Synthesis, photophysical evaluation, and computational study of 2-methoxy- and 2-morpholino pyridine compounds as highly emissive fluorophores in solution and the solid state

Article abstract of DOI:10.1016/j.dyepig.2019.107705

Two 2-pyridone tautomeric analogs, methoxypyridine 4 and N-methylpyridone 5, were synthesized, and their spectroscopic properties were investigated both experimentally and computationally. A detailed photophysical study reveals that 4 shows high fluoresce

Full text of DOI:10.1016/j.dyepig.2019.107705

Accepted Manuscript
Synthesis, photophysical evaluation, and computational study of 2-methoxy- and 2-
morpholino pyridine compounds as highly emissive fluorophores in solution and the
solid state
Masayori Hagimori, Yasuhisa Nishimura, Naoko Mizuyama, Yasuhiro Shigemitsu
PII:
S0143-7208(19)31188-X
DOI:
https://doi.org/10.1016/j.dyepig.2019.107705
Article Number: 107705
Reference:
DYPI 107705
To appear in: Dyes and Pigments
Received Date: 23 May 2019
Revised Date: 2 July 2019
Accepted Date: 8 July 2019
Please cite this article as: Hagimori M, Nishimura Y, Mizuyama N, Shigemitsu Y, Synthesis,
photophysical evaluation, and computational study of 2-methoxy- and 2-morpholino pyridine compounds
as highly emissive fluorophores in solution and the solid state, Dyes and Pigments (2019), doi: https://
doi.org/10.1016/j.dyepig.2019.107705.
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Synthesis, photophysical evaluation, and computational study of 2-methoxy-
and 2-morpholino pyridine compounds as highly emissive fluorophores in
solution and the solid state
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Masayori Hagimori,a,* Yasuhisa Nishimura,b Naoko Mizuyama,c and Yasuhiro Shigemitsu,b,d,*
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aGraduate School of Biomedical Sciences, Nagasaki University, 1-7-1 Sakamoto, Nagasaki
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852-8501, Japan
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bGraduate School of Engineering, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki
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852-8131, Japan
cClinical Research Center, Nagasaki University Hospital, 1-7-1 Sakamoto, Nagasaki 852-8501,
Japan
dIndustrial Technology Center of Nagasaki, 2-1303-8, Ikeda, Omura, Nagasaki 856-0026,
Japan
Author E-mail address: hagimori@nagasaki-u.ac.jp (M Hagimori); shige@tc.nagasaki.go.jp
(Y Shigemitsu)
*Corresponding author.
Masayori Hagimori. Telephone: +81784417540. Fax: +81784417541. E-mail:
hagimori@nagasaki-u.ac.jp.
Yasuhiro Shigemitsu. Telephone: +81-957521133. Fax: +81-957521136. E-mail:
shige@tc.nagasaki.go.jp.
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Abstract
Two 2-pyridone tautomeric analogs, methoxypyridine 4 and N-methylpyridone 5, were
synthesized, and their spectroscopic properties were investigated both experimentally and
computationally. A detailed photophysical study reveals that 4 shows high fluorescence
quantum yields not only in chloroform but also in ethanol, and the strong fluorescence in
solution might be attributed to the enol form (pyridine) of the 2-pyridone. Furthermore, we
designed and synthesized novel 2-substitued pyridines to achieve more intense emissions in
both solution and the solid state. Substituent modification with phenylsulfonyl, morpholino,
and 4-diethylamino groups greatly affected the fluorescence properties, and methoxypyridine
7 and morpholinopyridine compound 8 showed fluorescence in various solvents (Ф =
0.59–0.95) and the solid state (Ф = 0.12–0.15). A hypsochromic shift in the emission
maximum wavelength and strong fluorescence in the solid state (Ф = 0.39) were observed for
dimorpholinopyridine 9. Morpholinopyridine 11 showed intense fluorescence in all nonpolar
and polar solvents. Systematic time-dependent density functional theory calculations were
performed for the compounds whose electronic and fluorescent maxima were computationally
reproduced with good agreement to those from experiment. In detail, the drastic difference in
the emission intensity between 4 and 5 in solution was successfully explained using CASSCF
calculations, which revealed conical intersections between the ground and the excited states.
Keywords: keto–enol tautomerism of 2-pyridone; pyridine; fluorescence; TDDFT; CASSCF;
conical intersection
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1. Introduction
Fluorophores are one of the most useful materials in various chemical, biological, and material
sciences because of their sensitivity, simplicity, color tunability, and low cost [1–3]. Each
fluorophore, which could be an organic molecule, fluorescent protein, or quantum dot, for
example, has a specific wavelength of absorbance and emission of light from the visible to near
infrared region [1,4–6]. In organic molecules, particularly heterocyclic compounds, these
fluorescence characteristics can be easily tuned by chemical modification [7,8]. Therefore,
there has been significant effort to develop fluorophores based on organic molecules for
applications as clinical diagnostic probes and organic light-emitting materials [9-15].
2-Pyridone is a nitrogen-containing heterocyclic compound and is used as a scaffold for
antibacterial, anticancer, antiviral, and antimalarial agents [16–19]. In addition,
2-pyridone-based fluorophores exhibiting strong fluorescence have been reported [20–22].
Previously, we also reported several fluorescent 2-pyridone compounds,
6-(4-dialkylamino)phenyl-2-pyridones, that exhibit aggregation-induced emission
enhancement (AIEE)-based fluorescence in the solid state [23,24]. These 2-pyridone
compounds also exhibited fluorescence in solution, and the fluorescence quantum yields (Ф)
in chloroform were very high (Ф = 0.90–0.92) [25]. However, the fluorescence intensity of
the 2-pyridone compounds decreased in polar solvents such as ethanol (Ф = 0.11–0.22) [25]. It
has been reported that the 2-pyridone ring has two tautomeric forms (keto and enol); the
favored form depends on the solvent polarity. The 2-hyroxypyridine enol form is favored in
nonpolar solvents, whereas the 2-pyridone keto form is favored in polar solvents [26–29].
