Synthesis and solid-state fluorescence properties of pentacyclic 7-substituted-indeno[1′,2′:4,5]pyrido[2,1-a]isoindol-5-ones

Article abstract of DOI:10.1039/c4ra12155d

With the aim to design fluorescent solids, a series of indeno[1′,2′:4,5]pyrido[2,1-a]isoindol-5-ones with various substituents was prepared. In these π-extended pentacyclic derivatives, the presence of a methyl group in the 7-position was found to have a critical influence on the fluorescence properties in the solid state. Crystal packing of the non-substituted derivatives shows strong π-π interactions causing quenching of the fluorescence. In contrast, by introducing a methyl substituent in the 7-position we obtained compounds with fluorescence quantum yield up to 32% in the solid state.

Full text of DOI:10.1039/c4ra12155d

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Synthesis and solid-state fluorescence properties
of pentacyclic 7-substituted-indeno[10,20:4,5]pyrido
[2,1-a]isoindol-5-ones†
Cite this: RSC Adv., 2015, 5, 2715
a
b
a
c
a
b
a
*
*
Z. Chamas, E. Marchi, B. Presson, E. Aubert, Y. Fort, P. Ceroni and V. Mamane‡
With the aim to design fluorescent solids, a series of indeno[10,20:4,5]pyrido[2,1-a]isoindol-5-ones with
various substituents was prepared. In these p-extended pentacyclic derivatives, the presence of a methyl
group in the 7-position was found to have a critical influence on the fluorescence properties in the solid
state. Crystal packing of the non-substituted derivatives shows strong p–p interactions causing
quenching of the fluorescence. In contrast, by introducing a methyl substituent in the 7-position we
obtained compounds with fluorescence quantum yield up to 32% in the solid state.
Received 10th October 2014
Accepted 1st December 2014
DOI: 10.1039/c4ra12155d
www.rsc.org/advances
Introduction
Solid-state organic luminescent compounds1,2 have received
considerable attention for practical use in organic electrolu-
minescence devices (OLED),3 solid-state dye laser4 and sensors.5
Only a few compounds exhibit strong uorescence both in
solution and in the solid state because most of them undergo
uorescence quenching in aggregation state. Indeed, strong
intermolecular interactions between neighbouring uo-
rophores generally lead to uorescence quenching in the solid
state.6
We have recently described the synthesis of N-containing
pentacyclic compounds via a cascade reaction between 2,5-
dihalopyridines and 2-formylbenzeneboronic acids.7 Most of
the compounds exhibited excellent uorescence properties in
solution,8 but not in the solid state. However, compounds 1 and
2 bearing a methyl group in 7-position (Fig. 1) were identied as
uorescent solids. Introduction of a methyl substituent in 7-
position could prevent strong intermolecular packing through
p/p interactions in the solid state thus avoiding quenching of
the uorescence. In the non-substituted pentacycles (for
instance 3 and 4), the uorescence is quenched as a result of
strong p/p stacking interactions in such extended p-
Fig. 1 Fluorescent pentacyclic compounds.
conjugated systems.7 Based on these preliminary observations,
we report herein the preparation and the photophysical study of
new derivatives bearing a methyl or aryl substituent in 7-posi-
tion. The uorescence measurements conrm that all
compounds with a methyl group in 7-position possess high
quantum yields of uorescence in the solid state whereas they
are low in case of the aryl substituted compounds. The crystal
structures of selected compounds were analysed in order to
investigate the inuence of the crystal packing on the uores-
cence properties.
Results and discussion
Synthesis
aLaboratoire SRSMC, UMR CNRS 7565, Universite de Lorraine, 54506
´
Vandoeuvre-les-Nancy, France
Pentacyclic compounds bearing an electron-donating substit-
bDepartment of Chemistry “G. Ciamician”, University of Bologna, Via Selmi 2, 40126
uent (OCH3) were prepared starting from pyridine 5 (Scheme 1).
Laboratoire CRM2, UMR CNRS 7036, Universite de Lorraine, 54506 Vandoeuvre-les- The cascade reaction of 5 with 3 eq. of boronic acid 6b yielded
Bologna, Italy. E-mail: paola.ceroni@unibo.it
c
´
Nancy, France
7b. Alternatively, the reaction of 5 with one eq. of 2-for-
† Electronic supplementary information (ESI) available: Copy of 1H and 13C NMR
mylbenzeneboronic acid 6a furnished intermediate
8 in
spectra of all compounds, ORTEP view of compounds 2, 15a and 15d. CCDC
1027764–1027766. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4ra12155d
moderate yield along with pentacycle 1 which formation was
initiated in situ by a competitive second Suzuki coupling. Next,
the reaction of 8 with 1.5 eq. of 6b gave pentacycle 9b having one
methoxy substituent. Compounds 7b and 9b represent the
‡ New address: Institut de Chimie de Strasbourg, UMR 7177, Equipe LASYROC, 1
rue Blaise Pascal, 67008 Strasbourg, France, E-mail: vmamane@unistra.fr.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 2715–2723 | 2715

View Article Online
RSC Advances
Paper
(Scheme 3) bearing a substituent in 6-position. For this
purpose, the trihalopyridine substrate 11 was chosen as the key
compound since it could allow a selective cross-coupling in 6-
position. Pyridine 11 was prepared from 2-amino-6-bromo-
pyridine 12 in two steps with an overall good yield.
Electrophilic bromination of 12 furnished the dibromoami-
nopyridine 13,9 followed by the replacement of the amino group
by a chlorine through a Sandmeyer-type reaction to give 11
(Scheme 2). The cross-coupling of 11 in 6-position was per-
formed with 1 eq. of various boronic acids to deliver the
expected 2-chloro-5-bromo-6-arylpyridines 10a–e in good yields.
Little change of the procedure allowed obtaining the pyridine-
substituted derivative 10f in good yield. The Sonogashira
coupling of 11 with a slight excess of phenylacetylene performed
also smoothly to give 14 in good yield (Scheme 3).
Pyridine 10a was then reacted with 2.5 eq. of 2-for-
mylphenylboronic acid 6a under standard conditions to give the
expected pentacycle 15a in low yield and a large amount of non-
cyclized bis-aldehyde 16. Obviously the presence of the bulky
phenyl group reduced the pyridine nitrogen reactivity toward
the aldehyde10,11 thus increasing the stability of 16.12 Moreover,
when bis-aldehyde 16 was subjected to the same reaction
conditions, pentacycle 15a was formed in good yield. When the
catalyst was omitted the pentacycle was still formed although in
a lower yield of 20% because of the important formation of
degradation products (Scheme 4).
Scheme 1 Synthesis of pentacycles 7b and 9b.
analogues with a methyl substituent in 7-position of 7a and 9a,
respectively (see Fig. 2 for the structures of 7a and 9a).
