N
N
N
N
S
S
Ni
Ni
3
4
S
S
R
N
N
R
NMe2
NMe2
NMe2
NMe2
R
N
N
N
N
N
N
S
S
Ni
Ni
S
S
R
N
N
R
Chart 2. An extended !-electronic conjugation system of OEP-DHBTh-LB (1-4).
So far, it has been revealed in this system that addition of
trifluoroacetic acid (TFA: pKa 0.23)10 into its sample solution
changes both 1H NMR and electronic absorption spectra via the
two-steps processes. The first step process corresponds to the
regular changes arising from a simple protonation of TFA on
the N atom of LB, and the second step process corresponds to
the drastic changes arising from a direct interaction of TFA
onto the OEP component (Chart 3, vide infra).11 Yet, it has
been experimentally demonstrated that quenching TFA with
ordinary bases like triethylamine (NEt3) recovers their original
spectra quite well. This is a common phenomenon of
OEP-DHBTh-LB in the reversible spectral changes, as well as
the solution-color changes, with DHBTh and LB reflecting on
the electronic structure of OEP.
Our original OEP chromatic system in the present study
carries Lewis base (LB) at one terminal position in the
!-electronic conjugation chain and dihexyl-2,2’-bithiophene
(DHBTh) as a spacer (SPC) in its middle position (Chart 1),
described as OEP-DHBTh-LB, in which all the three
components are combined with
a skeletally rigid but
!-electronically mobile linkage of 1,3-butadiyne (diacetylene)
(Chart 2).8 A whole molecular planarity in its !-electronic
conjugation system is readily adjusted by an orientation of the
two 3-hexylthiophene (3HTh) rings in DHBTh; head-to-head
(HH) or head-to-tail (HT) or tail-to-tail (TT).9 Yet, since the
1

-
CF3CO2
H+
-
2 CF3CO2
-
-
-
CF3CO2
CF3CO2
LBH+
CF3CO2
TFA
TFA
NEt3
TFA
NH
N
N
N
N
N
N
N
N
N
N
N
N
N
Ni
Ni2+
+
H
+
LBH+
H
+
Ni
Ni
SPC
LBH+
SPC
SPC
SPC
LB
N
HN
NEt3
OEP-SPC-LBH+
H+OEP-SPC-LBH+
H2+OEP-SPC-LBH+
OEP-SPC-LB
Chart 3. The protonation processes of OEP-SPC-LB with TFA at the first and second stages.
Based on the TFA-sensing examinations (vide infra), it has
been proved that the sensitivity to TFA of this system increases
in order of 2<<3<1 and its reversible stability increases in order
of 1<<2<3, suggesting that the derivative 3 is rather promising
in both sensitivity and stability.11 These results indicate that the
lone-pair electrons on the N atom of LB stereo-electronically
plays an important role in an extended !-electronic conjugation
chain of this system prior to the proton-acceptable ability
(basicity) of LB, since the conjugated acids of pyridine (Py)
and N,N-dimethylaminobenzene (DMAB) themselves are well
known to possess almost the same pKa value as each other
(5.14 for Py-H+ and 5.06 for DMAB-H+) (Chart 4).10
Accordingly, taking this consequence into consideration,
3,5-bis(N,N-dimethylamino)benzene (BisDMAB: pKa(1) 2.65
and pKa(2) 4.88)12 could be a promising LB for enhancing their
sensitivity and stability to TFA (Chart 1). As expected, among
1-4, the derivative 4 showed the highest function in both
sensitivity and stability (Chart 2).11
In addition to these two valuations (sensitivity and stability),
another essential one for the acid-sensing materials is to put the
visibility, i.e., to construct the molecular structure with the
greater spectral changes in magnitude between neutral and
acidic conditions.3-6 The higher visibility means the more
performable functions in accuracy, leading to the more
sophisticated material. And, our aim and goal in this research is
to achieve a methodology for producing the desired electronic
structures of OEP purposively, without changing their skeletal
features, by choosing an adequate pair of SPC and LB like a
building-brick from a wide variety of SPC and LB. Previously
it was shown from the electronic spectral study with 1-4 that
the TT-DHBTh SPC with the higher !-electronic conjugation
In our continuous investigations of OEP-SPC-LB toward
the higher functionality in respect of those three valuations
(sensitivity, stability, and visibility), the OEP-SPC-LB
derivatives 5-10 were newly synthesized. In this study, benzene
(abbreviated as Phen) and anthracene (Anth) are employed as
SPC, while Py, DMAB, and BisDMAB are employed as LB
(Charts 1 and 5). The structure-property relationships of 5-10
were conclusively studied, as compared with those of the
DHBTh derivatives 1-4. Basically, the behaviors of
OEP-SPC-LB between before and after the protonation
1
processes were examined by means of H NMR and electronic
absorption spectral measurements, and were comparatively
analyzed in terms of the inductive and conjugation effects on
their spectral changes. Successively, their relative sensitivity
and reversible stability to TFA were estimated, on the basis of
the minimum amount of TFA necessary for completion of the
spectral changes at each stage. Then, toward our final goal, the
structurally tractable elements in the present OEP chromatic
system will be proposed, in order to derive a guideline for
further enhancement of the proton-sensing functionality in
sensitivity, stability, and visibility.
N
N
N
N
N
N
N
N
Ni
Ni
NMe2
N
5
6
NMe2
NMe2
N
N
N
N
Ni
7
N
N
N
N
N
N
N
N
Ni
N
Ni
NMe2
plane brings the greater spectral changes into their Soret- and
Q-bands,13,
8
9
14
than the HH isomer.11 Moreover, from the
NMe2
NMe2
N
N
consequence performed with the diacetylene-group connected
dimeric OEP derivatives (OEP-SPC-OEP), it was suggested
that an introduction of SPC with the higher mobile !-electrons
is preferable to an extension of !-electronic conjugation into
the skeletal chain, for further enhancement of their visibility.15
Ni
N
N
10
Chart 5. Diacetylene-group connected OEP-SPC-LB derivatives 5-10.
2. Results and Discussion
2.1. Synthesis of The OEP-SPC-LB Derivatives 5-10.
H+
.
.
H+
.
.
.
.
.
.
.
.
.
.
N
N
The title OEP-SPC-LB derivatives 5-10 were synthesized,
as shown in Schemes 1 and 2.8,11 The counterparts of terminal
OEP-SPC acetylenes 15 and 19 were prepared by our
conventional way. Oxidative cross coupling reactions of the
OEP acetylene 1116 with the ethynyl compounds 1217 and 1618
were carried out under the modified Eglinton conditions in
ordinary yields,19 followed by ethynylation of the bromo
substituent of 13 and 17 with trimethylsilylacetylene
(TMS-acetylene) by Sonogashira coupling reaction and
alkaline hydrolysis.20 Then, the derivatives 5-10 were led, again
by Eglinton cross coupling reaction of 15 or 19 with the
respective LB acetylenes 20,21 21,21 and 2221. The reaction of
15 with an excessive amount (ca. 10 eq. to 15) of 20, 21, or 22
was carried out in a mixture of Py and methanol (MeOH) (5:1
in v/v) in the presence of copper(II) acetate [Cu(OAc)2]. In
general, the reaction mixtures were chromotographed on
Py
H+
.
.
H+
N
N
H+
DMAB (4-yl)
DMAB (3-yl)
.
.
H+
N
N
.
.
.
.
Chart 4. Delocalization mode of the lone pair electrons ( ) on the N
atom of LB (left). Distribution mode of the positive charge ( ) of the
N-protonated species LBH+ (right).
2

silica-gel (SiO2) column, to afford the desired products 5, 6,
and 7 in 25-45% yields, together with the corresponding
homo-coupling dimers 23,22 24,23 and 2511 in quantity.
Similarly, the reactions of 19 with 20-22 gave the
corresponding 8, 9, and 10 in similar yields to those of 5-7. All
the highly extended !-electronic conjugated OEP derivatives
5-10 are dark green to black purple microcrystallines and are
stable under the room light at an ambient temperature (see
Experimental part).
Similar to the above consequence from 1H NMR spectra, IR
spectral behavior would appear on the stretching vibrations due
to the C-C triple (C:::C) bond, reflecting the molecular
planarity of this system. All the diacetylene linkages in the
OEP-SPC-LB skeleton were practically observed, as a set of
medium and weak absorption peaks (Table 1). The TT isomers
of 1-4 showed the lower wave numbers, as compared with the
corresponding HH isomers, indicating that the diacetylene
linkage takes part in conjugation well with the higher planar
SPC, though by a little.8 However, the reformation efficiency of
the diacetylene linkage in this system is quite different between
the OEP-SPC-LB derivatives. The C:::C vibrations in a group
of the DHBTh derivatives weaken largely in the order of LB;
Py>DMAB>BisDMAB, while those in two groups of the Phen
and Anth derivatives largely in the order of LB;
DMAB>Py>BisDMAB, indicating an existence of some
suggestive interaction between SPC and LB. It is hopefully
expected that a combination between Anth and BisDMAB
possesses the electronically highest transmission ability to
OEP.
