Additional insights into luminescence process of polycyclic aromatic hydrocarbons with carbonyl groups: Photophysical properties of secondary N -alkyl and tertiary N, N -dialkyl carboxamides of naphthalene, anthracene, and pyrene

Article abstract of DOI:10.1021/jo300317r

Here we report the substitution effects of N-alkyl and N,N-dialkyl carboxamide groups on the fluorescence properties of polycyclic aromatic hydrocarbon chromophores, so as to control their fluorescence properties. The fluorescence properties of compounds obtained using solvents with different polarities showed very little change, indicating that the modified compounds do not form charge transfer states. TD-DFT calculations and measurements performed at low temperature (78 K) and in viscous solvents revealed that the N-alkyl and N,N-dialkyl carboxamide groups tend to reduce the contributions from intersystem crossing and increase those from internal conversion. Considering that the fluorescence mechanism of low-fluorescence carbonyl compounds such as aldehyde and ketone is dominated by intersystem crossing and that of high-luminescence carbonyl compounds such as carboxylic acid and ester is dominated by a radiative process, it can be said that the photophysical process of N-alkyl and N,N-dialkyl carboxamides is novel. In addition, the calculation results for excited states indicated that such contributions can be controlled by selecting the appropriate polycyclic aromatic hydrocarbon or amide structure, in addition to solvent viscosity and temperature.

Full text of DOI:10.1021/jo300317r

Article
pubs.acs.org/joc
Additional Insights into Luminescence Process of Polycyclic Aromatic
Hydrocarbons with Carbonyl Groups: Photophysical Properties of
Secondary N-Alkyl and Tertiary N,N-Dialkyl Carboxamides of
Naphthalene, Anthracene, and Pyrene
Yosuke Niko,† Yuki Hiroshige,† Susumu Kawauchi,† and Gen-ichi Konishi*,†,‡
†Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Tokyo 152-8552, Japan
‡PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan
S
* Supporting Information
ABSTRACT: Here we report the substitution effects of N-alkyl and N,N-
dialkyl carboxamide groups on the fluorescence properties of polycyclic
aromatic hydrocarbon chromophores, so as to control their fluorescence
properties. The fluorescence properties of compounds obtained using
solvents with different polarities showed very little change, indicating that
the modified compounds do not form charge transfer states. TD-DFT
calculations and measurements performed at low temperature (78 K) and
in viscous solvents revealed that the N-alkyl and N,N-dialkyl carboxamide
groups tend to reduce the contributions from intersystem crossing and
increase those from internal conversion. Considering that the fluorescence
mechanism of low-fluorescence carbonyl compounds such as aldehyde and
ketone is dominated by intersystem crossing and that of high-luminescence carbonyl compounds such as carboxylic acid and
ester is dominated by a radiative process, it can be said that the photophysical process of N-alkyl and N,N-dialkyl carboxamides is
novel. In addition, the calculation results for excited states indicated that such contributions can be controlled by selecting the
appropriate polycyclic aromatic hydrocarbon or amide structure, in addition to solvent viscosity and temperature.
control their emission properties is extremely valuable for the
molecular design of a wide variety of materials. As there are
many potential substituents that have not yet been studied,
there is a great deal of knowledge to be gained that may lead to
the acquisition of a new design guide for new materials in this
field.
Most carbonyl substituents have well-known characteristic
effects on the emission properties of chromophores. The
photophysical processes of chromophores modified by such
substituents have been examined in detail. For instance, dyes
directly bearing aldehyde or ketone groups fluoresce weakly
because of intersystem crossing, as rationalized by the El-Sayed
rule.60−66 In addition, luminophores such as benzamide
modified by anilide groups exhibit low levels of luminescence
because they form twisted intramolecular charge transfer
(TICT) states.67−70 In contrast, chromophores possessing a
carboxylic acid or its ester groups exhibit strong fluores-
cence.71−79 Many of these carbonyl compounds have already
been used in environmentally responsive probes or sensi-
tizers.70,74−76
INTRODUCTION
■
For decades, organic emission dyes have attracted considerable
attention owing to their potential application as molecular
electronic materials in organic electroluminescent and photo-
luminescent devices ,as well as their use in organic field effect
transistors, liquid crystal laser dyes, and fluorescence probes
and sensors. A large number of organic dyes based on
luminescent polycyclic aromatic hydrocarbon structures such as
naphthalene,1 anthracene,2−6 pyrene,7−19 fluorene,20−25 and
perylene26−28 have been developed. Organic dye molecules
have specifically been designed for many purposes, including
the enhancement of emission efficiency, control of emission
color, and improvement of solubility in organic solvents or
other matrices. The general strategy for the development of
novel dyes relies on the introduction of various substituents to
the target molecule. In particular, enhancement of emission
properties or control of emission color has been achieved
through the expansion of π-conjugation induced by, e.g., phenyl
or ethynyl groups,29−33 introduction of σ−π conjugation
induced by silyl groups,34−37 and the use of charge transfer
emission induced by highly polarized groups.38−45 These
chromophores can be introduced into structures that are
suitable for emissions, such as polymers in the main or side
chain,46−50 spiro skeletons,51−55 and rod- or star-shaped
chromophores.56−59 Thus, understanding the manner in
which substituents affect chromophores and finding ways to
Although carbonyl compounds have been widely inves-
tigated, research on the synthesis and photoluminescence
properties of N-alkyl or N,N-dialkyl aromatic carboxamide
Received: February 21, 2012
Published: March 29, 2012
© 2012 American Chemical Society
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compounds is surprisingly limited, except the studies by our
group on the environmentally responsive emission83,84 or other
groups on the use as fluorescence probes80−82 of pyrene-1-
carboxamides and those by Sturgeon and Schulman group and
Werner and Rodgers group on N,N-diethylanthracene-9-
carboxamide.85,86 None of these studies investigated the effects
of N-alkyl or N,N-dialkyl carboxamide groups on chromo-
phores in much detail, assessing only a small number of
compounds or collecting only partial experimental data. The
photophysical properties of most aromatic carbonyl com-
pounds have been generally rationalized by intersystem
crossing, internal conversion, and charge transfer. Our previous
studies have indicated that the photophysical properties of N-
alkyl and N,N-dialkyl carboxamides are strongly dependent on
the contribution of internal conversion;83 however, little was
investigated in terms of the other two processes. Each of these
processes has recently been recognized as considerably
important because of their utility in electronic devices.87−89
Therefore, it is important to understand not only the
fluorescence properties of a material but also the photophysical
processes that can be induced by fundamental compounds such
as N-alkyl and N,N-dialkyl carboxamides.
synthesized several N-alkyl and N,N-dialkyl polycyclic aromatic
carboxamides based on naphthalene, anthracene, and pyrene as
target polycyclic aromatic hydrocarbon dyes. We then
examined their photoluminescence properties in detail to
understand how these substituent groups affect the photo-
physical properties of such chromophores. The main
advantages of N-alkyl and N,N-dialkyl carboxamide groups
are their convenient synthesis and flexibility in molecular
design, which make them attractive candidates for controlling
the fluorescence properties of dyes and their subsequent
application to the production of functional materials.