Therefore, we assumed that the tautomerism of the 2-pyridone ring affects the fluorescence
intensity in nonpolar and polar solvents.
Thus, to elucidate this hypothesis, we synthesized 2-pyridone tautomeric analogs,
methoxypyridine compound 4 and N-methylpyridone compound 5, and characterized their
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fluorescence properties using photophysical studies, as well as quantum chemical
calculations. We have found that the enol form greatly contributes to the fluorescence intensity
in both nonpolar and polar solvents. In heterocyclic compounds, the arrangement of the
electron–donating or electron–withdrawing groups affects the intramolecular charge transfer
(ICT) and enhances the fluorescence intensity [22,30–32]. In addition, we reported that the
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steric hindrance of the alkyl group reduces the molecular aggregation of 2-pyridone and
induced AIEE-based fluorescence [23,25]. Most AIEE materials previously reported exhibited
strong fluorescence in the solid state, but their fluorescence in solution was very weak [33].
Therefore, the development of fluorophores exhibiting fluorescence in both solution and the
solid state has attracted attention. In this paper, we report the synthesis and characterization
of novel 2-substituted pyridine compounds (7–9 and 11) that exhibit strong fluorescence in
various solvents and the solid state.
2. Materials and methods
All chemicals were reagent grade and used without further purification unless otherwise
specified. The identification of new compounds and the measurement of the fluorescence
properties were performed with the following equipment. Melting points were measured using
a Laboratory Devices Mel-Temp II apparatus and a Mitamura Riken Kogyo Mel-Temp
apparatus. The NMR spectra of the compounds were obtained using Gemini 300NMR (300
MHz) and JEOL-GX-400 (400 MHz) spectrometers. Mass spectra (MS) and high-resolution
(HR) MS were obtained using a JEOL DX-303 mass spectrometer. Elemental microanalyses
were recorded using a Perkin-Elmer CHN analyzer.
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2.1 Synthesis of
6-(4-dimethylamino)phenyl-4-methylsulfanyl-2-methoxypyridine-3-carbonitrile (4) and
6-(4-dimethylamino)phenyl-1-methyl-4-methylsulfanyl-3-cyano-2H-pyridone (5)
As described previously [25],
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6-(4-(dimethylamino)phenyl)-4-(methylsulfanyl)-2-oxo-1,2-dihydropyridine-3-carbonitrile
(3; 86 mg, 0.29 mmol, 29%) was prepared by the reaction of 4'-dimethylaminoacetophenone
(1a; 1.63 g, 10.0 mmol) and 3,3-bis(methylsulfanyl)malononitrile (2a; 2.86 g, 10.0 mmol)
using powdered NaOH (1.60 g, 40 mmol) as a base in dimethyl sulfoxide (DMSO, 20 mL). To
a suspension of 3 (285 mg, 1.0 mmol) in DMSO (5.0 mL) and 2 N sodium hydroxide (3.0 mL),
dimethyl sulfate (189 mg, 1.5 mmol) was added over 20 min, and the resulting suspension was
stirred for 1.5 h. After pouring 50 mL water into the reaction mixture, a precipitate formed,
which was collected by filtration and washed several times with water. Purification by silica gel
column chromatography (10 g of silica gel) eluted with toluene gave 4 (86 mg, 0.29 mmol,
29%) and that with toluene and methanol (ratio 4:1) gave 5 (107 mg, 0.36 mmol, 36%). An
analytical sample was recrystallized from methanol to give pale yellow needles of 4 (mp
171–172 °C). IR (KBr, cm-1): 2921, 2211, 1609, 1566, 1539, 1364, 1187, 1166, 1034, 812.
1H-NMR (CDCl3, 400 MHz): 2.62 (3H, s, SMe), 3.06 (6H, s, NMe2), 4.11 (3H, s, OMe), 6.75
(2H, d, J = 9.1 Hz, 3’, 5’-H), 7.06 (1H, s, 5-H), 7.96 (2H, d, J = 9.1 Hz, 2’, 6’-H). 13C-NMR
(CDCl3, 100 MHz): 14.4, 41.3, 54.2, 106.4, 114.5, 128.7, 157.1, 164.4. MS m/z: 300 (M+ + 1,
70), 299 (M+, 100), 298 (83), 282 (11), 240 (22), 236 (11). Anal. Calcd for C16H17N3SO =
299.1092: C, 64.19%; H, 5.72%; N, 14.04%. Found: C, 64.36%; H, 5.74%; N, 14.10%. An
analytical sample was recrystallized from methanol to give yellow needles of 5 (mp
218–220 °C). IR (KBr, cm-1): 3250, 3000, 2910, 2820, 2210 (CN), 1640 (C=O), 1600, 1510,
1490, 1440, 1420, 1360, 1310, 1290, 1240, 1215, 1180, 1060, 1040. 1H-NMR (CDCl3, 400
MHz): 2.52 (3H, s, Me), 3.07 (6H, s, NMe2), 3.44 (3H, s, NMe), 6.05 (1H, s, 5-H), 6.80 (2H, d,
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J = 9.1 Hz, 3’,5’-H), 7.27 (2H, d, J = 9.1 Hz, 2’, 6’-H). 13C-NMR (CDCl3, 100 MHz): 14.4,
34.9, 40.3, 95.68, 103.5, 111.9, 115.0, 129.3, 151.2, 154.3, 160.7, 161.1. MS m/z: 300 (M+ + 1,
47), 299 (M+, 100), 298 (13), 127 (11), 112 (12), 99 (15). Anal. Calcd for C16H17N3SO =
299.1092: C, 64.19%; H, 5.72%; N, 14.04%. Found: C, 64.01%; H, 5.68%; N,13.86%.
