Synthesis of a Carbazole-[pi]-carbazole Molecular Rotor with Fast Solid State Intramolecular Dynamics and Crystallization-Induced Emission

Article abstract of DOI:10.1021/acs.cgd.6b00395

Herein we report the synthesis of the highly stable crystalline carbazole-based rotor 3 with simultaneous rapid solid state internal rotation and good fluorescence emission. Single crystal and powder X-ray diffraction studies along with microscopy revealed a phase transition from a labile benzene solvate (phase I) to highly stable crystals (phase II) that feature fast intramolecular rotation in the megahertz regime at room temperature, according to variable temperature ²H solid state NMR experiments using isotopically enriched analogues. In addition to the megahertz rotation within its crystals, this crystal phase II displays enhanced solid state fluorescence with a higher quantum yield of ? = 0.28, relative to the emission of this compound in THF solution (? = 0.06). These two solid state properties are significantly different from shorter compounds 1 and 2 (static and nonemissive) included here for comparison purposes.

Full text of DOI:10.1021/acs.cgd.6b00395

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Article
Synthesis of a carbazole-[pi]-carbazole molecular rotor with fast solid
state intramolecular dynamics and crystallization-induced emission
Andres Aguilar-Granda, Salvador Perez-Estrada, Arián E. Roa, Joelis Rodriguez-
Hernandez, Simón Hernandez-Ortega, Mario Rodriguez, and Braulio Rodríguez-Molina
Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b00395 • Publication Date (Web): 19 Apr 2016
Downloaded from http://pubs.acs.org on April 21, 2016
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Synthesis of a carbazoleꢀ[pi]ꢀcarbazole molecular rotor with fast solid state
intramolecular dynamics and crystallizationꢀinduced emission.
Andrés Aguilar-Granda,a Salvador Pérez-Estrada,b Arian E. Roa,c Joelis Rodríguez-Hernández,d
Simón Hernández-Ortega,a Mario Rodriguez,c and Braulio Rodríguez-Molina.a*
aInstituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad
Universitaria, Ciudad de México, 04510, México.
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bDepartment of Chemistry and Biochemistry, University of California, Los Angeles, California
90095, United States.
cCentro de Investigaciones en Óptica, A.P. 1ꢀ948, León, Guanajuato, 37000, México
dCentro de Investigación en Química Aplicada (CIQA), Blvd. Enrique Reyna Hermosillo No.
140, Saltillo, Coahuila, 25294, México.
Corresponding author: *brodriguez@iquimica.unam.mx.
Abstract
Herein we report the synthesis of the highly stable crystalline carbazoleꢀbased rotor 3 with
simultaneous rapid solid state internal rotation and good fluorescence emission. Single crystal
and powder Xꢀray diffraction studies along with microscopy revealed a phase transition from a
labile benzene solvate (phase I) to highly stable crystals (phase II) that feature fast intramolecular
rotation in the megahertz regime at room temperature, according with VT 2H solid state NMR
experiments using isotopically enriched analogs. In addition to the megahertz rotation within its
crystals, this crystal phase II displays enhanced solid state fluorescence with a higher quantum
yield of φ = 0.28, relative to the emission of this compound in THF solution (φ = 0.06). These
two solid state properties are significantly different to shorter compounds 1 and 2 (static and
nonꢀemissive) included here for comparison purposes.
(a)
(b)
295 K
6 MHz
ꢀ200
ꢀ100
0
100
200
1.5 MHz
275 K
ꢀ200
ꢀ100
0
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(c)
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0.45 MHz
255 K
Compound
3
y = ꢀ4.2943x + 30.034
R² = 0.9887
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ꢀ100
0
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235 K
0.15 MHz
ꢀ200
ꢀ100
0
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3.3
3.6
3.9
1000/T (Kꢀ1
4.2
)
KHz
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Synthesis of a carbazoleꢀ[pi]ꢀcarbazole molecular
rotor with fast solid state intramolecular dynamics
and crystallizationꢀinduced emission.
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Andrés Aguilar-Granda,a Salvador Pérez-Estrada,b Arian E. Roa,c Joelis Rodríguez-Hernández,d
Simón Hernández-Ortega,a Mario Rodriguez,c and Braulio Rodríguez-Molina.a*
aInstituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad
Universitaria, Ciudad de México, 04510, México.
bDepartment of Chemistry and Biochemistry, University of California, Los Angeles, California
90095, United States.
cCentro de Investigaciones en Óptica, A.P. 1ꢀ948, León, Guanajuato, 37000, México
dCentro de Investigación en Química Aplicada (CIQA), Blvd. Enrique Reyna Hermosillo No.
140, Saltillo, Coahuila, 25294, México.
Abstract
Herein we report the synthesis of the highly stable crystalline carbazoleꢀbased rotor 3 with
simultaneous rapid solid state internal rotation and good fluorescence emission. Single crystal
and powder Xꢀray diffraction studies along with microscopy revealed a phase transition from a
labile benzene solvate (phase I) to highly stable crystals (phase II) that feature fast
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intramolecular rotation in the megahertz regime at room temperature, according with VT H
solid state NMR experiments using isotopically enriched analogs. In addition to the megahertz
rotation within its crystals, this crystal phase II displays enhanced solid state fluorescence with a
higher quantum yield of φ= 0.28, relative to the emission of this compound in THF solution (φ=
0.06). These two solid state properties are significantly different to shorter compounds 1 and 2
(static and nonꢀemissive) included here for comparison purposes.
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Introduction
Biomolecular machines found in Nature represent extremely refined examples of how multiple
molecular motions can collectively translate into complex functions; for example, the
conformational changes occurring in proteins that define their specific activity.1 A great effort
has been devoted to design compounds that can be regarded as synthetic molecular machines as
they emulate the functions of their natural counterparts.2ꢀ4 In some cases, the intended function is
the result of combined molecular motion (rotation) that modify the mechanical or optical
properties of a material,5 or large structural changes that change the conjugation and thus the
absorption and emission of the compounds (fluorescence),6 among other properties that can be
modulated for the development of responsive materials.7ꢀ10 Other functional materials with
externally controllable properties, e.g. nonlinear optics or electric conductivity have been
envisioned to arise also from the control of the molecular rotation, giving rise to the field of
molecular rotors, molecular machines that feature a highly mobile molecular fragment attached
to static components.11
In this context, it is clear that both molecular rotation and fluorescence are exciting properties
that should be interesting to combine in organic solids. In order to develop such new compounds,
it is worth to consider the AggregationꢀInduced Emission phenomenon (AIE),12ꢀ14 in which fast
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rotation of the molecular components in solution produces nonꢀemissive solutions. Conversely,
these AIE compounds render highly fluorescent solids attributed to the restricted rotation upon
crystallization. Similarly, some weakly emitting compounds in solution show enhanced
fluorescence when they form aggregates, a property that has been described as Crystallizationꢀ
Induced Emission or AggregationꢀInduced Enhanced Emission (CIE and AIEE, respectively),
again as a result of the restriction of the intramolecular rotations.15ꢀ18 However, to the best of our
knowledge, information about the precise frequency of the resulting motion in the solid state, or
the lack of it, is still limited.19ꢀ21
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On the other side, systematic studies of the nature and frequency of the molecular rotation in
crystals have been carried out in the already mentioned field of the molecular rotors. Very
important contributions highlighting the structural requirements that promote fast molecular
motion in solids have been reported by the groups of Michl,22ꢀ24 Sozzani,25,26 GarciaꢀGaribay27ꢀ29
and Batail30,31 among others.32ꢀ37 In those previous works, it has been described that the rotating
component (rotator) should be attached to an axis that imposes low rotational friction and this
resulting fragment should be effectively protected from intermolecular interactions by a
voluminous framework (stator) in order to reach high rotational frequencies. Importantly, solid
state emission has been scarcely reported in crystalline molecular rotors,38 perhaps due to the low
extent of conjugation of the resulting molecules.