N
N
N
N
N
N
N
N
Ni
Ni
+
H
X
H
Br
12
11
13: X=Br
14:X=
TMS
H
15:X=
N
N
N
Ni
N
+
11
H
Br
X
16
17: X=Br
18:X=
TMS
H
19:X=
Table 1. The wave numbers (!/cm-1) due to the triple bond vibrations
of OEP-SPC-LB measured by IR spectra (KBr disc)
Scheme 1. Preparation of the terminal acetylenes 15 and 19 of OEP-SPC.
H
N
OEP-SPC-LB
medium band
2200
weak band
2130
20
21
1HH
5
6
1TT
2HH
2TT
3HH
2196
2189
2184
2183
2122
2131
2129
2130
+
H
15
NMe2
NMe2
NMe2
H
3TT
4HH
4TT
2178
2182
2178
2128
2132
2129
22
7
20
21
22
5
6
7
2188
2202
2175
2173
2180
2168
2163
2137
2137
2131
2127
2121
8
9
+
19
8
10
9
Me2
N
N
NMe2
NMe2
10
Me2
N
NMe2
N
N
Me2
23
24
25
In contrast with a fairly high similarity in the molecular
skeletal features, the electronic absorption spectral behaviors in
a region of 400-600 nm, characteristic of OEP nucleus,13b, 14 are
affected dramatically by the nature of SPC (Fig. 1). A set of
4HH and 4TT is a typical example, where the greater extension of
!-electronic conjugation over the molecule is performed in 4TT
due to the higher planarity of TT-DHBTh effective for
!-electronic conjugation.11 On the other hand, the Phen
derivative 7 showed almost the same spectrum as 4HH in both
absorption maxima and intensity, clearly indicating that the
transmissible ability of SPC from LB to OEP in this system is
almost identical between Phen and HH-DHBTh (vide infra).
As compared with the spectral behaviors of the DHBTh and
Phen derivatives, the Anth derivative 10 exhibited much drastic
changes in both Soret and Q bands. The much further
reformation of electronic structure of OEP was achieved,
affording the completely separated Soret band with two clear
maxima and the much sharper Q band at the longer wavelength
region. The connection mode of 9 and 10 positions of Anth
would be also important for the more efficient reformation of
the electronic structure of OEP, as observed in the
diacetylene-group connected OEP-Anth-OEP derivatives.15 In
particular, with respect to the longer wavelength Q band, the
absorption intensity of 10 proved to increase up to !=37500,
almost twice and three times as large as that of 4TT and 7,
which is of significance for development of the OEP chromatic
system in both sensitivity and visibility.
Scheme 2. Synthesis of OEP-SPC-LB 5-10 by the oxidative coupling reactions
of 15 or 19 with the LB terminal acetylenes 20-22 and their homo-coupling
products 23-25.
2.2. Molecular Skeletal and Electronic Structural Features
1
of OEP-SPC-LB from H NMR, IR, and UV-Vis Spectral
Measurements.
1
All the H NMR spectra of OEP-SPC-LB 5-10 are almost
comparable to the simply combined ones between
corresponding components (S1), similar to those of 1-4.15 Yet,
all the H signals belonging to OEP and Anth of 10 appeared at
almost the same chemical shifts as those of 8 and 9, indicating
that the connection of OEP, SPC, and LB components with the
diacetylene linkage brings no particular reformation into their
skeleton. Nevertheless, the H signals due to LB rings (LB-H) of
8-10 appeared in a slightly but apparently lower field region
(~0.1 ppm), as compared with the corresponding LB-H of 5-7,
due to the greater diamagnetic ring current effect of the Anth
SPC on these LB-H signals. Otherwise, this result suggests that
the molecular planarity of the Anth derivatives 8-10 is higher
and thus their !-electronic conjugation extends further than that
of the Phen derivatives 5-7, because the central Phen moiety of
Anth in 8-10 is more fragile and mobile than Phen in 5-7 (vide
infra). In other word, even if the central Phen moiety of Anth
participates into !-electronic extension over the molecule more
or less, the two more benzene rings substantially remain in the
Anth component of 8-10. Such a dibenzo-1,4-phenylene
character of Anth magnetically affects those LB-H more
intensively than one benzene ring of Phen in 5-7.15
3

Based on the fact that the Phen and Anth derivatives 5-10
are more compact molecules in conjugation length than the
DHBTh derivatives 1-4, it suggests that an introduction of the
mobile !-electronic component into the present system is much
preferable to
a canonical extension of the !-electronic
conjugation, for construction of the particular electronic
structure of OEP as an acid-sensing material of this type.
2.3. The Spectral Behavior of OEP-SPC-LB Under The
Acidic Conditions and Cooperative Effect of SPC and LB
on Their Spectral Changes.
1
2.3.1. H NMR Spectral Changes. All the experiments
were achieved under the same conditions as previously
reported for 1-4.11 As seen in the spectral changes of 5 (Fig. 2),
6 (S2) and 7 (S3), on increasing TFA content in each sample
solution, the signals due to LB-H regularly shift to the lower
field at the first stage more or less until they reach to the
equilibrium state, because the positive charge is introduced into
LB ring by protonation on its N atom and thus magnetically
deshields LB-H. Further addition of TFA suddenly starts to
broaden the meso-H signals with their chemical shifts
unchanged and finally makes them hide into the base line.8
Although the amounts of TFA necessary for completion of
those spectral changes are different from each other, the Phen
derivatives 5-7 substantially showed the similar behavior to the
DHBTh derivatives 1-4.11 Also, it should be noted that all the
Phen-H signals in 5-7 remain unchanged in both neutral and
acidic media, similar to the DHBTh-H signals of 1-4.8
In order to seek some structural element at the molecular
level, the HOMO and LUMO energies were preliminarily
calculated for the SPC-LB derivatives 26-37 (Chart 6) with a
program of PM7 level and were summarized in Table 2.24 It
largely shows that the HOMO energies elevate in the order of
LB; Py<DMAB<BisDMAB, while the LUMO energies lower
in the order of LB; DMAB>BisDMAB>>Py. Consequently, in
all sets of derivatives with the same LB, the gaps (") between
HOMO and LUMO decreased in the order of SPC;
Phen>HH-DHBTh>TT-DHBTh>Anth, resulting in the largest
(8.3611 eV) for 32 and the smallest (6.6792 eV) for 37. These
results indicate that the combination of Phen and Py is the
hardest to collapse their electronic structures, while the
combination of Anth and BisDMAB is the easiest for
reformation of their electronic structures to enter into an
extended conjugation system through the diacetylene linkage.25
This is exactly in accord with the empirical results from the
C:::C bond vibrations of OEP-SPC-LB (vide supra).
Table 2. HOMO and LUMO energies (/eV) of diacetylene-group connected
SPC-LB derivatives 26-37
SPC-LB
HOMO
LUMO
! (HOMO - LUMO)
-1.3290
-0.9000
-0.9580
-1.3840
-1.0260
-1.0630
-1.0156
-0.4485
-0.4980
-1.6420
-1.3060
-1.3648
7.5620
7.1660
7.0830
7.3730
6.9970
6.9620
8.3611
7.6972
7.5340
6.7640
6.7560
6.6792
26
27
28
29
30
31
32
33
34
35
36
37
-8.8910
-8.0660
-8.0410
-8.7570
-8.0230
-8.0250
-9.3767
-8.1457
-8.0320
-8.4060
-8.0620
-8.0440
Molecular orbital calculation was performed by a program of PM7 level (MOPAC2012)24b, c
together with optimization of each molecular structure with a Winmoster program.24a
R
R
R
R
NMe2
R
R
S
S
NMe2
S
N
N
S
S
S
NMe2
NMe2
28
27
30
26
R=C6H13
In contrast with a high regularity in TFA-response between
the Phen derivatives 5-7, the Anth derivatives 8-10 exhibited
the characteristic behavior, with reflection of the nature of LB.
The Py-H signals of 8 (# 8.69 and 7.47 ppm) scarcely shifted to
the lower field but unexpectedly moved toward the higher field
to reach the final stationary positions at ca. 8.1 and ca. 7.2 ppm
(Fig. 3). This is entirely reverse to the behavior of the Py-H
signals of 1 and 5. Yet, all the Anth-H signals were also
observed to move toward the higher field and were almost
independently positioned from each other at the end. The
DMAB-H signals (# 7.51 and 6.66 ppm) of 9 once shifted to
the lower field (# 7.55 and ca. 7.0 ppm) but on further addition
R
R
R
S
S
S
NMe2
S
S
S
R
R
R
NMe2
NMe2
NMe2
29
32
31
NMe2
N
33
34
NMe2
NMe2
N
NMe2
35
36
37
Chart 6. Diacetylene-group connected SPC-LB derivatives 26-37.
