Optically Active Phenylethene Dimers Based on Planar Chiral Tetrasubstituted [2.2]Paracyclophane

Article abstract of DOI:10.1002/chem.201605598

Optically active phenylethene dimers based on a planar chiral 4,7,12,15-tetrasubstituted [2.2]paracyclophane were synthesized. We succeeded in controlling the molecular motion by binding luminophores in close proximity with the [2.2]paracyclophane scaffol

Full text of DOI:10.1002/chem.201605598

A Journal of
Accepted Article
Title: Optically Active Phenylethene Dimers Based on Planar Chiral
Tetrasubstituted [2.2]Paracyclophane
Authors: Masayuki Gon, Yasuhiro Morisaki, and Yoshiki Chujo
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Chemistry - A European Journal
Optically Active Phenylethene Dimers Based on
Planar Chiral Tetrasubstituted [2.2]Paracyclophane
Masayuki Gon[a], Yasuhiro Morisaki*,[a],[b], and Yoshiki Chujo*,[a]
[a] Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Nishikyo-ku, Katsura, Kyoto 615-8510, Japan.
[b]
Present address: School of Science and Technology, Kwansei Gakuin University, 2-1
Gakuen, Sanda, Hyogo 669-1337 Japan.
E-mail: ymo@kwansei.ac.jp or chujo@chujo.synchem.kyoto-u.ac.jp
Keywords: chirality; conjugation; aggregation-induced emission; luminescence;
paracyclophanes
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Abstract
Optically active phenylethene dimers based on a planar chiral 4,7,12,15-
tetrasubstituted [2.2]paracyclophane were synthesized. We succeeded in controlling the
molecular motion by binding luminophores in close proximity with the
[2.2]paracyclophane scaffold. For example, aggregation-induced emission (AIE)-active
luminophores were converted to show intense photoluminescence (PL) even in a diluted
solution at room temperature and the resulting compound worked as a single-molecule
thermo-responsible material around room temperature. Because of the AIE-active unit,
the molecular motion could be easily activated by heating, leading to variable and
reversible PL intensity. Furthermore, the π-conjugated systems with the planar chirality
of 4,7,12,15-tetrasubstituted [2.2]paracyclophane provided excellent characteristics on
circular dichroism (CD) and circularly polarized luminescence (CPL). The obtained
dimers showed high CPL performances both in a diluted solution and in an aggregation
state. We succeeded in proving that the simple molecular designs composed of only
carbon and hydrogen atoms can create versatile optical functionalities.
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Introduction
The establishment of molecular design for controlling luminescent properties in π-
conjugated systems is of much importance for the applications not only to improve
performances of organic opto-electronic devices[1] but also to produce optical sensors.[2]
In the most of organic luminescent molecules, strong emission can be observed only in a
diluted solution, and weak or no emission in an aggregation state. This behavior is called
aggregation-caused quenching (ACQ).[3] Especially, in planar molecules, ACQ is
critically induced by strong intermolecular π–π interaction which promotes radiation-less
deactivation via exciton delocalization or excimer formation.[4] In contrast, recent reports
presented another class of compounds which exhibits the opposite luminescent
characteristics. Aggregation-induced emission (AIE)-active molecules show subtle
emission in the solution state, whereas bright emission can be observed in the aggregation
state. It has been proposed that radiation-less deactivation processes should be caused by
vigorous intramolecular motion in the solution state. By suppressing the molecular
motion in the aggregation state, strong emission can be recovered, leading to significant
solid-state emissions.[5] Because of versatility of this switching properties, a wide variety
of optical sensors have been developed.[6]
A large number of stimuli-responsive materials based on AIE behaviors have been
accomplished.[5e] The target-selective emission enhancements can be achieved by the
immobilization of the movable units in AIE-active molecules with covalent or non-
covalent bonds triggered by the target recognition.[7] Additionally, AIE properties were
also varied corresponded to drastic environmental changes such as freezing of matrices,[8]
polarity alteration[9] and addition of external forces.[10] These systems were applicable for
sensitive environmental sensors. Although various methodologies have been established
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so far, there are much room to explore precise control of molecular stacking and reflect
external stimuli in the degree of stacking as optical property changes. Our target is to
develop the single molecular system involving the stacking unit with luminescent
property and to realize the stimuli-responsive materials toward environmental factors.
