The synthesis, X-ray structure analysis and photophysical characterization of 2-(9-anthrylmethylideneamino)- 5-methylphenol

Article abstract of DOI:10.1007/s10870-011-0100-0

The Schiff base 2-(9-anthrylmethylideneamino)- 5-methylphenol has been prepared in good yield (55%) from commercially available starting materials. The photophysical properties of this compound and its precursor have been determined. The room temperature absorption spectra of both in various solvents exhibited two p → p* transitions that had similar maxima, one that was more intense at approximately 260 nm and a weaker one at approximately 400 nm. Solutions of both compounds in methylcyclohexane and propanenitrile were luminescent at room temperature with maxima in the range 450-500 nm. The emission spectra of both at 77 K in methylcyclohexane solution were similar and exhibited vibrational structure with maxima in the range 460-522 nm. At room temperature and 77 K both compounds had short excited state lifetimes that characterized their emission as fluorescence. The title compound, C ₂₂H₁₇NO, crystallized in the triclinic space group P1 with a = 8.5533 (5) A , b = 14.0926 (10) A , c = 14.9382 (11) A , α = 104.204 (6)°, β = 106.480 (5)°, c = 105.091 (5)°, V = 1564.9 (2) A 3, T = 90 K, Dc = 1.322 Mg m _-3, Z = 4, R = 0.033. Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s10870-011-0100-0

J Chem Crystallogr (2011) 41:1342–1347
DOI 10.1007/s10870-011-0100-0
ORIGINAL PAPER
The Synthesis, X-ray Structure Analysis and Photophysical
Characterization of 2-(9-Anthrylmethylideneamino)-
5-methylphenol
•
´
Andres Villalpando Frank R. Fronczek
Ralph Isovitsch
•
Received: 12 January 2011 / Accepted: 15 April 2011 / Published online: 27 April 2011
Ó Springer Science+Business Media, LLC 2011
Abstract The Schiff base 2-(9-anthrylmethylidenea-
mino)-5-methylphenol has been prepared in good yield
(55%) from commercially available starting materials. The
photophysical properties of this compound and its precur-
sor have been determined. The room temperature absorp-
tion spectra of both in various solvents exhibited two
p ? p* transitions that had similar maxima, one that was
more intense at approximately 260 nm and a weaker one at
approximately 400 nm. Solutions of both compounds in
methylcyclohexane and propanenitrile were luminescent at
room temperature with maxima in the range 450–500 nm.
The emission spectra of both at 77 K in methylcyclohexane
solution were similar and exhibited vibrational structure
with maxima in the range 460–522 nm. At room temper-
ature and 77 K both compounds had short excited state
lifetimes that characterized their emission as fluorescence.
The title compound, C22H17NO, crystallized in the triclinic
Introduction
Schiff bases are a diverse class of useful compounds that
can be represented by the general formula RR0C = NR00,
where R00 is an alkyl or aryl group that serves to stabilize
the C–N double bond. Schiff bases have traditionally been
synthesized via acid catalysis [1]. More recent preparations
have been devised that are acid-free or utilize metal ions as
templates for the construction of larger macrocyclic sys-
tems [2, 3]. One unique approach to the synthesis of Schiff
bases involves microwave irradiation [4].
Schiff bases have been utilized in numerous research
areas. In organic synthesis, they have found use as precur-
sors to novel heterocyclic compounds [5]. The medicinal
chemistry and pharmaceutical fields have utilized Schiff
bases as antibacterial and antifungal agents [6]. Schiff bases
have also been used extensively in the field of coordination
chemistry. For example, they have been used to prepare
recyclable and water soluble palladium(II) complexes for
use in the Suzuki coupling reaction as well as novel lumi-
nescent rhenium(I) tricarbonylchloro complexes for use in
solar energy collection [7, 8]. Certain Schiff bases have
been found to possess nonlinear optical properties, which
make them attractive materials for optoelectronics [9].