Naphthalene, anthracene, and pyrene are used for the
evaluation of substituent effects, as they are very simple
polycyclic aromatic hydrocarbons and their photophysical
processes have been well characterized.90−93 Moreover, these
polycyclic aromatic hydrocarbons, especially anthracene and
pyrene, are easy to use because they have been employed
widely in the development of emissive materials.
RESULTS AND DISCUSSION
■
Synthesis. Using a previously reported method,83 we
synthesized secondary N-alkyl and tertiary N,N-dialkyl
carboxamide derivatives of naphthalene, anthracene, and
pyrene, designated as Nap 1, Nap 2, Anth 1, Anth 2, Py 1a,
and Py 2a, respectively. Naphthalene, anthracene, and pyrene
were derivatized at the 2, 9, and 1 positions, respectively. Their
chemical structures are shown in Figure 2. With respect to the
pyrene derivatives, we have previously prepared several N-alkyl
and N,N-dialkyl carboxamide (Py 1b, 1c and 2a, 2c) and
demonstrated that the fluorescence behavior of both N-alkyl
type and N,N-dialkyl type pyrene-1-carboxamides did not
depend significantly on changes in the structure of the alkyl
chain in an ethanol solution.83 Therefore, here we have focused
on one derivative per chromophore for both the N-alkyl and
N,N-dialkyl derivatives.
In this study, we demonstrated that polycyclic aromatic
hydrocarbons with N-alkyl or N,N-dialkyl carboxamide groups
show a new photophysical process where internal conversion is
a more competitive process and which is apparently different
from other carbonyl compounds as described in Figure 1. We
Structures and Photophysical Properties. The UV−vis
spectra, fluorescence spectra, absolute fluorescence quantum
yields, and fluorescence lifetimes of N-alkyl and N,N-dialkyl
aromatic carboxamides were measured in deaerated ethanol. In
addition, optimized structures were calculated by the density
functional theory (DFT) method at the ωB97X-D/6-31G(d.p)
level (Figure 1S, Supporting Information). These measure-
ments were performed to examine the photoluminescence
properties and compare the secondary N-alkyl carboxamides
with the tertiary N,N-dialkyl carboxamides. Measurements were
also carried out in other solvents in order to investigate the
changes in the absorption and emission spectra caused by
solvent polarization. The results are shown in Figure 2S, Figure
3S, and Table 1S (Supporting Information).
Figure 1. Relationships between fluorescence quantum yield and
photophysical process in carbonyl compounds. kr, knr: Rate constants
for radiative and non-radiative process, respectively. kISC, kIC, kq[O2]:
Rate constants for intersystem crossing, internal conversion,
quenching by oxygen, respectively.
Figure 2. Chemical structures of N-alkyl and N,N-dialkyl aromatic carboxamides used in this study.
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Naphthalene. As shown in Figure 3, no significant
differences were observed between the UV−vis spectra for
of approximately 26.9° and 43.2° with respect to the
naphthalene rings and carbonyl groups, respectively.
Anthracene. Similar to the naphthalene derivatives, no
significant differences were observed between the absorption
spectra for Anth 1 and Anth 2. In addition, the spectra were
red-shifted relative to unsubstituted anthracene. Anth 1 and
Anth 2 showed fluorescence at similar wavelengths, but the
vibrational structures were somewhat different. As seen in
Table 1, Anth 1 had a fluorescence quantum yield smaller than
that of unsubstituted anthracene but larger than that of Anth 2.
Similar to anthracene carboxylic acid and its ester derivatives,
Anth 1 and Anth 2 showed large dihedral angles of
approximately 64.4° and 82.9° with respect to the anthracene
rings and carbonyl groups, respectively.
Pyrene. In our previous work, the absorption and
fluorescence wavelengths of Py 1a and Py 2a were found to
be similar and red-shifted and the vibrational structures were
found to be same. Furthermore, in the fluorescence spectra of
Py 1a and Py 2a, the well-known “Ham effect”,90 i.e., the clear
vibrational structure seen in the fluorescence spectrum of
unsubstituted pyrene, was lost. Py 1a showed a fluorescence
quantum yield higher than that of pyrene, whereas Py 2a
exhibited a much weaker emission. Optimized structures of Py
1a and Py 2a were found to form dihedral angles of 45.4° and
76.8° with respect to the pyrene rings and carbonyl groups,
respectively.
From these results, we note the following important trends:
(1) Fluorescence quantum yields of N-alkyl carboxamides
were higher than those of N,N-dialkyl carboxamides,
especially for the naphthalene and pyrene derivatives.
(2) The absorption and emission wavelengths of all the
compounds were red-shifted. Simultaneously, the Stokes
shifts of all of the compounds were slightly enlarged.
These trends were observed when other solvents such as
cyclohexane, dichloromethane, and acetonitrile were
used (Figure 2S and Table 1S, Supporting Information).
However, in almost all of the compounds, no clear
relationships between the solvent polarities and Stokes
shifts were observed. From the small slopes of all of the
Lippert−Mataga plots in Supplementary Figure 3S, it was
demonstrated that the changes in the dipole moments in
the ground and excited states were small.95 This means
that these compounds did not accept the charge transfer
states, e.g., via twisted intramolecular charge transfer
(TICT).
Figure 3. UV−vis and fluorescence spectra of N-alkyl and N,N-dialkyl
carboxamides, measured in ethanol (room temperature, λex = λabs).
Nap 1 and Nap 2. As compared to the spectra of unsubstituted
naphthalene, those of substituted naphthalene were red-shifted
and did not retain their clear vibrational structure. The
fluorescence spectra and absolute fluorescence quantum yield
measurements revealed that Nap 1 showed a strong emission
(Φfl = 0.28) around 350 nm and exhibited a rather broad
spectrum. In contrast, Nap 2 exhibited extremely weak
emission (Φfl < 0.01) around 340 nm, with an intensity close
to that of the ethanol Raman signal at around 300 nm. From
the optimized ground-state structures calculated by the DFT
method, Nap 1 and Nap 2 were found to form dihedral angles
Table 1. Photophysical Parameters of N-Alkyl and N,N-Dialkyl Carboxamides in Ethanol
a
b
entry
λabs [nm]
log ε [M−1 cm−1
]
λem [nm]
322, 332, 336
τ [ns]
50.594
Φfl
kr [s−1
]
knr [s−1
]
naphthalene
Nap 1
272
277
274
3.67
3.90
0.14
0.28
0.003
2.8 × 106
3.0 × 107
1.7 × 107
7.8 × 107
341, 354
351
9.19
Nap 2
0.51 (0.17)
1.58 (0.65)
6.70 (0.18)
5.0794
1.54
anthracene
Anth 1
Anth 2
pyrene
Py 1a
372
378
380
330
337
338
3.89
3.94
4.01
4.62
4.49
4.49
378, 400, 423, 449
390, 409, 432
0.26
0.10
0.062
0.39
0.61
0.061
5.1 × 107
6.6 × 107
5.4 × 107
3.5 × 106
2.3 × 107
2.0 × 106
1.5 × 107
5.8 × 108
8.2 × 108
5.4 × 107
1.4 × 107
3.1 × 107
388, 410, 434, 462
373, 379, 384, 389, 393
383, 402, 425
1.15
11394
27.1
Py 2a
377, 387, 397, 419
30.4
a
b
kr: radiative rate constant. kr = Φfl/τ. knr: non-radiative rate constant. knr = (1 − Φfl)/τ.