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Figure 1. Compounds 1ꢀ3 showing the possible intramolecular effects that restrict rotation. The
elongation of the molecular axis frees their internal motion in crystals (double headed arrow).
In this work, we have focused in the synthesis and solid state characterization of an initial
series of symmetrical, conjugated carbazoleꢀ[pi]ꢀcarbazole compounds 1ꢀ3, adapting some of the
elements from the molecular rotors blueprints for intramolecular dynamics and using an
architecture that enhances the electrodonating property of the carbazole for emission purposes,39
similar to those that have been previously employed in organic lightꢀemitting diodes (OLEDs).40ꢀ
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This heterocycle was also chosen given its modifiable structure46,47 and because it represents
an equilibrium between a thermally stable compound, has a great ability to form edge to face
interactions in the solid state and is medium size stator that could enable intramolecular motion.
We intended to facilitate their internal rotation and to increase their emission properties by
extending the conjugation producing linear structures as illustrated in Figure 1. Interestingly,
when the 1,4ꢀdiethynylphenylene fragment is bound to two 9ꢀphenylcarbazole units in compound
2
3, rotation in the fast exchange regime is attained as evidenced by detailed solid state H NMR,
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calorimetric and Xꢀray diffraction studies. In addition to the precise nature of the internal
rotation, this work describes the enhanced fluorescence of compound 3 in its crystalline form
when compared to its emission in THF solution, as indicated by photoluminescence experiments
described below.
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Experimental
All reagents were purchased from SigmaꢀAldrich and used as received. THF was dried prior to
use by distillation (Na/benzophenone). Flash column chromatography and flash chromatography
were performed with SigmaꢀAldrich silica gel (230ꢀ400 mesh), unless otherwise stated.
Reactions were monitored by TLC on silica gel plates 60 F254 and the spots were detected by a
combination of UV/Seebach’s stain. Inert atmosphere reactions were carried out under nitrogen.
13
1H and C NMR spectra were recorded at ambient temperature using Bruker Fourier 300, Jeol
Eclipse 300, Bruker Avance, Bruker Avance500 with Cryoprobe spectrometers and referenced to
TMS (0.0 ppm) and CDCl3 (77.0 ppm) respectively, unless otherwise noted. The FTꢀIR spectral
data were recorded in a Bruker ATR in the 450ꢀ4000 cmꢀ1 range. Uncorrected melting points
were determined in a Fisher Johns melting point apparatus. HRMS were obtained by Direct
Analysis in Real Time (DART) or by Fast Atom Bombardment (FAB+) in a MStation, JMSꢀ700
spectrometer.
Bis(carbazol-9-yl)phenylene (1). In a two neck roundꢀbottom flask a mixture of carbazole (0.500
g, 2.99 mmol), 1,4ꢀdiiodobenzene (0.493 g, 1.49 mmol), CuI (0.028 g, 0.14 mmol), 18ꢀcrownꢀ6
(0.013 g, 0.04 mmol), K2CO3 (0.826 g, 5.97 mmol) and N,N′ꢀDimethylpropylene urea (3 mL)
was heated to 140 °C and stirred for 1 h under nitrogen atmosphere. The mixture was cooled to
room temperature then added 40 mL of saturated solution of NH4Cl and extracted with
dichloromethane (3x30 mL). The combined organic layers were dried over Na2SO4 and the
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solvent was removed under vacuum. The resulting residue was precipitated (from what solvent)
using acetonitrile to give a beige solid (1.0992g, 90%, M. P. by DSC 322ꢀ324 °C). The solid was
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recrystallized twice from dichloromethane/ethyl acetate (1:1) to afford colorless crystals. IR νmax
:
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1
3051, 1592, 1513, 1444, 1311, 1224, 748, 720 cmꢀ1. H NMR (500 MHz, CDCl3) δ: 8.2 (d, 4H,
3J= 7.8 Hz), 7.8 (s, 4H), 7.6 (d, 4H, 3J= 8.2 Hz), 7.5 (m, 4H), 7.4 (m, 4H). 13C NMR (125 MHz,
CDCl3) δ: 140.8 (C9a), 136.7 (C10), 128.4 (C11), 126.2 (C2), 123.6 (C4a), 120.4 (C4), 120.3
(3), 109.8 (C1). HMRS (DART) m/z [C30H21N2]+ calcd. 409.1704, found 409.1703.
Bis(carbazol-9-yl)phenyleneꢀd4 (1ꢀd4). The same procedure for 1 was used to prepare 1ꢀd4
using the following amounts: carbazole (0.500 g, 2.99 mmol), 1,4ꢀdiiodobenzeneꢀd4 (0.458 g,
1.49 mmol), CuI (0.028 g, 0.14 mmol), 18ꢀcrownꢀ6 (0.013 g, 0.04 mmol), K2CO3 (0.826 g, 5.97
mmol) and N,N′ꢀDimethylpropylene urea (3 mL) was heated to 140 °C and stirred for 1 h under
nitrogen atmosphere according with the previous methodology. The resulting product was beige
(1.099g, 90%, M. P. by DSC 322ꢀ324 °C). IR νmax: 3050, 1592, 1445, 1309, 1225, 748, 720 cmꢀ1.
1H NMR (300 MHz, CDCl3) δ: 8.21 (d, 4H, 3J= 7.8 Hz), 7.59 (d, 4H, 3J= 8.21 Hz), 7.49 (m, 4H),
7.36 (m, 4H). 13C NMR (75 MHz, CDCl3) δ: 140.8 (C9a), 136.7 (C10), 128.4 (C11), 126.2 (C2),
123.6 (C4a), 120.4 (C4), 120.3 (3), 109.8 (C1). HMRS (DART) m/z [C30H17H4N2]+ calcd.
413.19558, found 413.19551.