Our research explores the preparation and photophysics
of Schiff bases that incorporate polycyclic aromatic
hydrocarbons with the goal of applying them to light
emitting diode construction. Toward this end, we have
prepared and determined the X-ray structure of the novel
phenolic Schiff base 2-(9-anthrylmethylideneamino)-
5-methylphenol (1, Scheme 1). The photophysical proper-
ties of 1 have also been determined at room temperature
and 77 K. The first detailed photophysical characterization
of 9-anthracenecarboxaldehyde, the precursor to 1, has also
been completed at these temperatures.
ꢀ
˚
space group P1 with a = 8.5533 (5) A, b = 14.0926 (10)
˚
˚
A, c = 14.9382 (11) A, a = 104.204 (6)°, b = 106.480
3
˚
(5)°, c = 105.091 (5)°, V = 1564.9 (2) A , T = 90 K,
Dc = 1.322 Mg m-3, Z = 4, R = 0.033.
Keywords Schiff base ꢀ Crystal structure ꢀ Absorption ꢀ
Emission ꢀ Lifetime
A. Villalpando ꢀ R. Isovitsch (&)
Department of Chemistry, Whittier College, Whittier,
CA 90608, USA
e-mail: risovits@whittier.edu
F. R. Fronczek
Department of Chemistry, Louisiana State University,
Baton Rouge, LA 70803, USA
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J Chem Crystallogr (2011) 41:1342–1347
1343
Scheme 1 The synthesis of
compound 1
H
O
H
N
4 Å molecular sieves
MeOH/reflux
H2N
HO
CH3
CH3
HO
1
Experimental
color. The solution was filtered hot and allowed to cool,
yielding brown needle-like crystals. 0.171 g (55%) of 1
was obtained. MP 119–122 °C; IR (KBr pellet) 3445,
3394, 3047, 2935, 2867, 2822, 1624, 1578, 1259 cm-1; 1H
NMR (300 MHz, DMSO-d6) ppm 9.73 (s, 1H), 9.27 (s,
Reagents and Techniques
The synthetic procedure was carried out using standard
techniques. Solvents and reagents were purchased from
Simga-Aldrich or Acros Organics and used as received. 1H-
and 13C NMR spectra were recorded on a JEOL ECX
300 MHz spectrometer using TMS as the internal standard.
The IR spectrum was recorded as a KBr disk on a JASCO
460 FT-IR. Elemental analysis was done by M–H–W
Laboratories of Tucson Arizona. Mass spectrometry was
provided by the Washington University Mass Spectrometry
Resource with support from the NIH National Center for
Research Resources (Grant No. P41RR0954).
3
1H), 8.79 (d, J = 8.26 Hz, 2H), 8.73 (s, 1H), 8.14 (d,
3
3J = 7.22 Hz, 2H), 7.57 (m, 4H), 7.25 (d, J = 7.91 Hz,
1H), 6.78 (s, 1H), 6.72 (d, 3J = 7.91 Hz, 1H), 2.27 (s, 3H);
13C NMR (75 MHz, DMSO-d6) ppm 159.3, 150.8, 137.8,
137.2, 131.4, 130.4, 130.3, 129.4, 128.5, 127.6, 126.1, 125.7,
120.9, 120.7, 117.3, 21.2; EI-HR-MS: m/z for [M ? H]?
=
312.1374, Calcd. m/z for [M ? H]? = 312.1388 Anal.
Calcd. for C22H17NO (311.4): C, 84.85; H, 5.51, N, 4.50.
Found: C, 85.06; H, 5.64; N, 4.51.
Emission and absorption spectra were recorded at room
temperature and at 77 K in spectrophotometric grade meth-
ylcyclohexane and propanenitrile (99% purity) utilizing a
HoribaJobinYvon FluoroMax-4 fluorometer and a Hewlett
Packard 8453 diode array spectrometer. Measurements were
taken from deoxygenated solutions whose concentrations
were approximately 1 9 10-4 or 1 9 10-5 M. All emission
spectra were corrected for detector response utilizing a cor-
rection curve supplied by the fluorometer manufacturer.