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Figure 4. Fluorescence spectra of N-alkyl and N,N-dialkyl carboxamides at 298 and 78 K (EPA solvent, λex = λabs).
carboxylic acid or ester groups and, as a result, form rigid
structures. In addition, some compounds are quenched by
another mechanism. For example, it is known that the low level
of fluorescence of anilide-type compounds such as benzanilide
is due to the formation of twisted intramolecular charge transfer
(TICT) states with subsequent quenching by internal
conversion.67−70 Thus, the following hypotheses can be
proposed.
From trends 1 and 2, it is expected that the photophysical
processes of the N-alkyl and N,N-dialkyl aromatic carboxamides
are determined not by the charge transfer state as in benzanilide
but by the contributions of both intersystem crossing and
internal conversion, similar to aromatic aldehyde, ketone, and
carboxylic acid and its ester derivatives. Furthermore, trend 3
suggests that if the deactivations are caused by internal
conversion, the contribution of internal conversion depends
strongly on the dihedral angle between the polycyclic aromatic
rings and carbonyl groups in the ground and excited states.
(3) In the ground states, both N-alkyl and N,N-dialkyl
carboxamides formed large dihedral angles with respect
to the aromatic rings and carbonyl groups, as generally
observed for anilide type compounds96,97 or 9-
substituted anthracene carbonyl compounds.61,62,73,77−79
In general, the fluorescence emission properties of aromatic
carbonyl compounds are explained by contributions from two
deactivation processes. The first is the electronic factor for
intersystem crossing, rationalized by the El-Sayed rule,64−66 and
the second is the Franck−Condon factor for internal
conversion.76 It is known that the low fluorescence efficiencies
of aldehyde and ketone derivatives are due to the former
process.60−63 On the other hand, it is known that carboxylic
acid and ester derivatives of naphthalene, anthracene, and
pyrene are highly emissive. These compounds undergo
intersystem crossing inefficiently and can prevent internal
conversion owing to the planar rigid structures formed in the
excited states.71−79 Such planar structures enable the formation
of hydrogen bonds between the aromatic rings and the
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Solvent Thermal and Viscosity Effect on Photo-
physical Properties. To investigate the photophysical
processes of N-alkyl and N,N-dialkyl aromatic carboxamides
in detail, the dependence of fluorescence on temperature and
solvent viscosity were measured for Nap 1, Nap 2, Anth 1,
Anth 2, Py 1a, and Py 2a. The thermal dependence was
evaluated by measuring the fluorescence spectra and relative
quantum yields at room temperature as well as at low
temperatures (298 and 78 K) using the organic glass solvent
EPA (a mixture of diethyl ether, isopentane, and ethanol).
Furthermore, the relative fluorescence quantum yields were
calculated using the absolute fluorescence quantum yield at 298
K as the standard. The solvent viscosity dependence was
evaluated by measuring the fluorescence spectra, absolute
quantum yields, and fluorescence lifetimes in ethanol, ethylene
glycol, and glycerin solutions. These results are summarized in
Table 2S and Figure 4S (Supporting Information).
triplet near S1.99 Therefore, we also investigated the thermal
dependence of naphthalene, anthracene, and pyrene (Figure 5S,
Supporting Information). In the measurements for unsub-
stituted pyrene and naphthalene, increases in the fluorescence
intensities were observed at 78 K. This occurred because the
intersystem crossing was suppressed by the inefficient internal
conversions from S1 to S0 generally observed for such rigid
hydrocarbons.90 On the other hand, the fluorescence intensity
of unsubstituted anthracene remained almost constant. This
was because, in the photophysical processes of anthracene, the
contribution of internal conversion was originally small, as
noted above, and the energy gap between S1 and T2 was too
small to prevent intersystem crossing, as previously re-
ported.93,100
In the measurements for Py 1a and Py 2a, both compounds,
especially Py 1a, showed high fluorescence levels at 78 K, which
were stronger than those of unsubstituted pyrene. Given that
the rate constants of the internal conversion were almost zero
at 78 K, it is likely that Py 1a and Py 2a possess electronic
structures with inefficient intersystem crossings relative to
unsubstituted pyrene, leading to strong emission at 78 K.
However, at room temperature, Py 2a had extremely low
fluorescence, whereas Py 1a was highly emissive. It was
hypothesized that this is because Py 2a underwent another
competitive deactivation process, internal conversion, which
was due to the N,N-dialkyl carboxamide group.
Similar to the pyrene derivatives, the anthracene derivatives,
Anth 1 and Anth 2, exhibited fluorescence levels stronger than
those of unsubstituted anthracene at 78 K. We interpreted this
to mean that the intersystem crossings of Anth 1 and Anth 2
were less efficient than those of anthracene. Furthermore, it can
be said that the weak emissions of Anth 1 and Anth 2
compared to anthracene at room temperature were the result of
internal conversion because of the new deactivation compo-
nents supplied by the N-alkyl and N,N-dialkyl carboxamide
groups.
In the investigation into the naphthalene derivatives, it was
demonstrated that Nap 1 showed similar behavior as Py 1a,
possessing an electronic structure where the intersystem
crossing was less efficient than for the unsubstituted
naphthalene. Therefore Nap 1 emitted more strongly at both
78 K and room temperature. In contrast, Nap 2 had extremely
low luminescence at both 78 K and room temperature. As
discussed above, because the N-alkyl and N,N-dialkyl
carboxamides may possess new competitive components of
internal conversion, we think that, for Nap 2, the contributions
of both the intersystem crossing and internal conversion were
large.
As shown in Figure 4 and Table 2, the fluorescence
intensities and quantum yields of almost all of the compounds
Table 2. Photophysical Parameters of Naphthalene,
Anthracene, Pyrene, and Their N-Alkyl and N,N-Dialkyl
Carboxamide Derivatives at 298 and 78 K
c
T [K]
λem [nm]
322, 336, 348
Φfl
naphthalene
Nap1
298
78
0.023
0.22
0.12
0.39
0.007
0.08
0.25
0.23
0.086
0.28
0.043
0.34
0.16
0.45
0.69
0.94
0.054
0.66
316, 321, 331, 336, 341, 347
336, 352, 370
298
78
334, 350, 368, 389
330
Nap2
298
78
329, 344, 360
anthracene
Anth 201
Anth 216
pyrene
298
78
377, 399, 422, 448
380, 402, 426, 453
387, 407, 431
298
78
388, 411, 436
298
78
387, 409, 433, 461
388, 394, 411, 436, 465
373, 379, 384, 393
372, 378, 383, 393, 415
382, 401, 424
298
78
Py 1a
298
78
376, 387, 396, 418
376, 387, 397, 419
375, 380, 386, 395, 418
Py 2a
298
78
c
Φfl: fluorescence quantum yields at 78 K were calculated using the
value of absolute fluorescence quantum yield at room temperature
(298 K) as the standard.
dramatically increased at low temperatures. Similarly, the
fluorescence intensities and quantum yields were enhanced
with an increase in the solvent viscosity. Additionally, the non-
radiative rate constant knr decreased with an increase in the
TD-DFT Calculations. Electronic Structure and Singlet
and Triplet Energies of N-Alkyl and N,N-Dialkyl Aromatic
Carboxamides. In order to examine whether quenching by the
electronic factors occurred for intersystem crossing, electronic
structures and energies of singlet and triplet states were
calculated using the time-dependent density functional theory
(TD-DFT) method at the ωB97X-D/6-31G(d,p) level. The
TD-DFT is one of the theories treating for the excited states.
