Thermally stable nonaggregating pyrenylarenes for blue organic light-emitting devices

Article abstract of DOI:10.1021/jo2011768

A new series of thermally stable blue light-emitting nonplanar pyrenylarenes having an amine donor and a nitrile acceptor group was prepared from a ketene-S,S-acetal under conventional heating and/or microwave irradiation. The photophysical, electrochemic

Full text of DOI:10.1021/jo2011768

ARTICLE
pubs.acs.org/joc
Thermally Stable Nonaggregating Pyrenylarenes for Blue Organic
Light-Emitting Devices†,^
Atul Goel,*,‡,# Vijay Kumar,‡ Pankaj Nag,‡ Vikas Bajpai,§ Brijesh Kumar,§ Charan Singh,||
Sattey Prakash,|| and R. S. Anand||
‡Divisions of Medicinal and Process Chemistry, and §Sophisticated Analytical Instrument Facility, CSIR-Central Drug Research
Institute, Lucknow 226001, India
Department of Electrical Engineering, Indian Institute of Technology, Kanpur 208016, India
S Supporting Information
b
ABSTRACT: A new series of thermally stable blue light-
emitting nonplanar pyrenylarenes having an amine donor and
a nitrile acceptor group was prepared from a ketene-S,S-acetal
under conventional heating and/or microwave irradiation. The
photophysical, electrochemical, and optical behavior of donorꢀ
acceptor pyrenylarenes are demonstrated. The performance of
blue light-emitting pyrenylarenes was investigated by fabricat-
ing a multilayer device with the device configuration of ITO/
PEDOT:PSS (40 nm)/NPB (30 nm)/pyrenylarene (55 nm)/
BCP (8 nm)/LiF (0.6 nm)/Al (200 nm), which exhibited low
turn-on voltage (5 V) with luminance efficiency of 0.8 Cd/A with nonaggregation behavior in both solution and solid state.
’ INTRODUCTION
The most common procedure for aryl/aryl couplings at posi-
tion 1 of pyrene is the Gomberg reaction of diazonium arenes
with pyrene.11 The products obtained in low yields are accom-
panied by regioisomers. Suzuki cross-coupling reactions,12 being
presently the most efficient and widely applicable aryl/aryl bond-
forming reactions, have been employed as the key reaction for the
coupling of pyrene with substituted aryl partners in low yields.13
Over the past decade, our group is involved in developing new
methodologies for preparing arenes and heteroarenes of biolo-
gical and material importance. We recently developed a new
methodology14 for the synthesis of functionalized fluoranthenes
and demonstrated that donorꢀacceptor fluoranthenes are po-
tential candidates for developing yellow organic light-emitting
diodes. We have also shown that appropriately functionalized
donorꢀacceptor quateraryls15 and 9-unsubstituted fluorenes
and fluorenones exhibited efficient, stable blue emission and
demonstrated their potential application in developing effi-
cient blue OLEDs.16 We have revealed how the positioning
of donorꢀacceptor groups onto the fluorene-fluorenone back-
bone transforms the green emission to blue emission.16 In order
to investigate photophysical and optical properties of pyrenylar-
enes, a simple, general, and efficient synthetic route that
could offer flexibility of substituent variations in their molecular
framework was desirable. Herein, we report a suitable pro-
tocol for generating a variety of pyrenylarene derivatives with
donorꢀacceptor and various chromophoric functionalities in a
Pyrene belongs to the class of polycyclic aromatic hydrocar-
bons (PAHs), which by virtue of their interesting photophysical1
and electrochemical2 properties have been widely used in many
applications such as molecular probes,3 fluorescent sensors,4
liquid crystalline materials,5 and supramolecular self-assembly6
and in carbon nanotube functionalization.7 Pyrene-containing
receptors for transition metal ions were also reported as a ver-
satile class of photoactive supramolecular systems.8 Recently,
pyrene derivatives have been developed as hole-transporting
materials or host blue-emitting materials in organic light-emitting
diodes (OLEDs).9 However, the use of pyrenes as emitters in
OLEDs is limited because pyrenes easily form π-aggregates,
leading to excimer emission with low quantum efficiency.10 Thus,
there is substantial interest10d in design and synthesis of new
pyrene-based blue light-emitting molecules which have no aggre-
gating behavior in the solid state.
In order to prevent aggregation, we designed a new series of
thermally stable pyrenylarenes as blue emissive materials, in
which the pyrene ring is attached with a nonplanar teraryl moiety
having a donor and an acceptor group to tune the electronꢀhole
combination efficiency. We surmised that the sterically con-
gested teraryl ring at position 1 of pyrene would lie perpendicular
to the plane of the core pyrene ring to prevent undesirable face-
to-face π-stacking, so that self-quenching may be prevented to
permit efficient emission in solution and the solid state.
Received: June 20, 2011
Published: August 01, 2011
† CDRI communication No. 8097.
r
2011 American Chemical Society
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rapid manner and further explore their nonaggregating behavior
for potential use in blue OLEDs.
functionality, a good leaving methylsulfanyl group of lactone 3 was
replaced with an amine (piperidine/4-methylpiperidine) to furnish
2-oxo-4-(piperidin-1-yl/4-methylpiperidin-1-yl)-6-(pyren-1-yl)-
2H-pyran-3-carbonitrile (4a,b) in quantitative yields. To prepare
pyrenylarenes with substituents particularly at the ortho position
around the biaryl axis to inhibit πꢀπ overlapping, an equimolar
mixture of 4a was reacted with aliphatic aldehydes 5a,b in the
presence of KOH and DMF at room temperature for 12ꢀ14 h to
furnish pyrenylarenes 6a,b as shown in Scheme 1.