2.2 Synthesis of
6-(4-dimethylamino)phenyl-4-methylsulfanyl-3-phenylsulfonyl-2-methoxypyridine (7)
As described previously [25],
6-(4-(dimethylamino)phenyl)-4-(methylsulfanyl)-3-(phenylsulfonyl)pyridin-2(1H)-one (6)
(0.96 g, 2.40 mol) was prepared by the reaction of 1a (1.63 g, 10.0 mmol) and
3,3-bis(methylsulfanyl)-2-phenylsulfonyl-acrylonitrile (2b; 1.43 g, 5.0 mmol) using powdered
NaOH (1.12 g, 28 mmol) and morpholine (1.5 g, 17.2 mmol) in DMSO (20 mL). To a
suspension of 6 (150 mg, 3.75 mmol) in DMSO (10 mL) and a solution of 1 N sodium
hydroxide (6.0 mL), dimethyl sulfate (250 mg, 1.5 mmol) was added over 30 min, and the
resulting suspension was stirred for 1.5 h. After the addition of 50 mL water to the reaction
mixture, the formed precipitate was collected by filtration and washed several times with water.
Purification by silica gel column chromatography (10 g of silica gel) eluted with toluene gave
pale yellow needles of 7 (65 mg, 0.157 mmol, 42%, mp 194–195 °C). IR (KBr, cm-1): 2920,
2367, 2337, 1615, 1527, 669. 1H-NMR (CDCl3, 400 MHz): 2.55 (3H, s, Me), 3.07 (6H, s,
NMe2), 3.93 (3H, s, OMe), 6.73 (2H, d, J = 9.3 Hz, 3”,5”-H), 7.11 (1H, s, 5-H), 7.48 (2H, m,
3’,5’-H), 7.56 (1H, m, 4’-H), 7.91 (2H, d, J = 9.3 Hz, 2”,6”-H), 8.06 (2H, m, 2’,6’-H).
13C-NMR (CDCl3, 100 MHz): 16.0, 16.1, 40.1, 40.1, 53.8, 107.0, 107.1, 111.7, 124.5, 127.6,
128.2, 128.4, 142.7, 151.8, 155.8, 157.4, 160.9. MS (FAB) m/z: 415 (M + H+).
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2.3 Synthesis of 6-(4-(dimethylamino)phenyl)-4-(methylsulfanyl)-2-morpholinonicotinonitrile
(8) and 6-(dimethylamino)phenyl-2,4- dimorpholinopyridine-3-carbonitrile (9)
A solution of 1a (1.63 g, 10.0 mmol), 2a (2.86 g, 10.0 mmol), and NaOH (1.60 g, 40 mmol) in
DMSO (20 mL) was stirred at 10–15 °C for 5 h. After the addition of 300 mL of ice water to the
reaction mixture, the mixture was acidified with 10% hydrochloric acid. The resulting
caramel-colored intermediate was collected by decantation and washed with ice cold water
several times. A solution of the intermediate in water and morpholine (3.0 g, 34.4 mmol) was
heated for 20 min at about 200 °C. After filtration, the filtrate was concentrated in vacuo.
Purification by silica gel column chromatography (20 g of silica gel) eluted with
toluene:methanol (4:1) gave 3 (960 mg, 2.40 mmol, 24%), 8 (92 mg, 0.26 mmol, 2.6%), and 9
(82 mg, 0.21 mmol, 2.1%). An analytical sample was recrystallized from methanol to give
colorless needles of 8 (mp 167–168 °C). IR (KBr, cm-1): 2854, 2367, 2336, 1570, 1532, 1112.
1H-NMR (CDCl3, 400 MHz): 3.04 (6H, s, NMe2), 3.42 (2H, m, N–CH2–), 3.70 (2H, m,
N–CH2–), 3.87 (4H, m, –CH2–O–CH2–), 6.73 (2H, d, J = 8.8 Hz, 3’, 5’-H), 7.91 (2H, d, J = 8.8
Hz, 2’, 6’-H). 13C-NMR (CDCl3, 100 MHz): 14.5, 40.4, 48.8, 66.8, 89.3, 104.9, 112.2, 116.8,
128.5, 157.3, 157.4, 161.6. MS m/z: 355 (M+ + 1, 28), 354 (M+, 100), 339 (14), 324 (16), 323
(20), 297 (60), 296 (87), 269 (14), 222 (11). Anal. Calcd for C19H22N4SO = 354.1514: C,
64.38%; H, 6.26%; N, 15.81%. Found: C, 64.32%; H, 6.22%; N, 15.85%. In addition, an
analytical sample was recrystallized from methanol to give colorless needles of 9 (mp
197–198 °C). IR (KBr, cm-1): 2966, 2851, 2193 (CN), 1608, 1570, 1536, 1112, 819. 1H-NMR
(CDCl3, 400 MHz): 3.04 (6H, s, NMe2), 3.44 (4H, m, 2 × N–CH2–), 3.70 (4H, m, 2 × N–CH2–),
3.88 (8H, m, 2 × O–CH2–). 13C-NMR (CDCl3, 100 MHz): 40.4, 49.2, 50.6, 66.6, 66.8, 82,3,
98.2, 112.0, 118.8, 128.3, 158.9, 163.7, 163.9. MS m/z: 394 (M+ + 1, 24), 393 (M+, 94), 336
(41), 335 (100), 315 (16), 299 (29). Anal. Calcd for C22H27N5O2 = 393.2165: C, 67.15%; H,
6.92%; N, 17.80%. Found: C, 67.01%; H, 7.05%; N, 17.77%.
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2.4 Synthesis of
6-(4-diethylamino)phenyl-4-methylsulfanyl-2-morpholinopyridine-3-carbonitrile (11)
Compound 11 (54 mg 0.141 mmol, 2.8% yield) was prepared from
4-(diethylamino)phenylacetophenone (1b, 0.86 g, 5.0 mmol) and 2a (0.85 g, 5.0 mmol) in a
manner similar to that described for the synthesis of 8. An analytical sample was recrystallized
from dimethylformamide (DMF) and methanol to give pale yellow needles (mp 137–138 °C).