The functional (ωB97X-D), which was different from that used
previously (B3LYP/6-31G(d)),83 is the long-range corrected
one with dispersion effect.
solvent viscosity. knr can be expressed as knr = kISC + kIC
+
kq[O2], where kISC, kIC, and kq[O2] denote the rate constants
for intersystem crossing, internal conversion, and fluorescence
quenching by oxygen, respectively. Considering that all the
samples were deoxygenated, kq[O2] was assumed to be almost
zero. Furthermore, kIC is assumed to be small at a low
temperature or in viscous media.98 Therefore, it is inferred that
the above-mentioned phenomena were the result of the
suppression of internal conversion.
Generally, it is well-known that an intersystem process is
dominated by spin−orbit interactions, as rationalized by the El-
Sayed rule64−66 and the energy gap rule.90 Therefore, we
focused on the nature and excitation energies of the lowest
However, it has been shown that the fluorescence intensity is
enhanced when the intersystem crossing is reduced by the
suppression of the activation energies between S1 and the
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Table 3. Excitation Energy, Oscillator Strength, Main Transition Orbital, and Their Contribution Calculated for Nap 1 and Nap
2 Using TD-DFT (ωB97X-D/6-31G(d,p))
entry
state
T6
excitation energy [eV]
4.53
oscillator strength
-
main transition orbital
contribution
Nap 1
HOMO-5 − LUMO
HOMO-1 − LUMO
HOMO-1 − LUMO+1
HOMO-2 − LUMO
HOMO − LUMO
HOMO − LUMO+1
HOMO-2 − LUMO+1
HOMO − LUMO+1
HOMO-2 − LUMO+1
HOMO-1 − LUMO+1
HOMO − LUMO+1
HOMO-2 − LUMO
HOMO-1 − LUMO
HOMO − LUMO
HOMO − LUMO+1
HOMO − LUMO
HOMO-5 − LUMO
HOMO-3 − LUMO
HOMO − LUMO+4
HOMO − LUMO
HOMO-1 − LUMO
HOMO-4 − LUMO
HOMO − LUMO+2
HOMO − LUMO
HOMO-1 − LUMO
HOMO − LUMO+1
HOMO-7 − LUMO
HOMO − LUMO+1
HOMO − LULMO+4
HOMO − LUMO
0.27
0.18
0.1
S1
4.55
0.018
0.31
0.41
0.23
0.63
0.16
0.42
0.2
T7
T6
4.62
4.58
-
-
Nap 2
0.17
0.18
0.26
0.18
0.35
0.74
0.30
0.22
0.41
0.98
0.88
0.42
0.35
1.0
S1
4.59
0.011
S2
4.73
3.35
0.056
-
Anth 1
Anth 2
Py 1a
T2
S1
3.62
3.71
3.36
0.14
T3
T2
-
-
S1
3.63
3.74
0.13
-
T3
0.29
0.50
0.32
0.1
T6
3.88
-
0.33
0.82
0.45
0.45
S1
S2
3.96
4.03
0.42
0.057
HOMO-1 − LUMO
HOMO − LUMO+1
T7
T5
4.12
3.92
-
-
HOMO-1 − LUMO+1
HOMO-5 − LUMO
HOMO − LUMO+3
HOMO-1 − LUMO
HOMO − LUMO
HOMO − LUMO+1
HOMO-1 − LUMO
HOMO − LUMO
0.91
0.37
0.4
Py 2a
S1
S2
T6
4.03
4.05
4.11
0.21
0.18
-
0.21
0.52
0.22
0.25
0.41
0.30
0.88
HOMO − LUMO+1
HOMO-1 − LUMO+1
excited singlet states (S1) and the excited triplet states around
S1 of N-alkyl and N,N-dialkyl carboxamides.
crossing would be inefficient. As a result, Py 1a and Py 2a
showed high fluorescence efficiencies at 78 K.
Clear n−π* transition was not observed for any of the
compounds at S1 or at the excited triplet states around S1. In
other words, for the transitions that might be assigned to n−π*,
almost all electronic structures in the ground state had shapes
similar to a mixture of n- and π-orbitals. These molecular
orbitals are shown in Supplementary Figure 6S, and several
parameters, including excitation energies and oscillator strength
only for the singlet excited states, are summarized in Table 3.
From the shapes of the orbitals, it is expected that the n-
orbital contributions would be relatively small in Py 1a and Py
2a. Therefore, the mixing between S1 and its near triplet state
can be considered to be weak, which means the intersystem
When comparing the results with those obtained for pyrene,
the anthracene derivatives also seem to possess only minor n-
orbital contributions, e.g., HOMO-3 and HOMO-5 in Anth 1
and HOMO-1 in Anth 2. However, it should be noted that the
energy gap between S1 and T2 was 0.27 eV for both Anth 1 and
Anth 2, and this value was much larger than that of
unsubstituted anthracene (0.05 eV).93 We think that such a
large energy gap is more favorable for fluorescence emission
than the mixing between the n−π * and π−π* states and that,
as a result, the intersystem crossing contributions were reduced
in Anth 1 and Anth 2 and stronger emissions were observed at
78 K compared to that of anthracene.
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On the other hand, the naphthalene derivatives showed
relatively clear n-orbital components such as HOMO-1,
HOMO-2, and HOMO-5 in Nap 1 and HOMO-1 and
HOMO-2 in Nap 2. In addition, the energy gaps between S1
and the triplet around S1 of Nap 1 and Nap 2 were very small.
This means that the intersystem crossing processes were highly
likely to occur for Nap 1 and Nap 2. Furthermore, in terms of
Nap 2, the second lowest singlet excited state, S2, was the
closest to the upper state of S1. In this situation, it is possible
that a “proximity effect”,100−102 which induced internal
conversion, could have occurred. Therefore, the calculation
results supported two reasons for the low fluorescence of Nap
2, i.e., the presence of both intersystem crossing and internal
conversion. However, these could not explain the high
fluorescence of Nap 1 compared to Nap 2. While it is very
difficult to estimate the detailed contributions of n−π*
transitions, slight differences in either or both such contribu-
tions and the energy gap between S1 and the triplet may be
responsible for this difference in the fluorescence levels of the
two molecules.
carboxamides Nap 2 and Py 2a, we inferred that the extremely
low luminescence properties of Nap 2 and Py 2a were not only
because of intersystem crossing but also because of internal
conversion induced by such effects. However, the above-
mentioned relationships between the planarity of structures and
the emission properties of anthracene derivatives did not match
those of naphthalene and pyrene derivatives. This is likely
because the changes in dihedral angle between the anthracene
ring and carbonyl groups and bond lengths of N−(CO) in
amide groups were small and subtle in both Anth 1 and Anth 2.