4

of TFA reversely shifted to the higher field just by a little (S4).
And, only a set of the Anth-H signals near by the diacetylene
linkage moved toward the higher field from beginning to end.
In the case of 10 (Fig. 4), the BisDMAB-H signals (# 6.45 and
6.12 ppm) did not exhibit a typical movement arising from its
diacid base property, distinct from 4 and 7,11 but simply shifted
to the lower field (# ca. 7.1 and ca. 7.0 ppm). Yet, quite similar
to the behavior of 9, only a set of the Anth-H signals near by
the diacetylene linkage shifted to the higher field. With respect
to the meso-H signals, no particular difference between these
Phen and Anth derivatives was observed in spectral changes.
shielding the protons of the PyH+ ring to some extent. Thus, the
!-electronic reformation of this type would induce both Anth-H
and Py-H signals to shift to the higher field.
As a result, it is experimentally verified that the !-electron
mobility of SPC plays an important role not only in the
purposive construction of the skeletal feature of this system,
but also in the transmissible efficiency of this system from LB
to OEP through the diacetylene linkage under both neutral and
acidic conditions.
2.3.2. Electronic Absorption Spectral Changes.
It is apparent that such a big difference of 8-10 from the
derivatives 1-7 in their spectral behavior in acidic media is
attributable to the high !-electron mobility of Anth and
cooperatively to its interactive efficiency with LB, as also
suggested from the stretching vibrations of C:::C bond in their
IR spectral study (vide supra). Under the acidic conditions, the
mono-protonated LB species (LBH+) must be stabilized
somehow, because the positive charge is introduced into the
OEP-SPC-LB skeletal system (Charts 3 and 4). In the case of
8, the positive charge of PyH+ would localize on the N atom of
Py to have the strong electron-withdrawing power, because of
no charge relaxation through the !-electronic conjugation with
any !-electronic components. In contrast with PyH+, the
positive charge of DMABH+ (9) and BisDMABH+ (10) would
have the weak electron-withdrawing power, because these
species delocalize their positive charge for stabilization.
Therefore, the difference in electronically inductive power
between these mono-protonated species likely affects the
!-electron mobility of Anth more or less, according to
circumstances. For example, the PyH+ intensively induces Anth
to collapse its 14!-electron ring system by withdrawing
!-electrons to the PyH+ site and to reduce its ring current effect
to some extent. Oppositely, the PyH+ ring increases the electron
density by accepting !-electrons from the Anth site, resulting in
All the experiments were achieved under the same
conditions as previously reported for 1-4.11 Generally, on
adding TFA into the sample solution, Soret and Q bands of all
the derivatives regularly decrease their intensity at first, and
then both bands start to deform their shapes from the certain
point of TFA content in the sample, accompanied by a new
absorption band at the longer wavelength with a long tail. As
contrasted with the absorption terminal (~ ca. 900 nm) of the
derivatives 1-7, those of 8-10 extended over the visible region
5

up to ca. 1200-1400 nm (Figs. 1 and 5). In accord with these
spectral changes, the derivatives change their solution-color
appearance, mostly from greenish to pale yellow for the
DHBTh derivatives 1-4 at the end (Fig. 6a-c). This is almost
the same change in color for all the Phen derivatives 5-7.27 And,
the Anth derivatives 8-10 exhibited much wider solution-color
change from greenish to reddish at the end (Fig. 6d-f).
Table 3.
Minimum amount of TFA necessary for
completion of the respective step processes in the OEP-SPC-LB
system examined by means of 1H NMR spectral measurements
Added TFA (equiv.)
OEP-SPC-LB
1st step
2nd step
1TT
2TT
3TT
4TT
5
1.1
10
2.5
25
35
60
20
25
25
60
60
80
5.0
1.5
10
6
7
15
1.0
1.2
1.5
1.0
8
9
10
All experiments were carried out at 25
C using the
sample solutions adjusted to the conccentration of ca. 8.5x
10-3 mol/103 cm3. The 1st step is for completion of the mono-
protonation onto LB and the 2nd step is for completion of the
disappearance of meso-H signals.
At this moment, it is hard to make a general rationale of
sensitivity and stability of this system quantitatively, but the
acid-base interaction principle somewhat throws a light on the
above results. Thus, at the first stage, the sensitivity correlates
with the higher electron-donating ability of LB to TFA or with
As shown from the 1H NMR and IR spectral experiments, it
is realized that the Anth SPC works cooperatively with LB in
high efficiency and possesses a remarkable influence on the
electronic absorption spectral behavior of 8-10 also under the
acidic conditions (see the next section).
the more localized electrons on the
N atom of LB.
Simultaneously, when the N-protonated species of LB formed
at the first stage can stabilize sufficiently by relaxation of its
positive charge somehow (Chart 4), the protonation onto LB
would take place efficiently with the less amount of TFA than
otherwise. At the second stage, such thermodynamically higher
stability of the conjugated acid, OEP-SPC-LBH+, would
reversely retard the acid-base reaction of its OEP component
with TFA, and thus need the greater amount of TFA for
completion of the meso-H signal disappearance (vide supra).
Thus, the stability of the present system decisively reflects the
thermodynamical stability of OEP-SPC-LBH+ (Chart 3).
2.3.3. Sensitivity, Stability, and Visibility to TFA.
In this study, the minimum amount of TFA necessary for
completion of the mono-protonation onto LB is regarded as a
measure of sensitivity to TFA; the less value means the higher
sensitivity.11 On the other hand, in general, the metal
complexes of porphyrin are labile under the acidic conditions to
extrude the metal ions (Chart 3).13, 28 Therefore, in order to
guarantee the reversibility between neutral and acidic media in
the spectral changes, the minimum amount of TFA necessary
for completion of the meso-H signal disappearance was
employed,11 correlating the greater value with the higher
reversible stability (Table 3).
In a group of OEP-SPC-Py, both DHBTh and Anth
derivatives 1 and 8 showed almost the same sensitivity, to be ca.
10 times as sensitive as the Phen derivative 5. In a group of
OEP-SPC-DMAB, the Anth SPC derivative 9 showed the
highest sensitivity, to be ca. 7 times as sensitive as the DHBTh
derivative 2 and 10 times as sensitive as the Phen derivative 6.
And, in a group of OEP-SPC-BisDMAB, all the derivatives 4,
7, and 10 showed the fairly high sensitivity, regardless of SPC,
exactly due to a high proton-acceptable ability of BisDMAB. In
particular, a combination between Anth and BisDMAB brought
the highest sensitivity, as also expected in their IR and
electronic spectral studies (Tables 1-3). On the other hand,
among the derivatives carrying the same LB, the Anth group
mostly proved to show the higher reversible stability than the
other DHBTh and Phen groups. In particular, the OEP-Anth-
BisDAMB derivative 10 possesses the reversibility 32 times as
stable as the OEP-DHBTh-Py derivative 1. Meantime, the
reversible stability of the Phen derivatives 5-7 showed an
irregular trend, depending on the LB component. As compared
with the corresponding DHBTh derivatives 1-4, the Py
derivative 5 was more stable than 1, the DMAB derivative 6
was stable similar to 2, and the BisDMAB derivative 7 was less
stable than 4 (vide infra).
As mentioned previously, the lone pair electrons of Py
reside on N atom stubbornly in an sp2-hybridized orbital, while
those of DMAB and BisDMAB partially take part in
!-electronic conjugation (Chart 4). Accordingly, Py would
show the higher basicity and thus would possess the higher
sensitivity than DMAB and BisDMAB. Table 3 also shows a
particular contribution to the basicity in BisDAMB, affording a
high sensitivity of 4 and 10 almost comparable to that of 1 and
8. This result probably comes from a strong assistance of the
non-protonated amino group in BisDMAB. not only toward the
on-going protonated amino group for enhancement of
proton-acceptable ability but also toward the already protonated
amino group for enhancement of thermodynamical stability.11
In addition to the lone pair electrons on the N atom of LB,
the !-electron mobility of SPC would play a significant role in
not only sensitivity but also stability, reflecting the difference
in efficiency of the !-electron supply from SPC to LB. In this
situation, for example, the resonance energy of SPC could be
regarded as a measure of efficiency in the !-electron supply
from SPC; Phen moiety of Anth<3HTh of DHBTh<Phen.29 The
SPC with the smaller resonance energy would provide its
!-electron more readily to the necessitated sites through an
extension of the !-electronic conjugation, to heighten the
basicity of LB under the neutral conditions and to enhance the
thermodynamical stability of LBH+ under the acidic conditions.