Excited state lifetimes were measured utilizing a Hori-
baJobinYvon Time Correlated Single Photon Counting
(TCSPC)apparatuswithexcitationfroma pulsedLED laserat
388 nm. Theabsorbances of the analyte solutions were keptat
or below 0.1 to avoid inner filter effects. All solutions were
deoxygenated prior to measurement acquisition. A multiex-
ponential decay analysis program provided by the instrument
manufacturerwasusedtoanalyze thedata. Three criteriawere
used to assess the quality of fitted decay curves: chi-squared
values (v2) that were less than 1.2; plots of the residuals that
displayed the least oscillation and varied no more than three
standard deviations; and visual inspection of the goodness-of-
fit between the experimental and fitted decay curves.
X-ray Structure Determination
An orange plate of 1 (0.25 9 0.25 9 0.13 mm) was used for
data collection at T = 90 K on a Bruker Kappa Apex-II
CCD area detector diffractomer equipped with an Oxford
Cryosystems Cryostream chiller and graphite-monochro-
˚
mated Cu Ka radiation (k = 1.54178 A). A total of 14,165
measured reflections with hmax ¼ 68:7ꢁ yielded 5,532
unique data. The structure was solved by direct methods, and
structure refinement was carried out using SHELXL-97 [10].
All hydrogen atoms were visible in difference maps, and
their coordinates were refined, except for those of the methyl
groups, which were idealized with refined torsional param-
eters. Table 1 lists the details of X-ray data collection,
structure solution and refinement. Figure 2was created using
Mercury 2.3, a program for crystal structure visualization,
that can be downloaded for free from the Cambridge Crys-
tallographic Data Centre via http://www.ccdc.cam.ac.uk/
products/mercury. CCDC 781653 contains the supplemen-
tary crystallographic data for this article. These data can be
obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccd.cam.ac.uk/data_request/cif.
Synthesis of 2-(9-anthrylmethylideneamino)-
5-methylphenol (1)
Results and Discussion
20 mL of methanol, 9-anthracenecarboxaldehyde (0.251 g,
1.22 mmol), and 6-amino-m-cresol (0.125 g, 1.01 mmol)
were added to a 50 mL round bottom flask with a magnetic
Synthesis and Characterization of 1
Compound 1 was prepared in good yield (55%) via a con-
densation reaction between 9-anthracenecarboxaldehyde
and 6-amino-m-cresol (Scheme 1). It exhibited spectroscopic
˚
stir bar and dry 4 A molecular sieves. The solution was
refluxed over night, until it turned a dark orange/brown
123

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J Chem Crystallogr (2011) 41:1342–1347
Table 1 Crystal and experimental data
Compound
C22H17NO
311.37
Formula weight
CCDC deposit no.
781653
ꢀ
Space group
Triclinic, P1
Crystal dimension
0.25 9 0.25 9 0.13 mm3
Unit cell parameters
˚
8.5533 (5) A
a
˚
14.0926 (10) A
b
˚
14.9382 (11) A
c
a
104.204(6)8
106.480 (5)8
105.091(5)8
b
c
3
˚
1564.9 (2) A
V
Temperature
90.5 (5) K
Z
4
Dc (Mg m-3
Radiation
l(CuKa)
F(000)
)
1.322
˚
CuKa (k = 1.54178 A)
0.63 mm-1
Fig. 1 ORTEP view of the two independent molecules of 1.
Ellipsoids are represented at the 50% probability level
656
hmax
68.7°
1
observed for the HC=N and OH moieties in the H NMR
Index ranges
-10 B h B 10, -16 B k B 16,
-16 B l B 18
spectrum of 1, and the HC=N carbon resonance was
observed at 159.3 ppm in the 13C NMR spectrum [14]. The
identity of 1 was corroborated by an elemental analysis that
yielded acceptable values and a HR-EI-MS that had an
[M ? H]? peak at m/z = 312.1374, which was approxi-
mately 3 ppm less than the calculated value.