To demonstrate the synthetic utility and scope of this meth-
odology for preparing functionally hindered pyrenylarenes, a
reaction of 2-oxo-4-(piperidin-1-yl/4-methylpiperidin-1-yl)-6-
(pyren-1-yl)-2H-pyran-3-carbonitriles (4a,b) with 1-(4-methox-
yphenyl)propan-2-one 7 was carried out, which afforded sub-
stituted pyrenes 8a,b in good yields (Scheme 2).
To generalize this methodology further for furnishing func-
tionally congested pyrenes, an independent reaction of 4a with
functionalized deoxybenzoin 9aꢀd was carried out to afford
10aꢀd at room temperature (Scheme 3). The ring transforma-
tion reaction proceeded slowly, yielding 65ꢀ76% of desired
product after 15ꢀ17 h (Table 1). In order to optimize the reac-
tion conditions, these reactions were performed under conven-
tional heating as well as under microwave irradiation at 100 ꢀC
using an internal probe.
’ RESULTS AND DISCUSSION
Synthesis. The designed pyrenylarene compounds for blue
light-emitting applications were synthesized by preparing a key
intermediate R-oxo-ketene-S,S-acetal17 2 from easily accessible
precursors methyl cyanoacetate, carbon disulfide, and methyl
iodide, following the Tominaga protocol.18 Substrate 2, upon
Michael additionꢀcyclization reaction with 1-(pyren-1-yl)etha-
none 1 under alkaline conditions, furnished 4-(methylthio)-2-oxo-
6-(pyren-1-yl)-2H-pyran-3-carbonitrile 3in excellent yield (Scheme 1).
In order to prepare compounds with a donor (N,N-dialkylamine)
Scheme 1. Synthesis of Pyrenes 6a,b
When the reactions were carried out under conventional
heating at 100 ꢀC, the reaction time was reduced from 17 to
1 h and yields were comparable to that obtained at room
temperature (Table 2). Longer reaction time or higher tempera-
ture did not show any further improvement. Therefore, micro-
wave-assisted methodology was attempted and compared with
the conventional heating protocol using the same reagents and
solvent (Table 2). Notably, the reaction time was significantly
reduced from 17 h (at room temperature condition) to 1 h
(under conventional heating) and further to 10 min (under
microwave irradiation) without compromising the yields. The
cycloaddition reactions between 2H-pyran-2-ones as a diene and
alkene or alkyne as a dienophile under microwave conditions
generally lead to a mixture of endo/exo products or a mixture of
product with unreacted starting material. However for the first
time, we report the reaction of 2H-pyran-2-one with a methylene
carbonyl compound under microwave condition to afford a
single aromatic compound in good yield.
Studies of Photophysical, Optical, and Electrochemical
Properties. The optical, thermal, and electrochemical properties
of these pyrenylarenes in dilute solutions and in the solid state
Scheme 2. Synthesis of Pyrenes 8a,b
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Scheme 3. Synthesis of Pyrenes 10aꢀd
Table 1. Synthesis of 10aꢀd at Room Temperature
entry
R1
R2
reaction time (h)
yield (%)
10a
10b
10c
10d
H
H
H
16
15
15
17
70
72
74
68
OMe
OMe
OMe
OMe
phenyl
Table 2. Synthesis of 10aꢀd under Conventional Heating or
Microwave Irradiation
reaction time (min)
yield (%)
entry
R1
R2
Δ
μW
Δ
μW
Figure 1. Absorbance and fluorescence spectra of pyrenes 6b, 8a, and
10c in THF (∼10ꢀ6 M).
10a
10b
10c
10d
H
H
H
60
60
60
60
10
10
10
10
72
75
76
68
70
74
75
65
OMe
OMe
OMe
OMe
phenyl
an additional low intensity broad band in the vicinity of
470 nm.19 In order to evaluate the behavior of synthesized pyreny-
larenes (6a,b, 8a,b, and 10aꢀd) at different concentrations, we
examined the concentration effect of 10c with respect to fluores-
cence emission in dry THF. By increasing the concentration from
10ꢀ6 M to 10ꢀ3 M (Figure 2), the intensity of PL band increased
gradually up to the concentration of 10ꢀ4 M and then reduced at
10ꢀ3 M. Importantly, in all concentrations, the emission corre-
sponded only to the monomer at 454ꢀ456 nm (Figure 2). No red
shift or additional peak of excimer formation was observed in
pyrenylarene 10c.