As deduced from a low sensitivity and stability of 5-7, it is
indicated that the Phen itself is much hard to collapse the
6!-electron ring system for an extension of the !-electronic
6

conjugation due to its greater resonance energy, as compared
with other SPC. In case of the DHBTh derivatives 1-4, their
behavior seems variable. The fact that they carry two 3HTh
rings with the medium resonance energy may result in a
characteristic behavior in both sensitivity and stability, distinct
from other SPC derivatives. Each 3HTh ring of DHBTh likely
plays an independent role as the !-electron-provider component
to enhance the basicity of the nearby LB or OEP ring, and to
increase the thermodynamical stability of their conjugated acids
(LBH+ or H+OEP), according to circumstances (Chart 7).
skeleton, but also in performing them systematically and
simply by incorporation of SPC and LB with its skeletal
features remaining. Based on the guideline of molecular design
derived from the present study, further investigations of the
OEP derivatives composed of the higher !-electron mobile
SPC and the more basic LB are now in progress.
4. Experimental
EI and FAB mass spectra were recorded with a JEOL
JMS-700 spectrometer. IR spectra were measured on a Jasco
FT/IR 7300 spectrophotometer as KBr or nujol or neat disk
sample; only significant absorptions are recorded in $ values
(/cm-1). 1H NMR spectra were measured in CDCl3 solution on a
JEOL ECX-300A (300 MHz) or a JEOL JMN-EPC 600 (600
MHz) spectrometer and were recorded in # values (/ppm) with
TMS as an internal standard. The coupling constants (J) are
given in Hz. Similarly, 13C NMR spectra were measured on a
JEOL JMN-EPC 600 (150 MHz) spectrometer, in which their
signals were not satisfactorily assigned to each carbon yet.
Electronic absorption spectra were measured in CHCl3 solution
on a Shimadzu UV-2200A spectrophotometer and absorption
maxima of respective bands are reported in %max (/nm) values
together with their molecular extinction coefficient (!) and note
(sh; shoulder). SiO2 (Fujisilysia BW 820MH or BW 127ZH)
was used for column chromatography. Reactions were followed
by TLC, on aluminum sheets pre-coated with Merck SiO2 F254
or with Merck Al2O3 GF254. Organic extracts were dried over
anhydrous sodium sulfate (Na2SO4) or magnesium sulfate
(MgSO4) prior to removal of the solvents.
H+
R
N
N
N
N
S
R
LBH+
Ni
S
Chart 7. Independent interaction of each 3HTh ring in DHBTh
on the nearby component OEP or LB through the diacetylene
linkage.
From the results on the structure-property relationships in
the OEP-SPC-LB system, it is simply noted that the
combination between the higher basic LB and the lower
resonance energy SPC is useful for further enhancement of the
sensitivity and stability. In this respect, the OEP-Anth-
BisDMAB derivative 10 proved to be the most promising
candidate at present for the OEP chromatic system with highly
reversible spectral changes between neutral and acidic media.
According to the literatures, the OEP terminal acetylenes of
15 and 19 as counterparts for OEP-SPC-LB were prepared,
according to our conventional way.8, 11
3. Conclusion
Preparation of the diacetylene-group connected OEP-
phenylacetylene 15; To a solution of Cu(OAc)2 (5.34 g, 29.4
mmol) in Py-MeOH (120 cm3, 5:1) was added the mixture of
1116 (600 mg, 0.97 mmol) and 1217 (619 mg, 3.42 mmol) in
Py-MeOH (240 cm3, 5:1) at 40-45 C over 12h and was stirred
there for 1d. Poured into water, the reaction mixture was
extracted with CHCl3. The extracts were washed with dil. HCl,
sat. NaHCO3, and brine successively, and then dried. The
residue obtained after removal of the solvent was
chromatographed on SiO2 (3 x 30 cm) with hexane-CHCl3 (1:4)
to afford 13 (248 mg, 32%) as dark green microcrystallines. 13:
MS (EI); m/z 793 (M+) and 795 (M++2) for C46H47N4BrNi
(MW 794.47, based on Ni=58.69). IR (KBr) $ 2961, 2926, and
2866 (CH) and 2199 and 2137 (C:::C). 1H NMR; # 9.42 (2H, s,
meso-H), 9.40 (1H, s, meso-H), 7.52 (2H, d, J 8.4, Phen-H),
7.47 (2H, d, J 8.4, Phen-H), 4.13 (4H, q, J 8.3, CH2), 3.85-3.75
(12H, m, CH2), and 1.83-1.70 (24H, m, CH3). 13C NMR; #
145.79, 145.00, 143.77, 143.01, 142.21, 140.34, 140.16, 137.75,
133.70, 131.77, 123.43, 121.41, 97.90, 97.84, and 92.29 (sp2-C),
90.80, 87.31, 82.14, and 76.00 (sp-C), 31.94, 29.72, 29.67,
22.70, 21.77, 19.50, 18.14, and 17.27 (sp3-C). Uv-vis; %max 437
(110000), 565 (13100), and 603 (13700). To a solution of 13
(150 mg, 0.19 mmol), (Ph3P)4Pd (436 mg, 3.8 x 10-2 mmol),
and CuI (3.6 mg, 1.9 x 10-2 mmol) in toluene-NEt3 (30 cm3,
1:1) was added TMS-acetylene (0.11 cm3, 0.76 mmol) over 3h.
The mixture was refluxed with stirring for 12 h. The reaction
mixture was poured into water and extracted with CHCl3. The
extracts were washed with brine and then dried. The residue
obtained after removal of the solvents was chromatographed on
SiO2 (3.5 x 24 cm) with hexane-CHCl3 (4:1) to afford 14 (123
mg, 80%) as black purple microcrystallines. 14: MS (EI); m/z
811 (M+) for C51H56N4NiSi (MW 811.78, based on Ni=58.69).
IR (nujol) $ 2962, 2927, and 2869 (CH) and 2193 and 2136
(C:::C). 1H NMR; # 9.42 (2H, s, meso-H), 9.40 (1H, s, meso-H),
In this study, the features of our original OEP-SPC-LB
chromatic system in reversible spectral change between neutral
and acidic media were further elucidated in view of sensitivity,
stability, and visibility, as focused on the electronic properties
of LB and SPC. It was studied on their structural properties that
the lone pair electrons on the N atom of LB interact with TFA
strongly or weakly, depending on the circumstances where they
take part in !-electronic conjugation for stabilization in an
extended system or in a definite cyclic system. This feature
primarily produces the inherent basicity of LB in the present
system and results in the difference in their sensitivity to TFA.
The !-electron mobility of SPC also plays a significant role for
!-electronic conjugation with LB through the diacetylene
linkage to reform the electronic structures, resulting in the
difference in their reactivity with TFA. Simultaneously, these
electronic properties of LB and SPC contribute to the
stabilization of the conjugated acids under the acidic conditions
as well. The higher basic LB derivatives did not always exhibit
the higher reversible stability, but the SPC derivatives with the
higher !-electron mobility certainly brought the higher
sensitivity and stability (Table 3). In this respect, the Phen
moiety of Anth proved to be the most effective SPC for the
present system, presumably due to the smallest loss of
resonance energy for reformation of the electronic system to
provide its !-electrons to the necessitated sites. Especially, the
combination between Anth and BisDMAB is highly promising
for the OEP chromatic system in view of the three valuations of
sensitivity, stability, and visibility.
A wide variety of porphyrin-based chromatic systems are
well known to demonstrate one or two particular valuations
with the same efficiency as 10 or more efficiently.3 Our OEP
chromatic system is rather independent from others not only in
aiming at all the three valuations based on the same molecular
7

7.53 (2H, d, J 7.8, Phen-H), 7.46 (2H, d, J 7.8, Phen-H), 4.13
(4H, q, J 8.2, CH2), 3.85-3.75 (12H, m, CH2), 1.83-1.70 (24H,
m, CH3), and 0.27 (9H, s, TMS-H). 13C NMR; # 146.29, 145.53,
144.27, 143.51, 142.69, 140.84, 140.64, 138.24, 134.21, 132.63,
124.19, 122.91, 98.33, 97.73, and 92.79 (sp2-C), 91.29, 88.49,
87.81, 83.03, 82.62, and 76.49 (sp-C), 30.21, 22.26, 20.05,
20.00, 19.97, 18.65, 17.78, and 0.51 (sp3-C). One sp3-C signal
could not be ascertained, implying that the signal possesses the
same chemical shift as the firmly specified one. Uv-vis; %max
441 (112000), 568 (9120), and 608 (9400). A mixture of 14
(151 mg, 0.19 mmol) and K2CO3 (13 mg, 9.3 x 10-2 mmol) in
CHCl3-MeOH (30 cm3, 1:1) was stirred at an ambient
temperature under Ar atmosphere for 6 h. Poured into water,
the reaction mixture was extracted with CHCl3. The extracts
were washed with brine and then dried. The residue obtained
after removal of the solvents was chromatographed on SiO2 (5
x 8.0 cm) with CHCl3 to afford 15 (137 mg, quantitative) as
dark purple microcrystallines. 15: MS (EI); m/z 739 (M+) for
C48H48N4Ni (MW 739.59, based on Ni=58.69). IR (KBr) $
3293 (C:::CH), 2961, 2925, and 2854 (CH), and 2193 and 2136
(C:::C). 1H NMR; # 9.42 (2H, s, meso-H), 9.40 (1H, s, meso-H),
7.55 (2H, d, J 8.7, Phen-H), 7.47 (2H, d, J 8.7, Phen-H), 4.13
(4H, q, J 7.2, CH2), 3.84-3.74 (12H, m, CH2), 3.18 (1H, s,
C:::CH), and 1.84-1.72 (24H, m, CH3). 13C NMR; # 145.80,
145.06, 143.76, 143.00, 142.31, 140.40, 140.21, 137.83, 132.21,
132.16, 122.97, 122.73, 97.93, 97.87, and 92.38 (sp2-C), 90.91,
87.81, 83.19, 82.65, 79.48, and 76.79 (sp-C), 32.02, 29.79,
21.82, 20.68, 19.58, 19.50, 18.15, and 17.28 (sp3-C). Uv-vis;
Anth-H), 4.26 (4H, q, J 7.5, CH2), 3.88-3.76 (12H, m, CH2),
1.94 (6H, t J 7.2, CH3), 1.80-1.74 (24H, m, CH3), and 0.45 (9H,
s, TMS-H). 13C NMR; # 145.69, 144.78, 143.58, 142.83,
142.09, 140.17, 139.99, 137.60, 133.61, 133.48, 132.81, 132.14,
128.51, 128.32, 128.27, 127.28, 127.12, 101.31, and 97.81
(sp2-C), 92.69, 90.93, 87.33, 85.81, and 85.69 (sp-C), 21.69,
19.35, 19.28, 17.97, 17.95, 17.18, and 0.05 (sp3-C). One sp-C
and two sp3-C signals could not be ascertained, implying that
their signals possess the same chemical shift as the firmly
specified one (ones). In order to specify those signals, the 13C
NMR spectra will be taken in other solvents in the future.