1,2-bis(4-(9H-carbazol-9-yl)phenyl)ethyne (2). In a twoꢀneck roundꢀbottom flask a mixture of
Nꢀ(4ꢀethynylphenyl)carbazole (6) (0.500 g, 1.87 mmol), Nꢀ(4ꢀIodophenyl)carbazole (4) (0.690 g,
1.87 mmol), PdCl2(PPh3)2 (0.131, 0.187 mmol), CuI (0.017 g, 0.089 mmol), dry THF (6 mL) and
1 mL of triethylamine was stirred for 2 h at room temperature under nitrogen atmosphere, then
the mixture was washed with 30 mL of a saturated solution of NH4Cl and the organic phase was
extracted with dichloromethane (3x30 mL). The combined organic layers were dried over
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Na2SO4 and the solvent was removed by evaporation. The resulting product was precipitated
from dichloromethane using acetonitrile to give a yellow solid (0.626 g, 70%, M. P. by DSC
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308ꢀ310 °C). IR νmax: 3052, 1598, 1516, 1447, 1336, 1223, 833, 748 cmꢀ1. H NMR (500 MHz,
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CDCl3) δ: 8.2 (d, 4H, 3J= 7.8 Hz), 7.8 (d, 4H, 3J= 8.26 Hz), 7.6 (d, 4H, 3J= 8.3 Hz), 7.5 (m, 4H),
7.3 (m, 4H). 13C NMR (125 MHz, CDCl3) δ: 140.6 (C9a), 137.9 (C10), 133.3 (C12), 127.0
(C11), 126.2 (C2), 123.7 (C4a), 122.0 (C13), 120.5 (C4), 120.4 (C3), 109.8 (C1), 89.7 (C14).
HMRS (FAB) calcd for m/z [C38H24N2]+ calcd. 508.1939, found 508.1944.
1,2-bis(4-(9H-carbazol-9-yl)phenyl)ethyneꢀd8 (2ꢀ d8). The same procedure for compound 2
was used to prepare 2ꢀd8 with the following amounts: Nꢀ(4ꢀethynylphenyl)carbazoleꢀd4 (6ꢀd4).
(0.500 g, 1.84 mmol), Nꢀ(4ꢀIodophenyl)carbazoleꢀd4 (4ꢀd4) (0.687 g, 1.84 mmol), PdCl2(PPh3)2
(0.129 g, 0.184 mmol), CuI (0.017 g, 0.092 mmol), dry THF (6 mL) and triethylamine (1mL)
was stirred by 2 h at room temperature under nitrogen atmosphere according to the previous
methodology. The resulting product was precipitated dichloromethane using using acetonitrile to
give a yellow solid (0.627g, 70%, M. P. by DSC 308ꢀ310 °C). IR νmax: 3042, 1593, 1554, 1449,
1319, 1226, 991, 745, 422 cmꢀ1. 1H NMR (300 MHz, CDCl3) δ: 8.2 (d, 4H, 3J= 7.7 Hz), 7.5 (m,
13
4H), 7.3 (m, 4H9). C NMR (75 MHz, CDCl3) δ: 140.6 (C9a), 137.8 (C10), 126.2 (C2), 123.7
(C4a), 121.9 (C13), 120.5 (C4), 120.3 (C3), 109.9 (C1), 89.5 (C14). HMRS (DART) m/z
2
[C38H17 H8N2]+ calcd. 517.25199, found 517.25233.
1, 4-bis(9H-carbazol-9-yl)phenyl)ethynyl)benzene (3). Under nitrogen atmosphere in a two
neck roundꢀbottom flask a mixture of Nꢀ(4ꢀethynylphenyl)carbazole (6) (0.500 g, 1.85 mmol),
1,4 diiodobenzene (0.306 g, 0.92 mmol), PdCl2(PPh3)2 (0.130 g, 0.185 mmol), CuI (0.017 g, 0.08
mmol), dry THF (6 mL) and 1 mL of triethylamine was stirred by 2 h at room temperature, then
to the mixture was added 30 mL of a saturated solution of NH4Cl and the organic phase was
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extracted with dichloromethane (3x30 mL). The combined organic layers were dried over
Na2SO4 and the solvent was reduced by evaporation. The desired compound was precipitated
from dichloromethane using acetonitrile to give an orange solid (0.398g, 70%, M. P. by DSC
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303ꢀ305 °C). IR νmax: 3038, 1593, 1513, 1448, 1332, 1222, 835, 720 cmꢀ1. H NMR (500 MHz,
3
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CDCl3) δ: 8.2 (d, 4H, J= 7.8 Hz), 7.8 (d, 4H, J= 8.6 Hz), 7.6 (d, 4H, J= 8.5 Hz), 7.6 (s, 4H),
7.4 (m, 4H), 7.3 (m, 4H), 7.3 (m, 4H). 13C NMR (125 MHz, CDCl3) δ: 140.5 (C9a), 137.5 (C10),
133.2 (C12), 131.7 (C17), 126.9 (C11), 126.1 (C2), 123.6 (C4a), 123.1 (C16), 122.0 (C13) 120.4
(C4), 120.3 (3), 109.8 (C1), 90.7 (C14), 90.0 (C15). HMRS (FAB) m/z [C46H28N2]+ calcd.
608.2252, found 608.2248.
1, 4-bis(9H-carbazol-9-yl)phenyl)ethynyl)benzeneꢀd8 (3ꢀd8). The same procedure for
compound
3
was used to prepare 3ꢀd8 using the following amounts: Nꢀ(4ꢀ
ethynylphenyl)carbazoleꢀd4 (6ꢀd4). (0.500 g, 1.84 mmol), 1,4ꢀdiiodobenzene (0.303 g, 0.92
mmol), PdCl2(PPh3)2 (0.129, 0.184 mmol), CuI (0.017 g, 0.092 mmol), dry THF (6 mL) and
triethylamine (1mL) was stirred by 2 h at room temperature under nitrogen atmosphere. The
resulting product was an orange solid (0.391g, 69%, M. P. by DSC 303ꢀ305 °C). IR νmax: 3040,
1573, 1451, 1307, 1222, 1009, 873, 739, 647 cmꢀ1. H NMR (300 MHz, CDCl3) δ: 8.2 (d, 4H,
1
3J= 7.8), 7.6 (s, 4H), 7.4 (m, 4H,) 7.3 (m, 4H). 13C NMR (75 MHz, CDCl3) δ: 140.5 (C9a), 137.7
(C10), 132.9 (C12, JC-D= 24.05 Hz),131.7 (C17), 126.5 (C11, JC-D= 24.05 Hz), 126.1 (C2), 123.6
(C4a), 123.1 (C16), 121.7 (C13), 120.4 (C4), 120.3 (3), 109.8 (C1), 90.6 (C14), 90.0 (C15).
2
HMRS (DART) m/z [C46H21 H8N2]+ calcd. 617.28329, found 617.28100.
1, 4-bis(9H-carbazol-9-yl)phenyl)ethynyl)benzeneꢀd4 (3ꢀd4). The same procedure for
compound
3
was used to prepare 3ꢀd4 using the following amounts: Nꢀ(4ꢀ
ethynylphenyl)carbazoleꢀd4 (6) (0.500 g, 1.80 mmol), 1,4ꢀdiiodobenzeneꢀd4 (0.302 g, 0.90
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mmol), PdCl2(PPh3)2 (0.127 g, 0.180 mmol), CuI (0.017 g, 0.090 mmol), dry THF (6 mL) and
triethylamine (1mL) was stirred for 2 h at room temperature under nitrogen atmosphere. The
resulting product was an orange solid (0.391g, 69%, M. P. by DSC 303ꢀ305 °C). IR νmax: 3044,
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1597, 1512, 1448, 1314, 1223, 1001, 834, 718 cmꢀ1. H NMR (300 MHz, CDCl3) δ: 8.2 (d, 4H,
3J= 7.7 Hz), 7.8 (d, 4H, 3J= 8.6 Hz), 7.6 (d, 4H, 3 J= 8.6Hz), 7.4 (m, 4H,) 7.3 (m, 4H). 13C NMR
(75 MHz, CDCl3) δ: 140.5 (C9a), 137.8 (C10), 133.1 (C12), 131.3 (C17, JC-D=25.4 Hz), 126.8
(C11), 126.1 (C2), 123.6 (C4a), 122.9 (C16), 121.9 (C13), 120.4 (C4), 120.3 (3), 109.8 (C1),
90.7 (C14), 90.0 (C15). HMRS (DART) m/z [C46H25 H4N2]+ calcd. 613.25818, found 613.25770.