4,7,12,15-Tetrasubstituted [2.2]paracyclophane framework[11] makes it realized to
achieve controlling the orientation and the number of stacking molecules. In addition, the
behavior was easily detected by the optical and chiroptical properties because the [2.2]
paracyclophane scaffold can arrange two luminophores in close proximity at the chiral
position without losing the PL performance.[12] Chiroptical properties, such as CD and
CPL spectra measurements, provide detail information about the molecular conformation
and intermolecular interaction in the ground state and in the excited state, respectively.[13]
Exploring the system is important not for understanding interaction of π-conjugated
molecules but also for producing functional materials, for example, high-performance
CPL ones or stimuli-responsive ones. CPL is the phenomenon that chiral compound emits
circularly polarized light and it is available for optically active light. In these days, CPL
has received much attention for the potential application to a light source of 3D display,
biochemistry, chirality induction in the field of organic synthesis and optical cryptography.
For those reasons, we selected the optically active [2.2]paracyclophane framework and
investigated the behaviors of ACQ and AIE monomers and dimers both in the dilute
solution state and in the aggregation state.
Herein, we synthesized the mono and diphenylethene-derivative monomers (MPh1
and MPh2) and dimers (DPh1 and DPh2) based on a planar chiral 4,7,12,15-
tetrasubstituted [2.2]paracyclophane (Figure 1). MPh1 includes a scaffold for exhibiting
ACQ property, while MPh2 possesses a framework for showing AIE property.14 By
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connecting two MPh1 molecules to form the [2.2]paracyclophane framework, the
resulting DPh1 provided strong emission in the diluted solution and weak emission in the
aggregation state, which was the same property of MPh1. In contrast, the DPh2 showed
strong emission even in the diluted solution and moderate emission in the aggregation
state. This result means that the stacking formation with MPh2 induced distinct different
optical properties from the single molecular unit. Furthermore, it was demonstrated that
DPh2 showed thermo-responsive photoluminescence (PL) changes around room
temperature in the diluted solution. Moreover, because of planar chirality of the dimers,
DPh1 and DPh2 presented high performance CPL profiles in diluted solutions and in the
aggregation state. From these results, it can be expected that the tetrasubstituted
[2.2]paracyclophane framework is promised to be a fundamental molecular unit with the
simple composition of the only carbon and hydrogen atoms for receiving stimuli-
responsive material as well as optically active materials.
Figure 1
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Synthesis
The optical resolution of planar chiral 4,7,12,15-tetrasubstituted [2.2]paracyclophane
was carried out using the diastereomer method that we previously developed, and the
obtained enantiopure compounds were converted to the corresponding (Sp)- and (Rp)-
4,7,12-tribromo-15-(trifluoromethanesulfonate)[2.2]paracyclophanes ((Sp)-CpOTf, (Rp)-
CpOTf).[12d] The synthetic routes to the target optically active cyclic compounds are
shown in Schemes 1 and 2. According to the previous study on the syntheses of DPh1
and MPh1,[15] we modified the synthetic route to obtain optically active dimer
compounds. A bromide of compound 1[16] was converted to a boronate ester to obtain
compound 2 in 97% isolated yield. Compound 2 was readily used in the Suzuki−Miyaura
coupling[17] (Scheme 1). Scheme 2 shows the synthesis of the target planar chiral dimers
DPh1 and DPh2. In this scheme, only the reactions of the (Sp)-isomers are shown; the
(Rp)-isomers were synthesized under identical conditions with (Rp)-CpOTf.