Uv-vis; %max 419 (77400), 440 (61100, sh), 465 (66300), 491
(100000), 563 (16200), and 601 (29400). A solution of 18 (170
mg, 0.20 mmol) and K2CO3 (12.9 mg, 9.3 x 10-2 mmol) in
CHCl3-MeOH (30 cm3, 1:1) was stirred at an ambient
temperature under Ar atmosphere for 10 h. Poured into water,
the reaction mixture was extracted with CHCl3. The extracts
were washed with brine and then dried. The residue obtained
after removal of the solvents was chromatographed on SiO2 (5
x 7.0 cm) with CHCl3 to afford 19 (153 mg, 98%) as dark
purple microcrystallines. 19: MS (FAB); m/z 839.72 (M+) for
C56H52N4Ni (MW 839.71, based on Ni=58.69). IR (KBr) $
3300 (C:::CH), 2962, 2923, and 2869 (CH), and 2174 and 2122
(C:::C). 1H NMR; # 9.45 (2H, s, meso-H), 9.42 (1H, s, meso-H),
8.72-8.69 (2H, dm, Anth-H), 8.69-8.64 (2H, dm, Anth-H),
7.73-7.64 (4H, m, Anth-H), 4.26 (4H, q, J 7.2, CH2), 4.13 (1H,
s, C:::CH), 3.86-3.76 (12H, m, CH2), 1.96 (6H, t, J 7.2, CH3),
and 1.78-1.74 (24H, m, CH3). 13C NMR; # 145.91, 144.95,
143.80, 143.03, 142.29, 140.39, 140.19, 137.81, 132.93, 132.61,
132.10, 128.55, 127.35, 127.09, 118.14, 118.00, 98.02, 97.92,
and 92.56 (sp2-C), 91.04, 90.35, 87.61, 85.93, 85.79, and 80.36
(sp-C), 31.97, 29.75, 22.45, 21.89, 19.55, 19.48, 18.17, and
17.37 (sp3-C). Uv-vis; %max 419 (93500), 437 (89600, sh), 456
(81500), 488 (93200), 563 (20800, sh), and 602 (32100).
Among LB counterparts 20-22 for OEP-SPC-LB, the LB
acetylenes 20 and 21 are commercially available. Thus, the
BisDMAB acetylene 22 was prepared from the corresponding
bromo derivative, according to the reported procedures.21 To a
solution of 1-bromo-3,5-bis(N,N-dimethylamino)benzene21
(500 mg, 2.06 mmol), (Ph3P)2PdCl2 (40 mg, 57 x 10-3 mmol)
and CuI (9.5 mg, 49.9 x 10-3 mmol) in TEA (20 cm3) was
added TMS-acetylene (1.50 cm3, 10.8 mmol). The mixture was
stirred with refluxing for 1 d. The reaction mixture was poured
into water and extracted with ethyl acetate (AcOEt). The
extracts were washed with brine and then dried. The residue
obtained after removal of the solvent was chromatographed on
Al2O3 (35 x 18 cm) with hexane-AcOEt (1:1) to afford the
TMS-protected product (402 mg). Then, a solution of the crude
solid and K2CO3 (430 mg, 3.1 mmol) in THF-MeOH (90 cm3,
1:2) was stirred at an ambient temperature under Ar atmosphere
for 10 h. Poured into water, the reaction mixture was extracted
with CHCl3. The extracts were washed with brine and then
dried. The residue obtained after removal of the solvents was
chromatographed on Al2O3 (3 x 20 cm) with benzene to afford
22 (287 mg, 74%) as brownish oil. 22:21 MS (EI); m/z 189
(M++1) for C12H16N2 (MW 188.27). IR (neat); $ 3314 (C:::CH)
and 2110 (C:::C). 1H NMR; # 6.30 (2H, d, J 2.4, BisDMAB-H),
6.04 (1H, br t, J 2.4, BisDMAB-H), 2.93 (1H, s, C:::CH), and
2.92 (12H, s, NMe2-H).
%
max 443 (99700), 567 (7930), and 608 (8300).
Preparation of the diacetylene-group connected OEP-
Anthrylacetylene 19; To a solution of Cu(OAc)2 (5.18 g, 28.7
mmol) in Py-MeOH (120 cm3, 5:1) was added the mixture of
1116 (600 mg, 0.97 mmol) and 1618 (960 mg, 3.42 mmol) in
Py-MeOH (240 cm3, 5:1) at 40-45 C over 6 h and was stirred
there for 12 h. Poured into water, the reaction mixture was
extracted with CHCl3. The extracts were washed with dil. HCl,
sat. NaHCO3, and brine successively, and then dried. The
residue obtained after removal of solvent was chromatographed
on SiO2 (3 x 27 cm) with hexane-CHCl3 (4:1) to afford 17 (288
mg, 33%) as dark green microcrystallines. 17: MS (FAB); m/z
894.56 (M+) for C54H51N4BrNi (MW 894.58, based on
Ni=58.69). IR (KBr) $ 2961, 2927, and 2868 (CH), and 2180
and 2128 (C:::C). 1H NMR; # 9.44 (2H, s, meso-H), 9.40 (1H, s,
meso-H), 8.70 (2H, dm, Anth-H), 8.57 (2H, dm, Anth-H),
7.70-7.63 (4H, m, Anth-H), 4.28 (4H, q, J 7.5, CH2), 3.87-3.75
(12H, m, CH2), 1.94 (6H, t, J 7.8, CH3), and 1.78-1.73 (18H, m,
CH3). 13C NMR; # 145.86, 144.89, 143.75, 142.99, 142.26,
140.36, 140.18, 140.06, 137.79, 133.90, 130.26, 128.39, 127.55,
127.04, 125.23, 117.25, 97.98, 97.87, and 92.73 (sp2-C), 91.07,
86.94, 85.49, and 85.46 (sp-C), 31.93, 29.71, 29.37, 21.89,
19.53, 19.47, 18.16, and 17.48 (sp3-C). Uv-vis; %max 414
(66300), 448 (78300), 482 (99800), 565 (14900, sh), and 598
(22400). To a solution of 17 (150 mg, 0.17 mmol), (Ph3P)4Pd
(39.1 mg, 3.4 x 10-2 mmol), and CuI (3.5 mg, 18.4 x 10-2 mmol)
in toluene-TEA (30 cm3, 2:1) was added TMS-acetylene (0.1
cm3, 0.72 mmol) and the mixture was refluxed with stirring for
12 h. The reaction mixture was poured into water and extracted
with CHCl3. The extracts were washed with brine and then
dried. The residue obtained after removal of the solvent was
chromatographed on SiO2 (3.5 x 21 cm) with hexane-CHCl3
(4:1) to afford 18 (128 mg, 84%) as black purple
microcrystallines. 18: MS (FAB); m/z 911.95 (M+) for
C59H60N4SiNi (MW 911.92, based on Ni=58.69). IR (KBr) $
All the title OEP-SPC-LB derivatives 5-10 were
synthesized, in a similar way for the DHBTh derivatives 1-4.8
As a typical reaction procedure, the synthesis of 5 is described
in the following. A mixture of 15 (80 mg, 0.11 mmol) and 20
(154 mg as HCl salt, 1.1 mmol, 10 eq. to 15) in a mixed
solution of Py-MeOH (150 cm3, 5:1) was added dropwise at
40-45 C with stirring into a solution of Py-MeOH (50 cm3, 5:1)
1
2962, 2928, and 2869 (CH) and 2176 and 2134 (C:::C). H
NMR; # 9.45 (2H, s, meso-H), 9.41 (1H, s, meso-H), 8.74-8.68
(2H, m, Anth-H), 8.64-8.59 (2H, m, Anth-H), 7.73-7.63 (4H, m,
8

containing an excessive amount of Cu(OAc)2 (728 mg, 4.0
mmol) over 1.5 hr. Then, the reaction mixture was kept stirring
at 40 C for 12 hr. Poured into water, the reaction mixture was
extracted with CHCl3. The extracts were washed with diluted
HCl aq., with brine several times successively, and then dried.