The solid-state fluorescence of 10c was further examined using
both powder and a thin film prepared by vacuum evaporation on
glass substrate (Figure 3). The thin film on the glass substrate was
continuous and exhibited emission at 450 nm. The powder of
10c exhibited strong blue emission with a maximum peak at
440 nm as shown in Figure 3 (for other compounds, see the
Supporting Information), which was 10 nm blue-shifted from the
emission maxima of the thin film (Figure 3). In comparison to
the emission spectra in the dilute solution, the solid-state
emission was slightly blue-shifted, which confirmed that indeed
there is no excimer formation in the solid state.
were investigated. The electronic absorbance maxima (λmax),
emission maxima (λmax), the fluorescence quantum yield,
HOMO/LUMO energy levels, and electrochemical band gap
(Eop) for all pyrene derivatives 6a,b, 8a,b, and 10aꢀd are
summarized in Table 3.
The UVꢀvis absorption and photoluminance (PL) spectra of
some of the representative pyrenylarenes 6b, 8a, and 10c are
shown in Figure 1. The absorption spectra of all pyrenylarenes
revealed a vibronic feature that was characteristic for unsubsti-
tuted parent pyrene with a short wavelength absorption
maximum at 277ꢀ279 nm.1 The long wavelength absorption
maxima for all pyrenylarenes (6a,b, 8a,b, and 10aꢀd) occur at
344ꢀ347 nm. Upon excitation at 350 nm, all pyrenylarenes
showed blue emission characteristics with the emission maxima
in the range of 445ꢀ456 nm with quantum yields up to 76% as
shown in Table 3. The full-width at half-maximum (fwhm) for
each individual emission was observed in the range from 62
to 70 nm.
Unsubstituted pyrene shows PLmax at 393 nm,10c while the
donorꢀacceptor pyrenylarenes 6a,b, 8a,b, and 10aꢀd showed a
PL emission maximum in the range of 445ꢀ456 nm. At a
concentration of 10ꢀ4 M and above, unsubstituted pyrene shows
excimer emission with stable steric configuration leading to
The electrochemical studies were carried out to ascertain the
redox behavior of the pyrenes (6a,b, 8a,b, and 10aꢀd). Cyclic
voltammetric measurements were performed in a three-electrode
cell setup using Ag/AgCl as standard electrode and Pt disk as the
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Table 3. Optical and Electrochemical Properties of Pyrenes 6a,b, 8a,b, and 10aꢀd
entry
λmax; absa (nm)
λmax; emb (nm)
Φfd (%)
HOMO (eV)
LUMO (eV)
Eope (eV)
6a
277, 344
277, 344
278, 345
278, 345
279, 346
279, 346
279, 347
278, 347
456 (70)c
448 (68)c
451 (67)c
452 (65)c
445 (62)c
446 (63)c
455 (65)c
450 (62)c
68
65
71
69
70
72
76
73
ꢀ5.50
ꢀ5.49
ꢀ5.51
ꢀ5.53
ꢀ5.54
ꢀ5.56
ꢀ5.50
ꢀ5.50
ꢀ2.68
ꢀ2.64
ꢀ2.70
ꢀ2.74
ꢀ2.72
ꢀ2.70
ꢀ2.68
ꢀ2.74
2.82
2.85
2.81
2.79
2.82
2.86
2.82
2.76
6b
8a
8b
10a
10b
10c
10d
a Longest wavelength absorption maximum in THF. b Fluorescence emission maximum in THF. c Full-width at half-maximum (fwhm). d Fluorescence
quantum yield relative to harmine in 0.1 M H2SO4 as a standard (Φ = 0.45). e Optical band gap from CV.
Figure 4. Cyclic voltammogram of 10c in DMF under N2 atmosphere.
Figure 2. Effect of concentration on the fluorescence emission spec-
trum of 10c in THF.
Figure 5. TGA plot of 10c under N2 atmosphere.
in DMF. All the potentials were calibrated with ferrocene, and the
data are summarized in Table 3.
Two irreversible oxidation and one reversible reduction peak
were observed for pyrenylarenes 10aꢀd as exemplary shown for
10c in Figure 4 (for 10a,b,d, see Supporting Information), which
indicates that radical anions are stable entities but the radical
cations (oxidized species) may react with the solvent DMF or the
supporting electrolyte. The HOMO and LUMO levels were
calculated by using onset of first oxidation and reduction peak.
The results are presented in Table 3. The calculated HOMO
values are in the range of ꢀ5.49 to ꢀ5.56 eV, indicating that
these materials are suitable for application in OLEDs.
The thermal properties of selected pyrenylarenes 6b, 8a, and
10c were gauged by thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC) (see Supporting In-
formation). Pyrenylarene 10c exhibited high thermal stability
as demonstrated by its TGA (Figure 5), with its 5% weight loss
temperature under nitrogen atmosphere being up to 370 ꢀC. The
DSC results of 6b, 8a, and 10c are shown in Figure 6. DSC was
Figure 3. PL spectrum of compound 10c in solution (in THF) and in
solid-state (powder and the thin film). The inset shows photograph of
the blue emission from 10c in THF.
working electrode, using 2 mM pyrenylarene and 0.2 M electrolyte
tetrabutylammonium hexafluorophosphate (Bu4NPF6) dissolved
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Figure 6. DSC plots of 6b, 8a, and 10c under N2 atmosphere.
Figure 8. IꢀLꢀV characteristics of device of 10c (insert shows the EL
spectrum).