Goodness of fit on F2
Reflections collected
Independent reflections
1.04
14165
5532
Reflections with I [ 2r(I) 5138
Refined parameters
R1/wR2
520
0.033/0.092
Measurement
Bruker Kappa Apex-II CCD area
detector diffractometer
Crystallographic Study
Refinement
Full-matrix least squares method on F2
Crystals of 1 suitable for X-ray analysis were obtained
from the slow evaporation of the reaction mixture. The
ORTEP representation of 1 is shown in Fig. 1 while the
intermolecular interactions of the anthracene p-system of 1
are illustrated in Fig. 2. Crystal data and structure refine-
ment data are presented in Table 1 and selected bond
lengths and angles are listed in Table 2.
Measurement
Bruker Kappa Apex-II CCD area
detector diffractometer
Extinction coefficient
0.0026 (3)
-3
˚
0.21–0.16 eA
ðDqÞmax;ðDqÞmin
characteristics similar to other phenolic Schiff bases that
exist as an enol-amine tautomer [11].
The asymmetric unit of 1 is comprised of two inde-
pendent molecules of 1, each of which was found to pos-
sess an intramolecular O–HꢀꢀꢀN hydrogen bond with HꢀꢀꢀN
The infrared spectrum of 1 exhibited absorptions that
indicated the hydroxyl group of 1 participated in hydrogen
bonding. Two O–H stretching absorptions at 3445 and
3394 cm-1, which are caused by the rotational dynamics of
an intermolecular hydrogen bond between two O–H
groups, were observed [12]. Intramolecular hydrogen
bonding between the hydroxyl proton and the neighboring
nitrogen atom was indicated by the absorptions at 2867 and
2822 cm-1 [13]. Other important absorptions from the
˚
distance of approximately 2.1 A. The OꢀꢀꢀN distances were
˚
observed to be 2.6665 (12) A for O1ꢀꢀꢀN1 and 2.7128 (12)
˚
A for O2ꢀꢀꢀN2. This type of hydrogen bonding has been
documented in similar Schiff bases and confirmed the
intramolecular hydrogen bonding first observed in the
infrared spectrum of 1 [13].
The p-systems of individual molecules of 1 were found
to participate in different types of intermolecular interac-
tions. For example, p-stacking about the inversion centers
between adjacent phenol rings and anthracene rings was
observed, the former with a centroid–centroid distance of
infrared spectrum include those at 1624 and 1259 cm-1
,
the former arising from the C–N double bond and the latter
from the C–O single bond. Proton resonances were
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J Chem Crystallogr (2011) 41:1342–1347
1345
intermolecular interactions have been observed in similar
molecules [15, 16].
The central linkage (C16–N1–C15–C1 and C38–N2–
C37–C23) between the phenol and anthracene ring systems
is constructed of bonds whose length correspond to alter-
nating single and double bonds starting with C16 and C38
[17]. The bond angles of the carbon and nitrogen atoms of
the C–N double bond approach 120°, and indicate their sp2
hybrid character. The linkages are fully extended, as given
by observed torsion angles of -176.68 (9)° (C38–N2–
C37–C23) and -175.65 (10)° (C16–N1–C15–C1). Conju-
gation between the anthracene and phenol groups is lim-
ited, as dihedral angles between these planes are 67.24 (1)°
for the molecule containing N1 and 77.98 (1)° for the
molecule containing N2.
a
b
c
Bond lengths for O2–C39 and O1–C17 were found to be
˚
1.3638 (15) and 1.3670 (14) A respectively. These values
correlate to a full C–O single bond and support 1 existing
in its enol-amine form in the solid state. Other bond angles
and lengths observed in 1 compare well with those found in
similar compounds [17–20].