However, it can be said with certainty that the relatively
unsubstituted anthracene chromophore lost its rigidity due to
the introduction of N-alkyl and N,N-dialkyl carboxamide
groups. Therefore, we attributed the improved emission of
Anth 1 and Anth 2 at 78 K to the effects induced by N-alkyl
and N,N-dialkyl carboxamide groups.
Proposed Photoluminescence Mechanism. On the
basis of our experiments, we can estimate the contributions
from intersystem crossing and internal conversion of
naphthalene, anthracene, pyrene, and their N-alkyl and N,N-
dialkyl carboxamide derivatives. Considering that the fluo-
rescence quantum yields increased in the order of naphthalene
< anthracene < pyrene, it can be said that contribution from
intersystem crossing increased in the reverse order. Using this
sequence, objective estimations with respect to N-alkyl and
N,N-dialkyl carboxamides were made and are summarized in
Table 5.
Geometries of N-Alkyl and N,N-Dialkyl Aromatic Carbox-
amides in Excited State. As shown in Table 4 and Figure 7S
Table 4. Relationships between Ground and First Excited
Singlet States of N-Alkyl and N,N-Dialkyl Carboxamides
N−(CO) bond
dihedral angle (deg)
length [Å]
a
entry
S0
S1
S0
S1
(μe − μg)2
Table 5. Contributions from Intersystem Crossing and
Internal Conversion of N-Alkyl and N,N-Dialkyl Aromatic
Carboxamides
Nap 1
Nap 2
Anth 1
Anth 2
Py 1a
26.9
43.2
64.4
82.9
45.4
76.8
10.5
1.3
1.364
1.371
1.363
1.363
1.363
1.366
1.381
1.450
1.368
1.360
1.381
1.450
2.24
4.8
50.1
79.5
25.6
1.2
0.088
0.0038
0.044
14.2
a
a
entry
intersystem crossing
internal conversion
naphthalene
Nap 1
++++
++
−
+
Py 2a
a
μe, μg: Dipole moments for excited state and ground state,
Nap 2
++++
+++
++
+++
−
++
++
−
respectively.
anthracene
Anth 1
Anth 2
pyrene
++
(Supporting Information), the optimized structures of N-alkyl
and N,N-dialkyl aromatic carboxamides in the excited states
were calculated. It was found that the dihedral angles between
the aromatic rings and carbonyl groups of N-alkyl and N,N-
dialkyl naphthalene and pyrene carboxamides tended to be
more planar in the excited states. Furthermore, the lengths of
the N−(CO) bonds were extended in the optimized states,
especially in Nap 2 and Py 2a. This implies that the partial
double bond characteristics of the N−(CO) bond in amide
groups were decreased. Calculations indicated that the
conjugations between aromatic rings and carbonyl groups
were more favorable than those between amide units for the
rearrangement from Franck−Condon states to optimized
states. In anthracene-9-carboxylic acid or its ester derivatives,
it has been demonstrated that such a planar structure prevents
the internal conversion process by inducing rigidity.73,76−79 On
the other hand, in N,N-dialkyl carboxamides, it is considered
that the decrease in the partial double bond characteristics of
the N−(CO) bond causes molecular motions in the amine
parts. In addition, it is likely that such molecular motions
caused either or both the “loose bolt effect” and “free-rotor
effect”,90 known as factors that induce the internal conversion
from S1 to S0 because of stretching σ-bond and twisted π-bond,
respectively. Therefore, considering that tendencies to be
planar were more strongly emphasized in N,N-dialkyl
++
Py 1a
−
+
+
Py 2a
+++
a
Number of (+) symbols indicate the tendency to accept the
corresponding processes.
As mentioned above, the deactivation processes of
naphthalene, anthracene, and pyrene involve intersystem
crossing. However, in Nap 1 and the anthracene and pyrene
derivatives, internal conversion is likely to be a more
competitive component. In other words, the N-alkyl and
N,N-dialkyl groups serve to reduce the contributions from
intersystem crossing. Therefore, we believe that the fluo-
rescence properties of the N-alkyl and N,N-dialkyl carbox-
amides depend on increased contributions from internal
conversion and decreased contributions from intersystem
crossing. The contributions from the internal conversion of
N-alkyl and N,N-dialkyl carboxamides tend to be increased
when the dihedral angles between the polycyclic aromatic rings
and carbonyl groups approach a planar structure in the excited
states, and those from the intersystem crossing tend to depend
on the nature of the chromophore itself. These insights mean
that the fluorescence properties of N-alkyl and N,N-
dialkylpolycyclic aromatic carboxamides may be controlled by
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The organic layer was washed with brine. It was dried over MgSO4 and
then evaporated in vacuo. The residue was subjected to silica column
chromatography using ethyl acetate/hexane = 1:5. Subsequent
recrystallization in ethyl acetate afforded amide as a colorless oil
the choices of chromophores and amide substituents, in
addition to solvent viscosity and temperature. It can be said
that such photophysical characteristics are not seen in other
aromatic carbonyl compounds, and these “unstable” emission
properties are unique.
1
(1.0 g, 88%). H NMR (400 MHz, CDCl3) δ 7.88−7.84 (m, 4H),
7.54−7.46 (m, 3H), 3.60−3.31 (m, 4H), 1.28−1.13 (m, 6H) ppm; 13C
NMR (100 MHz, CDCl3) δ 171.2, 134.5, 133.3, 132.7, 128.2, 128.1,
127.7, 126.6, 125.6, 123.8, 43.3, 39.2, 14.2, 12.9 ppm; FT-IR (KBr)
3054, 2972, 2943, 1627, 1480, 1454, 1424, 1381, 1363, 1348, 1314,
1288, 1243, 1218, 1176, 1130, 1088 cm−1. MS (FAB) calcd for
C15H18NO 228.1388, found 228.1389 ([M + H]+).
CONCLUSIONS
■
In summary, the photophysical properties and fluorescence
mechanisms of N-alkyl and N,N-dialkyl polycyclic aromatic
carboxamides were investigated, and the effects of the
substituents on polycyclic aromatic hydrocarbon chromophores
were evaluated. We chose naphthalene, anthracene, and pyrene
as the polycyclic aromatic hydrocarbons and prepared a
number of different target compounds. UV−vis and fluo-
rescence spectra of the molecules in solvents with different
polarities indicated that such compounds did not form charge
transfer states. Investigation of the dependence of the
fluorescence properties on the solvents’ thermal and viscosity
characteristics, along with TD-DFT calculations, showed that,
in almost all the N-alkyl and N,N-dialkyl carboxamides, the
contributions of intersystem crossing were reduced and those
of the internal conversions were increased. These photophysical
characteristics are specific and unique to aromatic carbonyl
compounds. Importantly, the calculations indicated that the
intersystem crossing and internal conversion contributions
could be controlled by selecting the appropriate aromatic
chromophore and the structure of the amide substituents, in
addition to solvent viscosity and temperature. We believe that
such effects are caused by the N-alkyl and N,N-dialkyl
carboxamides groups, and these insights into the substitution
effects will enable the successful design and development of
new emission materials. In future work, we will attempt to
create new functional emission dyes using this new knowledge.