Suzuki−Miyaura coupling of (Sp)-CpOTf was carried out with trans-2-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)styrene 3 in the catalytic system of Pd2(dba)3/PPh3
using CsCO3 as a base to afford (Sp)-DPh1 in 54% isolated yield. Using the same
procedure, (Sp)-DPh2 was also prepared in 67% isolated yield. In the case of (Sp)-DPh2,
unreacted OTf groups were converted to OH groups to remove byproducts by silica gel
column chromatography. The details are shown in the Supporting Information. Scheme 3
shows the syntheses of the monomeric model compounds, MPh1 and MPh2, which are
the half units of the dimers, DPh1 and DPh2, respectively. As shown in Scheme 3, the
same procedure as Scheme 1 was available for MPh1 and MPh2, and the isolated yields
of these molecules were 74% and 46%, respectively. The structures of all new compounds
1
13
in this study were confirmed by H and C NMR spectroscopies, high-resolution mass
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spectrometry (HRMS), and elemental analysis. The detailed synthetic procedures and
NMR spectra are shown in the Supporting Information.
Schemes 1−3
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Results and Discussion
Optical Properties
The optical properties of both enantiomers of π-conjugated dimers, DPh1 and DPh2
as well as their monomeric model compounds MPh1 and MPh2 were evaluated (Table
1). Figure 2 shows the UV–vis absorption spectra of the compounds in diluted solutions
(1,4-dioxane, 1.0 × 10−5 M) and the aggregation state produced in the poor solvent system
(1,4-dioxane/H2O = 1/99 v/v, 1.0 × 10−5 M). Maximum values of molar extinction
coefficient of DPh1 and MPh1 in diluted solutions were larger than those in the
aggregation state. In addition, the edges in the absorption band were observed in the red-
shifted wavelength region in the aggregation state. It is likely that intermolecular
interaction should occur in the aggregation state. In the aggregation state of MPh1, the
shoulder peak was observed at around 400 nm which was longer than the peak top
wavelength of the dimer, DPh1, in the dilute solution state. Two reasons were probable
for the explanation of the phenomenon. One is the difference of stacking formation
between DPh1 in the dilution state and MPh1 in the aggregation state. MPh1 could form
face-to-face stacking whereas DPh1 formed X-shape stacking and the former interaction
was stronger than the latter one. The other is the number of the interacted molecules. In
the aggregation state of MPh1, two or more molecules could interact each other.
Conversely, from the comparison with DPh2 and MPh2, smaller change of maximum
values of molar extinction coefficient was obtained than those with DPh1 and MPh1. In
the DPh2 and MPh2 systems, intermolecular interaction could be disturbed because of
steric hindrance. The peak top wavelengths of absorption bands of DPh1 (395 nm) and
DPh2 (403 nm) were red-shifted in comparison to those of the monomers MPh1 (353
nm) and MPh2 (337 nm), respectively. Through-space conjugation via the
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[2.2]paracyclophane framework should be responsible for the red-shifts of the absorption
bands in the dimers.[18] The peak top wavelength of MPh2 was shorter than that of MPh1
although MPh2 possesses larger numbers of the phenyl rings than those in MPh1. It is
suggested that structural distortion could be induced in MPh2 by steric hindrance,
resulting in the restriction of conjugation length. However, peak top wavelength of DPh2
was observed in the longer wavelength region than that of DPh1. It is proposed that the
molecular planarity could be improved by the dimerization via the [2.2]paracyclophane
framework. Those data imply the existence of the restriction of molecular motion.
Table 1 and Figure 2
Figure 3 shows the PL spectra of the compounds in the diluted solution (1,4-dioxane,
1.0 × 10−5 M) and the aggregation state (1,4-dioxane/H2O = 1/99 v/v, 1.0 × 10−5 M). ACQ
was clearly observed from DPh1 (Φlum = 0.78 in diluted solution, Φlum = 0.03 in
aggregation state) and MPh1 (Φlum = 0.87 in diluted solution, Φlum = 0.13 in aggregation
state). Intermolecular interaction should occur in the planar conformations. Interestingly,
MPh2 showed AIE property (Φlum = 0.04 in diluted solution, Φlum = 0.56 in aggregation
state), however DPh2 provided good PL properties in both solution and aggregation states
(Φlum = 0.58 in diluted solution, Φlum = 0.24 in aggregation state). To comprehend unique
optical properties of MPh2 and DPh2, detailed analyses were executed.