Photophysical Characterization
Fig. 2 Intermolecular interactions of the anthracene p-system of
compound 1. a Anthracene C-Hꢀꢀꢀp interaction (b) anthracene ring
p-stacking (c) O-Hꢀꢀꢀp interaction
The absorption and emission data for 1 and its precursor,
9-anthracenecarboxaldehyde, are listed in Table 3. Their
excited state lifetime data are listed in Table 4. Electronic
absorption and emission spectra of compound 1 and
˚
Table 2 Selected bond lengths [A] and angles [°] for compound 1
Table 3 Photophysical data for compound 1 and 9-anthracene-
carboxaldehydea
C23–C37
1.4764 (14) C1–C15
1.2791 (15) N1–C15
1.4160 (13) N1–C16
1.3638 (13) O1–C17
1.5085 (15) C19–C22
1.4204 (16) C4–C5
1.4390 (15) C2–C7
1.3956 (16) C7–C8
1.4716 (15)
1.2788 (15)
1.4146 (14)
1.3670 (14)
1.5065 (15)
1.4201 (16)
1.4400 (15)
1.3937 (16)
119.87 (9)
116.1 (8)
N2–C37
kmax,abs nm
(e)b
kmax,em nm
(kexc nm)
N2–C38
O2–C39
C41–C44
Compound 1
C26–C27
Methylcyclohexane solution
413 (12,900)
262 (66,600)
492 (398)
C24–C29
C29–C30
Methylcyclohexane glass at 77 K
CH3CH2CN solution
522 (398)
487
C38–N2–C37
C23–C37–H37
C24–C23–C36
C39–C38–C43
N2–C37–C23
119.43 (9)
116.6 (7)
C15–N1–C16
C1–C15–H15
462
120.48 (10) C2–C1–C14
118.75 (10) C21–C16–C17
122.99 (10) N1–C15–C1
120.38 (10)
118.41 (10)
124.56 (10)
404 (11,900)
257 (72,800)
493 (408)
9-Anthracenecarboxaldehyde
Methylcyclohexane solution
C38–N2–C37–C23 -176.68 (9) C16–N1–C15–C1 -175.65 (10)
398 (7,670)
459 (378)
263 (96,100)
Methylcyclohexane glass at 77 K
521 (398)
488
˚
3.718 (2) A and the later with a centroid–centroid distance
460
˚
of 3.730 (2) A. An O–Hꢀꢀꢀp interaction was observed
CH3CH2CN solution
398 (6,800)
480 (408)
between the hydrogen atom of the OH moiety and the
˚
263 (100,200)
anthracene p-system at a distance of 2.687 (2) A. The
a
˚
anthracene ring systems were observed to be 2.689 (2) A
Spectra were acquired at room temperature unless otherwise noted
Extinction coefficient units M-1cm-1
b
apart via an edge-on C–Hꢀꢀꢀp interaction. These types of
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J Chem Crystallogr (2011) 41:1342–1347
Table 4 Excited state lifetimes with standard deviations and chi-
squared (v2) values for compound 1 and 9-anthracenecarboxaldehydea
v2
s1ðnsÞ
s2ðnsÞ
Compound 1
Methylcyclohexane solution
6.3 0.1
0.73
Methylcyclohexane solution at 77 K 4.1 0.2 12.9 0.5 0.98
CH3CH2CN solution
3.5 0.2 7.8 0.1 0.98
9-Anthracenecarboxaldehyde
Methylcyclohexane solution
3.7 0.2 13.2 0.2 1.06
Methylcyclohexane solution at 77 K 4.1 0.2 18.0 0.4 1.06
CH3CH2CN solution 3.4 0.5 8.6 0.2 0.91
a
Excited state lifetimes were acquired at room temperature unless
otherwise noted
Fig. 3 Electronic absorption and emission spectra of compound 1 in
methylcyclohexane solution. Room temperature absorption spectrum
(ꢀꢀ–ꢀꢀ–); room temperature emission spectrum (kex = 398 nm) (- - - - -);
emission spectrum at 77 K (kex = 398 nm) (——)
9-anthracenecarboxaldehyde in methylcyclohexane solu-
tion are presented in Figs. 3 and 4 respectively.