IR (KBr, cm-1): 2898, 2845, 2200 (CN), 1608, 1537, 1524, 1419, 1366, 814. 1H-NMR (CDCl3,
400 MHz): 1.21 (6H, t, J = 7.0 Hz, 2 × CH2-CH3), 2.60 (3H, s, SMe), 3.43 (4H, d, J = 7.0 Hz,
2 × N-CH2-), 3.73 (4H, t, J = 5.1 Hz, 2 × -CH2-N), 3.68 (4H, t, J = 5.1 Hz, 2 × O-CH2-), 6.71
(2H, d, J = 9.2 Hz, 3’, 5’-H), 6.93 (1H, s, 5-H), 7.91 (2H, d, J = 9.1 Hz, 2’, 6’-H). 13C-NMR
(DMSO-d6, 100MHz): 12.4, 13.6, 43.7, 48.5, 65.94, 87.5, 104.6, 110.9, 116.6, 123.1, 129.0,
149.1, 156.7, 157.2, 161.1. Anal. Calcd for C21H22N2S2O3 = 382.1827: C, 65.94%; H, 6.85%;
N, 14.65%. Found: C, 65.78%; H, 6.76%; N, 14.63%.
2.5. Fluorescence measurements
The solid-state fluorescence of powdered samples was measured in a Shimadzu RF-5300pc
fluorescence spectrometer. After the excitation spectrum had been measured by scanning at the
fluorescent wavelength, the fluorescence spectrum was obtained using the excitation
wavelength. The fluorescence spectra in solution were obtained in a manner similar to that in
the solid state. To measure the fluorescence in solution, the concentrations of samples were
adjusted using a molar absorption coefficient of 0.05. The fluorescence spectra in solution were
obtained in the same way as the solid-state measurements. Fluorescence quantum yields were
determined using an Absolute PL Quantum Yield Measurement System (C9920-01) from
Hamamatsu Photonics.
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2.6. X-ray crystallography
X-ray diffractometry (XRD) data were obtained with a Rigaku Saturn724 diffractometer using
multilayer mirror monochromated Mo-Kα radiation at -179 ± 1 °C, and all calculations were
conducted using CrystalClear (Rigaku). The structure of 8 (CCDC-1896939) can be obtained
from the Cambridge Crystallographic Data Centre via request
(www.ccdc.cam.au.uk/data_request/cif).
Crystal data for 8: A crystal was obtained by recrystallization from MeOH/acetonitrile (1:1),
which yielded colorless blocks of formula C19H22N4OS having approximate dimensions of
0.270 × 0.080 × 0.020 mm. The crystal was mounted on a glass fiber for data collection.
Crystal data formula weight: 354.47; crystal color: colorless; habit: block; crystal system:
triclinic; lattice type: primitive; lattice parameters: a = 11.072(3) Å, b = 11.374(3) Å, c =
15.493(4) Å, β = 90.259(3)°, V = 1819.7(7) Å3; space group: P-1 (#2); Z-value: 4; calculated
density (Dcalcd): 1.294 g cm–3; F(000) = 752.00; and absorption coefficient (µ(Mo-Kα)) = 1.923
cm–1.
3. Computational details
The ground state geometries of all molecules in vacuo were fully optimized at the density
functional theory (DFT) B3LYP/6-311++G(d,p) level of theory. The lowest excited states (S1)
were geometrically optimized in vacuo by means of time-dependent DFT (TDDFT)
calculations at the B3LYP/6-31+G(d,p) level of theory using the default convergence criterion
for force and displacement implemented in Gaussian 09 [34]. For the optimized geometries, the
S0–S1 (absorption) and the S1–S0 transition energies (fluorescence) were evaluated at the
TDDFT/6-311++G(d,p) and 6-31+(d,p) levels using the B3LYP [35], CAM-B3LYP [36],
PBEPBE [37], M06 [38], and M06-2X [38] exchange–correlation (XC) functionals. Solvent
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effects were taken into account using the polarizable continuum model (PCM).
In the detailed study of 4 and 5, the relaxation paths in S1 were explored from the
Franck–Condon (FC) state to the S1-minimum and to the minimum energy conical
intersections (MECIs) [39], respectively. The MECIs were located using MOLPRO [40] at the
CASSCF(8,7)/def2-SV(P) level of theory. The single point calculations were carried out at the
TDDFT(B3LYP)/def-TZVP level of theory using the TURBOMOLE suite of program [41] to
refine the energies of the S1-FC, the S1-minima, and the S0/S1-MECIs states.
4. Results and discussion
4.1 Synthesis and fluorescence of 2-pyridone tautomeric analogs (4 and 5)
The synthesis of 2-methoxypyridine compound 4 and N-methylpyridone compound 5 is
shown in Scheme 1. The reaction of 4'-dimethylaminoacetophenone (1a) with cyano-keten
S,S-acetal (2a) in the presence of sodium hydroxide as a base in DMSO at room temperature
followed by the addition of 10% hydrochloric acid yielded 2-pyridone compound 3 in 29%.
The methylation of 3 was achieved using dimethyl sulfate in the presence of sodium
hydroxide, and the resultant mixture of 4 and 5 was easily separated by silica gel column
chromatography. Methoxypyridine compound 4 was firstly eluted using toluene in 29% yield,
and N-methylpyridone compound 5 was subsequently eluted using a mixture of toluene and
methanol (ratio 4:1) in 36% yield. Next, we analyzed the fluorescence properties of these
compounds in two solutions (chloroform and ethanol) and the solid state. The absorption
maxima (λmax), emission maxima (Emmax), and Ф values of compounds 3–5 are listed in Table
1. The Emmax values of 4 and 5 were observed at 461 nm in chloroform and at 491 nm in
ethanol, which is a hypsochromic shift of the same extent as that induced by the N- or O-
methylation of 3. The pyridine form compound 4 exhibited strong fluorescence in both
chloroform (Ф > 0.99) and ethanol (Ф = 0.61), whereas the Ф values of the pyridone form
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compound 5 were very low in both chloroform (Ф = 0.12) and ethanol (Ф = 0.05). Because
the fluorescence of 2-pyridone 3 was intense in chloroform (Ф = 0.90) but weak in ethanol
(Ф = 0.11), we speculated that the fluorescence of 2-pyridones 3 in chloroform is due to the
pyridine form (the enol of 2-pyridone), whereas that in ethanol is due to the pyridone form
(the keto of 2-pyridone). In the solid state, the Emmax values of 4 and 5 also occurred at
shorter wavelengths than that of 3; however, N-methylpyridone compound 5 exhibited
stronger fluorescence (Ф = 0.18) than methoxypyridine compound 4 (Ф = 0.03). In a
previous study, we revealed that 2-pyridones, including compound 3 (Ф = 0.17), show
moderate fluorescence in the solid state, and we also reported that the keto–enol equilibrium
of these 2-pyridones is remarkably shifted to the 2-pyridone tautomer on the basis of X-ray
crystal structure analysis [25]. Therefore, the fluorescence intensity of 5 in the solid state is
consistent with our previous results.
