H-Bond assisted mechanoluminescence of borylated aryl amines: Tunable emission and polymorphism

Article abstract of DOI:10.1039/c7tc01676j

Design, synthesis and structural characterization of borylated aryl amines, Mes₂BAr {Ar = C₆(CH₃)₄NR₂ (1, 4); C₆H₄NR₂ (2, 5); C₆H₃(NR₂)₂ (3, 6); R = H or CH₃}, were reported. The intriguing optical signatures undoubtedly revealed their donor-acceptor characteristics and a bright tunable solid state emission is readily realized. The solid state luminescence characteristics of 1 and 3 were sensitive to mechanical stress with distinguishable emission color changes. Multiple strong intermolecular hydrogen bonds (N-H?N and N-H?π) accompanied by subtle conformational changes play a significant role in the piezochromic response. PXRD and FT-IR spectroscopic studies and insensitivity of substituted derivatives to mechanical stress support the above inference. Interestingly, compound 3 crystallized in two different polymorphic forms 3BP and 3GP, which showed distinct luminescence, i.e., green and blue color under UV light. Such changes are due to their distinct hydrogen-bond network assembly in the solid state. Quantum mechanical calculations were performed in order to corroborate the optical properties.

Full text of DOI:10.1039/c7tc01676j

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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DOI: 10.1039/C7TC01676J
Journal Name
ARTICLE
H-bond Assisted Mechanoluminescence of Borylated Aryl Amines:
Tunable Emission and Polymorphism
Received 00th January 20xx,
Accepted 00th January 20xx
Pagidi Sudhakar, Kalluvettukuzhy K Neena and Pakkirisamy Thilagar*
Design, synthesis and structural characterization of borylated aryl amines, Mes2BAr {Ar = C6(CH3)4NR2 (1, 4); C6H4NR2 (2, 5);
C6H4(NR2)2 (3, 6); R=H or CH3} were reported. The intriguing optical signatures undoubtedly revealed their donor-acceptor
features and bright tunable solid state emission is readily realized. The solid state luminescence characteristics of 1 and 3
were sensitive to mechanical stress with distinguishable emission color changes. Multiple strong intermolecular hydrogen
bonds (N-HN and N-H) accompanied by subtle conformational changes play a significant role in the piezochromic
response. PXRD and FT-IR spectroscopic studies and insensitivity of substituted derivatives to mechanical stress support
the above inference. Interestingly, compound 3 crystallized in two different polymorphic forms 3BP and 3GP, which
showed distinct luminescence, i.e., green and blue color under UV light. Such changes are due to their distinct hydrogen-
bond network assembly in the solid state. Quantum mechanical calculations were performed in order to corroborate the
optical properties.
DOI: 10.1039/x0xx00000x
www.rsc.org/
thiazolyl)thiophene towards anisotropic grinding and isotropic
compression.8b Araki and co-workers investigated H-bond
assisted mechanochromic luminescent response of pyrene
Introduction
Recently, a lot of research effort has been devoted to the
development of smart materials which change their
luminescence color upon exposure to an external stimuli such
as pressure, mechanical force, temperature and chemical
vapours.1,2 Smart materials which change their emission
characteristics under mechanical force like shearing, grinding,
tension or hydrostatic pressure are called mechanochromic
assemblies with amide substituents as the H-bonding sites.8a,b
Most of reported hydrogen bond based materials/liquid
crystals consist of planar aromatic skeletons and hydrogen
bonding sites, and thus π..π stacking and hydrogen bonding
play a synergistic role for their switchable color changes when
pressure is applied.8,9 However, planar aromatic skeleton may
reduce the fluorescence in the solid state due to undesirable
interactions.10 In order to access highly fluorescent
mechanochromic materials, bulky groups or aggregation
induced emissive fluorogens (AIEgens) need to be
incorporated in the smart materials. Several designed
mechanochromic molecules are based on existing AIEgens.11
Considering the demand of smart materials in the global
market, there is an urgent need for developing novel
mechanochromic materials with strong solid state
fluorescence and good color contrast.