2
N-(4-Iodophenyl)carbazole (4). In a twoꢀneck roundꢀbottom flask a mixture of carbazole (0.500
g, 2.99 mmol), 1,4ꢀdiiodobenzene (1.97 g, 5.98 mmol), CuI (0.028 g, 0.14 mmol), 18ꢀcrownꢀ6
(0.013 g, 0.04 mmol), K2CO3 (0.826 g, 5.97 mmol) and N,N′ꢀDimethylpropylene urea (6 mL)
was heated to 140 °C and stirred for 1 h under nitrogen atmosphere. After cooling to room
temperature, the mixture was quenched with water and the resulting precipitate was filtered. The
resulting solid was dissolved in dichloromethane then washed with 40 mL of saturated solution
of NH4Cl and the aqueous layer was further extracted with dichloromethane (3x30 mL). The
combined organic layers were dried over Na2SO4 and the solvent was removed by evaporation.
The resulting residue was purified by column chromatography (100% hexanes) to afford
compound 4 as a white solid (0.993 g, 90%, M. P. 139ꢀ141 °C). IR νmax: 3054, 1578, 1479, 1447,
1338, 1001, 821, 746, 566 cmꢀ1. H NMR (300 MHz, CDCl3) δ: 8.2 (d, 1H, J= 7.7 Hz), 7.9 (d,
1
3
3
13
1H, J= 7.7 Hz), 7.4 (m, 2H), 7.3 (m, 3H). C NMR (75 MHz, CDCl3) δ: 140.6 (C9a), 139.2
(C12), 137.7 (C10), 129.0 (C11), 126.2 (C2), 123.6 (C4a), 120.5 (C4), 120.4 (C3), 109.7 (C1),
92.1 (C13). HMRS (DART) m/z [C18H13NI]+ calcd. 370.0092, found 370.0101.
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N-(4-Iodophenyl)carbazoleꢀd4 (4ꢀd4). The same procedure for compound 1 was used to prepare
4ꢀd4 with the following amounts: carbazole (0.500 g, 2.99 mmol), 1,4ꢀdiiodobenzene (1.99 g,
5.98 mmol), CuI (0.028 g, 0.14 mmol), 18ꢀcrownꢀ6 (0.013 g, 0.04 mmol), K2CO3 (0.826 g, 5.97
mmol) and N,N′ꢀDimethylpropylene urea (6 mL) was heated to 140 °C and stirred for 1 h under
nitrogen atmosphere. Compound 4ꢀd4 was obtained as a white solid (0.993 g, 90%, M. P. 139ꢀ
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141 °C). IR νmax 3041, 1552, 1449, 1404, 1334, 1227, 991, 746, 628 563 cmꢀ1. H NMR (300
3
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MHz, CDCl3) δ: 8.2 (d, 1H, J= 6.8 Hz), 7.4 (m, 2H), 7.3 (m, 1H). C NMR (75 MHz, CDCl3)
δ: 140.6 (C9a), 138.7 (C12, JC-D= 25.5 Hz), 137.7 (C10), 128.4 (C11, JCꢀD= 25.5 Hz), 126 (C2),
2
123.4 (C4a), 120.3 (C4), 120.2 (C3), 109.5 (C1), 91.6 (C13). HMRS (DART) m/z [C18H9 H4N1]ꢀ
/+? calcd. 374.03437, found 374.03462.
N-(4-trimethylsilylethynylphenyl)carbazole (5). To a twoꢀneck roundꢀbottom flask was added
Nꢀ(4ꢀiodophenyl)carbazole (4) (0.500 g, 1.35 mmol), PdCl2(PPh3)2 (0.95 g, 0.135 mmol), CuI
(0.012 g, 0.067 mmol), ethynyltrimethylsilane (0.132 g, 1.35 mmol), dry THF (6 mL) and
triethylamine (1 mL) under nitrogen atmosphere. The reaction mixture was stirred for 2 h at
room temperature then added 30 mL of saturated solution of NH4Cl and extracted with
dichloromethane (3x30 mL). The combined organic layers were dried over Na2SO4 and the
solvent was removed under vacuum. The crude product was purified by column chromatography
(100% hexanes) to afford compound 5 as a yellow solid (0.461 g, 95%, M. P. 158ꢀ160 °C). IR
νmax: 3053, 2957, 2157, 15985, 1507, 1224, 839 cmꢀ1. 1H NMR (300 MHz, CDCl3) δ: 8.1 (d, 2H,
3J= 7.8 Hz), 7.7 (d, 2H, 3J= 8.2 Hz), 7.5 (d, 4H, 3J= 8.7 Hz), 7.4 (m, 4H), 7.3 (m, 3H), 0.3 (s, 9)
13C NMR (75 MHz, CDCl3) δ: 140.6 (C9a), 137.9 (C10), 133.7 (C12), 126.8 (C11), 126.1 (C2),
123.6 (C4a), 122.2 (C13), 120.5 (C4), 120.3 (C3), 109.7 (C1), 104.4 (C15), 95.5 (C14), 0.30
(C16). HMRS (DART) m/z [C23H22N1Si1]+ calcd. 340.1521, found 340.1510.
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N-(4-trimethylsilylethynylphenyl)carbazole-d4 (5ꢀd4).
A
degased mixture of Nꢀ(4ꢀ
5
6
7
8
iodophenyl)carbazoleꢀd4 (4ꢀd4) (0.500 g, 1.35 mmol), PdCl2(PPh3)2 (0.95 g, 0.135 mmol), CuI
(0.012 g, 0.067 mmol), dry THF (6 mL), ethynyltrimethylsilane (0.132 g, 1.35 mmol) and
triethylamine (1 mL) was stirred for 2 h at room temperature. The reaction mixture was treated
with 30 mL of a saturated solution of NH4Cl, then extracted with dichloromethane (3x30 mL);
the combined organic layers were dried over Na2SO4 and concentrated to dryness under vacuum.
The crude product was purified by column chromatography (100% hexanes) to afford compound
5ꢀd4 as a yellow solid (0.460g, 95%, M. P. 158ꢀ160 °C). IR νmax: 2925, 1611, 1511, 1243, 1040,
726, 686 cmꢀ1. 1H NMR (300 MHz, CDCl3) δ: 8.2 (d, 2H, 3J= 7.7 Hz), 7.4 (m, 4H), 7.3 (m, 2H),
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0.3 (s, 9H). C NMR (75 MHz, CDCl3) δ: 140.5 (C9a), 137.6 (C10), 126.0 (C2), 123.6 (C4a),
120.3 (C4), 120.2 (C3), 109.7 (C1), 104.2 (C15), 95.4 (C14), 0.05 (C16). HMRS (DART) m/z
2
[C23H18 H4N1Si1]+ calcd. 344.17726, found 344.17703.