After removal of the solvents under reduced pressure, the
residue obtained was chromatographed on SiO2 column with
hexane- CHCl3 (4:1), to afford 5 (25 mg, 28%), together with
the Py homo-coupling dimer 2322 (38 mg, 34% based on 20).
5: Dark purple microcrystallines (benzene-CHCl3). MS
(FAB); m/z 840.68 for C55H51N5Ni (MW 840.70, based on
Ni=58.69). IR (KBr); $ 2963, 2928, and 2870 (C-H), 2188 and
tm, CH3). 13C NMR; # 149.88, 145.86, 145.80, 144.97, 144.90,
143.81, 143.02, 142.22, 140.38, 140.17, 137.77, 137.70, 132.62,
132.60, 132.36, 132.30, 126.06, 123.89, 121.47, 97.97, 97.93,
and 92.29 (sp2-C), 90.05, 89.05, 88.66, 87.90, 87.75, 83.38,
83.15, and 78.09 (sp-C), 21.76, 19.54, 19.47, 18.15, 18.14,
18.10, 17.27, and 17.20 (sp3-C). Uv-vis; %max 425 (91800), 508
(112000), and 610 (48700).
9: 40% yield. Black green powder (benzene-CHCl3). MS
(FAB); m/z 982.88 for C66H61N5Ni (MW 982.89, based on
Ni=58.69). IR (KBr); $ 2962, 2928, and 2869 (C-H), 2180 and
1
2127 (C:::C). H NMR; # 9.44 (2H, s, meso-H), 9.40 (1H, s,
meso-H), 8.71-8.63 (4H, m, Anth-H), 7.71-7.62 (4H, m,
Anth-H), 7.51 and 6.66 (2H and 2H, d, J 9.3, MDAB-H), 4.26
(4H, q, J 7.2, CH2), 3.88-3.75 (12H, qm, CH2), 3.02 (6H, s,
NMe2-H), 1.94 (6H, t, J 7.5, CH3) and 1.79-1.74 (18H, tm,
CH3). 13C NMR; # 150.75, 145.89, 144.97, 143.78, 143.01,
142.30, 140.38, 140.18, 137.80, 133.95, 133.22, 133.01, 127.47,
127.42, 127.24, 121.17, 118.57, 117.75, 111.71, 107.76, 98.02,
97.90, and 92.95 (sp2-C), 91.15, 88.26, 88.09, 87.91, 86.17,
86.16, 78.19, and 72.78 (sp-C), 40.08, 29.72, 29.71, 21.89,
19.55, 19.48, 18.19, 18.17, and 17.37 (sp3-C). Uv-vis; %max 425
(57900), 513 (88400), and 609 (41900).
1
2163 (C:::C). H NMR; # 9.42 (2H, s, meso-H), 9.40 (1H, s,
meso-H), 8.62 (2H, d, J 6.0, Py-H), 7.58 (2H, d, J 7.0, Phen-H),
7.53 (2H, d, J 7.0, Phen-H), 7.38 (2H, d, J 6.0, Py-H), 4.14 (4H,
q, J 7.2, CH2), 3.82-3.77 (12H, qm, CH2), and 1.82-1.70 (24H,
m, CH3). 13C NMR; # 149.92, 145.97, 144.87, 143.84, 143.04,
142.32, 140.44, 140.21, 137.82, 133.56, 132.81, 130.07, 125.96,
119.42, 116.52, 98.09, 98.03, and 92.77 (sp2-C), 90.83, 88.67,
86.81, 85.90, 85.81, 82.36, 81.18, and 78.57 (sp-C), 21.89,
19.55, 19.48, 18.19, 18.17, 18.15, 17.40, and 17.39 (sp3-C).
Uv-vis; %max 452 (95000) and 592 (11600).
1
23:22 Colorless solid (benzene-hexane). H NMR; # 8.57
10: 25% yield. Black green microcrystallines (benzene-
CHCl3). MS (FAB); m/z 1025.95 for C68H66N6Ni (MW 1025.96,
based on Ni=58.69). IR (KBr); $ 2963, 2927, and 2867 (C-H),
(4H, J 4.5, Py-H) and 7.31 (4H, J 4.5, Py-H).
6: 41% yield. Dark purple microcrystallines (benzene-
CHCl3). MS 882.76 (FAB); m/z 882.77 for C58H57N5Ni (MW
882.78, based on Ni=58.69). IR (KBr); $ 2958, 2927, and 2868
(C-H), 2202 and 2137 (C:::C). 1H NMR; # 9.42 (2H, s,
meso-H), 9.40 (1H, s, meso-H), 7.56 (2H, d, J 8.7, Phen-H),
7.49 (2H, d, J 8.7, Phen-H), 7.42 (2H, d, J 9.0, DMAB-H), 6.63
(2H, d, J 9.0, DMAB-H), 4.13 (4H, q, J 7.5, CH2), 3.82-3.75
(12H, qm, CH2), 3.01 (6H, s, NMe2-H), and 1.83-1.73 (24H, m,
CH3). 13C NMR; # 151.25, 145.78, 145.03, 143.74, 142.98,
142.22, 140.32, 140.13, 137.74, 133.91, 133.90, 132.25, 132.20,
123.05, 122.75, 116.65, 111.60, 97.90, and 97.82 (sp2-C), 87.88,
86.26, 85.84, 85.06, 83.15, 82.75, 78.15, and 72.35 (sp-C),
40.06, 21.76, 19.53, 19.46, 18.16, 18.13, 18.10, 17.25, and
17.20 (sp3-C). Uv-vis; %max 451 (131000) and 590 (14000).
24:23 28% yield based on 21. Pale yellow solid (benzene-
hexane). 1H NMR; # 7.40 (4H, J 8.2, Phen-H), 6.64 (4H, J 8.2,
Phen-H), and 2.98 (12H, s, NMe-H).
1
2168 and 2121 (C:::C). H NMR; # 9.45 (2H, s, meso-H), 9.41
(1H, s, meso-H), 8.70 and 8.65 (2H and 2H, dm, Anth-H),
7.73-7.66 (4H, m, Anth-H), 6.45 (2H, d, J 2.1, BisDMAB-H),
6.12 (1H, br s, BisDMAB-H), 4.26 (4H, q, J 7.2, CH2),
3.86-3.76 (12H, qm, CH2), 2.99 (12H, s, NMe2-H), and 1.94
(6H, t, J 7.2, CH3), 1.78-1.74 (18H, m, CH3). 13C NMR; #
151.43, 145.92, 144.95, 143.79, 143.02, 142.31, 140.40, 140.20,
137.81, 133.39, 132.97, 127.44, 127.40, 127.38, 127.21, 122.15,
118.21, 106.11, 98.86, 98.04, 97.94, 92.89, and 91.06 (sp2-C),
88.17, 88.10, 88.08, 87.61, 86.33, 86.05, 78.25, and 72.42
(sp-C), 40.68, 21.89, 19.55, 19.54, 19.47, 18.15, 18.14, 17.37,
and 17.36 (sp3-C). Uv-vis; %max 426 (67900), 507 (99400), and
607 (37500).
Acknowledgement
Financial support by a Grant-in-Aid for Scientific Research
from the Ministry of Education, Science, Sports, Culture and
Technology (Nos. 23550046 and 26410039) is gratefully
acknowledged. HH is also grateful to The Center of
Instrumental Analyses at University of Toyama for their
supporting measurements of physical properties of the new
compounds.
Note: This paper is dedicated to an emeritus professor
Soichi Misumi (Osaka University), on the occasion of his 90th
birth-year anniversary.