In order to extend the family of 7-substituted pentacycles, it
was necessary to access to new 2-chloro-5-bromo-pyridines
Nevertheless, these experiments suggest that a more robust
palladium catalyst could allow performing the cascade reaction
in a single step. The bulky monophosphine ligand such as
XPhos (2-dicyclohexylphosphino-20,40,60-triisopropylbiphenyl)
Fig. 2 Overview of the pentacyclic compounds.
2716 | RSC Adv., 2015, 5, 2715–2723
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Scheme 2 Synthesis of trihalopyridine 11.
Scheme 4 Synthesis of pentacycle 15a under standard conditions.
Scheme 3 Synthesis of 6-substituted 2-chloro-5-bromopyridines.
has shown high performances in Suzuki coupling13 and other
palladium-catalyzed reactions.14 The cascade reaction was
then performed with catalytic system [Pd(OAc)2, XPhos] and
it was noticed that 5 eq. of 2-formylphenylboronic acid 6a
were needed for the reaction to go to completion (Scheme 5).
Under these conditions, the yield for pentacycle 15a could be
increased to 53%. Pyridines 10b–d reacted smoothly to give
compounds 15b–d in good yields whereas a moderate yield
for 15f was obtained with bipyridine 10f. Complex mixtures
were obtained aer the reaction of substrates 10e and 14. As
for pentacycle 1,7 the relative syn conguration was
conrmed for compounds 2, 15a and 15d by XRD and was
applied to the other compounds of the series 15b–c and 15f
(vide infra).§
Scheme 5 Cascade reaction of 6-substituted pyridines 10 and 14.
To summarize, the structures of all the compounds consid-
ered in this study are depicted in Fig. 2.
Photophysical properties
In CH2Cl2 solution. The photophysical properties of
compounds 1–4 are very similar: as an example, the absorp-
tion and emission spectra of 2 are reported as solid black
lines in Fig. 3 and 4, respectively. Compounds 1–4 display the
same lowest-energy absorption band, a bright emission at ca.
500 nm, with an intensity decay of few ns, insensitive to the
presence of dioxygen in solution (Table 1), thus pointing to a
uorescent excited state. These results demonstrate that the
presence of the methyl substituents in position 7 and/or 13
does not signicantly affect the optical properties in
§ 2: C21H17NO2, Mr ¼ 315.36, crystal dimensions: 0.19 ꢀ 0.15 ꢀ 0.09 mm, triclinic,
ꢁ
˚
˚
˚
ꢀ
space group P1, a ¼ 8.3902(4) A, b ¼ 9.4235(5) A, c ¼ 10.5655(5) A, a ¼ 68.634(5) ,
3
ꢁ
ꢁ
˚
b ¼ 86.055(4) , g ¼ 83.059(4) , V ¼ 771.97(7) A , T ¼ 110(2) K, Z ¼ 2, rcalcd ¼ 1.357 g
cmꢂ3, m ¼ 0.688 mmꢂ1, 8377 reections collected, 3099 unique reections, Rint
¼
0.0408, 2qmax ¼ 152.34ꢁ, 223 parameters, R1 ¼ 0.0636, wR2 ¼ 0.1703, rmin ¼ ꢂ0.241
e Aꢂ3, rmax ¼ 0.359 e Aꢂ3. 15a: C25H17NO2, Mr ¼ 363.40, crystal dimensions: 0.23 ꢀ solution.
˚
˚
˚
˚
0.18 ꢀ 0.09 mm, monoclinic, space group P21/c, a ¼ 10.6552(3) A, b ¼ 8.1691(2) A,
Upon appending one (9b) or two methoxy units (7b) at the
external phenyl rings, a new band at ca. 330 nm arises in the
absorption spectra and it can be attributed to electronic tran-
sitions of the methoxybenzene units. The emission spectrum of
3
ꢁ
˚
˚
c ¼ 20.6721(6) A, b ¼ 104.472(3) , V ¼ 1742.28(8) A , T ¼ 110(2) K, Z ¼ 4, rcalcd
¼
1.385
g
cmꢂ3
,
m
¼
0.702 mmꢂ1
, 9695 reections collected, 3235, unique
reections, Rint ¼ 0.0146, 2qmax ¼ 140.26ꢁ, 254 parameters, R1 ¼ 0.0379, wR2
¼
0.0910, rmin ¼ ꢂ0.263 e Aꢂ3, rmax ¼ 0.283 e Aꢂ3. 15d: 2(C26H17NO3), CH2Cl2,
˚
˚
Mr ¼ 867.74, crystal dimensions: 0.20 ꢀ 0.14 ꢀ 0.09 mm, orthorhombic, space 9b is similar to the previously discussed spectrum of 2 (Fig. 3)
˚
˚
˚
group Pna21, a ¼ 26.5772(4) A, b ¼ 11.8718(2) A, c ¼ 12.8742(2) A, V ¼
with a remarkably high emission quantum yield (Table 1). On
the other hand, compound 7b displays a weak emission band
with no vibronic structure, a red-shied maximum and a
shorter lifetime. The photophysical properties of compounds 7b
and 9b are very similar, in terms of energy, lifetime and
4062.06(11) A , T ¼ 100(2) K, Z ¼ 4, rcalcd ¼ 1.419 g cmꢂ3, m ¼ 1.914 mmꢂ1
,
3
˚
40 982 reections collected, 7997, unique reections, Rint ¼ 0.0151, 2qmax
¼
145.80ꢁ, 571 parameters, R1 ¼ 0.0356, wR2 ¼ 0.0961, rened inversion twin
population parameter (Flack parameter): 0.244(10). rmin ¼ ꢂ0.277 e Aꢂ3, rmax
¼
˚
ꢂ3
˚
0.498 e A
.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 2715–2723 | 2717

View Article Online
RSC Advances
Paper
Table 1 Most relevant photophysical data for all the compounds in
air-equilibrated CH2Cl2 solution and in solid state at 298 K
Absorption
Emissiona
CH2Cl2
CH2Cl2
Solid
l (nm) 3 (Mꢂ1 cmꢂ1
)
lmax (nm) s (ns) Fem l (nm) Fem
a
1
2
3
4
421
425
423
424
430
432
422
423
22 000
17 000
18 000
500
512
497
505
518
523
498
501
502
502
501
503
501
4.60
5.27
4.30
—
0.7
0.47
5.10
5.05
4.88
4.60
4.79
5.27
5.33
0.67 520
0.31
0.29
0.77 531
b
b
0.62
0.71
0.11
—
—
—
—
c
c
b
d
b
—
—
d
7a
7b
9a
9b
15a 423
15b 422
15c 421
15d 422
15f 421
18 000
20 000
17 000
21 000
16 700
16 200
16 700
16 500
17 900
—
0.07 549
0.32
d
d
0.78
—
—
0.79 544
0.74 552
0.67 569
0.62 586
0.77 517
0.73 557
0.21
0.09
0.06
0.08
0.07
0.06
Fig. 3 Absorption spectra of compounds 2 (solid black line), 7b
(dashed gray line), 9b (dashed dotted black line) and 15a (dashed
dotted dotted gray line) in CH2Cl2 solution.