Figure 3
In the most of AIE-active molecules, the degree of molecular motion in the excited
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state plays a significant role in AIE properties. In order to confirm the effect of molecular
motion, kinetic information was gathered from the calculations of radiative (kr) and non-
radiative rate constants (knr) with PL lifetime measurements (Table 1 and Figure S11). In
diluted solutions, the krs of DPh2 and MPh2 were almost same (kr = 2.2 × 108 for DPh2,
2.1 × 108 for MPh2), whereas the knr of DPh2 was much smaller than that of MPh2 (knr
= 1.6 × 108 for DPh2, 5.1 × 109 for MPh2). These data clearly indicate that intramolecular
motion should occur in MPh2. In addition, the rigid and stable [2.2]paracyclophane
framework suppressed molecular motion in the excited state, leading to smaller knr than
that of MPh2. In the relationship of the knrs of DPh1 (knr = 6.7 × 107) and MPh1 (knr =
9.3 × 107), the same tendency was observed. In summary, DPh2 should intrinsically have
luminescent properties both in the solution and aggregation states. However, because of
molecular planarity as suggested in the UV–vis absorption spectrum, some degree of
ACQ was induced via the intermolecular π–π interaction in the aggregation state.
Therefore, the moderate level of emission can be observed. The knr of DPh1 was smaller
than that of DPh2 because the highly planar structure of DPh1 made efficient extension
of π-conjugated system and that contributed to the rigid conformation. In the PL spectra,
the wavelength of the peak top of MPh2 was shorter than that of MPh1 in spite of the
fact that the opposite result was obtained in the UV–vis absorption spectra. Considering
that the PL spectrum of MPh1 exhibited vibrational structure whereas that of MPh2 did
not show it, in the case of MPh2, structure relaxation occurred in the excited state, which
led to a red-shifted PL spectrum.
Variable Temperature PL Measurement
Variable temperature UV–vis absorption and PL measurements were carried out to
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obtain further information on the suppression of the molecular motion by the
[2.2]paracyclophane framework. These spectra were obtained in the diluted toluene
solution (1.0 × 10−5 M for absorption and 1.0 × 10−6 M for PL measurements) at 20, 40,
60 and 80 °C. Relative PL quantum efficiencies were calculated by using the absolute PL
quantum efficiency in 1,4-dioxane at 25 °C as a standard (Table 2). In the UV–vis
absorption spectra (Figures 4A and 4B), by increasing the temperature, the molar
extinction coefficients of DPh1 and DPh2 decreased, and the wavelengths of absorption
maxima were blue-shifted. The effective conjugation length should be shortened by the
molecular motion of the phenyl rings. In the PL spectra, the intensity of DPh2 drastically
decreased by increasing the temperature (Figures 4C and 4D). The PL quantum
efficiencies of DPh1 and DPh2 decreased 9% and 43% by increasing the temperature
from 20 °C to 80 °C, respectively and they were recovered by cooling. These results
represent that the molecular motion of the phenyl rings in DPh2 was suppressed at room
temperature. By increasing the solution temperature, the molecular motion should be
activated, resulting in acceleration of non-radiative deactivation. Taking advantage of the
sensitivity of AIE-active molecules and rigidity of [2.2]paracyclophane frameworks, we
successfully synthesized the single-molecule thermo-responsive material. Although
several thermo-responsive systems with AIE-active molecule were reported, most of all
were constructed based on a sol-gel transition or a composite system.[19] Three-
dimensionally binding AIE-active molecules in close proximity with covalent bonds is a
new strategy and the results are expected to contribute to a development of single-
molecule optical sensors.
Figure 4 and Table 2
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Dispersion of the Dimers in Polystyrene Film
To investigate the effect of molecular motion on ACQ, DPh1 and DPh2 were dispersed
in polystyrene (Mn = 80,000, PDI = 2.6) films, and their optical properties were monitored.