N-(4-ethynylphenyl)carbazole (6). A solution of Nꢀ(4ꢀtrimethylsilylethynylphenyl)carbazole
(5) (0.500 g, 1.47 mmol) in dry THF (6 mL) was treated with tetrabutylammonium fluoride 2.5M
in THF (0.385 g, 1.47 mmol). The reaction mixture was stirred at room temperature under
nitrogen atmosphere for 2 h to then quench with saturated solution of NH4Cl (30 mL). The
organics were extracted with dichloromethane (3x30 mL), then the combined organic layers
were dried over Na2SO4 and the solvent was removed by evaporation. The resulting residue was
purified by column chromatography (100% hexanes) to afford compound 6 as a white solid
1
(0.374 g, 95%, M. P.103ꢀ104 °C). IR νmax: 3258, 1597, 1446, 1332, 1222, 749 cmꢀ1. H NMR
3
3
3
(300 MHz, CDCl3) δ: 8.2 (d, 2H, J= 7.8 Hz), 7.7 (d, 2H, J= 8.7 Hz), 7.6 (d, 2H, J= 8.5 Hz),
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7.4 (m, 4H), 7.3 (m, 2H), 3.2 (s, 1H). C NMR (75 MHz, CDCl3) δ: 140.6 (C9a), 138.2 (C10),
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133.8 (C13), 126.9 (C12), 126.2 (C2), 123.7 (C4a), 121.2 (C11), 120.5 (C4), 120.3 (C3), 109.8
5
6
(C1), 83.0 (C14), 78.2 (C15). HMRS (DART) m/z [C20H14N]+ calcd. 268.1126, found 268.1124.
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N-(4-ethynylphenyl)carbazoleꢀd4
(6ꢀd4).
A
solution
of
Nꢀ(4ꢀ
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trimethylsilylethynylphenyl)carbazoleꢀd4 (5ꢀd4) (0.500 g, 1.45 mmol) in dry THF (6 mL) was
treated with tetrabutylammonium fluoride 2.5M in THF (0.380 g, 1.45 mmol). The reaction
mixture was stirred at room temperature under nitrogen atmosphere for 2 h, then quenched with
saturated solution of NH4Cl (30 mL) and extracted with dichloromethane (3x30 mL). The
combined organic layers were dried over Na2SO4 and the solvent was removed by evaporation.
The crude product was purified by column chromatography (100% hexanes) to provide
compound 6ꢀd4 as a white solid (0.375 g, 95%, M. P.103ꢀ104 °C). IR νmax: 3259, 3043, 2166,
1687, 1595, 1448, 1222, 834, 718 cmꢀ1. 1H NMR (300 MHz, CDCl3) δ: 8.2 (d, 2H, 3J= 7.75 Hz),
7.5 (m, 2), 7.3 (m, 1H) 3.2 (s, 1H). 13C NMR (75 MHz, CDCl3) δ: 140.5 (C9a), 138. (C10), 133.2
(C12, JC-D=25.3 Hz), 126 (C2), 123.6 (C4a), 120.4 (C4), 120.3 (C3), 109.7 (C1), 82.9 (C14),
78.2 (C15). HMRS (DART) m/z [C20H10 H4N]+ calcd. 272.13773, found 272.13765.
2
Results and discussion.
Synthesis and characterization. Natural abundance compounds 1 and 2 have been reported
by others,48ꢀ50 but studies of their potential internal dynamics have not been performed and
samples were synthesized to fully characterize them in the solid state and contrast their
properties with the novel molecular rotor 3 obtained in 57 % yield over four steps. In addition,
we also synthesized isotopically enriched derivatives 1ꢀd4, 2ꢀd8, 3ꢀd8, and 3ꢀd4 with deuterated
inner phenylenes to probe chemical exchange processes in the MHz regime as detailed in the
following sections. Natural abundance and isotopic analogs were obtained in good yields
following the synthetic route in Scheme 1, where 1,4ꢀdiiodobenzene or a homemade 1,4ꢀ
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diiodobenzeneꢀd4 was covalently linked to the carbazol units through Ullmanꢀtype reactions.
Subsequently, the extended conjugation was achieved by means of Pd(0)ꢀcatalyzed Sonogashira
reactions. Detailed spectroscopic characterization of all compounds is included in the Supporting
Information.
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Scheme 1. Synthesis of deuterium enriched derivatives 1ꢀd4, 2ꢀd8, 3ꢀd8, and 3ꢀd4
Single crystal Xꢀray diffraction studies
Crystals of compound 1 were grown as described previously in reference 49 but the crystal
structure was determined now at 295 K to better match the structural details with the
photophysics of the material which was also determined at room temperature. Crystals of
compound 2 were grown from slow evaporation of THF and solved in the space group P21/c. In
the case of molecular rotor 3, its considerably low solubility only allowed to grow a benzene
solvate (labeled phase I) which was collected at 150 K and solved in the space group C2/c
(Figure 2). Additionally, a second solventꢀfree phase of compound 3, labeled as phase II, was
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grown either from THF or from dichloromethane as small needles that were unsuitable for single
crystal Xꢀray diffraction experiments but with cell constants a = 9.774(1), b = 11.392(2) and c =
14.541(2) and angles alpha = 100.729(9), beta = 90.633(10) and gamma = 95.057(10), that
perfectly match with those obtained from the powder Xꢀray diffraction pattern51 with cell
constants a = 9.778(2), b = 11.404(1), c = 14.568(3) and angles alpha= 100.83(2), beta= 90.64(3)
and gamma= 95.27(2). The relevant crystallographic parameters of compounds 1ꢀ3 are compiled
in Table 1.
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Figure 2. ORTEP structures of (a) compound 1, (b) compound 2 and (c) compound 3 as a
benzene solvate.
A detailed inspection of compound 1 showed a highly twisted structure where each component
laid in different planes resulting in an array with one molecule per asymmetric unit (Z’=1). In
compound 2, the two internal phenyl rings are virtually coplanar, but the molecule adopts a
curved shape due to the carbazole units with perpendicular conformations, also resulting with
one molecule per asymmetric unit (Z’=1). In both compounds, the phenyl rings attached to the
carbazole experience a highly crowded environment from their neighboring molecules that could
affect their potential dynamics (see Supporting Information).
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Figure 3. Crystal packing of the solvate of compound 3, down the bꢀaxis with the entrapped
benzene molecules (highlighted in purple) in between the elongated molecules.
In the case of the benzene solvate of compound 3 illustrated in Figure 3, the three phenylene
rings adopt a fully coplanar conformation making a dihedral angle with respect to the carbazoles
of ca. 61º. Although the heterocycles laid in different planes, the asymmetric unit is only half a
molecule (Z’=0.5), resulting from an inversion point that coincides with the centroid of the
central phenyl ring. The crystal packing of 3 indicates a ladder array of molecules with
encapsulated benzene rings in between neighboring molecular rotors showing an edgeꢀtoꢀface
interaction with a CHbenzeneꢀcentroid distance of 2.72 Å and an angle of 152º.
Table 1. Relevant crystallographic parameters of compounds 1ꢀ3.