a
Fluorescence quantum yields in solution were measured using as
standard perylene in air equilibrated EtOH solution (Fem ¼ 0.92) and
in solid state by an integrating sphere (see Experimental section).
b
c
No emission detected in the solid state. These data are not
d
reported because the sample is not fully stable in solution. Data not
available.
compounds 15a–d and 15f, which are all strongly emissive in
CH2Cl2 solution, are either completely quenched or poorly
emissive as a powder (Table 1). On the contrary, compounds 1,
2, 7b and 9b display a strong emission (Fem ca. 30%) in the solid
state. The emission spectra in the solid state of two represen-
tative examples (1 and 15a) are reported in Fig. 5.
It is worth noting that compound 7b is poorly emissive in
solution. Indeed, based on the previous investigation,8 for the
lower emitting compounds the uorescent excited state is
mainly deactivated by non radiative pathways which are
strongly inhibited in rigid environment (as in the solid state or
Fig. 4 Normalized emission spectra of compounds 2 (solid black line),
7b (dashed gray line), 9b (dashed dotted black line) and 15a (dashed
dotted dotted gray line) in CH2Cl2 solution. lex ¼ 400 nm.
emission quantum yield, to the corresponding previously
investigated analogues 7a and 9a lacking the methyl substit-
uent in position 7 (Fig. 2).8 This experimental nding points to
the fact that the methyl substituent in that position does not
affect the electronic properties of the chromophores in
solution.
Compounds 15a–d and 15f have the same photophysical
properties and the absorption (Fig. 3) and emission spectra
(Fig. 4) of compound 15a, reported as a representative example,
are very similar also from a quantitative point of view (Table 1)
to those of compound 1.
In solid state. As previously discussed, highly luminescent
organic molecules in solution are oen not emissive in the solid
state. We thus decided to investigate the emission spectra and
the emission quantum yield in the solid state of all the above
Fig. 5 Emission spectra of compounds 1 (gray line) and 15a (black line)
as a powder. lex ¼ 400 nm. These spectra are not corrected for the
reabsorption of the emitted light.
reported compounds. Compounds
3 and 4, as well as
2718 | RSC Adv., 2015, 5, 2715–2723
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
˚
in lm): this may explain the strong increase of emission packing through C–H/N hydrogen bond (H/N ¼ 2.55 A;
ꢁ
˚
quantum yield in the case of 7b.
C–H/N ¼ 164.9 ) and p/p interactions (3.67 A) involving the
The discussed emission properties in the solid state are not a whole pentacyclic backbone, through its concave and convex
function of the degree of crystallinity, as demonstrated by sides (Fig. 7a). The molecular packing is also different in the
comparing the emission quantum yields measured for powder case of 1 where it is driven by multiple C–H/O, p hydrogen
samples and drop-cast solutions on glass slides.
bonds and contacts with no p/p interactions (Fig. 7b). As
To sum up these results, we can conclude that: (i) what is observed for 15a, 2 presents p/p interactions
˚
compounds with a methyl substituent in position 7 are the most involving the pentacyclic backbone by it concave side (3.42 A)
emissive in solid, (ii) lower emission intensities are displayed by but cannot display the additional stacking interactions
the phenyl substituted compounds, (iii) while compounds 3 and observed in 15a due to the non-aromatic nature of the R1
4 bearing no substituent are not emissive. Therefore, the pres- (methyl) group (Fig. 8).
ence of a methyl or phenyl substituent in position 7 does
Correlating these structural features to the photophysical
strongly affect the emissive properties in the solid state, but not properties shows that intermolecular p/p interactions are
in solution (see above).
detrimental to uorescence in the solid state. Indeed, with
strong p/p overlap as in 4 involving both side of the molecule,
no uorescence is observed in the solid state despite of a good
quantum yield in solution, while a small solid state quantum
yield is obtained when this overlap is reduced (15a and 15d). In
these last compounds, hydrogen bonding can also participate to
the uorescence quenching by bringing the molecules in close
proximity one to each other. The highest yield is obtained for
the crystal structure displaying no p/p interactions (1) or with
only the concave side of the molecule (2), where the quantum
yield is only halved going from solution to solid state.
X-ray diffraction analysis
Crystal structures were determined by single crystal X-ray
diffraction for compounds 2, 15a and 15d; the structures of
1, 4 and 7a were published in a previous article.7 In all
investigated structures, the OH and R1 group in 7-position are
in syn conformation. Moreover, in 15a and 15d the same
molecular synthons formed by O, C–H/O hydrogen bonding
are observed (Fig. 6). These synthons are built from four
molecules around an inversion center in 15a, and about a
pseudo inversion center in the non-centrosymmetric struc-
ture of 15d; in this latter structure, the loss of inversion
symmetry is induced by the ordering of the dichloromethane
solvent molecules that are cocrystallised together with the
pentacyclic compound. A similar molecular arrangement was
also found in 3,10-dimethoxy related pentacycle 7a but not in
4 and 1–2.7 The molecular packing in 15a presents p/p
interactions involving the pentacyclic backbone by its concave
˚
˚
side (3.59 A) and the phenyl group in 7-position (3.42 A)
separately.
On the contrary, in 15d p/p interactions couple together p-
CHO–C6H4 groups and pentacyclic backbones by their concave
˚
side (3.67 A).
These packing are noticeably different from the one dis-
played by other related compounds. In the case of 4, the pres-
ence of the H atom in 7-position induces strong molecular
Fig. 7 Molecular packing of (a) 4, showing the strong p/p interaction
involving the whole pentacyclic backbone together with the C–H/N,
O hydrogen bond (displayed as black lines) and of (b) 1 hydrogen
atoms not involved in hydrogen bonding are omitted for clarity.