The films including 1, 2, 5, 10, 20, 40, 60, 80 and 100 wt% of DPh1 and DPh2 in
polystyrene were prepared with a spin-coat method from 40 μL CHCl3 solution (1.0 ×
10−3 M of DPh1 and DPh2 in polystyrene). The results are summarized in Figure S12
and Table S1. DPh1 and DPh2 exhibited high absolute PL quantum efficiencies in the 1
wt% films (Φlum = 0.86 and 0.80, respectively). The Φlum value of the 1 wt% film of DPh2
was much higher than that in the diluted solution (Φlum = 0.58). This result indicates that
the molecular motion of DPh2 was largely stopped in the film and that was active in the
dilute solution. Conversely, the molecular motion of DPh1 was highly restricted even in
the dilute solution state because similar Φlums were obtained both in the dilute solution
state (Φlum = 0.79) and in the 1 wt% film state. The Φlum of DPh1 dropped rapidly from
2 wt% to 20 wt% films (Φlum = 0.79 for 2 wt%, 0.55 for 5 wt%, 0.42 for 10 wt%, 0.26 for
20 wt%), and the 40, 60, 80 and 100 wt% films showed low Φlum values (Φlum < 0.1). It
is likely that ACQ should occur in these films. On the other hand, increasing the rate of
DPh2 in polystyrene films, the decrease of the Φlum was moderately. High Φlum was kept
in the 2 wt% film (Φlum = 0.82) and it decreased from the 5 wt% film (Φlum = 0.69). Finally,
the Φlum value reached 0.27 in the 100 wt% film, which was pure DPh2. This value was
almost identical to the aggregate of DPh2 (Φlum = 0.24). Therefore, it was suggested that
the decrease of Φlum in the aggregate of DPh2 was caused by ACQ. Although decrease of
Φlum occurred, the obtained DPh2 films provided good PL quantum efficiencies even in
the condensed state and those results can be advantage for obtaining high brightness films.
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Molecular Models
In DPh2, experimental optical data strongly suggested the existence of suppression of
the molecular motion between two luminophores stacked at the [2.2]paracyclophane unit.
Further information about the molecular motion was evaluated by density functional
theory (DFT). The structures of MPh2 and DPh2 were optimized at the BLYP/def2-
TZVPP level. Resulting molecular structures are shown in Figure 5. From the molecular
models, it was clearly shown that the optimized structure of MPh2 was highly twisted,
whereas that of DPh2 was relatively planar because of the intramolecular stacking. The
two luminophores were located at the distance of 4–6 Å, which was sufficient to inhibit
the free rotation. The restriction of the molecular motion was corresponded to the high
Φlum value of DPh2 in the diluted solution. However, in the aggregation state, the ACQ
should occur. The highly-twisted structure of MPh2 should be favorable for maintaining
molecular motions in the solution and avoiding ACQ in the aggregation, leading to the
AIE behavior. Thus, it is summarized that the stacking at the [2.2]paracyclophane unit
should contribute to enhancing molecular planarity even in the presence of multiple
hindered groups. Then, unique emission behaviors were obtained.
Figure 5
Chiroptical Properties
Finally, the chiroptical properties of the ground and excited states of DPh1 and DPh2
were investigated by CD and CPL spectroscopies, respectively. Chiroptical data such as
CD and CPL dissymmetry factor[20] (gabs and glum, respectively) are summarized in Table
3. Figure 6 shows the CD and absorption spectra of both enantiomers of DPh1 and DPh2
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in the diluted solution (1,4-dioxane, 1.0 × 10−5 M) and in the aggregation state (1,4-
dioxane/H2O = 1/99 v/v, 1.0 × 10−5 M). From both enantiomer solutions, mirror image
Cotton effects were observed clearly in the CD spectra. In the diluted solution, the gabs
values of the first Cotton effect were estimated to be +3.5 × 10−3 for (Sp)-DPh1 and +1.0
× 10−3 for (Sp)-DPh2, respectively. In the aggregation state, the gabs values of the first
Cotton effect were estimated to be +3.0 × 10−3 for (Sp)-DPh1 and +0.87 × 10−3 for (Sp)-
DPh2, respectively. When these compounds formed the aggregates, the gabs values for
(Sp)- and (Rp)-DPh1 decreased and the pattern of Cotton effect was red-shifted in all
regions, whereas those for (Sp)- and (Rp)-DPh2 remained in almost all regions. This result
also indicates stronger intermolecular interaction of DPh1 and weaker intermolecular
interaction of DPh2 because the structure of DPh1 was planar and that of DPh2 was
twisted.