Scheme 1.
Table 1.
4.2 Synthesis and fluorescence of 2-substituted pyridines
The molecular packing arrangement and orientation caused by substituents often influence
the fluorescence intensity in the solid state [25,33]. We previously reported that the
introduction of sulfonyl group disrupts the molecular planarity of 2-pyridones, thus
decreasing the π—π stacking interactions [25,42]. Therefore, compounds showing strong
fluorescence in both solution and the solid state could be developed by introducing a
substituent into the pyridine that exhibits strong fluorescence in solution. Thus, we prepared a
series of 2-substitued pyridine compounds: 7–9 and 11 (Scheme 2). After sulfonyl pyridone
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compound 6 had been prepared from the reaction of 1a with 2b, the methylation of 6 using
dimethyl sulfate was conducted, similar to the syntheses of 4 and 5. In this reaction, however,
methoxypyridine compound 7 was only obtained in 42% yield. Morpholinopyridine
compounds 8 and 9 were prepared from 1a and 2a using morphine. After filtration the major
products, 3,2-morpholinopyridine compound 8 and 2,4-dimorpholinopyridine compound 9,
were obtained from the filtrate in 2.6% and 2.1% yields, respectively. Fig. 1 shows the X-ray
crystal structure of compound 8. We previously reported that the replacement of the
dimethylamino group with a diethylamino group at the 6-positon of the 2-pyridone ring
reduces the molecular aggregation, and diethylamino 2-pyridone compound 10 showed
stronger fluorescence than dimethylamino 2-pyridone compound 3 in solution [25,43].
6-(4-Diethylamino)phenyl-2-morpholinopyridine compound 11 was obtained in a similar
manner from the reaction of 1b and 2a.
Scheme 2.
Fig. 1.
The fluorescence properties of 7–9 and 11 in solution (chloroform and ethanol) and the solid
state are summarized in Table 2. The Ф values of phenylsulfonyl-methoxypyridine compound
7 were 0.95 in chloroform and 0.62 in ethanol, which are comparable to that of
methoxypyridine compound 4. Meanwhile, the solid state fluorescence of 7 was increased to
0.15, suggesting that molecular planarity disruption is induced by the introduction of the
phenylsulfonyl group, as in the 2-pyridones [25]. Compounds 8 and 9 contain a morpholino
group instead of a methoxy group and also exhibited strong blue fluorescence in the solid
state (Fig 2), especially dimorpholinopyridine compound 9, which showed intense
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fluorescence (Ф = 0.39). In contrast, the Ф values in solution decreased with increasing
number of morpholino groups. The Emmax of 9 exhibits hypsochromic shifts about 50–65 nm
in solution. 4-Diethylamino morpholinopyridine compound 11 exhibited stronger
fluorescence than 4-dimethylamino morpholinopyridine compound 8 in solution and the solid
state. The emission maximum wavelengths of 11 in chloroform and ethanol were
hypsochromically shifted by about 25 nm, and, interestingly, the solid state emission
wavelength was bathochromically shifted by about 55 nm. The results indicated that the
arrangement of substituents might enable the development of fluorophores exhibiting strong
fluorescence in both solution and the solid state, and these compounds had a potential to be a
fluorophore for clinical diagnostic probes and organic light-emitting materials.
Table 2.
Fig.2
4.3 Solvatochromic effects on absorption and emission
The fluorescence solvatochromic effects depend on the chemical structure and arrangement
of the substituents. We investigated the solvatochromism of compounds 4, 5, 7–9, and 11 in
various solvents except for water. All compounds were hardly soluble in water. The
absorption maxima, emission maxima and fluorescence spectra in nonpolar, aprotic polar, and
protic polar solvents are given in Table 3 and Fig. 3. The absorption maximum wavelengths
of all compounds did not change significantly, but the emission maximum wavelengths of
these compounds were bathochromically shifted as the polarity of the solvent increased. As a
consequence, their Stokes shifts increased in polar solvents. The fluorescence intensity of
pyridine compounds 4, 7–9, and 11 were stronger than that of the 2-pyridone compound 5 in
all solvents (Table 2). The Ф values of 4, 7, and 8 in nonpolar and aprotic polar solvents were
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higher than those in a protic solvent (ethanol). On the other hand, dimorpholinopyridine
compound 9 exhibited strong fluorescence in chloroform and DMSO. 4-Diethylamino
morpholinopyridine compound 11 exhibited intense fluorescence in all solvents, indicating
that it is possible to develop an efficient and stable emissive fluorophore unaffected by
solvent properties.
Table 3
Fig.3
4.4 Computational analysis of the spectroscopic properties: A drastic difference in emission
intensity between 4 and 5
Regarding the absorption spectra, Table 4 lists the computed first intense λmax values of all
compounds. Among the tested XC functionals, the best agreement between the experimental
and computed λmax values were obtained using B3LYP. The computed maxima exhibited red
shifting in order of CAM-B3LYP < M06-2X < M06 < B3LYP < PBEPBE. The long-range
corrected functional CAM-B3LYP severely overestimated the vertical transition energies,
whereas PBEPBE underestimated the energies used to predict the λmax. The inclusion of
solvent effects via the PCM resulted in a red shift in the B3LYP-maxima from 16 nm (9) to 41
nm (5) in chloroform. The B3LYP λmax dependency on the two basis set (6-31+(d,p),
6-311++G(d,p)) is limited to a variation of 2 nm for all the compounds, as shown in Table 5.