Fig. 6 Molecular synthon about inversion center (left part of the
figure) formed by O, C–H/O hydrogen bonds and p/p interactions Fig. 8 Molecular packing of 2, showing the p/p interaction involving
(displayed as black lines) in 15a. Hydrogen atoms not involved in the concave side of the pentacycle; the methyl group precludes such
intermolecular bonding are omitted for clarity.
interaction from the convex side of the molecule.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 2715–2723 | 2719

View Article Online
RSC Advances
Paper
Single crystal X-ray diffraction
Conclusions
Single crystals were obtained by slow evaporation from
dichloromethane solutions. Diffraction experiments were per-
formed on a SuperNova CCD diffractometer (Agilent Technolo-
We have succeeded in designing uorescent solids by slight
structural modication of the pentacyclic framework of indeno-
[10,20:4,5]pyrido[2,1-a]isoindol-5-ones. Indeed, the original
pentacyclic compounds exhibited high uorescence in solution
but led to non-uorescent solids due to p–p interactions which
maintained the molecules in close proximity thus leading to
uorescence quenching. The introduction of a methyl group on
the central pyridine ring close to the nitrogen (7-position)
induced weaker p–p interactions and increased uorescence in
the solid state. Aryl groups on the same 7-position did not have
the same improving effect on the solid state uorescence due to
additional p–p interactions between the added aryl groups.
˚
gies) using the CuKa radiation (l ¼ 1.5418 A) for 2, 15a and 15d.
Data collections under dinitrogen stream were obtained at 100 K
for 15a and 110 K for 2 and 15d, respectively. The structures were
solved by direct methods with the program SIR-92 18 and full
matrix least-square renements on F2 in SHELX-97 19 were per-
formed with anisotropic displacements for non-H atoms.
Hydrogen atoms were located in difference Fourier maps and
rened isotropically according to the riding model.
3,10-Dimethoxy-7,8-dihydro-8-hydroxy-7-methyl-indeno
[10,20:4,5]pyrido[2,1-a]isoindol-5-one (7b)
Experimental
To a degassed toluene solution (12 mL) containing Pd(PPh3)4
(116 mg, 0.1 mmol) and pyridine 5 (206.5 mg, 1 mmol),
degassed solution of boronic acid 6b (3 mmol) in methanol
(3 mL) and aqueous solution (4 mL) of Na2CO3 (636 mg,
6 mmol) and NaBr (103 mg, 1 mmol) were successively added.
Aer heating for 12 h at 100 ꢁC, the reaction mixture was cooled
to room temperature, extracted with ethyl acetate (3 ꢀ 20 mL)
and dried over anhydrous magnesium sulphate (MgSO4). Aer
ltration on Celite and concentration, the residue was puried
by chromatography on silica gel (cyclohexane/ethyl acetate) to
give compound 7b (150 mg, 42%); mp 152–154 ꢁC; 1HNMR
(CDCl3, 200 MHz) d 7.58 (d, J ¼ 8.4 Hz, 1H), 7.40 (d, J ¼ 8.4 Hz,
1H), 7.29 (d, J ¼ 2.3 Hz, 1H), 7.10–7.17 (m, 2H), 6.89 (ddd, J ¼
8.4, 2.3, 0.6 Hz, 1H), 6.37 (d, J ¼ 6.3 Hz, 1H), 6.19 (d, J ¼ 6.3 Hz,
1H), 5.51 (s, 1H, OH), 5.34 (d, J ¼ 0.6 Hz, 1H), 3.89 (s, 3H, OCH3),
3.87 (s, 3H, OCH3), 1.25 ppm (s, 3H, CH3); 13CNMR (CDCl3, 50
MHz) d 169.7, 161.3, 160.8, 145.4, 141.8, 132.3, 129.6, 128.4,
128.35, 122.5, 121.4, 120.6, 116.6, 110.2, 108.6, 105.6, 103.0,
79.7, 67.7, 55.8, 55.6, 17.5 ppm. HRMS m/z calcd for
General remarks
Toluene and dioxane were distilled over sodium/benzophenone
and stored over sodium. All other solvents and reagents were
used as received. TLC was performed on silica gel plates and
visualized with a UV lamp (254 nm). Chromatography was
performed on silica gel (70–230 mesh). Melting points were
measured on a Totoli apparatus. Proton and carbon NMR
spectra were recorded on Bruker AC-200, AC-250 or AM-400
Fourier transform spectrometers using an internal deuterium
lock. Chemical shis are quoted in parts per million (ppm)
downeld of tetramethylsilane. Coupling constants J are quoted
in Hz. Mass spectra with electronic impact (MS-EI) were recor-
ded from a Shimadzu QP 2010 apparatus. High resolution mass
spectra were recorded from a Brucker micrOTOFQ (APCI-TOF).
Photophysical measurements
UV-Vis absorption spectra were recorded in solution with quartz
cuvettes (optical pathlength 1 cm and 5 cm, Hellma®) by using a
Perkin Elmer l650 spectrophotometer. Corrected uorescence
emissions, excitation spectra and emission lifetimes were
recorded in solution with an Edinburgh FLS920 spectrouo-
C
22H19NNaO4 (M + Na): 384.1206, found: 384.1206.
2-(6-Chloro-2-methyl-pyridin-3-yl)-benzaldehyde (8)
rimeter equipped with Hamamatsu H5773-04 phototube and a To a degassed toluene solution (15 mL) containing Pd(PPh3)4
TCC900 card for data acquisition in time-correlated single- (173 mg, 0.15 mmol) and pyridine 5 (620 mg, 3 mmol) were
photon counting experiments (22 ps time resolution) by using successively
added
degassed
solutions
of
2-for-
a continuous 450 W Xenon arc lamp or a PicoQuant LDH-P-C- mylbenzeneboronic acid 6a (450 mg, 3 mmol) in methanol (6
405 pulsed diode laser as excitation source. Fluorescence mL) and Na2CO3 (636 mg, 6 mmol) in water (6 mL). Aer
ꢁ
quantum yields were measured following the method of Demas heating for 12 h at 100 C, the reaction mixture was cooled to
and Crosby15 (standard used: perylene in air equilibrated EtOH room temperature, extracted with ethyl acetate and dried over
solution, Fem ¼ 0.92).16 Solid emission spectra and solid MgSO4. Aer concentration, the residue was puried by chro-
emission quantum yields were measured by an Edinburgh matography on silica gel (cyclohexane/ethyl acetate) to give 8
1
ꢁ
FLS920 spectrouorimeter equipped with a barium sulfate (320 mg, 46%). Mp 88–90 C; HNMR (CDCl3, 200 MHz) d 9.81
coated integrating sphere (LabSphere, 4P-GPS-040-SF),
a
(s, 1H, CHO), 8.04 (dd, J ¼ 7.5, 1.3 Hz, 1H), 7.70 (dt, J ¼ 7.5, 1.3
continuous 450 W Xenon arc lamp as light source and a Hz, 1H), 7.59 (dt, J ¼ 7.6, 1.4 Hz, 1H), 7.47 (d, J ¼ 8.2 Hz, 1H),
Hamamatsu H5773-04 phototube, following the procedure 7.28 (d, J ¼ 8.2 Hz, 2H), 2.31 ppm (s, 3H, CH3); 13CNMR (CDCl3,
described by De Mello et al.17 The experimental errors are 50 MHz) d 190.9, 157.2, 150.2, 141.2, 140.0, 134.1, 133.7, 132.0,
within: ꢃ2 nm of the band maximum, 5% of the molar 130.7, 129.0, 128.8, 121.2, 22.9 ppm. MS (70 eV): m/z (%) 231
absorption coefficient, 10% of the lifetime measurements, and (M+, 100), 216 (58), 202 (33), 166 (33); HRMS m/z calcd for
15% of the emission quantum yield in solid.