The CPL spectra of both enantiomers of DPh1 and DPh2 in the diluted solution (1,4-
dioxane, 1.0 × 10−5 M) and in the aggregation state (1,4-dioxane/H2O = 1/99 v/v, 1.0 ×
10−5 M) are shown in Figure 7. Mirror image CPL spectra were obtained from the
enantiomers. The glum values were estimated to be +3.7 × 10−3 for (Sp)-DPh1 and +0.73
× 10−3 for (Sp)-DPh2 in the diluted solution, and +4.3 × 10−3 for (Sp)-DPh1 and +0.90 ×
10−3 for (Sp)-DPh2 in the aggregation state. In the aggregation systems of (Sp)- and (Rp)-
DPh1, CPL peak tops were red-shifted, and the glum values increased because of
intermolecular interaction in the excited state. On the other hand, small changes were
observed in the CPL peak top and glum values of (Sp)-DPh2 due to weak intermolecular
interaction in the excited state. In the diluted solution, DPh1 exhibited excellent CPL
profiles (εmax = 61,000 M−1cm−1, Φlum = 0.78 and glum = +3.7 × 10−3 for (Sp)-DPh1, εmax
:
maximum of molar extinction coefficient) in comparison to the recent reported CPL
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compounds.14a On the other hand, in the aggregation state, DPh2 showed good CPL
profiles (εmax = 31,000 M−1cm−1, Φlum = 0.24 and glum = +0.90 × 10−3 for (Sp)-DPh2).
Table 3 and Figures 6 and 7
Conclusions
Optically active phenylethene dimers, DPh1 and DPh2, were synthesized with a planar
chiral 4,7,12,15-tetrasubstituted [2.2]paracyclophane. From the series of experimental
data and theoretical calculation, it is strongly suggested that molecular motion can be
efficiently regulated by stacking with two luminophores in close proximity by the
[2.2]paracyclophane unit even in the presence of multiple steric hindered groups. As a
result, unique luminescent behaviors were monitored during phase transition. By
increasing the temperature, PL intensity of DPh2 decreased sensitively. Subsequently, the
intensity was recovered by cooling. Moreover, DPh1 and DPh2 showed good chiroptical
properties and the dissymmetry factors on the order of approximately 10−3. DPh1 had
excellent CPL profiles in the diluted solution, and DPh2 had good CPL profiles in the
aggregation state. Those effects are originated from the planar chiral, rigid and stable
4,7,12,15-tetrasubstituted[2.2]paracyclophane scaffold. Since these results are realized
only with carbon and hydrogen atoms, the [2.2]paracyclophane unit could be a versatile
building block for constructing advanced optical materials with multiple functions.
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Acknowledgements
This work was supported by Grant-in-Aid for Young Scientists (A) (no. 24685018) from
the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.
M.G. appreciates Research Fellowships (no. 14J02514) from the Japan Society for the
Promotion of Science for Young Scientists. The authors are grateful to Professor Kazuo
Akagi and Dr. Kazuyoshi Watanabe (Department of Polymer Chemistry, Graduate School
of Engineering, Kyoto University) for CPL data analysis and valuable discussions.
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[20]CD dissymmetry factor is defined as gabs = 2Δε/ε, where Δε indicates differences of
absorbance between left and right handed circularly polarized light. CPL
dissymmetry factor is defined as glum = 2(Ileft − Iright)/(Ileft + Iright), where Ileft and Iright
indicate luminescence intensities of left and right handed CPL, respectively.
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Scheme 1. Synthesis of compound 2.
Scheme 2. Synthesis of planar chiral dimers (Sp)-DPh1 and DPh2.
Scheme 3. Synthesis of model compounds MPh1 and MPh2.
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Figure 1. Structures of MPh1, DPh1, MPh2 and DPh2.