Both 4 and 5 undergo considerable intramolecular electron transfer from the dialkylaminoaryl
moiety to methylthioaryl moiety upon S0->S1 excitation, as shown in Fig. 4. The two molecules,
however, have contrasting molecular structures derived from the steric hindrance around the
central single bond. For example, 4 retains a nearly flat structure, whereas 5 has a considerable
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twist around the bond owing to the repulsion between the methylthio group and the counterpart
aryl group, as shown in Fig. 5.
Table 4
Table 5
Fig. 4
Fig. 5
For the fluorescence spectra, Table 6 shows the computed first intense emission maxima for all
compounds. The 6-31+G(d,p) basis set was uniformly employed considering the minor basis
set dependency mentioned above. The prediction trend is similar to that observed for
absorption, and λmax shifted bathochromically in order of CAM-B3LYP < M06-2X < M06 <
B3LYP < PBEPBE. The best agreement exists between B3LYP (overestimation) and PBEPBE
(underestimation), excluding 4 and 5, whose maxima were consistently predicted at shorter
wavelength using all XC functionals.
Table 6
Notably, 4 and 5 exhibited contrasting emission intensities in solution despite only differing in
the modification at the nitrogen atom of the pyridine ring. We attempted to elucidate the
mechanism by locating the S1-minima and the S0/S1 crossing seam along with the relaxation
pathways. The non-radiative decay channels occur along the seam of the S0/S1 conical
intersections (CIs), which are represented by its minimum energy points (MECIs). The
S0/S1-MECI geometries of 4 and 5 optimized at the CASSCF(8,7)/def2-SV(P) level of theory,
are shown in Fig. 6.
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Fig. 6
Our calculations clearly show the drastic differences in the energy gap between the S1-FC and
the S0/S1-MECI for the two molecules with severely distorted pyridine rings, as shown in Fig. 7.
Compound 4 has a large gap, which is sufficient to separate the two states and prohibit the
interconversion between S1-FC and the S0/S1-MECI states, resulting in 4 being highly emissive.
Conversely, 5 has a small gap, which allows the two states to be mutually accessible, and the S1
excited molecule can radiationlessly return to the ground state via the S0/S1-MECI. The S0
energy is not exactly identical to the S1 energy because the optimized MECI geometry was
obtained at the CASSCF(8,7)/def2-SV(P) level of theory (not B3LYP/def-TZVP).
Fig. 7
In the solid state, the fluorescence intensity of 4 became weak, whereas that of 5 was enhanced
in comparison with that in ethanol. This indicates that the intermolecular stacking interactions
dominate the emission intensities of the two molecules. That is, 4, which has a planar structure,
can stack in the solid state, which activates non-radiative energy dissipation pathways, whereas
the emission enhancement of 5, which has a twisted structure, is caused by the inaccessibility
of the S0/S1-MECI state owing to intermolecular steric hindrance. This is consistent with the
observation of the emission enhancement of 9, which has two bulky moieties, compared to the
emissions of 4 and 5.
5. Conclusion
To elucidate the influence of the keto–enol tautomerism of 2-pyridone rings on the
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fluorescence intensity, we synthesized two 2-pyridone tautomeric analogs, methoxypyridine
compound 4 and N-methylpyridone compound 5, and demonstrated that compound 4 (enol
form) shows strong fluorescence in both nonpolar and polar solvents, whereas 5 shows quite
weak fluorescence. The computational analysis successfully explained the drastic difference in
the fluorescence intensities between the two molecules in solution, which arises because of the
energy gap between the S1-FC and the S0/S1-MECI states of the two molecules. That is, 4 has a
gap that is sufficiently large to separate the two states and prohibit their interconversion, thus
maintaining 4 in a highly emissive state. On the other hand, 5 has a small gap that allows the
two states to transition between each other, and the molecule returns to the ground state via the
S0/S1-MECI radiationlessly. On the basis of these results, novel 2-substituted pyridine
compounds 7–9 and 11 were synthesized from dialkylaminoacetophenones with cyanoketen
S,S-acetals, and their fluorescence properties in solution and the solid state were evaluated.
The substituents including phenylsulfonyl, morpholino, and 4-diethylamino groups greatly
affected the fluorescence intensity in solution and the solid state. 2-Methoxypyridine
compound 7 and 2-morpholinopyridine compound 8 exhibited solid-state fluorescence and a
high fluorescence quantum yield in solution. Although its solution fluorescence was
decreased, dimorpholinopyridine compound 9 exhibited strong fluorescence (Ф = 0.39) in the
solid state. In addition, a 4-diethylamino morpholinopyridine compound having
4-diethylamino group (11) exhibited intense fluorescence in all solvents because aggregation
was prevented. These findings may be useful for the development of fluorophores exhibiting
strong fluorescence in solution and the solid state.
Acknowledgments
This work was partly supported by a research grant from The Mazda Foundation.
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References
423
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[1]
Chen X, Wang F, Hyun JY, Wei T, Qiang J, Ren X, Shin I, Yoon J. Recent progress
in the development of fluorescent, luminescent and colorimetric probes for detection
of reactive oxygen and nitrogen species. Chem Soc Rev 2016;45(10):2976–3016.
Specht EA, Braselmann E, Palmer AE. A critical and comparative review of
fluorescent tools for live-cell imaging. Annu Rev Physiol 2017;79:93–117.
Basabe-Desmonts L, Reinhoudt DN, Crego-Calama M. Design of fluorescent
materials for chemical sensing. Chem Soc Rev 2007;36(6):993–1017.
Shcherbakova DM, Baloban M, Emelyanov AV, Brenowitz M, Guo P, Verkhusha VV.
Bright monomeric near-infrared fluorescent proteins as tags and biosensors for
multiscale imaging. Nat Commun 2016;7:12405.
[2]
[3]
[4]
[5]
Zhao P, Xu Q, Tao J, Jin Z, Pan Y, Yu C, Yu Z. Near infrared quantum dots in
biomedical applications: current status and future perspective. Wiley Interdiscip Rev
Nanomed Nanobiotechnol 2018;10(3):e1483.