Figure 7. Relative energy-level alignment and layer thickness of OLED
10c and actual device picture of 10c.
performed in the temperature range from 50 ꢀC to 350 ꢀC. DSC
analysis indicates that there was no phase transformation of 6b,
8a, and 10c before the samples completely melted. Figure 6
display the DSC curve of 6b, 8a, and 10c. Pyrene 6b and 8b
melted at 159 ꢀC and 245 ꢀC, respectively, while 10c with a
higher molecular weight showed a higher melting temperature
of 287 ꢀC.
OLED Device Performance. On the basis of photophysical,
optical, and electrochemical studies, pyrenylarene 10c was
selected for further studies to demonstrate the application in
preparing a organic light-emitting device. A multilayer device was
fabricated to investigate the performance of blue light-emitting
pyrene 10c with the device configuration of ITO/PEDOT:PSS
(40 nm)/NPB (30 nm)/pyrenylarene (55 nm)/BCP (8 nm)/
LiF (0.6 nm)/Al (200 nm). The relative energy-level alignment
of the fabricated multilayered OLED and actual device picture of
10c are shown in Figure 7.
Figure 9. Electrochemical stability vs voltage curves of 10c. Insert
shows the luminance efficiency vs voltage curve of 10c.
S-acetals in good yields. For the first time, we successfully
demonstrated microwave-assisted carbanion-induced ring trans-
formation of 2H-pyran-2-ones into a benzene ring under mild
reaction conditions in a short time. Our methodology is oper-
ationally simple and convenient and does not require any
specialized organometal catalyst or reagents. In addition, we
have uncovered the photophysical, optical, and electrochemical
properties of these interesting nonaggregating and thermally
stable blue pyrenylarenes and demonstrated their potential use in
preparing high demanding blue OLEDs.
Figure 8 shows the IꢀLꢀV characteristics and EL spectrum of
10c as inset. The EL spectrum of device 10c showed a band at
465 nm, which was slightly red-shifted relative to PL in solution
(455 nm). To further evaluate the electrochemical stability of
pyrenylarene 10c, the EL characteristics of 10c was recorded
with an increase in applied voltage at an interval of 1 V (Figure 9).
The device of 10c was found to be stable even under bias stress
up to 9 V. The device of 10c was quite efficient with low turn-on
voltage (5 V) and exhibiting good luminance efficiency of 0.8
Cd/A (Figure 9).
’ EXPERIMENTAL SECTION
Synthesis of 4-(Methylsulfanyl)-2-oxo-6-(pyren-1-yl)-2H-
pyran-3-carbonitrile (3). A mixture of methyl 2-cyano-3,3-dimethyl-
sulfanylacrylate (2, 203 mg, 1 mmol), 1-(pyren-1-yl)ethanone (1, 293
mg, 1.2 mmol), and powdered KOH (67 mg, 1.2 mmol) in dry DMSO
(6 mL) was stirred at room temperature for 12 h. After completion, the
reaction mixture was poured into iceꢀwater with constant stirring. The
precipitate thus obtained was filtered and purified on a silica gel column
using chloroform as the eluent to afford 3 (323 mg, 88%) as a yellow
solid: Rf = 0.55 (n-hexane/ethyl acetate, 6:4, v/v); mp (chloroform) >
250 ꢀC; MS (ESI+) 368 [M + H+]; IR (KBr) ν = 2223 (s), 1723 (s),
In conclusion, we have developed an efficient method for the
preparation of pyrenylarenes with a variety of donorꢀacceptor
and chromophoric substituents from easily accessible ketene-S,
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1589 (s) cmꢀ1; 1H NMR (400 MHz, DMSO-d6 at 50 ꢀC): δ = 2.84 (s,
3H), 7.21 (s, 1H), 8.17 (t, J = 7.6 Hz, 1H), 8.28 (d, J = 8.7 Hz, 1H),
8.34ꢀ8.44 (m, 6H), 8.58 (d, J = 9.6 Hz, 1H) ppm; HRMS calculated for
C23H14NO2S (M+ + H) 368.07452, found: 368.07367.
[M + H+]; IR (KBr) ν = 3037 (m), 2931 (s), 2856 (w), 2806 (s), 2213
(s), 1598 (s), cmꢀ1; 1H NMR (300 MHz, DMSO-d6): δ = 0.46ꢀ0.56
(m, 3H), 1.16ꢀ1.27 (m, 2H), 1.46ꢀ1.55 (m, 2H), 1.62ꢀ1.72 (m,
4H), 2.12ꢀ2.38 (m, 2H), 3.08ꢀ3.16 (m, 4H), 7.01 (s, 1H), 7.61 (d,
J = 9.2 Hz, 1H), 7.77 (s, 1H), 7.93 (d, J = 7.8Hz, 1H), 8.08ꢀ8.18 (m, 2H),
8.22ꢀ8.42 (m, 5H) ppm; 13C NMR (75 MHz, CDCl3): δ = 13.6, 23.6,
24.0, 26.1, 29.7, 34.2, 53.2, 105.1, 118.9, 121.3, 124.3, 124.6, 124.8, 125.2,
125.4, 126.2, 126.8, 127.3, 127.6, 127.8, 128.7, 130.8, 131.3, 134.5, 134.7,
135.6, 146.1, 154.3 ppm; HRMS calculated for C31H29N2 (M+ + H)
429.2331, found: 429.2340.