Synthesis of N-Benzyl-N-diethylanthracene-9-carboxamide
(Anth 1). Anthracene-9-carboxylic acid chloride (1.0 g, 4.2 mmol),
triethylamine (1.2 g, 12 mmol), and CHCl3 (20 mL) were placed in a
100-mL two-necked flask under nitrogen. Benzylamine (1.3 g, 12
mmol) was added dropwise to the above solution at 0 °C. The mixture
was then allowed to be gradually warmed to rt. It was then stirred for
12 h. Subsequently, it was quenched with 1 N HCl to separate the
formed organic layer. The organic layer was washed with brine. It was
dried over MgSO4 and then evaporated in vacuo. The residue was
subjected to silica column chromatography using ethyl acetate/hexane
= 1:3. Subsequent recrystallization in ethyl acetate afforded amide as a
1
colorless solid (0.99 g, 76%). Mp 158.1−160.0 °C; H NMR (400
MHz, CDCl3) δ 8.46 (s, 1H), 8.08−8.06 (d, J = 8.54 Hz, 2H), 8.00−
7.98 (d, J = 8.17 Hz, 2H), 7.59−7.25 (m, 9H), 4.88−4.87 (d, J = 5.61
Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3) δ 169.3, 137.8, 131.5,
131.0, 128.8, 128.5, 128.3, 128.1, 128.0, 127.8, 126.7, 125.5, 125.0, 44.3
ppm; FT-IR (KBr) 3253, 3054, 1631, 1563, 1552, 1454, 1445, 1348,
1292, 1265, 1081, 1027, 1012 cm−1. MS (FAB) calcd for
C22H17NONa 334.1208, found 334.1209 ([M + Na]+). Anal. Calcd
for C22H17NO: C, 84.86; H, 5.50; N, 4.50. Found: C, 84.86; H, 5.50;
N, 4.48.
Synthesis of N,N-Diethylanthracene-9-carboxamide (Anth
2). Anthracene-9-carboxylic acid chloride (1.0 g, 4.2 mmol),
triethylamine (1.2 g, 12 mmol), and CHCl3 (20 mL) were placed in
a 100-mL two-necked flask under nitrogen. Diethylamine (0.88 g, 12
mmol) was added dropwise to the above solution at 0 °C. The mixture
was then allowed to be gradually warmed to rt. It was then stirred for
12 h. Subsequently, it was quenched with 1 N HCl to separate the
formed organic layer. The organic layer was washed with brine. It was
dried over MgSO4 and then evaporated in vacuo. The residue was
subjected to silica column chromatography using ethyl acetate/hexane
= 1:5. Subsequent recrystallization in ethyl acetate afforded amide as a
EXPERIMENTAL SECTION
■
Synthesis of N-Alkyl and N,N-Dialkyl Polyaromatic Carbox-
amides. Synthesis of N-Benzyl-2-naphthamide (Nap 1).
Napthalene-2-carboxylic acid chloride (1.0 g, 5.2 mmol),
triethylamine (1.5 g, 15 mmol), and CHCl3 (20 mL) were
placed in a 100-mL two-necked flask under nitrogen.
Benzylamine (1.6 g, 15 mmol) was added dropwise to the
above solution at 0 °C. The mixture was then allowed to be
gradually warmed to rt. It was then stirred overnight.
Subsequently, it was quenched with 1 N HCl to separate the
formed organic layer. The organic layer was washed with brine.
It was dried over MgSO4 and then evaporated in vacuo. The
residue was subjected to silica column chromatography using
ethyl acetate/hexane = 1:3. Subsequent recrystallization in ethyl
acetate afforded amide as a colorless solid (1.2 g, 89%). Mp
140.7−142.5 °C; 1H NMR (400 MHz, CDCl3) δ 8.31 (s, 1H),
7.91−7.84 (m, 4H), 7.58−7.51 (m, 2H), 7.42−7.26 (m, 5H),
6.57 (s, 1H), 4.72−4.71 (d, J = 5.67 Hz, 2H) ppm; 13C NMR
(100 MHz, CDCl3) δ 167.4, 138.2, 134.7, 132.5, 131.5, 128.9,
128.7, 128.4, 127.9, 127.7, 127.6, 127.5, 127.4, 126.7, 123.6,
44.1 ppm; FT-IR (KBr) 3290, 3055, 1637, 1624, 1548, 1496,
1450, 1436, 1415, 1361, 1321, 1264, 1208, 1147, 1120, 1078,
1049, 1019 cm−1. MS (FAB) calcd for C18H16NO 262.1232,
found 262.1231 ([M + H]+). Anal. Calcd for C18H15NO: C,
82.73; H, 5.79; N, 5.36. Found: C, 82.85; H, 5.71; N, 5.38.
Synthesis of N,N-Diethyl-2-naphthamide (Nap 2). Naptha-
lene-2-carboxylic acid chloride (1.0 g, 5.2 mmol), triethylamine (1.5 g,
15 mmol), and CHCl3 (20 mL) were placed in a 100-mL two-necked
flask under nitrogen. Diethylamine (0.44 g, 6.0 mmol) was added
dropwise to the above solution at 0 °C. The mixture was then allowed
to be gradually warmed to rt. It was then stirred for 6 h. Subsequently,
it was quenched with 1 N HCl to separate the formed organic layer.
1
colorless solid (1.1 g, (95%). Mp 116.5−118.5 °C; H NMR (400
MHz, CDCl3) δ 8.24 (s, 1H), 8.02−7.90 (m, 4H), 7.51−7.44 (m, 4H),
3.89−3.84 (dd, J = 7.13 Hz, 2H), 3.04−2.99 (dd, J = 7.01 Hz, 2H),
1.52−1.48 (t, J = 7.13 Hz, 3H), 0.87−0.83 (t, J = 7.19 Hz, 3H) ppm;
13C NMR (100 MHz, CDCl3) δ 169.4, 131.4, 131.1, 128.5, 127.4,
127.2, 126.4, 125.4, 124.8, 43.1, 38.9, 14.0, 13.1 ppm; FT-IR (KBr)
2976, 2933, 1618, 1557, 1521, 1489, 1473, 1430, 1406, 1380, 1364,
1345, 1315, 1287, 1264, 1220, 1160, 1141, 1100, 1081, 1028, 1012
cm−1. MS (FAB) calcd for C19H19NONa 300.1364, found 300.1366
([M + Na]+). Anal. Calcd for C19H19NO: C, 82.28; H, 6.90; N, 5.05.
Found: C, 82.57; H, 7.13; N, 5.13.
Synthesis of N-Benzylpyrene-1-carboxamide (Py 1a). Pyrene-
1-carboxylic acid chloride (0.54 g, 2.0 mmol), triethylamine (0.61 g, 6
mmol), and CHCl3 (20 mL) were placed in a 100-mL two-necked
flask under nitrogen. Benzylamine (0.64 g, 6.0 mmol) was added
dropwise to the above solution at 0 °C. The mixture was then allowed
to be gradually warmed to rt. It was then stirred overnight.
Subsequently, it was quenched with 1 N HCl to separate the formed
organic layer. The organic layer was washed with brine. It was dried
over MgSO4 and then evaporated in vacuo. The residue was subjected
to silica column chromatography using ethyl acetate/hexane = 1:2.