luminescent materials.3-5 Last decade has witnessed
a
tremendous progress in the field of mechanofluorochromic
materials.3-11 Tuning and switching the luminescence color of
organic materials by regulating the mode of molecular packing
or by changing the molecular conformations, instead of
alteration of the chemical structure is an attractive strategy for
both fundamental research and practical applications.5 Recent
studies on mechanofluorochromic materials have revealed
that the color changes in these materials are mainly due to
changes in their solid state packing, which are largely driven by
intermolecular interactions.6,7
In recent years, triarylborane (TAB) based systems have
attracted considerable attention because of their potential
applications in OLEDs, sensors etc.12-15 If a suitable donor is
attached to electron deficient triarylboranes, bright solid state
emission is achieved owing to the propeller geometry of TAB
and intramolecular charge transfer (ICT) features between
donor and acceptor. Although, numerous TAB based D-A
systems are well documented in the literature,12-15 the
mechanochromic luminescent characteristic of these systems
has not been realized in spite of the importance of such
materials in modern technology.
Despite the outburst developments happened in the field of H-
hydrogen bonding, there are only very few reports on
hydrogen bond assisted piezochromic materials.8 Yamaguchi
and co-workers elegantly demonstrated H-bond directed
distinct
luminescent
responses
of
2,3,4,5-tetra(2-
Recent work from our laboratory showed that subtle
conformational changes in TAB based D-A structures have
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tremendous impact on their optical properties.15 We compounds were characterized by multi-nuclear NMR (1H and
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envisaged that the introduction of propeller shaped TAB and 13C) and high resolution mass spectrometDryO(IH: 1R0M.10S3)9./C7TC01676J
hydrogen-bonding sites (-NH2) within the same molecular
Br
NH2
Br
N
framework could be an effective strategy for the development
of strongly fluorescent smart materials. Herein we report that
the designed molecules meet our anticipation that gentle
a) NaN3
a) NaH
b) MeI
a) n-BuLi (1.1eq)
b) Mes2BF
b) Proline
c) CuI
BMes2
BMes2
Br
BMes2
1b
1
4
grinding of
1 and 3 showed an altered emission (chart 1). To
demonstrate that hydrogen bonding does play a crucial for the
mechanofluorochromism, hydrogen atoms on the -NH2 moiety
were replaced with methyl groups to eliminate the formation
of hydrogen bonds and the corresponding methylated
derivatives did not show any response to external stress. We
R1
R2
R1
R2
R1
R2
R1
R2
a) n-BuLi (2eq)
b) TMCl
a) n-BuLi (1.1eq)
b) Mes2BF
a) NaH
b) MeI
Br
Br
BMes2
BMes2
2b: R1 = N(SiMe3)2; R2 = H
3b: R1 = R2 = N(SiMe3)2
2a: R1 = NH2; R2 = H
3a: R1 = R2 = NH2
2: R1 = NH2; R2 = H
3: R1 = R2 = NH2
5: R1 = NMe2; R2 = H
6: R1 = R2 = NMe2
also found that compound
optical features.
3 forms polymorphs with distinct
Scheme 1. Synthesis of compounds 1-6
R
N
R
R
R
N
R
R
Optical Properties
N
N
R
R
Hexane solutions (10
M) of compounds
1
-
6
showed two
major absorption features in the range 280-450 nm; in
contrast, compound displayed a single absorption band (280-
420 nm, Figure 1). In order to rationalise the absorption
features, the UV-Vis absorption profiles of all the compounds
were recorded in solvents of different polarity. Upon
4
BMes2
BMes2
BMes2
3: R=H
6: R=Me
2: R=H
5: R=Me
1: R=H
4:R=Me
increasing the solvent polarity, the lower energy band of
1, 2,
Chart 1. Chemical structures of borylated aryl amines 1-6.