Compound 3
(benzene solvate)
Compound 1a
Compound 2
Formula
C30H20N2
408.48
C38H24N2
508.59
C64H46N2
MW/g molꢀ1
843.03
Crystal system Orthorhombic
Monoclinic
P21/c
Monoclinic
C2/c
Space group
a/Å
Pbca
8.195 (5)
16.533 (12)
32.070 (2)
5.4678 (10)
34.8288 (10)
14.1542 (4)
18.7320 (5)
5.7487 (2)
44.4908 (14)
b/Å
c/Å
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α(°)
β(°)
90
90
90
97.28
90
90
99.890 (2)
90
γ(°)
90
9
V/Å3
4345.3 (5)
8
2673.7(1)
4
4719.8(3)
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Z
Z’
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1
0.5
ρc/g cmꢀ3
Collected Refl.
Ind. Ref. (Rint)
R[F2> 2σ(F2)]
Rw (all data)
ꢁρmax/e Å3
ꢁρmin/e Å3
T
1.249
3958
3958
0.073
0.1604
0.25
1.263
21222
4890
0.0536
0.1521
0.137
ꢀ0.198
296 (2)
1.186
18240
4277
0.0474
0.1194
0.229
ꢀ0.211
150 (2)
ꢀ0.19
298 (2)
aSimilar parameters to those reported in ref.49
Thermal stability experiments.
t = 1 h
t = 30 min
t = 1 min
t = 3 h
t = 3.5 h
t = 2 h
Figure 4. Optical micrographs of the benzene solvate of 3 taken every 30 minutes at room
temperature.
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Immediately after the Xꢀray diffraction experiments, it was noted that benzene solvate crystals
of 3 became opaque and the powder Xꢀray diffraction pattern of the resulting solid was in
excellent agreement with those obtained from crystals grown from THF or dichloromethane. In
order to obtain a timescale of this phase transition, freshly grown crystals of 3 from benzene
were monitored under an optical microscope at room temperature. As illustrated in Figure 4, the
solvate crystals fractured under illumination and lost their prime quality in less than two hours,
reflecting that the benzene is loosely bound. Given this information, we decided to further
explore the thermal stabilities of all compounds by differential scanning calorimetry (DSC) and
thermogravimetric analyses (TGA) looking for less evident phase transitions. Crystalline
samples of compounds 1 and 2, verified by powder Xꢀray diffraction analyses, showed only
endothermic peaks in their DSC traces attributed to their melting points at 322ꢀ324 ºC and 302ꢀ
310 ºC, respectively. Their TGA analyses indicated subtle losses of weight that were considered
as residual solvent of crystallization that did not affected their known crystal array. In the case of
molecular rotor 3, only the desolvated form was analyzed showing high thermal stability with a
melting point of 300ꢀ305 ºC. As noted, slightly lower melting points were observed in
compounds 1ꢀ3 as their molecular axis is larger, but no additional phases were discovered.
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Solid state NMR CPMAS analyses
Initial characterization by means of solid state 13C NMR CPMAS and dipolar dephasing
experiments allowed us to complement the peak assignment by solution NMR and
crystallographic information gathered by powder (degree of crystallinity) and single crystal Xꢀ
ray diffraction (molecules per asymmetric unit). For instance, in the 13C CPMAS trace of
compound 1 four peaks were readily distinguished at ca. 110 ppm from the nonꢀequivalent
carbons C1, C1’, C8 and C8’, as expected since one molecule per asymmetric unit was obtained
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(Figure 5). In the case of compound 2, slightly broader peaks were observed which was
attributed to slightly lower crystallinity suggested by the PXRD analysis; yet, two alkyne signals
C14 and C14’ were detected at 90 ppm confirming the crystal symmetry (Z’=1).
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2
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4a
5a
9a
N
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N
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Figure 5.13C NMR CPMAS experiments at room temperature of solvent free samples.
13
Lower resolution was observed in the C spectrum of the phase II of compound 3, showing
overlapped peaks in all regions which was somehow expected given its elongated structure.
Indeed, another reason for the broad peaks could be the combination of its moderate crystallinity
suggested by PXRD and the low resolution of the magnetic field (75 MHz). Finally, in order to
gain additional structural information a complementary 15N CPMAS experiment of 3 at room
temperature was acquired showing only one signal at 128 ppm, indicating that in this phase II
the halves have little or none crystallographic differences.
Activation energy to rotation by VT solid state 2H NMR
Since variable temperature 13C CPMAS experiments from 150 K to 435 K yielded only minor
changes or they were possibly obscured due to overlapping signals (Supporting Information), we
2
employed the deuterated analogs to explore solid state motion in the MHz regime using H
NMR. This technique has the advantage of probing the dynamics of the fragment under study as
it is sensitive to the angular reorientations of the CꢀD bond.52 Firstly, we studied all the
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isotopically enriched compounds where the deuterated phenyl rings are attached directly to the
carbazole units. In these cases, the experiments from room temperature up to 415 K of
compounds 1ꢀd4, 2ꢀd8 and the solvent free form of 3ꢀd8 showed a characteristic static Pake
pattern,53 leading us to conclude that they do not experience substantial rotation in crystals due to
intraꢀ and intermolecular steric effects (Supporting Information).
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(a)
(b)
295 K
6 MHz
ꢀ200
ꢀ100
0
100
200
1.5 MHz
275 K
ꢀ200
ꢀ100
ꢀ100
ꢀ100
0
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200
(c)
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0.45 MHz
255 K
Compound
3
y = ꢀ4.2943x + 30.034
R² = 0.9887
ꢀ200
0
100
200
235 K
0.15 MHz
ꢀ200
0
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3.3
3.6
3.9
1000/T (Kꢀ1
4.2
)
KHz
2
Figure 6. (a) Stacked experimental and simulated H NMR spectra of compound 3ꢀd4. (b) 2ꢀfold
exchange model employed for simulations, (c) Arrhenius plot of lnKrot vs Tꢀ1.
After establishing that rotation of the aromatic rings linked to the carbazoles is not permitted,
we studied the internal dynamics of the phenylene surrounded by two alkyne groups using the
desolvated sample of isotopolog 3ꢀd4. As mentioned before, voluminous groups are usually
employed as stators in molecular rotors because they provide a cavity that allows rapid rotation
of the inner fragment;29 however, in the case of compound 3 the peripheral 9ꢀphenylcarbazoles
stators was not considered bulky enough to expect fast internal rotation. To our delight, at room
temperature we observed a deuterium lineshape characteristic of a fast 180º exchange near the
limit of detection of this technique (megahertz) which was confirmed by high temperature
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experiments that only slightly narrowed the lineshape. Subsequently, low temperature
experiments were carried out to effectively reduce the frequency of this motion, as illustrated in
Figure 6. These experimental lineshapes were successfully fitted using a twoꢀfold model with a
logꢀGaussian distribution of rotational frequencies (σ=2)54 in accordance with a sample of
moderate crystallinity. From these simulations, a relatively low activation energy to rotation of
Ea=8.5 kcal/mol and an attempt factor of A= 1.1x1013 sꢀ1 were obtained. These results indicate
that crystallization does not completely restrict the internal motion in this flat rotor 3, implying
that compounds with similar architectures could have overlooked or underestimated dynamics.