C13H11ClNO (M + H): 232.0524, found: 232.0532.
2720 | RSC Adv., 2015, 5, 2715–2723
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
3-Methoxy-7,8-dihydro-8-hydroxy-7-methyl-indeno[10,20:4,5]
pyrido[2,1-a]isoindol-5-one (9b)
added degassed solutions of the corresponding boronic acid (1
mmol) in methanol (2 mL) and Na2CO3 (212 mg, 2 mmol) in
water (2 mL). Aer heating for 6 h at 100 ꢁC, the reaction
mixture was cooled to room temperature, extracted with ethyl
acetate and dried over MgSO4. Aer concentration, the residue
was puried by chromatography on silica gel (cyclohexane/ethyl
acetate) to give the desired compounds.
To a degassed toluene solution (2 mL) containing Pd(PPh3)4 (25
mg, 0.022 mmol) and pyridine 8 (50 mg, 0.216 mmol) were
successively added degassed solution of boronic acid 6b (58 mg,
0.324 mmol) in methanol (1 mL) and aqueous solution (1 mL) of
Na2CO3 (69 mg, 0.648 mmol) and NaBr (22.3 mg, 0.216 mmol).
Aer heating for 12 h at 100 ꢁC, the reaction mixture was cooled to
room temperature, extracted with ethyl acetate and dried over
MgSO4. Aer concentration, the residue was puried by chroma-
tography on silica gel (cyclohexane/ethyl acetate) to give 9b (34 mg,
48%). Mp 132–134 ꢁC; 1HNMR (CDCl3, 400 MHz) d 7.61 (d, J ¼ 6.4
Hz, 1H), 7.58 (d, J ¼ 8.4 Hz, 1H), 7.48 (d, J ¼ 6.4 Hz, 1H), 7.37 (dt, J
¼ 7.2, 1.2 Hz, 1H), 7.33 (t, J ¼ 6.4 HZ, 1H), 7.30 (d, J ¼ 2.0 Hz, 1H),
7.14 (dd, J ¼ 8.4, 2.4 Hz, 1H), 6.50 (d, J ¼ 6.2 Hz, 1H), 6.18 (d, J ¼
6.2 Hz, 1H), 5.55 (br s, 1H, OH), 5.23 (d, J ¼ 2.0 Hz, 1H), 3.89 (s, 3H,
OCH3), 1.25 (s, 3H, CH3); 13CNMR (CDCl3, 100 MHz) d 169.7, 161.0,
143.2, 141.8, 135.8, 133.4, 129.8, 129.4, 128.5, 128.2, 125.0, 121.6,
121.1, 120.6, 112.4, 105.8, 102.4, 79.8, 67.6, 55.8, 17.4 ppm. HRMS
m/z calcd for C21H17NNaO3 (M + Na): 354.1111, found: 354.1101.
3-Bromo-6-chloro-2-phenylpyridine (10a)
Yield: 92% (247 mg); mp 104–106 ꢁC; 1HNMR (CDCl3, 250 MHz)
d 7.91 (d, J ¼ 8.4 Hz, 1H), 7.75–7.65 (m, 2H), 7.50–7.40 (m, 3H),
7.16 ppm (d, J ¼ 8.4 Hz, 1H); 13CNMR (CDCl3, 62.5 MHz) d 158.3,
149.6, 143.7, 138.1, 129.3, 129.2, 128.0, 123.8, 117.8 ppm. MS (70
eV): m/z (%) 269 (M+, 35), 188 (100), 153 (50), 76 (40), 50 (35);
HRMS m/z calcd for C11H8BrClN (M + H): 267.9523, found:
267.9531.
3-Bromo-6-chloro-2-(4-methoxyphenyl)pyridine (10b)
Yield: 97% (289 mg); mp 93–95 ꢁC; 1HNMR (CDCl3, 200 MHz) d
7.90 (d, J ¼ 8.0 Hz, 1H), 7.70 (d, J ¼ 9.0 Hz, 2H), 7.13 (d, J ¼ 8.0
Hz, 1H), 6.99 (d, J ¼ 8.0 Hz, 1H), 3.87 ppm (s, 3H, OCH3);
13CNMR (CDCl3, 50 MHz) d 160.3, 157.7, 149.5, 143.7, 130.9,
130.5, 123.2, 117.5, 113.3, 55.2 ppm. MS (70 eV): m/z (%) 299
(M+, 100), 218 (95), 175 (40), 140 (75), 113 (45), 63 (55); HRMS m/
z calcd for C12H10BrClNO (M + H): 297.9629, found: 297.9640.
2-Amino-5,6-bromopyridine (13)
To a solution of 6-amino-2-bromopyridine 12 (3.46 g, 20 mmol)
in DMF (100 mL) was added NBS (3.56 g, 20 mmol). The solution
was stirred at room temperature for 6 h. The progress of the
reaction was monitored by TLC. Aer disappearance of starting
material, the mixture was poured into 200 mL of cold water. The
product precipitated immediately. Aer ltration and drying, 13
was obtained as a white powder (4 g, 80%). Mp 149–151 ꢁC; 1H
NMR (CDCl3, 200 MHz) d 4.65 (s, 2H, NH2), 6.37 (d, J ¼ 8.5 Hz,
2H), 7.56 ppm (d, J ¼ 8.5 Hz, 1H); 13CNMR (CDCl3, 50 MHz) d
156.7, 142.6, 140.9, 109.5, 108.6 ppm. MS (70 eV): m/z (%) 252
(M+, 100), 171 (42), 92 (65), 64 (40), 41 (42); HRMS m/z calcd for
C5H5Br2N2: 250.8814 (M + H), found: 250.8810.
3-Bromo-6-chloro-2-(4-(methylthio)phenyl)pyridine (10c)
Yield: 64% (201 mg); mp 116–118 ꢁC; 1HNMR (CDCl3, 200 MHz)
d 7.89 (d, J ¼ 8.0 Hz, 1H), 7.66 (d, J ¼ 8.5 Hz, 2H), 7.31 (d, J ¼ 8.5
Hz, 1H), 7.13 (d, J ¼ 8.0 Hz, 1H), 2.52 ppm (s, 3H, SCH3);
13CNMR (CDCl3, 50 MHz) d 157.5, 149.6, 143.7, 140.4, 134.4,
129.7, 125.3, 123.6, 117.6, 15.2 ppm. MS (70 eV): m/z (%) 315
(M+, 100), 219 (18), 140 (20); HRMS m/z calcd for C12H10BrClNS
(M + H): 313.9400, found: 313.9386.