7: 35% yield. Black green powder (benzene-CHCl3). MS
(FAB); m/z 925.87 for C60H62N6Ni (MW 925.85, based on
Ni=58.69). IR (KBr); $ 2964, 2925, and 2870 (C-H), 2175 and
1
2137 (C:::C). H NMR; # 9.42 (2H, s, meso-H), 9.40 (1H, s,
meso-H), 7.56 and 7.50 (2H and 2H, d, J 8.4, Phen-H), 6.35
(2H, br s, BisDMAB-H), 6.08 (1H, br s, BisDMAB-H), 4.13
(4H, q, J 7.2, CH2), 3.82-3.77 (12H, qm, CH2), 3.01 (12H, s,
NMe2-H), and 1.83-1.75 (24H, m, CH3). 13C NMR; # 145.80,
145.79, 145.00, 143.77, 143.01, 142.21, 140.34, 140.16, 137.75,
133.71, 133.70, 131.78, 131.77, 123.43, 121.41, 90.90, 97.84,
92.75, and 91.06 (sp2-C), 88.12, 88.10, 88.06, 87.58, 86.42,
86.17, 77.83, and 72.08 (sp-C), 40.68, 21.89, 19.55, 19.54,
19.48, 18.17, 18.15, 17.37, and 17.36 (sp3-C). Uv-vis; %max 450
(118000) and 590 (13500).
References
1.
(a) Y.-L. Gong, F.-H. Li, F. Lu, C. Dai, Bull. Mater.
Sci., 2015, 38, 847. (b) A. Quaranta, G. Charalambidis,
C. Herrero, S. Margiola, W. Leibl, A. Coutsolelos, A.
Aukauloo, Phys. Chem. Chemical Phys., 2015, 17,
24166. (c) S. Rangasamy, H. Ju, S. Um, D.-C. Oh, J. M.
Song, J. Med. Chem., 2015, 58, 6864. (d) N. P. F.
Goncalves, A. V. C. Simoes, A. R. Abreu, A. J.
Abrunhosa, J. M. Dabrowski, M. M. Pereira, J. Por.
Phthal, 2015, 19, 946.
25:11 45% based on 22. Brownish solid (benzene). 1H
NMR; # 6.34 (4H, d, J 2.4, BisDMAB-H), 6.07 (2H, t, J 2.4,
BisDMAB-H), and 2.93 (24H, s, NMe2-H).
8: 33% yield. Black purple powder (benzene-CHCl3). MS
(FAB); m/z 940.79 for C63H55N5Ni (MW 940.81, based on
Ni=58.69). IR (KBr); $ 2961, 2927, and 2868 (C-H), 2173 and
1
2131 (C:::C). H NMR; # 9.45 (2H, s, meso-H), 9.41 (1H, s,
2.
(a) R. H. Deibel, J. B. Evans, J. Bacteriol., 1960, 79, 356.
(b) M. R. Dayer, A. A. Moosavi-Movahedi, M. S. Dayer,
Protein Peptide Lett., 2010, 17, 473. (c) K. Komagoe, H.
Kato, T. Inoue, T. Katsu, Photochem. Photobiol. Sci.,
2011, 70, 363 and others.
meso-H), 8.74-8.71 (2H, dm, Anth-H), 8.69 (2H, d, J 6.2,
Py-H), 8.66-8.60 (2H, dm, Anth-H), 7.73-7.70 (4H, m, Anth-H),
7.47 (2H, d, J 6.2, Py-H), 4.26 (4H, q, J 7.5, CH2), 3.86-3.76
(12H, qm, CH2), 1.94 (6H, t, J 7.2, CH3) and 1.79-1.74 (18H,
9

3.
(a) C.-G. Niu, X.-Q. Gui, G.-M. Zeng, A.-L. Guan, P.-F.
Gao, P.-Z. Qin, Anal. Bioanal. Chem., 2005, 383, 349.
(b) Y. Egawa, R.. Hayashida, J. Anzai, Langumuir, 2007,
23, 13146. (c) A. Synytsya, A. Synytsya, P. Blafkova, J.
Ederova, J. Spevacek, P. Slepicka, V. Kral, K. Volka,
Biomacromol., 2009, 10, 1067. (d) X. Zhu, W. Lu, Y.
Zhang, A. Reed, B. Newton, Z. Fan, H. Yu, P. C. Ray, R.
Gao, Chem. Commun., 2011, 47, 10311. (e) S.
Thyagarajan, T. Leiding, S. P. Arskold, A. V. Cheprakov,
S. A. Vinogradov, Inorg. Chem., 2010, 49, 9909. (f) J.
Bhuyan, S. Sarkar, Chem. An Asian J., 2012, 7, 2690. (g)
W. L. Sitienei, L. M. Wangatia, T. Zeng, B. Sun, M. Zhu,
Adv. Mater. Res., 2013, 668, 696. (h) S. E. Rodrigues, A.
E. H. Machado, M. Berardi, A. S. Ito, L. M. Almeida, M.
J. Santana, L. M. Liao, N. N. M. Barbosa, P. J.
Goncalves, J. Mol. Struct., 2015, 1084, 284. (i) F. Dini,
G. Magna, E. Martinelli, G. Pomario, C. Di Natale, R.
Paolesse, I. Lundstrom, Anal. Bioanal. Chem., 2015, 407,
3975.
Sato, K. Miyabayashi, M. Miyake, H. Higuchi, Sci. Tec.
Adv. Mat., 2006, 7, 237. (p) N. Hayashi, T. Nishihara, T.
Matsukihira, H. Nakashima, K. Miyabayashi, M. Miyake,
H. Higuchi, Bull. Chem. Soc. Jpn., 2007, 80, 371. (q) V.
Borovkov, T. Yamamoto, H. Higuchi, Y. Inoue, Org.
Lett., 2008, 10, 1283.
(a) N. Hayashi, T. Matsukihira, K. Miyabayashi, M.
Miyake, H. Higuchi, Tetrahedron Lett., 2006, 47, 5585.
(b) H. Higuchi, N. Hayashi, T. Matsukihira, T.
Kawakami, T. Takizawa, J. Saito, K. Miyabayashi, M.
Miyake, Heterocycles, 2008, 76, 353.
(a) N. Hayashi, H. Nishi, K. Morizumi, I. Kobayashi, H.
Sakai, R. Akaike, K. Tani, H. Higuchi, Chemistry Book:
Recent Research Developments in Organic Chemistry,
Chapter 16, ed. Pandalai, S. G., Transworld Research
Network (Kerala), 2004, 8, 401-424. (b) N. Hayashi A.
Matsuda, E. Chikamatsu, M. Murayama, K. Mori, K.
Tani, K. Miyabayashi, M. Miyake, H. Higuchi,
Tetrahedron, 2004, 60, 6363.
8.
9.
4.
(a) D. Gust, A. Thomas, A. L. Moore, H. K. Kang, J. M.
DeGraziano, P. A. Liddell, G. R. Seely, J. Phys. Chem.,
1993, 97, 13637. (b) M. Inamo, A. Tomita, Y. Inagaki, N.
Asano, K. Suenaga, M. Tabata, S. Funahashi, Inorg.
Chim. Acta, 1997, 256, 77. (c) J. J. A. van Kampen, T.
M. Luider, P. J. A. Ruttink, P. C. Burgers, J. Mass Spect.,
2009, 44, 1556 (d) Z. Valicsek, O. Horvath, Macrochem.
J., 2013, 107, 47 and others.
10. (a) In “Determination of Organic Structures by
Physical Methods”, ed. E. D. Braude and F. C.
Nachod, Academic Press (New York), 1955. (b) W. P.
Jencks and J. Regenstein, In Handbook of
Biochemistry and Molecular Biology, ed. R. L.
Lundblad and F. M. MacDonald, CRC Press (New
York), 4th Ed., Chapter 67; Ionization Constants of
Acids and Bases, pp 595-635.
5.
(a) Q. Yan, J. Yuan, Y. Kang, Z. Cai, L. Zhou, Y. Yin,
Chem. Commun., 2010, 46, 2781. (b) Y. Iijima, H.
Sakaue, Sensors and Actuators, A: Phys., 2012, 184, 128.
(c) F. Hammerer, G. Garcia, P. Charles, A. Sourdon, S.
Achelle, M.-P. Teulade-Fichou, P. Maillard, Chem.
Commun., 2014, 50, 9529 and others.
(a) S. Yang, Y. Wo, M. E. Meyerhoff, Anal. Chim.
Acta, 2014, 843, 89. (b) Y. F. Huan, Q. Fei, H. Y.
Shan, B. J. Wang, H. Xu, G. D. Feng, Analyst, 2015,
140, 1655. (c) S. Rangasamy, H. Ju, S. Um, D.-C. Oh,
J. M. Song, J. Med. Chem., 2015, 58, 6864.
11. H. Kempe, J. Yoshino, N. Hayashi, and H. Higuchi,
Tetrahedron, 2015, 71, 1322.
12. To our best knowledge, the pKa(1) and pKa(2) values of
conjugated acid of BisDMAB are unknown yet. The
pKa value (4.58) of conjugated acid aniline-H+ with
aniline in water at 25 C is known to be slightly
smaller, i.e., a little higher acidity, as compared with
that of 5.15 between DMAB and DMAB-H+. Thus,
based on this fact, the pKa(1) and pKa(2) values of
BisDMAB could be slightly larger than those (pKa(1)
2.65 and pKa(2) 4.88) of corresponding 1,3-phenylene-
diamine.10
6.