Synthesis of 40-Methoxy-2-methyl-4-(piperidin-1-yl)-6-
(pyren-1-yl)biphenyl-3-carbonitrile (8a). A mixture of 2-oxo-
4-(piperidin-1-yl)-6-(pyren-1-yl)-2H-pyran-3-carbonitrile (4a, 404 mg, 1
mmol, 1 equiv), 1-(4-methoxyphenyl)propan-2-one (7, 185 μL, 1.2
mmol, 1.2 equiv), and KOH (67 mg, 1.2 mmol, 1.2 equiv) in dry
DMF (5 mL) was stirred at room temperature for 10 h. The progress of
reaction was monitored by TLC, and upon completion, the reaction
mixture was poured onto crushed ice with vigorous stirring and finally
neutralized with 10% HCl. The precipitate obtained was filtered and
purified on a neutral alumina column using 3% ethyl acetate in
n-hexane as the eluent to afford 8a (380 mg, 75%) as a white solid:
Rf = 0.52 (n-hexane/ethyl acetate, 9:1, v/v); mp (n-hexane/ethyl
acetate) 242ꢀ244 ꢀC; MS (ESI) 507 [M + H+]; IR (KBr) ν = 3041
(m), 2931 (s), 2852 (w), 2208 (s), 1578 (s), 1513 (w) cmꢀ1; 1H NMR
(300 MHz, CDCl3): δ = 1.58ꢀ1.61 (m, 2H), 1.75ꢀ1.84 (m, 4H), 2.41
(s, 3H), 3.15ꢀ3.21 (m, 4H), 3.51 (s, 3H), 6.24ꢀ6.29 (m, 1H),
6.58ꢀ6.68 (m, 2H), 6.94 (s, 1H), 6.97ꢀ7.02 (m, 1H), 7.57 (d, J = 7.9
Hz, 1H), 7.85 (d, J = 9.2 Hz, 1H), 7.92ꢀ8.05 (m, 5H), 8.12ꢀ8.18 (m, 2H),
ppm; 13C NMR (75 MHz, CDCl3): δ = 20.1, 24.0, 26.2, 53.4, 54.7,
106.9, 112.9, 113.1, 118.1, 119.3, 123.8, 124.4, 124.5, 124.9, 125.2,
125.9, 127.3, 127.4, 127.6, 128.6, 130.2, 130.5, 130.7, 131.2, 135.7,
136.5, 142.6, 145.7, 155.6, 157.9 ppm; HRMS calculated for
C36H31N2O (M+ + H) 507.2436, found: 507.2584.
Synthesis of 40-Methoxy-2-methyl-4-(4-methylpiperidin-
1-yl)-6-(pyren-1-yl)biphenyl-3-carbonitrile (8b). A mixture of
4-(4-methylpiperidin-1-yl)-2-oxo-6-(pyren-1-yl)-2H-pyran-3-carboni-
trile (4b, 418 mg, 1 mmol, 1 equiv), 1-(4-methoxyphenyl)propan-2-one
(7, 185 μL, 1.2 mmol, 1.2 equiv), and KOH (67 mg, 1.2 mmol, 1.2 equiv)
in dry DMF (5 mL) was stirred at room temperature for 10 h. The
progress of reaction was monitored by TLC, and upon completion, the
reaction mixture was poured onto crushed ice with vigorous stirring and
finally neutralized with 10% HCl. The precipitate obtained was filtered
and purified on a neutral alumina column using 3% ethyl acetate in
n-hexane as the eluent to afford 8b (375 mg, 72%) as a white solid: Rf =
0.54 (n-hexane/ethyl acetate, 9:1, v/v); mp (n-hexane/ethyl acetate)
218ꢀ220 ꢀC; MS (ESI) 521 [M + H+]; IR (KBr) ν = 3040 (w), 2927
(s), 2814 (w), 2210 (s), 1580 (s), 1514 (w) cmꢀ1; 1H NMR (300 MHz,
CDCl3): δ = 1.0 (d, J = 5.5 Hz, 3H), 1.45ꢀ1.62 (m, 3H), 1.72ꢀ1.82 (m,
2H), 2.42 (s, 3H), 2.71ꢀ2.84 (m, 2H), 3.53 (s, 3H), 3.58ꢀ3.72 (m, 2H),
6.26ꢀ6.32 (m, 1H), 6.58ꢀ6.72 (m, 2H), 6.96 (s, 1H), 6.98ꢀ7.05 (m,
1H), 7.58 (d, J =7.7 Hz, 1H), 7.85 (d, J =8.9Hz, 1H), 7.92ꢀ8.08(m, 5H),
8.12ꢀ8.18 (m, 2H), ppm; 13C NMR (75 MHz, CDCl3): δ = 20.1, 21.8,
30.6, 34.5, 52.5, 53.1, 54.8, 107.0, 113.0, 113.2, 118.1, 119.4, 123.9, 124.5,
124.7, 125.0, 125.2, 126.0, 127.3, 127.4, 127.5, 127.6, 128.7, 130.3, 130.6,
130.9, 131.3, 135.7, 136.6, 142.7, 145.8, 155.5, 158.0 ppm; HRMS
calculated for C37H33N2O (M+ + H) 521.2593, found: 521.2573.