Subsequent recrystallization in ethyl acetate afforded amide as a
1
colorless solid (0.64 g, 95%). Mp 160.9−162.5 °C; H NMR (400
MHz, CDCl3) δ 8.65−8.63 (d, J = 9.09 Hz, 1H), 8.25−8.04 (d, 8H),
7.49−7.47 (d, J = 7.01 Hz, 2H), 7.43−7.32 (m, 3H), 6.42 (s, 1H),
4.85−4.84 (d, J = 5.37 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3) δ
169.8, 138.3, 132.3, 131.0, 130.5, 130.5, 128.7, 128.4, 127.8, 127.5,
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126.9, 126.1, 125.6, 125.5, 124.4, 124.3, 124.2, 124.1, 124.0, 44.1 ppm;
FT-IR (KBr) 3274, 3030, 2919, 1631, 1531, 1291 cm−1. MS (FAB)
calcd for C24H17NONa 358.1208, found 358.1208 ([M + Na]+). Anal.
Calcd for C24H17NO: C, 85.94; H, 5.11; N, 4.18. Found: C, 85.64; H,
4.74; N, 4.14.
flask under nitrogen. Piperidine (0. Five g, 6 mmol) was added to the
above solution at 0 °C. The mixture was then allowed to be gradually
warmed to rt. It was then stirred overnight. Subsequently, it was
quenched with 1 N HCl to separate the formed organic layer. The
organic layer was washed with brine. It was dried over MgSO4 and
then evaporated in vacuo. The residue was subjected to silica column
chromatography using ethyl acetate/hexane = 1:5. Subsequent
recrystallization in hexane afforded amide as a colorless solid (0.47
Synthesis of N-n-Butylpyrene-1-carboxamide (Py 1b).
Pyrene-1-carboxylic acid chloride (0.54 g, 2.0 mmol), triethylamine
(0.61 g, 6.0 mmol), and CHCl3 (20 mL) were placed in a 100-mL two-
necked flask under nitrogen. n-Butylamine (0.44 g, 6.0 mmol) was
added dropwise to the above solution at 0 °C. The mixture was then
allowed to be gradually warmed to rt. It was then stirred overnight.
Subsequently, it was quenched with 1 N HCl to separate the formed
organic layer. The organic layer was washed with brine. It was dried
over MgSO4 and then evaporated in vacuo. The residue was subjected
to silica column chromatography using ethyl acetate/hexane = 1:3.
Subsequent recrystallization in ethyl acetate afforded amide as a
1
g, 79%). Mp 148.5−150.5 °C; H NMR (400 MHz, CDCl3) δ 8.19−
7.89 (m, 9H), 4.02−3.88 (m, 2H), 3.13−3.10 (m, 2H), 1.85−1.76 (m,
2H), 1.69−1.63 (m, 2H), 1.40−1.35 (m, 2H) ppm; 13C NMR (100
MHz, CDCl3) δ 169.6, 131.6, 131.1, 130.8, 128.5, 128.0, 127.3, 127.1,
126.2, 125.6, 125.4, 124.7, 124.5, 124.5, 124.0, 123.5, 48.3, 42.8, 26.6,
25.8, 24.5 ppm; FT-IR (KBr) 3039, 2988, 2939, 2857, 1620, 1508,
1464, 1428, 1367, 1348, 1285, 1270, 1201, 1181, 1141, 1126, 1087,
1024 cm−1. MS (FAB) calcd for C22H19NO 313.1467, found 313.1469
(M+). Anal. Calcd for C22H19NO: C, 84.31; H, 6.11; N, 4.47. Found:
C, 84.54; H, 6.04; N, 4.47.
1
colorless solid (0.43 g, 72%). Mp 159.5−161.5 °C; H NMR (400
MHz, CDCl3) δ 8.59−8.56 (d, J = 9.51 Hz, 1H), 8.24−8.03 (m, 8H),
6.10 (s, 1H), 3.67−3.62 (m, 2H), 1.76−1.69 (m, 2H), 1.47−1.56 (m,
2H), 1.04−1.01 (t, J = 7.38 Hz, 3H) ppm; 13C NMR (100 MHz,
CDCl3) δ 169.9, 132.2, 131.3, 131.1, 130.6, 128.4, 128.3, 127.0, 126.2,
125.6, 125.5, 124.6, 124.4, 124.3, 124.3, 124.1, 40.0, 31.8, 20.2, 13.8
ppm; FT-IR (KBr) 3297, 3042, 2955, 2931, 2871, 1621, 1601, 1551,
1536, 1470, 1291, 1155 cm−1. MS (FAB) calcd for C21H19NONa
324.1364, found 324.1360 ([M + Na]+). Anal. Calcd for C21H19NO:
C, 83.69; H, 6.35; N, 4.65. Found: C, 83.63; H, 6.18; N, 4.63.
Synthesis of N-tert-Butylpyrene-1-carboxamide (Py 1c).
Pyrene-1-carboxylic acid chloride (0.54 g, 2.0 mmol), triethylamine
(0.61 g, 6.0 mmol), and CHCl3 (20 mL) were placed in a 100-mL two-
necked flask under nitrogen. tert-Butylamine (0.44 g, 6.0 mmol) was
added dropwise to the above solution at 0 °C. The mixture was then
allowed to be gradually warmed to rt. It was then stirred overnight.
Subsequently, it was quenched with 1 N HCl to separate the formed
organic layer. The organic layer was washed with brine. It was dried
over MgSO4 and then evaporated in vacuo. The residue was subjected
to silica column chromatography using ethyl acetate/hexane = 1:3.
Subsequent recrystallization in ethyl acetate afforded amide as a
Synthesis of N-Benzyl-N-tert-butylpyrene-1-carboxamide
(Py 2c). Pyrene-1-carboxylic acid chloride (1.1 g, 4.1 mmol),
triethylamine (1.2 g, 12 mmol), and CHCl3 (20 mL) were placed in
a 100-mL two-necked flask under nitrogen. N-tert-Butylbenzylamine
(2.0 g, 12 mmol) was added dropwise to the above solution at 0 °C.
The mixture was then allowed to be gradually warmed to rt. It was
then stirred overnight. Subsequently, it was quenched with 1 N HCl to
separate the formed organic layer. The organic layer was washed with
brine. It was dried over MgSO4 and then evaporated in vacuo. The
residue was subjected to silica column chromatography using ethyl
acetate/hexane = 1:5. Subsequent recrystallization in ethyl acetate
afforded amide as a colorless solid (0.82 g, 51%). Mp 213.5−214.7 °C;
1H NMR (400 MHz, CDCl3) δ 8.21−7.94 (m, 9H), 7.26−7.14 (m,
5H), 4.52−4.50 (d, J = 6.52 Hz, 2H), 1.69 (s, 9H) ppm; 13C NMR
(100 MHz, CDCl3) δ 173.0, 139.6, 133.7, 131.2, 131.2, 130.8, 128.7,
128.4, 127.8, 127.2, 126.9, 126.9, 126.2, 126.0, 125.6, 125.4, 124.7,
124.6, 124.6, 123.7, 123.4, 58.7, 51.6, 29.0 ppm; FT-IR (KBr) 2956,
1626, 1507, 1495, 1454, 1395, 1358, 1276, 1255, 1195, 1176, 1159,
1144, 1132, 1076, 1026 cm−1. MS (EI) calcd for C28H25NO 391.1936,
found 391.1938 (M+). Anal. Calcd for C28H25NO: C, 85.90; H, 6.44;
N, 3.58. Found: C, 85.67; H, 6.52; N, 3.59.