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Solution and solid state fluorescence
Once the dynamic properties of the conjugated compounds 1ꢀ3 was explored, we set out to
define their absorption and photoluminescence properties at room temperature. Spectra of
compounds 1ꢀ3 were recorded both in solution and, in the solid state, using the same crystalline
phases described above with the results listed in Table 1. In solution, all compounds presented
intense absorption bands in the UVꢀregion, particularly compounds 2 and 3 showed bands at 341
nm which can be attributed to the n→π* transition. Additionally, the photoluminescence spectra
carried out in THF solution showed one intense band at 401 nm for compound 1, while a band at
402 nm was observed for compound 2 and at 417 nm for compound 3, with the redꢀshift
attributed to the extended πꢀsystem (Figure 7).
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Figure 7. Comparison of fluorescence spectra of compounds 1ꢀ3 in THF solution (dotted line)
and in the solid state (solid line) using the crystalline forms described above.
In the case of solid state photoluminescence experiments, the crystalline samples of
compounds 1 and 2 showed similar shapes as those observed in solution but with a significant
reduction of their quantum yields from solution (φ= 0.56 and 0.18, respectively) to powder (φ=
0.09), attributed to the typical quenching due to aggregate formation.55ꢀ57 On the other hand, the
solid state emission spectrum of the phase II of rotor 3 is markedly different from that obtained
in solution, showing two intense emission bands at 473 and 593 nm (Figure 7, blue solid line).
Moreover, the quantum yield in the solid state (φ= 0.28) was significantly improved when
compared to that observed in THF solution (φ= 0.06). The very low quantum yield of 3 in THF
was attributed to the very fast motions occurring in solution, which include rotations and/or
librations of several molecular fragments that may enable an efficient nonꢀradiative channel
causing the low quantum yield. Conversely, its crystallization reduced the frequency of the
molecular motions occurring in solution resulting in the observed emission enhancement,
allowing only the rotation of the central phenylene in the limit of the 2H NMR technique, at MHz
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frequency. Additional variable temperature photophysical experiments in the solid state that
would yield further information are currently unavailable for us but they will be pursued in
future experiments.
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Table 2. Optical properties of compounds 1ꢀ3.
Compound
λmax λem
Stokes
shift
ф
ф
(nm) (nm)
Solution powder
abs
PL in (cmꢀ1)
solution
292
341
343
401
402
417
9.31E+03
0.56
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0.09
0.28
1
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3
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5.17E+03
Gas phase computational studies of rotation
The MHz frequency of rotation observed in the phase II of compound 3 could be considered
moderately fast in the field of molecular rotors, but is not fast enough to enable an efficient nonꢀ
radiative pathway in these crystalline compounds, where solid state dynamics in the gigahertz
(109) or terahertz (1012) will be required. In order to calculate what conditions would produce
such interference between the two properties, we performed computational studies using the
B3LYP basis set58,59 to explore the energy requirements for the reorientations of the phenylene
ring in the gas phase. The simulations were performed using the Xꢀray crystal coordinates and
explored angular displacements on the phenylene rings with 15º steps. They indicated that while
the central phenylene ring in compound 1 has a barrier to rotation as high as 29 Kcal/mol, the
mobile component in compound 3 would require only 2 Kcal/mol, thanks to the low friction to
rotation of the alkyne axis.
Considering the solid state 2H NMR and theoretical results together, it seems very difficult that
the steric effects over the phenylene ring in crystalline compound 1 would allow motion in a rate
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that affects its emission in the solid. Conversely, compound 3 indeed may show faster rotation of
the 1,4ꢀdiethynylphenylene fragment, but this is affected by intermolecular interactions that are
not fully prevented by the relatively flat carbazole stator. Certainly, it is possible that a large
increment of the temperature could increase the rotating frequency. If one assume that the
rotational dynamics of 3 indefinitely follows the behavior described in the Arrhenius plot of
Figure 6, it is possible to extrapolate the temperature at which the rotation would be in the
gigahertz regime (109 Hz), to approximately 450 K or higher. The studies presented here indicate
that although the crystallinity and chemical structure of 3 would hold at that temperature;
deuterium NMR would not detect further changes and other techniques to characterize solid state
internal dynamics, i.e. relaxometry,60 would be required.
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Conclusions
In summary, the synthesis of a series of carbazoleꢀ[pi]ꢀcarbazole compounds 1ꢀ3 and their
deuterated analogs was accomplished in good yields. Solid state techniques allowed us to
characterize in detail the high crystallinity and slow or fast internal dynamics in these
2
compounds. In particular, variableꢀtemperature solid state H NMR experiments led us to
pinpoint which rings are unable to reorient within the crystals of all compounds, as well as to
describe precisely the frequency of that which is highly mobile, i.e. the inner phenylene in the
rotor 3, which experiences rapid twoꢀfold flips of 6 MHz at room temperature. In addition to
13
2
solid state C and H NMR, photoluminescence experiments helped us define that this phase II
encompasses for the first time a rapid rotary fragment and good solid state emission. Given the
high thermal stability evidenced by DSC and TGA, this compound can be subjected to very high
temperatures without loosing its crystallinity. Extensive photophysical studies for these
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compounds as well as synthetic modifications seeking faster solid state rotation in the GHz
regime are currently underway.
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ASSOCIATED CONTENT
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Supporting Information. Synthetic procedures, solution and solid state NMR spectra, Xꢀray
diffraction refinement details, DSC, UVvis spectra in solution and computational details. CCDC
deposit numbers 1462885, 1440776 and 1440777. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*brodriguez@iquimica.unam.mx.
Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval
to the final version of the manuscript.
Funding Sources
DGAPA PAPIITꢀUNAM (IA200615) and CONACYT (238913)
ACKNOWLEDGMENTS
This work was financially supported by projects DGAPA PAPIITꢀUNAM (IA200615) and
CONACYT (238913). AAG thanks to CONACYT for the PhD scholarship 279212. We
2
acknowledge the UCLA Department of Chemistry and Biochemistry for solid state H NMR
experiments. We thank the technical assistance from Dr. Francisco Javier Pérez Flores, Dr.
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María del Carmen García Gonzalez, Q. María de los Ángeles Peña González and M. C. Elizabeth
Huerta Salazar (MS and NMR).
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REFERENCES
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21
22
23
24
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27
28
29
30
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1. Han, K.ꢀL., Zhang, X.; Yang, M.ꢀJ. Protein Conformational Dynamics; Springer:
Switzerland, 2014.
2. Watson, M. A.; Cockroft, S. L. Chem. Soc. Rev. 2016, DOI: 10.1039/c5cs00874c.
3. ErbasꢀCakmak, S.; Leigh, D. A.; McTernan, C. T.; Nussbaumer, A. L. Chem. Rev. 2015,
115, 10081.