General Procedure for the Synthesis of 10aꢀd at Room
Temperature or Conventional Heating. A mixture of 2-oxo-
4-(piperidin-1-yl)-6-(pyren-1-yl)-2H-pyran-3-carbonitrile (4a, 404 mg,
1 mmol), deoxybenzoins (9aꢀd, 1.2 mmol), and KOH (67 mg, 1.2
mmol, 1.2 equiv) in dry DMF (5 mL) was stirred at room temperature or
at 100 ꢀC. The progress of reaction was monitored by TLC, and upon
completion, the reaction mixture was poured onto crushed ice with
vigorous stirring and finally neutralized with 10% HCl. The precipitate
General Procedure for the Synthesis of 4a,b. A mixture
of 4-(methylsulfanyl)-2-oxo-6-(pyren-1-yl)-2H-pyran-3-carbonitrile (3,
367 mg, 1 mmol) and piperidine or 4-methylpiperidine (1.2 mmol) in
methanol was refluxed for 6ꢀ7 h, the reaction mixture was cooled to
room temperature, and the solid obtained was filtered to furnish 2-oxo-
4-(piperidin-1-yl/4-methylpiperidin-1-yl)-6-(pyren-1-yl)-2H-pyran-3-
carbonitriles 4a,b in 92ꢀ94% yields, respectively.
Synthesis of 4-(Piperidin-1-yl)-2-oxo-6-(pyren-1-yl)-2H-
pyran-3-carbonitrile (4a). White solid; Rf = 0.40 (n-hexane/ethyl
acetate, 6:4, v/v); mp (chloroform/methanol) 256ꢀ258 ꢀC; MS (FAB)
405 (M+ + 1); IR (KBr) ν = 2198 (s), 1690 (s), 1628 (s), 1531 (s) cmꢀ1
;
1H NMR (300 MHz, CDCl3) δ = 1.79ꢀ1.83 (m, 6H), 3.85ꢀ3.88 (m,
4H), 6.48 (s, 1H), 8.00ꢀ8.10 (m, 2H), 8.11ꢀ8.19 (m, 4H), 8.21ꢀ8.27
(m, 2H), 8.39 (d, J = 9.3 Hz, 1H) ppm; HRMS calculated for
C27H21N2O2 (M+ + H) 405.16030, found: 405.16133.
Synthesis of 4-(4-Methylpiperidin-1-yl)-2-oxo-6-(pyren-1-
yl)-2H-pyran-3-carbonitrile (4b). White solid; Rf = 0.42 (n-hex-
ane/ethyl acetate, 6:4, v/v); mp (chloroform/methanol) > 250 ꢀC; MS
(ESI+) 419 [M + H+]; IR (KBr) ν = 2201 (s), 1690 (s), 1631 (s), 1529
(s) cmꢀ1; 1H NMR (300 MHz, CDCl3): δ = 1.02 (d, J = 6.06 Hz, 3H),
1.32ꢀ1.48 (m, 2H), 1.74ꢀ1.96 (m, 3H), 3.21ꢀ3.36 (m, 2H),
4.36ꢀ4.48 (m, 2H), 6.46 (s, 1H), 7.98ꢀ8.28 (m, 8H), 8.40 (d, J = 9.3
Hz, 1H) ppm; 13C NMR (75 MHz, DMSO d6): δ = 21.1, 29.7, 34.1,
49.6, 70.2, 101.3, 117.8, 123.4, 123.7, 123.9, 124.7, 126.1, 126.4, 126.5,
126.8, 127.1, 127.4, 128.3, 129.0, 129.1, 130.0, 130.6, 132.5, 159.8, 161.3,
162.4 ppm; HRMS calculated for C28H23N2O2 (M+ + H) 419.17595,
found: 419.17578.
Synthesis of 5-Methyl-2-(piperidin-1-yl)-4-(pyren-1-yl)-
benzonitrile (6a). A mixture of 2-oxo-4-(piperidin-1-yl)-6-(pyren-
1-yl)-2H-pyran-3-carbonitrile (4a, 404 mg, 1 mmol, 1 equiv), pro-
pionaldehyde (5a, 86 μL, 1.2 mmol, 1.2 equiv), and KOH (67 mg, 1.2
mmol, 1.2 equiv) in dry DMF (5 mL) was stirred at room temperature
for 10 h. The progress of reaction was monitored by TLC and upon
completion, the reaction mixture was poured onto crushed ice with
vigorous stirring and finally neutralized with 10% HCl. The pre-
cipitate obtained was filtered and purified on a neutral alumina
column using 2% ethyl acetate in n-hexane as the eluent to afford
6a (296 mg, 74%) as a white solid: Rf = 0.56 (n-hexane/ethyl acetate,
9:1, v/v); mp (n-hexane/ethyl acetate) 158ꢀ160 ꢀC; MS (ESI) 401
[M + H+]; IR (KBr) ν = 3038 (m), 2932 (s), 2857 (w), 2807 (s), 2214
(s),1597 (s), 1489 (s) cmꢀ1 1H NMR (300 MHz, CDCl3): δ =
;
1.59ꢀ1.65 (m, 2H), 1.74ꢀ1.84 (m, 4H), 1.97 (s, 3H), 3.09ꢀ3.25 (m,
4H), 7.01 (s, 1H), 7.57 (s, 1H), 7.64ꢀ7.67 (m, 1H), 7.81ꢀ7.83 (m,
1H), 7.92ꢀ8.26 (m, 7H) ppm; 13C NMR (75 MHz, CDCl3): δ =
19.1, 24.0, 26.1, 53.2, 105.1, 118.7, 121.1, 124.5, 124.7, 125.2, 125.4,
126.2,126.5, 127.3, 127.7, 128.0, 128.4, 130.2, 130.8, 130.9, 131.3,
135.2, 135.7, 146.4, 154.6 ppm; HRMS calculated for C29H25N2
(M+ + H) 401.2018, found: 401.2010.