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Table 1. Optical properties of the compounds.
f
λabsc/ nm
λlumd/ nm
τe/ ns
3.28
χ2
Φlum
krg/ s−1
knr g/ s−1
DPh1a
DPh1-aggb
MPh1a
395
394
353
344
455
1.02
0.78
0.03
0.87
0.13
2.4×108
6.7×107
0.24 (80.9%)
1.59 (19.1%)
1.40
470
401, 424
443
1.58
1.09
1.44
1.3×108 h
6.2×108
4.0×109 h
9.3×107
0.24 (80.6%)
0.88 (19.4%)
2.60
MPh1-aggb
5.4×108 h
3.6×109 h
DPh2a
DPh2-aggb
MPh2a
403
403
337
341
494
503
468
473
1.17
1.13
1.19
1.07
0.58
0.24
0.04
0.56
2.2×108
1.7×108
2.1×108
2.4×108
1.6×108
5.4×108
5.1×109
1.9×108
1.40
0.19
MPh2-aggb
2.30
−5
−6
a
b
c
d
In 1,4-dioxane. In 1,4-dioxane/H2O = 1/99 v/v. 1.0 × 10 M. 1.0 × 10 M,
e
f
excited at absorption maxima. Emission lifetime at λlum. Absolute PL quantum
efficiency. g kr = Φlum/τ, knr = (1 − Φlum)/τ. h Calculated by using the major component.
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Figure 2. UV–vis absorption spectra in 1,4-dioxane (solid line) and 1,4-dioxane/H2O
= 1/99 v/v (dotted line) (1.0 × 10−5 M); (A) DPh1 and MPh1; (B) DPh2 and MPh2.
Figure 3. PL spectra in 1,4-dioxane (solid line) and 1,4-dioxane/H2O = 1/99 v/v
(dotted line) (1.0 × 10−5 M); (A) DPh1 and MPh1; (B) DPh2 and MPh2.
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Figure 4. UV–vis and PL variable temperature spectra in toluene (1.0 × 10−5 M for
UV–vis and 1.0 × 10−6 M for PL, excited at absorption maximum) at 20 °C, 40 °C,
60 °C, 80 °C; (A) UV–vis spectra of DPh1; (B) UV–vis spectra of DPh2; PL spectra
of DPh1; PL spectra of DPh2.
Table 2. Relative PL quantum efficienciesa,b.
20 °C
0.70
40 °C
0.68
60 °C
0.65
80 °C
0.63
DPh1
DPh2
0.51
0.44
0.39
0.29
−6
a
b
In toluene (1.0 × 10 M excited at absorption maximum). Relative PL quantum
efficiencies were calculated from absolute PL quantum efficiencies of DPh1 and DPh2
in 1,4-dioxane (Table 1), respectively.
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Figure 5. Molecular models of MPh2 and DPh2. The structure was optimized by
DFT at BLYP/def2-TZVPP levels.
Table 3. Chiroptical properties: Spectroscopic data of (Sp)-isomers.
gabsa/ 10−3
+3.5
glumb/ 10−3
+3.7
(Sp)-DPh1
(Sp)-DPh1-agg
(Sp)-DPh2
+3.0
+4.3
+1.0
+0.73
+0.90
(Sp)-DPh2-agg
+0.87
a gabs = 2Δε/ε, where Δε indicates differences of absorbance between left and right
handed circularly polarized light, respectively. The gabs value of the first peak top
b
was estimated. glum = 2(Ileft − Iright)/(Ileft + Iright), where Ileft and Iright indicate
luminescence intensities of left- and right- handed CPL, respectively. The average
g
lum value of the around peak top was estimated.
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Figure 6. CD, gabs, and absorption spectra in 1,4-dioxane (solid line) and in 1,4-
dioxane/H2O = 1/99 v/v (dotted line) (1.0 × 10−5 M); (A) (Sp)- and (Rp)-DPh1; (B)
(Sp)- and (Rp)-DPh2.
Figure 7. CPL, glum, and PL spectra in 1,4-dioxane (solid line) and 1,4-dioxane/H2O
= 1/99 v/v (dotted line) (1.0 × 10−5 M); (A) (Sp)- and (Rp)-DPh1; (B) (Sp)- and (Rp)-
DPh2. Excitation wavelength: 350 nm.
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Table-of-Contents
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