7.
(a) H. Imahori, H. Higuchi, Y. Matsuda, A. Itagaki, Y.
Sakai, J. Ojima, Y. Sakata, Bull. Chem. Soc. Jpn., 1994,
67, 2500. (b) H. Higuchi, K. Shimizu, J. Ojima, K.
Sugiura, Y. Sakata, Tetrahedron Lett., 1995, 36, 5359.
(c) H. Higuchi, M. Takeuchi, J. Ojima, Chem. Lett. 1996,
593. (d) H. Higuchi, K. Shimizu, M. Takeuchi, J. Ojima,
K. Sugiura, Y. Sakata, Bull. Chem. Soc. Jpn., 1997, 70,
1923. (e) H. Higuchi, M. Takeuchi, Y. Hasegawa, J.
Ojima, Nonlinear Optics, 1999, 22, 333. (f) H. Higuchi,
M. Shinbo, M. Usuki, M. Takeuchi, Y. Hasegawa, K.
Tani, J. Ojima, Bull. Chem. Soc. Jpn., 1999, 72, 1887.
(g) H. Higuchi, T. Ishikura, K. Miyabayashi, M. Miyake,
K. Yamamoto, Tetrahedron Lett., 1999, 40, 9091. (h) H.
Higuchi, M. Shinbo, M. Usuki, M. Takeuchi, K. Tani, K.
Yamamoto, Bull. Chem. Soc. Jpn., 2000, 73, 1259. (i) H.
Higuchi, T. Ishikura, K. Mori, Y. Takayama, K.
Yamamoto, K. Tani, K. Miyabayashi, M. Miyake, Bull.
Chem. Soc. Jpn., 2001, 74, 889. (j) H. Higuchi, T.
Maeda, K. Miyabayashi, M. Miyake, K. Yamamoto,
Tetrahedron Lett., 2002, 42, 3097. (k) N. Hayashi, H.
Nakashima, Y. Takayama, H. Higuchi, Tetrahedron Lett.,
2003, 44, 5423. (l) N. Hayashi, A. Matsuda, E.
Chikamatsu, K. Mori, H. Higuchi, Tetrahedron Lett.,
2003, 44, 7155. (m) N. Hayashi, A. Naoe, K.
Miyabayashi, M. Yamada, M. Miyake, H. Higuchi,
Tetrahedron Lett., 2004, 45, 8215. (n) N. Hayashi, A.
Naoe, K. Miyabayashi, M. Miyake, H. Higuchi,
Tetrahedron Lett., 2005, 46, 6961. (o) N. Hayashi, M.
13. (a) J. W. Buchler, In Porphyrin and Metalloporphyrins,
K. M. Smith, ed. Elsevier: Amsterdam, The Netherlands,
1975, pp 157-231. (b) J. W. Buchler, In The Porphyrins,
D. Dolphin, ed. Academic: New York, NY, 1978, pp
389-483.
14. M. Gouterman, In The Porphyrins, D. Dolphin, ed.
Academic: New York, NY, 1978, pp 1-165.
15. (a) 7g. (b) N. Hayashi, K. Tachibana, T. Tsuchiya, K.
Miyabayashi, M. Miyake, T. Takizawa, J. Saito, H.
Higuchi, Sci. Tec. Adv. Mat., 2007, 8, 296. (c) H. Kempe,
N. Kuroda, J. Yoshino, N. Hayashi, H. Higuchi,
Tetrahedron Lett., 2014, 55, 5164.
16. D. P. Arnold, A. W. Johnson, M. Mahendran, J. Chem.
Soc., Perkin Trans. 1, 1978, 366.
17. Prepared from p-bromoiodobenzene: (a) S. Thorand, N.
Krause, J. Org. Chem., 1998, 63, 8551. (b) B. Zhou, H.
Chen, C. Wang, J. Am. Chem. Soc., 2013, 135, 1246.
18. Prepared from 9,10-dibromoanthracene: S. Destri, W.
Porzio, L. Khotina, C. Botta, R. Consonni, Macromol.
Chem. Phys., 2001, 202, 2572.
19. G. Eglinton, A. R. Galbraith, Chem. Ind., 1956, 737.
20. K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron
Lett. 1975, 4467.
21. 20: Purchased as HCl salt from Sigma-Aldrich Fine
Chemicals Co., Ltd., Product No. 530921-1 and used for
the reaction as it is. 21: Purchased from Sigma-Aldrich
Fine Chemicals Co., Ltd., Product No. 592609-1. 22: H.
10

K. Kim, S. K. Kim, J. H. Park, S. W. Yoon, M. H. Lee,
Y. Do, Chem. Asian J., 2008, 3, 1912.
22. (a) L. D. Ciana and A. Haim, J. Heterocycl. Chem., 1984,
21, 607. (b) E. Merkul, D. Urselmann, T. J. J. Muller,
Eur. J. Org. Chem., 2011, 238.
23. J. G. Rodriguez, J. L. Tejedor, A. Rumbero, L. Canoira,
Tetrahedron, 2006, 62, 3075.
24. For Winmoster program: (a) N. Senda, Idemitsu
Technical Report, 2006, 49, 106. For PM7 program
(MOPAC2012): (b) J. D. C. Maia, G. A. U. Carvalho, C.
P. Mangueira, Jr., S. R. Santana, L. A. F. Cabral, G. B.
Rocha, J. Chem. Theory Comput., 2012, 8, 3072. (c) J. J.
P. Stewart, J. Mol. Model, 2013, 19, 1.
25. (a) H. Fukumoto, R. Hoffmann, J. Phys. Chem., 1974,
78, 1167. (b) H. Fukumoto, S. Kato, S. Yamabe, K.
Fukui, J. Chem. Phys., 1974, 60, 572.
26. At present, it is extremely hard to reach the steady
solutions with the full structure of 1-10 by the usual
calculation methods, generally due to not only their large
molecular formula but also poor parameters for
metalloporphyrin ring.
27. J. Yoshino, M. Tsujiguchi, N. Hayashi, H. Higuchi,
Chem. Lett., 2011, 40, 944.
28. (a) J. Rosenthal, E. R. Young, D. G. Nocera, Inorg.
Chem., 2007, 46, 8668. (b) T. D. Lash, A. L. Von
Ruden, J. Org. Chem., 2008, 73, 9417. (c) M. Krouit,
R. Granet, P. Krausz, Eur. Polym. J., 2009, 45, 125.
(d) P. J. Chmielewski, J. Maciolek, L. Szterenberg,
Eur. J. Org. Chem., 2009, 3930. (e) D. K. Singh, M.
Nath, Beil. J. Org. Chem., 2015, 11, 1434. (f) G.
Battogtokh, Y. T. Ko, J. Mater. Chem. B, 2015, 3,
9349.
29. (a) G. W. Wheland, J. Am. Chem. Soc., 1941, 63, 2025.
(b) J. L. Franklin, J. Am. Chem. Soc., 1950, 72, 4278. (c)
G. W. Wheland, “Resonance in Organic Chemistry”,
John Wiley & Sons: New York, NY, 1955, 830 pp. (d)
Resonance energies of 36 kcal/mol for benzene, 28
kcal/mol for thiophene, and 83.5 kcal/mol for anthracene
are generally employed for discussion. According to
these empirical and/or theoretical estimates, the central
Phen moiety in anthracene is kinetically ready for taking
part in !-electronic conjugation for extension with an
external !-electronic system just by losing 11.5 kcal/mol
or so at least. Then, the extension efficiency in
!-electronic conjugation over the molecule should be
achieved thermodynamically, depending on the energy
gain by reformation of the electronic structure between
the components OEP, SPC, and LB, through the
diacetylene linkage.
11

Graphical Abstract
<Title> Cooperative Effect of Spacer and Lewis Base on Highly Reversible Spectral Changes of The
Octaethylporphyrin Chromatic System in Sensitivity, Stability, and Visibility to Trifluoroacetic Acid
<Authors' names> H. Kempe, J. Yamamoto, M. Ishida, N. Takahashi, J. Yoshino, N. Hayashi, H. Higuchi*
<Summary> The [octaethylporphyrin]-[spacer]-[Lewis base] chromatic system (OEP-SPC-LB) was conclusively studied, in which a
trigger-like interaction of the terminal LB with trifluoroacetic acid (TFA) dramatically affects the inherent electronic properties of
OEP. The structural elements for molecular design were proposed in order to improve their reversible spectral changes between
neutral and acidic media in terms of sensitivity, stability, and visibility to TFA.
<Diagram>
C6H13
S
Spacer:
S
N
N
N
N
[ Spacer ]
[ Lewis base ]
Ni
C6H13
NMe2
NMe2
Lewis base:
N
NMe2
OEP-SPC-LB
12