2,3-Dibromo-6-chloropyridine (11)
To a solution of 2-amino-5,6-bromopyridine 13 (3.65 g, 14.5
mmol) in conc. HCl (35 mL) at ꢂ20 ꢁC was added NaNO2 (2 g, 29
mmol) slowly by small portions and the mixture was stirred at
room temperature for 4 h. NaOH 10 M was added until pH 11
and the product was extracted with ethyl acetate (3 ꢀ 150 mL).
The organic phase was washed with brine (100 mL) and dried
over MgSO4 and concentrated. The crude was puried by
chromatography on silica gel (cyclohexane/ethyl acetate 4/1) to
give 11 as a white powder (2.73 g, 70%). Mp 67–69 C; HNMR
(CDCl3, 200 MHz) d 7.82 (d, J ¼ 8.0 Hz, 1H), 7.18 ppm (d, J ¼ 8.0
Hz, 1H); 13CNMR (CDCl3, 50 MHz) d 148.8, 143.5, 142.4, 124.3,
122.4 ppm. MS (70 eV): m/z (%) 271 (M+, 85), 192 (72), 110 (50),
75 (100), 50 (76); HRMS m/z calcd for C5H3Br2ClN: 269.8315 (M +
H), found: 269.8305.
4-(3-Bromo-6-chloropyridin-2-yl)benzaldehyde (10d)
Yield: 97% (287 mg); mp 143–145 ꢁC; 1HNMR (CDCl3, 200 MHz)
d 10.10 (s, 1H, CHO), 8.01–7.96 (m, 3H), 7.86 (d, J ¼ 8.0 Hz, 2H),
7.24 ppm (d, J ¼ 8.5 Hz, 1H); 13CNMR (CDCl3, 50 MHz) d 191.8,
157.0, 150.0, 143.9, 143.7, 136.5, 130.2, 129.4, 124.7, 117.9 ppm.
MS (70 eV): m/z (%) 297 (M+, 100), 266 (20), 216 (100), 187 (25),
152 (52), 125 (32), 75 (47), 50 (60); HRMS m/z calcd for C12H8-
BrClNO (M + H): 295.9472, found: 295.9476.
1
ꢁ
3-Bromo-6-chloro-2-[4-(dimethylamino)phenyl]pyridine (10e)
1
Yield: 61% (190 mg); HNMR (CDCl3, 200 MHz) d 3.03 (s, 6H,
N(CH3)2), 6.77 (d, J ¼ 8.8 Hz, 2H), 7.04 (d, J ¼ 8.3 Hz, 1H), 7.73
(d, J ¼ 8.8 Hz, 2H), 7.85 ppm (d, J ¼ 8.3 Hz, 1H); 13CNMR (CDCl3,
50 MHz) d 40.1, 111.0, 117.0, 122.2, 125.5, 130.56, 143.7, 149.3,
150.8, 158.0 ppm. MS (70 eV): m/z (%) 312 (M+, 100), 195 (26),
General procedure for the preparation of 3-bromo-6-chloro-2-
arylpyridine (10)
To a degassed toluene solution (4 mL) containing Pd(PPh3)4 (58 152 (22), 42 (30); HRMS m/z calcd for C13H13BrClNO (M + H):
mg, 0.05 mmol) and 11 (269 mg, 1 mmol) were successively 310.9945, found: 310.9948.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 2715–2723 | 2721

View Article Online
RSC Advances
Paper
4-(3-Bromo-6-chloropyridin-2-yl)pyridine (10f)
7,8-Dihydro-8-hydroxy-7-phenyl-indeno[10,20:4,5]pyrido[2,1-a]-
isoindol-5-one (15a)
Pyridine 11 (272 mg, 1 mmol), 4-pyridine boronic acid (85%
purity, 174 mg, 1.41 mmol) and Pd(PPh3)4 (58 mg, 0.05 mmol) Mp 237–239 ꢁC; 1HNMR (CDCl3, 250 MHz) d 7.98 (d, J ¼ 7.3 Hz,
were placed in a Schlenk tube under argon. Degassed dioxane 1H), 7.74 (d, J ¼ 7.8 Hz, 1H), 7.66 (dt, J ¼ 7.4, 1.9 Hz, 2H), 7.57
(7 mL) and a degassed solution of aqueous Na2CO3 (1 M, 3 mL, 3 (dt, J ¼ 7.4, 1.9 Hz, 2H), 7.50–7.38 (m, 2H), 7.18–7.05 (m, 3H),
mmol) were added and the mixture was heated under reux for 6.82 (dd, J ¼ 8.0, 1.9 Hz, 2H), 6.62 (d, J ¼ 6.3 Hz, 1H), 6.32 (d, J ¼
18 h. Aer heating cooling to room temperature, the mixture 6.3 Hz, 1H), 5.98 (brs, 1H, OH), 4.86 (d, J ¼ 1.9 Hz, 1H); 13CNMR
was extracted with ethyl acetate and dried over MgSO4. Aer (CDCl3, 62.5 MHz) d 170.7, 144.1, 142.0, 137.9, 137.4, 135.2,
concentration, the residue was puried by chromatography on 135.1, 132.5, 129.9, 129.6, 128.9, 128.2, 127.7, 126.4, 124.9,
silica gel (cyclohexane/ethyl acetate 4/1) to give pyridine 10f as a 123.9, 121.0, 120.6, 113.6, 104.4, 81.4, 73.3 ppm. MS (70 eV): m/z
1
white powder (150 mg, 56%). Mp 115–117 C; HNMR (CDCl3, (%) 363 (M+, 95), 286 (100), 258 (32), 202 (20), 77 (55), 51 (30);
ꢁ
200 MHz) d 8.75 (s, 2H), 7.95 (d, J ¼ 8.5 Hz, 1H), 7.61 (d, J ¼ 4.0 HRMS m/z calcd for C25H17NNaO2 (M + Na): 386.1151, found:
Hz, 2H), 7.25 ppm (d, J ¼ 8.5 Hz, 1H); 13CNMR (CDCl3, 50 MHz) 386.1176.
d 155.5, 150.1, 149.7, 145.4, 144.0, 125.1, 123.7, 117.7 ppm. MS
(70 eV): m/z (%) 270 (M+, 44), 189 (100), 162 (30), 127 (24); HRMS
m/z calcd for C10H7BrClN2 (M + H): 268.9476, found: 268.9484.