Synthesis of N-tert-Butyl-N-ethylpyrene-1-carboxamide (Py
2d). Pyrene-1-carboxylic acid chloride (1.1 g, 4.1 mmol), triethylamine
(1.2 g, 12 mmol), and CHCl3 (20 mL) were placed in a 100-mL two-
necked flask under nitrogen. N-tert-Butylethylamine (1.2 g, 12 mmol)
was added to the above solution at 0 °C. The mixture was then
allowed to be gradually warmed to rt. It was then stirred overnight.
Subsequently, it was quenched with 1 N HCl to separate the formed
organic layer. The organic layer was washed with brine. It was dried
over MgSO4 and then evaporated in vacuo. The residue was subjected
to silica column chromatography using ethyl acetate/hexane = 1:5.
Subsequent recrystallization in hexane afforded amide as a colorless
solid (0.58 g, 43%). Mp 118.5−120.5 °C; 1H NMR (400 MHz,
CDCl3) δ 8.21−7.91 (m, 9H), 3.38−3.15 (m, 2H), 1.74 (s, 9H),
0.98−0.94 (t, J = 7.38 Hz, 3H) ppm; 13C NMR (100 MHz, CDCl3) δ
172.0, 134.4, 131.1, 130.9, 130.8, 128.3, 127.6, 127.1, 126.7, 126.1,
125.4, 125.2, 124.6, 124.5, 123.9, 123.3, 57.4, 41.8, 29.0, 17.4 ppm. FT-
IR (KBr) 3041, 2958, 1624, 1510, 1489, 1454, 1397, 1379, 1360, 1281,
1211, 1179, 1146, 1113, 1079, 1040 cm−1. MS (FAB) calcd for
C23H23NO 329.1780, found 329.1779 (M+).
1
colorless solid (0.45 g, 74%). Mp 233.0−235.0 °C; H NMR (400
MHz, CDCl3) δ 8.55−8.53 (d, J = 8.66 Hz, 1H), 8.24−8.03 (m, 8H),
5.93 (s, 1H), 1.61 (s, 9H) ppm; 13C NMR (100 MHz, CDCl3) δ
169.5, 132.6, 132.2, 131.2, 130.7, 128.5, 128.4, 128.2, 127.1, 126.2,
125.7, 125.6, 124.7, 124.5, 124.4, 124.3, 124.3, 52.3 ppm; FT-IR (KBr)
3326, 3045, 2976, 1639, 1601, 1521, 1446, 1384, 1354, 1330, 1297,
1220, 1151. cm−1. MS (FAB) calcd for C21H19NONa 324.1364, found
324.1360 ([M + Na]+). Anal. Calcd for C21H19NO: C, 83.69; H, 6.35;
N, 4.65. Found: C, 83.66; H, 5.99; N, 4.64.
Synthesis of N,N-Diethylpyrene-1-carboxamide (Py 2a).
Pyrene-1-carboxylic acid chloride (1.1 g, 4.1 mmol), triethylamine
(1.2 g, 12 mmol), and CHCl3 (20 mL) were placed in a 100-mL two-
necked flask under nitrogen. Diethylamine (0.88 g, 12 mmol) was
added to the above solution at 0 °C. The mixture was then allowed to
be gradually warmed to rt. It was then stirred overnight. Subsequently,
it was quenched with 1 N HCl to separate the formed organic layer.
The organic layer was washed with brine. It was dried over MgSO4 and
then evaporated in vacuo. The residue was subjected to silica column
chromatography using ethyl acetate/hexane = 1:5. Subsequent
recrystallization in ethyl acetate afforded amide as a colorless solid
1
(0.70 g, 57%). Mp 108.5−109.5 °C; H NMR (400 MHz, CDCl3) δ
8.19−7.89 (m, 9H), 3.19−3.61 (m, 2H), 3.13−3.06 (m, 2H), 1.45−
1.41 (t, J = 7.07 Hz, 3H), 0.95−0.92 (t, J = 7.07 Hz, 3H) ppm; 13C
NMR (100 MHz, CDCl3) δ 170.6, 132.0, 131.3, 131.1, 130.8, 128.5,
127.9, 127.2, 127.1, 126.2, 125.5, 125.4, 124.6, 124.5, 124.4, 123.9,
123.3, 43.2, 39.2, 14.2, 13.1 ppm; FT-IR (KBr) 3039, 2969, 1624,
1510, 1473, 1455, 1428, 1377, 1346, 1312, 1284, 1217, 1183, 1156,
1142, 1123, 1096, 1085 cm−1. MS (FAB) calcd for C21H19NONa
324.1364, found 324.1367 ([M + Na]+). Anal. Calcd for C21H19NO:
C, 83.69; H, 6.35; N, 4.65. Found: C, 83.49; H, 6.29; N, 4.68.
Synthesis of Piperidin-1-yl(pyren-1-yl)methanone (Py 2b).
Pyrene-1-carboxylic acid chloride (0.5 g, 1.9 mmol), triethylamine (0.6
g, 6 mmol), and CHCl3 (20 mL) were placed in a 100-mL two-necked
ASSOCIATED CONTENT
■
S
* Supporting Information
Additional experimental methods for polycyclic aromatic
hydrocarbons with N-alkyl or N,N-dialkyl carboxamide groups.
The results of calculations (Figure S1, Figure S6−S7) and
solvent dependence (Figure S2−S5, Table S1−S3), synthesis
1
conditions and H NMR and 13C NMR spectra (Figure S8−
S13). This material is available free of charge via the Internet at
http://pubs.acs.org.
3994
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The Journal of Organic Chemistry
Article
(29) Armitt, D. J.; Crisp, G. T. J. Org. Chem. 2006, 71, 3417−3422.
(30) Zhao, Z.; Xu, X.; Jiang, Z.; Lu, P.; Yu, G.; Liu, Y. J. Org. Chem.
2007, 72, 8345−8353.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: konishi.g.aa@m.titech.ac.jp.
Notes
(31) Maeda, H.; Maeda, T.; Mizuno, K.; Fujimoto, K.; Shimizu, H.;
Inouye, M. Chem.Eur. J. 2006, 12, 824−831.
(32) Gano, J. E.; Osborn, D. J.; Kodali, N.; Sekher, P.; Liu, M.; Luzik,
E. D., Jr. J. Org. Chem. 2003, 68, 3710−3713.
The authors declare no competing financial interest.
(33) Wang, J. L.; Zhou, Z.; Li, Y.; Pei, J. J. Org. Chem. 2009, 74,
7449−7456.
ACKNOWLEDGMENTS
■
We thank Prof. Katsumi Tokumaru (Emeritus Professor of
Tsukuba University) for helpful discussion.
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