Synthesis of 2-(Piperidin-1-yl)-5-propyl-4-(pyren-1-yl)-
benzonitrile (6b). A mixture of 2-oxo-4-(piperidin-1-yl)-6-(pyren-
1-yl)-2H-pyran-3-carbonitrile (4a, 404 mg, 1 mmol, 1 equiv), valer-
aldehyde (5b, 128 μL, 1.2 mmol, 1.2 equiv), and KOH (67 mg, 1.2
mmol, 1.2 equiv) in dry DMF (5 mL) was stirred at room temperature
for 12 h. The progress of reaction was monitored by TLC, and upon
completion, the reaction mixture was poured onto crushed ice with
vigorous stirring and finally neutralized with 10% HCl. The pre-
cipitate obtained was filtered and purified on a neutral alumina
column using 2% ethyl acetate in n-hexane as the eluent to afford
6b (308 mg, 72%) as a white solid: Rf = 0.58 (n-hexane/ethyl acetate,
9:1, v/v); mp (n-hexane/ethyl acetate) 152ꢀ154 ꢀC; MS (ESI) 429
7479
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The Journal of Organic Chemistry
ARTICLE
obtained was filtered and purified on a neutral alumina column using 3%
ethyl acetate in n-hexane as the eluent to afford 10aꢀd.
137.9, 140.1, 145.7, 147.3, 155.9, 158.9 ppm; HRMS calculated for
C47H37N2O (M+ + H) 645.2906, found: 645.3248.
General Procedure for the Microwave-Assisted Synthesis
of 10aꢀd. A mixture of 2-oxo-4-(piperidin-1-yl)-6-(pyren-1-yl)-2H-
pyran-3-carbonitrile (4a, 101 mg, 0.25 mmol), deoxybenzoin (9aꢀd, 0.3
mmol), and KOH (17 mg, 0.3 mmol) in dry DMF (5 mL) was placed in
a microwave vial. The solution was heated at 100 ꢀC for 10 min using
internal probe in microwave (Biotage). The reaction mixture was cooled
to room temperature, poured onto crushed ice with vigorous stirring,
and finally neutralized with 10% HCl. The precipitate obtained was
filtered and purified on a neutral alumina column using 3% ethyl acetate
in n-hexane as the eluent to afford 10aꢀd.
’ ASSOCIATED CONTENT
Supporting Information. 1H and 13C NMR spectra,
S
b
UVꢀvis and fluorescence spectra, DSC, TGA, cyclic voltammo-
grams for compounds 6a,b, 8a,b, and 10aꢀd and a device
efficiency graph for compound 10c. This material is available
free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Synthesis of 2,3-Diphenyl-6-(piperidin-1-yl)-4-(pyren-1-
yl)benzonitrile (10a). White solid; Rf = 0.45 (n-hexane/ethyl acetate,
9:1, v/v); mp (n-hexane/ethyl acetate) 188ꢀ190 ꢀC; MS (ESI) 539
[M + H+]; IR (KBr) ν = 3034 (m), 2932 (s), 2811 (w), 2217 (s), 1567
(s) cmꢀ1; 1H NMR (300 MHz, DMSO d6): δ = 1.52ꢀ1.58 (m, 2H),
1.65ꢀ1.76 (m, 4H), 3.18ꢀ3.26 (m, 4H), 6.48ꢀ6.90 (m, 5H),
7.18ꢀ7.28 (m, 6H), 7.80 (d, J = 7.9 Hz, 1H), 7.93 (d, J = 9.2 Hz,
1H), 8.02ꢀ8.18 (m, 5H), 8.22ꢀ8.30 (m, 2H) ppm; 13C NMR (75 MHz,
CDCl3): δ = 24.0, 26.2, 53.4, 106.8, 117.8, 121.2, 123.9, 124.5, 124.6,
125.0, 125.1, 125.3, 125.9, 126.0, 126.9, 127.3, 127.4, 127.5, 127.6, 127.7,
127.8, 128.8, 130.2, 130.4, 130.8, 131.3, 135.2, 136.2, 138.0, 138.3, 145.7,
147.5, 155.8 ppm; HRMS calculated for C40H31N2 (M+ + H) 539.2487,
found: 539.2457.
Corresponding Author
*E-mail: atul_goel@cdri.res.in.
Present Addresses
#Institute for Organic Chemistry, University of W€urzburg, Am
Hubland, 97074 W€urzburg, Germany.
’ ACKNOWLEDGMENT
We gratefully acknowledge financial support by the Depart-
ment of Science and Technology (DST), New Delhi, India. A.G.
thanks Alexander von Humboldt Foundation and Prof. Dr. Dr. h.
c. Gerhard Bringmann for a research stay in Germany. V.K. and P.