[6]
[7]
Wang X, Liu L, Zhu S, Li L. Fluorescent platforms based on organic molecules for
chemical and biological detection. Phys Status Solidi RRL 2018:1800521.
He L, Lin W, Xu Q, Ren M, Wei H, Wang JY. A simple and effective "capping"
approach to readily tune the fluorescence of near-infrared cyanines. Chem Sci
2015;6(8):4530–36.
[8]
[9]
Sueki S, Takei R, Zaitsu Y, Abe J, Fukuda A, Seto K, Furukawa Y, Shimizu I.
Synthesis of 1,4-dihydropyridines and their fluorescence properties. Eur J Org Chem
2014;2014(24):5281–301.
Duan L, Qiao J, Sun Y, Qiu Y. Strategies to design bipolar small molecules for
OLEDs: donor-acceptor structure and non-donor-acceptor structure. Adv Mater
2011;23(9):1137–44.
[10] Terai T, Nagano T. Small-molecule fluorophores and fluorescent probes for
bioimaging. Pflugers Arch 2013;465(3):347–59.
18

ACCEPTED MANUSCRIPT
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
[11] Zhu H, Fan J, Du J, Peng X. Fluorescent probes for sensing and imaging within
specific cellular organelles. Acc Chem Res 2016;49:2115–26.
[12] Hagimori M, Taniura M, Mizuyama N, Karimine Y, Kawakami S, Saji H, Mukai T.
Synthesis of a novel pyrazine–pyridone biheteroaryl-based fluorescence sensor and
detection of endogenous labile zinc ions in lung cancer cells. Sensors 2019;19(9):
2049–60.
[13] Duan C, Won M, Verwilst P, Xu J, Kim HS, Zeng L, Kim JS. In vivo imaging of
endogenously produced HClO in zebrafish and mice using a bright, photostable
ratiometric fluorescent probe. Anal Chem 2019;91:4172−8.
[14] Duan C, Zhou Y, Shan GG, Chen Y, Zhao W, Yuan D, Zeng L, Huang X, Niu G.
Bright solid-state red-emissive BODIPYs: facile synthesis and their high-contrast
mechanochromic properties. J Mater Chem C 2019;7:3471—8.
[15]
Duan C, Zhang JF, Hu Y, Zeng L, Su D, Bao GM. A distinctive near-infrared
fluorescence turn-on probe for rapid, sensitive and chromogenic detection of sulfite
in food. Dyes Pigm 2019;162:459-65.
[16] Li Q, Mitscher LA, Shen LL. The 2-pyridone antibacterial agents: bacterial
topoisomerase inhibitors. Med Res Rev 2000;20(4):231–93.
[17] Li LN, Wang L, Cheng YN, Cao ZQ, Zhang XK, Guo XL. Discovery and
characterization of 4-hydroxy-2-pyridone derivative sambutoxin as a potent and
promising anticancer drug candidate: Activity and molecular mechanism. Mol Pharm
2018;15(11):4898–911.
[18] Jia H, Song Y, Yu J, Zhan P, Rai D, Liang X, Ma C, Liu X. Design, synthesis and
primary biological evaluation of the novel 2-pyridone derivatives as potent
non-nucleoside HBV inhibitors. Eur J Med Chem 2017;136:144–53.
[19] Isaka M, Tanticharoen M, Kongsaeree P, Thebtaranonth Y. Structures of
cordypyridones A-D, antimalarial N-hydroxy- and N-methoxy-2-pyridones from the
insect pathogenic fungus Cordyceps nipponica. J Org Chem 2001;66:4803–8.
19

ACCEPTED MANUSCRIPT
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
[20] Ershov OV, Fedoseev SV, Ievlev MYu, Belikov MYu. 2-Pyridone-based
fluorophores: Synthesis and fluorescent properties of pyrrolo[3,4-c]pyridine
derivatives. Dyes Pigm 2016;134:459–64.
[21] Sellstedt M, Nyberg A, Rosenbaum E, Engström P, Wickström M, Gullbo J,
Bergström S, Johansson L. B.-Å, Almqvist F. Synthesis and characterization of a
multi ring-fused 2-pyridone-based fluorescent scaffold. Eur J Org Chem
2010;2010(32):6171–8.
[22]
Hagimori M, Uto T, Mizuyama N, Temma T, Yamaguchi Y, Tominaga Y, Saji H.
Fluorescence ON/OFF switching Zn2+ sensor based on pyridine–pyridone scaffold.
Sens Act B Chem 2013;181:823–8.
[23] Shigemitsu Y, Hagimori M, Mizuyama N, Wang BC, Tominaga Y. Theoretical
interpretations of electronic and fluorescence spectra of new 2(1H)-pyridone
derivatives in solution and solid state. Dyes Pigm 2013;99(3):940–9.
[24] Hagimori M, Temma T, Mizuyama N, Uto T, Yamaguchi Y, Tominaga Y, Mukai T,
Saji H. A high-affinity fluorescent Zn2+ sensor improved by the suppression of
pyridine-pyridone tautomerism and its application in living cells. Sens Act B Chem
2015;213:45-52.
[25]
Hagimori M, Shigemitsu Y, Murakami R, Yokota K, Nishimura Y, Mizuyama N,
Wang BC, Tai CK, Wang SL, Shih TL, Wu KD, Huang ZS, Tseng SC, Lu JW, Wei
HH, Nagaoka J, Mukai T, Kawashima S, Kawashima K, Tominaga Y.
2-Pyridone-based fluorophores containing 4-dialkylamino-phenyl group: Synthesis
and fluorescence properties in solutions and in solid state. Dyes Pigm
2016;124:196–202.
[26] Wong MW, Wiberg KB, Frisch MJ. Solvent effects. 3. Tautomeric equilibria of
formamide and 2-pyridone in the gas phase and solution: an ab initio SCRF study. J
Am Chem Soc 1992;114:1645–52.
[27]
Forlani L, Cristoni G, Boga C, Todesco PE, Del Vecchio E, Selva S, Monari M.
20

ACCEPTED MANUSCRIPT
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
Reinvestigation of tautomerism of some substituted 2-hydroxypyridines. Arkivoc
2002;XI:198–215.