4. Abendroth, J. M.; Bushuyev, D. S.; Weiss, P. S.; Barrett, C. J. ACS Nano 2015, 9, 7746.
5. Pawle, R. H.; Hass, T. E.; Müller, P.; Thomas S. W. Chem. Sci. 2014, 5, 4184.
6. Bleger, D. Macromol. Chem. Phys. 2016, 217, 189.
7. Sagara, Y.; Yamane, S.; Matani, M.; Weder, C.; Kato, T Adv. Mater. 2016, 28, 1073.
8. Zhang, Y.; Barboiu, M. Chem. Rev. 2016, 116, 809.
9. Tanaka, T.; Osuka, A. Chem. Soc. Rev. 2015, 44, 943.
10. Mutai, T.; Satou, H.; Araki, K. Nat. Mater. 2005, 4, 685.
11. Kottas, G. S.; Clarke, L. L.; Horinek, D.; Michl, J. Chem Rev. 2005, 105, 1281.
12. Mei, J.; Leung, N. L. C.; Kwok, R. T. K.; Lam, J. W. Y.; Tang, B. Z. Chem. Rev. 2015,
115, 11718.
13. Yan. D.; Yang, H.; Meng, Q.; Lin, H.; Wei, M. Adv. Funct. Mater. 2014, 24, 587.
ACS Paragon Plus Environment
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Page 27 of 32
Crystal Growth & Design
1
2
3
4
14. Mei, J.; Hong, Y.; Lam, J. W. Y.; Qin, A.; Tang, Y.; Tang, B. Z. Adv. Mater. 2014, 26,
5
6
5429.
7
8
9
15. Fan, G.; Yang, X.; Liang, R.; Zhao, J.; Li, S.; Yan, D. CrystEngComm, 2016, 18, 240.
16. Tong, J.; Wang, Y. L.; Wang, Z.; Sun, J Z.; Tang, B. Z. J. Phys. Chem. C 2015, 119,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
21875.
17. Han, T.; Feng, X.; Chen, D; Dong, Y. J. Mater. Chem. C. 2015, 3, 744.
18. Yan, D.; Evans, G. D. Mater. Horiz. 2014, 1, 46.
19. Li, J.; Zhang, Y.; Mei, J.; Lam, J. W. Y.; Hao, J.; Tang, B. Z. Chem. Eur. J., 2015, 21,
907.
20. Parrott, E. P. J.; Tan, N. Y.; Hu, R.; Zeitler, J. A.; Tang, B. Z.; PickwellꢀMacPherson, E.
Mater. Horiz., 2014, 1, 251.
21. Shustova, N. B.; Ong, T.ꢀC.; Cozzolino, A. F.; Michaelis, V. K.; Griffin, R. G.; Dinca, M.
J. Am. Chem. Soc., 2012, 134, 15061.
22. Kaleta, J:, Dron, P. I.; Zhao, K.; Shen, Y.; Císarová, I.; Rogers, C. T.; Michl, J. J. Org.
Chem. 2015, 80, 6173.
23. Kaleta, J.; Michl, J.; Mézière, C.; Simonov, S.; Zorina, L.; Wzietek, P.; RodríguezꢀFortea,
A.; Canadell, E.; Batail, P. CrystEngComm, 2015, 17, 7829.
24. Kobr, L.; Shen, Y.; Shoemaker, R. K.; Rogers, C. T.; Michl, J. Cryst. Growth Des. 2014,
14, 559.
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Page 28 of 32
1
2
3
4
25. Comotti, A.; Bracco, S. Yamamoto, Y.; Beretta, M.; Hirukawa, T.; Tohnai, N.; Miyata, M.;
5
6
Sozzani, P. J. Am. Chem. Soc. 2014, 136, 618.
7
8
9
26. Comotti, A.; Bracco, S.; Valsesia, P.; Beretta, M.; Sozzani, P. Angew. Chem. Int. Ed. 2010,
49, 1760.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
27. PérezꢀEstrada, S.; RodríguezꢀMolina, B.; Xiao, L.; Santillan, R.; JimenezꢀOses, G.; Houk,
K. N.; GarciaꢀGaribay, M. A. J. Am. Chem. Soc., 2015, 137, 2175.
28. Commins, P.; GarciaꢀGaribay, M. A. J. Org. Chem. 2014, 79, 1611.
29. Vogelsberg C. S.; GarciaꢀGaribay, M. A. Chem. Soc. Rev. 2012, 41, 1892.
30. Lemouchi, C.; Yamamoto, H. M.; Kato, P.; Simonov, S.; Zorina, L.; RodríguezꢀFortea, A.;
Canadell, E.; Wzietek, P.; Iliopoilos, K.; Gindre, D.; Chrysos, M.; Batail, P. Cryst. Growth, Des.
2014, 14, 3375.
31. Lemouchi, C.; Iliopoulos, K.; Zorina, L.; Simonov, S.; Wzietek, P.; Cauchy, T.; Rodríguezꢀ
Fortea, Enric Canadell, E.; Kaleta, J.; Michl, J.; Gindre, D.; Chrysos, M.; Batail, P. J. Am. Chem.
Soc. 2013, 135, 9366.
32. Nishiyama, Y.; Inagaki, Y.; Yamaguchi, K.; Setaka W. J. Org. Chem. 2015, 80, 9959.
33. Setaka, W.; Inoue, K.; Higa, S.; Yoshigai, S.; Kono, H.; Yamaguchi, K. J. Org. Chem.
2014, 79, 8288.
34. Prack, E.; O’Keefe, C. A.; Moore, J. K.; Lai, A.; Lough, A. J.; Macdonald, P. M.; Conradi,
M. S.; Schurko, R. W.; Fekl, U. J. Am. Chem. Soc. 2015, 137, 13564.
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Page 29 of 32
Crystal Growth & Design
1
2
3
4
35. Sakai, K.ꢀI.; Tsuchiya, S.; Kikuchi, T.; Akutagawa, T. J. Mater. Chem. C 2016,
5
6
DOI:10.1039/c5tc04290a.
7
8
9
36. Zhang, Q.ꢀC.; Takeda, T.; Hoshino, N.; Noro, S.ꢀi.; Nakamura, T.; Akutagawa, T. Cryst.
Growth Des. 2015, 15, 5705.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
37. Akutagawa, T.; Nakamura, T. Dalton Trans. 2008, 6335.
38. Hughs, M.; Jimenez, M.; Khan, S. I.; GarciaꢀGaribay, M. A. J. Org. Chem. 2013, 78, 5293.
39. Xue, P.; Sun, J.; Chen, P.; Gong, P.; Yao, B.; Zhang, Z.; Qian, C.; Lu, R. J. Mater. Chem.
C 2015, 3, 4086.
40.Ding, J.; Zhang, B.; Lu, J.; Xie, Z.; Wang, L.; Jing, X.; Fosong Wang, F. Adv. Mater. 2009,
21, 4983.
41. Yu, M.; Wang, S. Shao, S.; Junqiao Ding, J. Wang, L. Jinga, X.; Wang. F. J. Mater. Chem.
C 2015, 3, 861.
42. Sun, K.; Jiang, W.; Ban, X.; Huang B.; Zhang Z.; Ye, M.; Sun, Y. Adv. 2016, 6, 22137.
43. Shilh, C.ꢀH.; Rajamalli, P.; wu, C.ꢀA.; Hsieh, W.ꢀT.; Cheng, C.ꢀH. Appl. Mater. Interfaces
2015, 7, 10466.
44. Kim, D.; Coropceanu, V.; Brédas, J.ꢀL. J. Am. Chem. Soc. 2011, 133, 17895.
45. Fundamentals of Solid-State Lighting. Khanna, V. K. Boca Raton, FL, USA, CRC Press,
2014.
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