N. are thankful to UGC and CSIR, New Delhi, for research
fellowships. R.S.A. thanks the MHRD, New Delhi, for financial
support. The spectroscopic data provided by SAIF, CDRI, is
gratefully acknowledged.
Synthesis of 2-(4-Methoxyphenyl)-6-(piperidin-1-yl)-3-
phenyl-4-(pyren-1-yl)benzonitrile (10b). White solid; Rf = 0.42
(n-hexane/ethyl acetate, 9:1, v/v); mp (n-hexane/ethyl acetate)
198ꢀ200 ꢀC; MS (ESI) 569 [M + H+]; IR (KBr) ν = 3044 (m),
1
2932 (s), 2848 (w), 2214 (s), 1574 (s), 1509 (s), 1444 (s) cmꢀ1; H
NMR (300 MHz, DMSO d6): δ = 1.48ꢀ1.58 (m, 2H), 1.65ꢀ1.74 (m,
4H), 3.15ꢀ3.24 (m, 4H), 3.69 (s, 3H), 6.52ꢀ6.92 (m, 7H), 7.12ꢀ7.17
(m, 3H), 7.76 (d, J = 7.9 Hz, 1H), 7.89 (d, J = 9.2 Hz, 1H), 8.02ꢀ8.15
(m, 5H), 8.23ꢀ8.28 (m, 2H) ppm; 13C NMR (75 MHz, CDCl3): δ =
24.0, 26.2, 53.5, 55.0, 107.0, 113.2, 118.1, 121.0, 123.9, 124.5, 124.6,
125.0, 125.2, 125.3, 125.8, 126.0, 126.9, 127.3, 127.4, 127.6, 127.8, 128.8,
130.3, 130.6, 130.8, 131.3, 131.5, 135.4, 136.3, 138.2, 145.7, 147.2, 155.9,
158.9 ppm; HRMS calculated for C41H33N2O (M+ + H) 569.2593,
found: 569.2582.
’ DEDICATION
^Dedicated to Prof. Dr. Dr. h. c. Gerhard Bringmann on the
occasion of his 60th birthday.
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Synthesis of 2,3-Bis(4-methoxyphenyl)-6-(piperidin-1-yl)-
4-(pyren-1-yl)benzonitrile (10c). White solid; Rf = 0.40 (n-hexane/
ethyl acetate, 9:1, v/v); mp (n-hexane/ethyl acetate) 286ꢀ288 ꢀC; MS
(ESI) 599 [M + H+]; IR (KBr) ν = 3023 (s), 2934 (w), 2848 (w), 2212
(s), 1574 (s), 1518 (s), 1432 (s) cmꢀ1; 1H NMR (300 MHz, CDCl3): δ =
1.52ꢀ1.60 (m, 2H), 1.74ꢀ1.86 (m, 4H), 3.18ꢀ3.32 (m, 4H), 3.43 (s,
3H), 3.77 (s, 3H), 6.10ꢀ6.28 (m, 2H), 6.52ꢀ6.84 (m, 4H), 6.96ꢀ7.15
(m, 2H), 7.36 (s, 1H), 7.58 (d, J = 7.9, 1H), 7.94ꢀ8.08 (m, 6H),
8.12ꢀ8.18 (m, 2H) ppm; 13C NMR (75 MHz, CDCl3): δ = 24.0, 26.2,
53.5, 54.7, 55.1, 107.1, 112.5, 113.3, 118.1, 121.0, 124.0, 124.5, 124.7,
125.0, 125.1, 125.2, 126.0, 127.3, 127.6, 127.8, 128.8, 130.3, 130.5, 130.7,
130.8, 131.3, 131.5, 131.9, 135.0, 136.6, 145.9, 147.4, 155.7, 157.3, 158.8
ppm; HRMS calculated for C42H35N2O2 (M+ + H) 599.2699, found:
599.2692.
Synthesis of 3-(Biphenyl-4-yl)-2-(4-methoxyphenyl)-
6-(piperidin-1-yl)-4-(pyren-1-yl)benzonitrile (10d). White solid;
Rf = 0.38 (n-hexane/ethyl acetate, 9:1, v/v); mp (n-hexane/ethyl acetate)
234ꢀ236 ꢀC; MS (ESI) 645 [M + H+]; IR (KBr) ν = 3035 (w), 2926 (s),
2859 (s), 2213 (s), 1577 (m), 1508 (m), 1454 (s) cmꢀ1; 1H NMR (300
MHz, CDCl3): δ = 1.54ꢀ1.65 (m, 2H), 1.72ꢀ1.88 (m, 4H), 3.16ꢀ3.36
(m, 4H), 3.74 (s, 3H), 6.62ꢀ7.30 (m, 14H), 7.58ꢀ7.62 (m, 1H),
7.88ꢀ8.08 (m, 6H), 8.12ꢀ8.22 (m, 2H) ppm; 13C NMR (75 MHz,
CDCl3): δ = 24.0, 26.2, 53.4, 55.0, 107.0, 113.3, 118.1, 121.1, 124.0, 124.5,
124.6, 125.0, 125.1, 125.3, 125.4, 126.0, 126.5, 126.9, 127.3, 127.4, 127.7,
127.8, 128.4, 128.8, 130.3, 130.5, 130.8, 131.3, 131.5, 134.9, 136.3, 137.3,
7480
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