General procedure for the preparation of pentacycles (15)
An oven-dried resealable tube was charged with Pd(OAc)2 (11.2
mg, 0.05 mmol, 5.0 mol%), XPhos ligand (24 mg, 0.05 mmol, 5.0
3-Bromo-6-chloro-2-(phenylethynyl)pyridine (14)
An oven-dried resealable tube was charged with 11 (269 mg, 1 mol%), 2-formylbenzeneboronic acid (750 mg, 5 mmol), K3PO4
mmol), CuI (5 mg, 0.03 mmol) and PdCl2(PPh3)2 (7 mg, 0.01 (1.37 g, 7.0 mmol) and pyridine 10 or 14 (1.0 mmol). The ask
mmol) then placed under argon. Degassed acetonitrile (1.5 mL) was evacuated and backlled with argon then degassed dioxane
and triethylamine (0.2 mL, 1.5 mmol) were added. Finally, (6 mL) was added through the rubber septum. Aer heating for
phenylacetylene (112.3 mg, 1.1 mmol) was added and the 12 h at 100 ꢁC, the reaction mixture was cooled to room
mixture was heated at 60 ꢁC for 12 h. Aer cooling, the mixture temperature, extracted with ethyl acetate (3 ꢀ 20 mL) and dried
was extracted with ethyl acetate (3 ꢀ 15 mL), dried and over MgSO4. Aer ltration on Celite and concentration, the
concentrated. The residue was puried by chromatography on residue was puried by chromatography on silica gel
silica gel (cyclohexane/ethyl acetate 3/1) to give 14 as a white (cyclohexane/ethyl acetate) to give the pentacycles.
product (200 mg, 68%). Mp 148–150 ꢁC; 1HNMR (CDCl3, 200
MHz) d 7.15 (d, J ¼ 8.4 Hz, 1H), 7.37–7.41 (m, 3H), 7.62–7.67 (m,
2H), 7.85 ppm (d, J ¼ 8.4 Hz, 1H). 13CNMR (CDCl3, 50 MHz) d
7,8-Dihydro-8-hydroxy-7-(4-methoxy-phenyl)-indeno[10,20:4,5]-
149.6, 143.4, 142.1, 132.2, 129.6, 128.4, 124.4, 122.1, 121.4, 95.4,
pyrido[2,1-a]isoindol-5-one (15b)
86.5 ppm. MS (70 eV): m/z (%) 252 ([M ꢂ C3H3]+, 99), 171 (45), 92
Yield: 52% (102 mg); mp 159–161 ꢁC; 1HNMR (CDCl3, 400 MHz)
(83), 64 (100), 41 (86); HRMS m/z calcd for C13H8BrClN (M + H):
d 7.94 (d, J ¼ 7.2 Hz, 1H), 7.80–7.45 (m, 5H), 7.50–7.40 (m, 2H),
291.9523, found: 291.9503.
6.77 (d, J ¼ 9.0 Hz, 2H), 6.63 (d, J ¼ 9.0 Hz, 2H), 6.61 (d, J ¼ 6.2
Hz, 1H), 6.32 (d, J ¼ 6.2 Hz, 1H), 5.94 (s, 1H), 4.91 (br s, 1H, OH),
3.65 ppm (s, 3H, OCH3); 13CNMR (CDCl3, 100 MHz) d 170.6,
158.9, 144.0, 142.1, 137.2, 135.1, 134.9, 132.4, 129.95, 129.9,
Cascade reaction of 10a under standard conditions.
Formation of 16 and 15a
To a degassed toluene solution (7.5 mL) containing Pd(PPh3)4 129.5, 128.9, 127.65, 127.6, 124.8, 123.8, 121.0, 120.5, 113.6,
(58 mg, 0.05 mmol) and pyridine 10a (134 mg, 0.5 mmol), 113.3, 104.4, 81.2, 72.7, 55.0 ppm. HRMS m/z calcd for
degassed solutions of 2-formylbenzeneboronic acid 6a (186 mg,
1.25 mmol) in methanol (1.25 mL) and Na2CO3 (265 mg, 2.5
mmol) in water (2.5 mL) were successively added. Aer heating
for 12 h at 100 ꢁC, the reaction mixture was cooled to room
temperature, extracted with ethyl acetate (3 ꢀ 20 mL) and dried
over anhydrous MgSO4. Aer ltration on Celite and concen-
tration, the residue was puried by chromatography on silica
gel (cyclohexane/ethyl acetate 9/1) to give 16 (90 mg, 61%) and
15a (30 mg, 15%).
C26H19NNaO3 (M + Na): 416.1257, found: 416.1265.
7,8-Dihydro-8-hydroxy-7-(4-methylthio-phenyl)-indeno-
[10,20:4,5]pyrido[2,1-a]isoindol-5-one (15c)
Yield: 50% (100 mg); mp 97–99 ꢁC; 1HNMR (CDCl3, 400 MHz) d
7.94 (d, J ¼ 7.8 Hz, 1H), 7.73 (d, J ¼ 7.8 Hz, 1H), 7.68–7.62 (m,
2H), 7.60–7.54 (m, 2H), 7.48–7.38 (m, 2H), 6.90 (d, J ¼ 9.0 Hz,
2H), 6.76 (d, J ¼ 9.0 Hz, 2H), 6.62 (d, J ¼ 6.0 Hz, 1H), 6.33 (d, J ¼
6.0 Hz, 1H), 5.69 (m, 1H), 4.90 (d, J ¼ 2.5 Hz, 1H, OH), 2.33 ppm
(s, 3H, SCH3); 13CNMR (CDCl3, 100 MHz) d 170.6, 143.9, 141.8,
2-[2-(6-Phenyl-pyridin-2-yl)-benzaldehyde]-benzaldehyde (16)
1HNMR (CDCl3, 200 MHz) d 10.35 (s, 1H, CHO), 9.84 (s, 1H, 138.0, 137.2, 135.1, 134.9, 134.7, 132.5, 129.9, 129.6, 128.9,
CHO), 8.05 (d, J ¼ 7.4 Hz, 1H), 8.00–7.00 ppm (m, 14H). MS (70 127.6, 126.9, 126.1, 124.8, 123.9, 121.0, 120.5, 113.5, 104.3, 81.3,
eV): m/z (%) 363 (M+, 80), 286 (100), 258 (30), 202 (30), 77 (80), 51 72.9, 15.4 ppm. HRMS m/z calcd for C26H19NNaO2S (M + Na):
(65).
409.1029, found: 432.1047.
2722 | RSC Adv., 2015, 5, 2715–2723
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
M. Gingras and P. Ceroni, J. Mater. Chem. C, 2013, 1, 2717;
(c) L. Chen, Y. Jiang, H. Nie, P. Lu, H. H. Y. Sung,
I. D. Williams, H. Sing Kwok, F. Huang, A. Qin, Z. Zhao
and B. Z. Tang, Adv. Funct. Mater., 2014, 24, 3621.
3 (a) Highly Efficient OLEDs with Phosphorescent Materials, ed.