[28] Hejazi SA, Osman OI, Alyoubi AO, Aziz SG, Hilal RH. The thermodynamic and
kinetic properties of 2-hydroxypyridine/2-pyridone tautomerization: A theoretical and
computational revisit. Int J Mol Sci 2016;17(11):E1893.
[29] Frank J, Katritzky AR. Tautomeric pyridines. Part XV. Pyridone–hydroxypyridine
equilibria in solvents of differing polarity. J Chem Soc Perkin Trans 2 1976:1428–31.
[30] El-Kemary M, Rettig W. Multiple emission in coumarins with heterocyclic
substituents. Phys Chem Chem Phys 2003;5:5221–8.
[31] Yamaguchi E, Wang C, Fukazawa A, Taki M, Sato Y, Sasaki T, Ueda M, Sasaki N,
Higashiyama T, Yamaguchi S. Environment-sensitive fluorescent probe: a
benzophosphole oxide with an electron-donating substituent. Angew Chem Int Ed
Engl 2015;54(15):4539–43.
[32] Hagimori M, Mizuyama N, Shigemitsu Y, Wang BC, Tominaga Y. Development of
fluorescent 2-pyrone derivatives using ketene dithioacetals for organic EL devices.
Heterocycles 2009;78(3):555–70.
[33] Sun Y, Sun Y, Zhao S, Cao D, Guan R, Liu Z, Yu X, Zhao X. Efficient solution- and
solid-state fluorescence for a series of 7-diethylaminocoumarin amide compounds.
Asian J Org Chem 2018;7:197–202.
[34] Gaussian 09, Rev. A.2. Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA,
Cheeseman JR, et al: Gaussian, Inc. Pittsburgh PA.
[35] Becke, A.D. Becke’s three parameter hybrid method using the LYP correlation
functional. J Chem Phys 1993;98:5648–52.
[36] Yanai T, Tew DP, Handy NC. A new hybrid exchange–correlation functional using
the Coulomb-attenuating method (CAM-B3LYP). Chem Phys Lett 2004;393(1–3):
51–7.
[37] Adamo C, Barone V. Toward reliable density functional methods without adjustable
21

ACCEPTED MANUSCRIPT
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
parameters: The PBE0 model. J Chem Phys 1999;110:6158–69
[38] Zhao Y, Truhlar DG. The M06 suite of density functionals for main group
thermochemistry, thermochemical kinetics, noncovalent interactions, excited states,
and transition elements: two new functionals and systematic testing of four M06-class
functionals and 12 other functionals. Theor Chem Acc 2008; 120: 215–41.
[39] Yarkony DR. Conical intersections: Diabolical and often misunderstood. Acc Chem
Res 1998;31(8):511–8.
[40] Werner HJ, Knowles PJ, Knizia G, Manby FR, Schütz M, et al. MOLPRO, version
2015.1, a package of ab initio programs, see http://www.molpro.net.
[41] TURBOMOLE V7.1 2017, a development of University of Karlsruhe and
Forschungszentrum Karlsruhe GmbH, 1989-2007,TURBOMOLE GmbH, since 2007;
available fromhttp://www.turbomole.com.
[42] Hagimori M, Matsui S, Mizuyama N, Yokota K, Nagaoka J, Tominaga Y. Novel
synthesis of 4H-quinolizine derivatives using sulfonyl ketene dithioacetals. Eur J Org
Chem 2009;2009(33):5847–53.
[43] Hagimori M, Mizuyama N, Yokota K, Nishimura Y, Suzuta M, Tai CK, Wang BC,
Wang SL, Shih TL, Wu KD, Huang ZS, Tseng SC, Chen CY, Lu JW, Wei HH,
Kawashima
K,
Kawashima
S,
Tominaga
Y.
Synthesis
of
6-(4-diethylamino)phenyl-2-oxo-2H-pyran-3-carbonitorile derivatives and their
fluorescence in solid state and in solutions. Dyes Pigm 2012;92(3):1069–74.
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Computed absoption
B3LYP
(nm) and Oschillator strength f using several XC-functionals
Table 4
λmax
B3LYP in CHCl3
CAM-B3LYP
PBEPBE
λmax
M06
M06-2X
λmax
Compounds
λmax
377
374
370
380
363
382
f
λmax
409
415
396
403
379
404
f
λmax
330
331
323
335
319
336
f
f
λmax
366
362
360
370
352
371
f
f
4
5
0.77
0.54
0.73
0.57
0.44
0.63
0.93
0.57
0.87
0.85
0.81
0.88
0.97
0.65
0.97
0.67
0.65
0.71
440
447
444
437
414
441
0.55
0.32
0.40
0.43
0.34
0.39
0.82
0.59
0.78
0.62
0.56
0.66
331
331
325
337
320
337
0.98
0.67
0.97
0.69
0.67
0.73
7
8
9
11

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Computed absoption
Compounds
(nm) and Oschillator strength f using the two basis sets
Table 5
λmax
6-31+G**
6-311++G**
λmax
377
374
370
380
363
382
f
λmax
f
4
5
0.77
0.54
0.73
0.57
0.44
0.63
378
375
372
381
364
383
0.77
0.54
0.73
0.56
0.44
0.62
7
8
9
11

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Computed fluorescence
B3LYP
(nm) and Oschillator strength f using several XC-functionals
Table 6
λmax
CAM-B3LYP
PBEPBE
M06
M06-2X
λmax
Compounds
λmax
351
363
386
392
372
402
f
λmax
f
λmax
f
λmax
349
435
377
383
365
388
f
f
4
5
0.03
0.24
0.95
0.82
0.79
0.77
337
349
344
347
334
347
0.00
0.26
1.11
1.00
1.03
1.00
415
460
446
457
421
482
0.02
0.02
0.69
0.47
0.57
0.51
0.03
0.02
0.98
0.86
0.9
312
352
345
348
335
348
0.03
0.18
1.12
1.01
1.03
0.99
7
8
9
11
0.83

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Fig. 1. ORTEP drawing of 8.