Two bands, an intense one at approximately 260 nm and
a weak one at approximately 400 nm characterized the
absorption spectra of compound 1 and 9-anthracenecar-
boxaldehyde in methylcyclohexane and propanenitrile
solution. The observed similarity was not unexpected, as
the absorption spectra of polycyclic aromatic hydrocarbons
have been observed to resemble those of their parent
molecules [21]. Extinction coefficients for these bands
were large and suggest that they originate p ? p* transi-
tions [22].
Solutions of 1 and 9-anthracenecarboxaldehyde in
methylcyclohexane yielded emission spectra with broad,
featureless bands centered at 492 and 459 nm respectively.
The longer wavelength emission maximum of 1 is ratio-
nalized in terms of small resonance interaction between the
anthracene and phenol moieties.
The emission spectra obtained from a solution of 1 in
propanenitrile and methylcyclohexane were very similar,
while a dilute propanenitrile solution of 9-anthracenecar-
boxaldehyde yielded an emission spectrum with a maxi-
mum red-shifted by 21 nm when compared to the
maximum obtained in methylcyclohexane. This red-shift
can be explained in terms of increased resonance interac-
tion between the anthracene rings and the aldehyde moiety,
which can arise from solvent intermolecular interactions
that keep it coplanar with the aromatic system [22].
The excitation of methylcyclohexane solutions of 1 and
9-anthracenecarboxaldehyde at 77 K yielded emission
spectra that had similar maxima that exhibited vibrational
structure. This similarity of these spectra arose from the
low temperature, which resulted in a majority of the sub-
stituents in the 9-position being locked in an angle that
approached perpendicularity with the anthracene moiety.
This would minimize resonance interactions between the
substituent and the anthracene ring system, resulting in
emission spectra originating from transitions based mainly
Fig. 4 Electronic absorption and emission spectra of 9-anthracene-
carboxaldehyde in methylcyclohexane solution. Room temperature
absorption spectrum (ꢀꢀ–ꢀꢀ–); room temperature emission spectrum
(kex = 378 nm) (- - - - -); emission spectrum at 77 K (kex = 398 nm)
(——)
on the anthracene rings. The energy differences between
the best-resolved maxima in the emission spectra of 1 and
9-anthracenecarboxaldehyde are ca. 1100 cm-1 and ca.
1250 cm-1, both of which correspond to vibrational modes
of the anthracene rings [23].
Compound 1 and 9-anthracenecarboxaldehyde, at room
temperature and at 77 K, were both observed to possess
excited state lifetimes on the nanosecond timescale, which
characterized their emission as fluorescence (p* ? p).
The excited state decay trace from a room temperature
methylcyclohexane solution of compound 1 was fit to a
monoexponential curve that gave a lifetime of 6.3
0.1 ns. All other decay traces were fit to biexponential and
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J Chem Crystallogr (2011) 41:1342–1347
1347
LEQSF(1999–2000)-ENH-TR-13, administered by the Louisiana
Board of Regents.
triexponential curves that gave two different lifetimes
(s1 and s2): a longer one that ranged from 8–18 ns and a
shorter one that ranged from 3–4 ns. Triexponential fitted
curves exhibited very short lifetimes (90–280 ps) that arose
from scattered light. These were not considered in the
assessment of the lifetime data [24].
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Acknowledgments The authors would like to thank the Fletcher
Jones Foundation for funds that allowed the purchase of the fluo-
rometer and the TCSPC apparatus. Whittier College is acknowledged
for the funds that supported this research. The Edison International
Foundation is thanked for a summer research stipend for AV. The
purchase of the diffractometer was made possible by grant No.
123