H. Yersin, Wiley-VCH, Berlin, 2007; (b) G. M. Farinola and
R. Ragni, Chem. Soc. Rev., 2011, 40, 3467.
7,8-Dihydro-8-hydroxy-7-(4-formyl-phenyl)-7H-indeno-
[10,20:4,5]pyrido[2,1-a]isoindol-5-one (15d)
Yield: 71% (139 mg); mp 151–153 ꢁC; 1HNMR (CDCl3, 400 MHz)
d 9.85 (s, 1H, CHO), 7.95 (d, J ¼ 7.2 Hz, 1H), 7.75 (d, J ¼ 7.6 Hz,
1H), 7.70–7.63 (m, 2H), 7.62–7.54 (m, 2H), 7.60 (d, J ¼ 8.6 Hz,
2H), 7.46 (dt, J ¼ 7.2, 1.2 Hz, 1H), 7.42 (t, J ¼ 7.6 Hz, 1H), 7.00 (d,
J ¼ 8.6 Hz, 2H), 6.63 (d, J ¼ 6.0 Hz, 1H), 6.32 (d, J ¼ 6.0 Hz, 1H),
5.99 (d, J ¼ 2.4 Hz, 1H), 4.84 ppm (d, J ¼ 2.5 Hz, 1H, OH);
13CNMR (CDCl3, 50 MHz) d 191.6, 170.5, 144.8, 143.6, 141.0,
137.0, 135.5, 134.9, 132.7, 130.1, 129.7, 129.4, 129.2, 127.3,
127.1, 124.8, 123.9, 121.1, 120.6, 114.1, 104.3, 81.4, 73.1 ppm.
HRMS m/z calcd for C26H17NNaO3 (M + Na): 414.1101, found:
414.1107.
4 (a) I. D. W. Samuel and G. A. Turnbull, Chem. Rev., 2007, 107,
´
1272; (b) S. Forget and S. Chenais, Organic Solid-State Lasers,
Springer Series in Optical Science, 2013, vol. 175; (c)
G. M. Akselrod, E. R. Young, K. W. Stone, A. Palatnik,
V. Bulovic and Y. R. Tischler, Phys. Rev. B: Condens. Matter
Mater. Phys., 2014, 90, 035209.
5 See e.g.: (a) S. W. Thomas III, G. D. Joly and T. M. Swager,
Chem. Rev., 2007, 107, 1339; (b) M. Schferling, Angew.
Chem., Int. Ed., 2012, 51, 3532.
7,8-Dihydro-8-hydroxy-7-(4-pyridyl)-7H-indeno[10,20:4,5]pyrido
[2,1-a]isoindol-5-one (15f)
¨
6 H. Langhals, T. Potrawa, H. Noth and G. Linti, Angew. Chem.,
Yield (22%, 40 mg); mp 135–137 ꢁC; 1HNMR (CDCl3, 200 MHz) d
8.32 (d, J ¼ 6.2 Hz, 2H), 7.96 (d, J ¼ 7.2 Hz, 1H), 7.78–7.51 (m,
5H), 7.50–7.40 (m, 2H), 6.70 (d, J ¼ 6.2 Hz, 2H), 6.63 (d, J ¼ 6.4
Hz, 1H), 6.33 (d, J ¼ 6.4 Hz, 1H), 5.98 (s, 1H), 4.85 ppm (br s, 1H,
OH); 13CNMR (CDCl3, 50 MHz) d 170.4, 149.1, 147.5, 143.4,
140.5, 136.8, 134.9, 134.85, 132.9, 130.3, 129.9, 129.3, 127.3,
124.9, 124.0, 121.5, 121.1, 120.7, 114.2, 104.1, 81.2, 72.7 ppm.
HRMS m/z calcd for C24H17N2O2 (M + H): 365.1285, found:
365.1269.
Int. Ed. Engl., 1989, 28, 478.
7 Z. Chamas, O. Dietz, E. Aubert, Y. Fort and V. Mamane, Org.
Biomol. Chem., 2010, 8, 4815.
8 Z. Chamas, E. Marchi, A. Modelli, Y. Fort, P. Ceroni and
V. Mamane, Eur. J. Org. Chem., 2013, 2316.
9 P. Eastwood, J. Gonzalez, S. Paredes, A. Nueda, T. Domenech,
J. Alberti and B. Vidal, Bioorg. Med. Chem. Lett., 2010, 20,
1697.
10 V. Mamane and Y. Fort, Tetrahedron Lett., 2006, 47, 2337.
¨
11 V. Mamane, F. Louerat, J. Iehl, M. Abboud and Y. Fort,
Acknowledgements
Tetrahedron, 2008, 64, 10699.
12 The stability of 16 was however reduced in solution which
prevented obtaining clean 13C NMR analysis.
13 For a review, see: R. Martin and S. L. Buchwald, Acc. Chem.
Res., 2008, 41, 1461.
14 For an example from our laboratory, see: M. Abboud,
E. Aubert and V. Mamane, Beilstein J. Org. Chem., 2012, 8,
253.
15 J. N. Demas and G. A. Crosby, J. Phys. Chem., 1971, 75, 991.
16 M. Montalti, A. Credi, L. Prodi and M. T. Gandol, in
Handbook of Photochemistry, Taylor & Francis, London, 3rd
edn, 2006, ch. 10.
´
This research is supported by CNRS, Universite de Lorraine,
`
´
Ministere de l'Enseignement Superieur et de la Recherche
(Grant to Z.C.), the European Commission ERC Starting Grant
(PhotoSi, 278912) and MAE (DirezioneGenerale per la Promo-
zione del Sistema Paese). The authors thank the Service Com-
´
mun de Diffraction X (Universite de Lorraine) for providing
access to crystallographic experimental facilities.
Notes and references
1 (a) M. Shimizu and T. Hiyama, Chem.–Asian J., 2010, 5, 1516;
(b) Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Commun.,
2009, 4332 and references therein; (c) Y. Hong,
J. W. Y. Lam and B. Z. Tang, Chem. Soc. Rev., 2011, 40, 5361.
2 For some recent examples of highly luminescent solids, see:
(a) O. Bolton, K. Lee, H. J. Kim, K. Y. Lin and J. Kim, Nat.
Chem., 2011, 3, 205; (b) G. Bergamini, A. Fermi, C. Botta,
U. Giovanella, S. Di Motta, F. Negri, R. Peresutti,
17 J. C. De Mello, H. F. Wittmann and R. H. Friend, Adv. Mater.,
1997, 9, 230.
18 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M. C. Burla, G. Polidori and M. Camalli, J. Appl.
Crystallogr., 1994, 27, 435.
¨
19 G. M. Sheldrick, SHELXL-97, University of Gottingen,
Germany, 1997.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 2715–2723 | 2723