3
,
5
and was bathochromically shifted, while the higher
6
energy band was unaffected (Figure S25 and Table S1). From
these results, we can infer that the lower energy band arises
from amine to boron intramolecular charge transfer and the
higher energy band is from boron bound aryl centred π-π*
Results and discussions
Synthesis and characterization
transitions. However, the absorption spectra of
any significant changes in solvents of varying polarity. Absence
of ICT band in can be attributed to the poor electronic
4 did not show
Unsubstituted borylated aryl amines can be conveniently
prepared by the Williams16 and Asher’s17 method. Recently,
Thilagar et al15a developed a facile synthetic route which has
several advantages such as a less reaction time and excludes
the use of heavy metal (Pd). A similar procedure has been
4
communication between boron and nitrogen; presumably due
to the presence methyl groups on the nitrogen centre twisted
the duryl (spacer) unit significantly.
followed for the synthesis of
2 and 3, in 90% and 80% yield,
respectively (Scheme S1). First lithiation of appropriate
bromoanilines using required amount of n-BuLi (two
equivalents for 2a and four equivalents for 3a) generated
anion on nitrogen centre(s), which was trapped with
trimethylsilyl chloride to yield the corresponding N-
bistrimethylsilyl protected bromoanilines 2b and 3b
.
Subsequently, addition of one equivalent of n-BuLi replaces
bromine and generates a carbanion, which was then quenched
with dimesitylfluoroborane followed by methanolysis to obtain
Figure 1. Absorption (left) and emission (right) spectra of 1-6 in hexane solutions
the respective borylated aryl amines
involves heating mixture
2
of
and
3
. Synthesis of
1
(Conc. 10 M, λex = 350 nm).
a
(4-bromo-2,3,5,6-
To gain an in-depth understanding of the electronic structure
of geometry optimizations were carried out with density
tetramethylphenyl)dimesitylborane with L-proline, sodium
azide and copper(I) iodide in DMSO at 100 °C (Scheme 1).
1-6
functional theory using B3LYP hybrid functional and 6-31G (d)
basis set.20 The geometric parameters of energy minimized
structures (Figure S28) of the compounds closely resembled
the data from X-ray crystal structures (Table S4). The
molecular orbital coefficients of HOMO in 1-6 are localised on
arylamine unit. The LUMO of 1-6 is localised on the
triarylborane moiety (Figure 2). The non-crossing HOMO and
LUMO molecular orbitals (MOs) of 1-6 support the presence of
ICT from donor amine to acceptor boryl unit. Further, the
Compounds
methylation of
iodide. The synthesis of compound
and co-workers using Williams Method,16f but its optical
properties have not been investigated. Hence, we prepared
for comparative studies to get an insight into the optical
properties of other compounds and . Compounds 1-
are quite stable under ambient conditions. All the
4
,
5
1
and
6
were synthesized in moderate yields by
and using sodium hydride and methyl
was reported by Wang
,
2
3
2
2
1
,
3
,
4
,
5
6
6
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calculated HOMO-LUMO gap in 1-6 follows the trend
experimentally observed in UV-Vis spectral studies (Figure 1).
Compounds 1-6 showed an excitation wavelength
independent broad emission around 455, 412, 451, 435, 438
and 484 nm respectively in hexane solutions (Figure 1). Unlike
the absorption spectra, fluorescence spectra of these
compounds are remarkable and showed significant
solvatochromism with higher Stokes shift (Figure S26 and
Table S1), which are characteristic of boron based D-A system
reported elsewhere.13,14 Dipole moment of the fluorescent
state of the compounds were calculated using Lippert-Mataga
equation,19 i.e., from the Stokes shift and the solvent
orientation parameter. The estimated excited state dipole
View Article Online
DOI: 10.1039/C7TC01676J
moments of 1, 2, 3, 4, 5 and 6 are 13.34, 16.83, 11.96, 14.39,
13.02, and 11.20 respectively, undoubtedly support the
charge-transfer character of the excited state (Table S2). .
Fluorescence life times were recorded in hexane,
dichloromethane and DMSO. The decay data could be fitted
into a double exponential function (Table S3). Increase in
longer lifetime species in polar dichloromethane or DMSO
compared to non-polar hexane clearly indicates that the
longer life time species originated from highly polarized
ICT/TICT (twisted intramolecular charge transfer) state and
shorter life time species arose from the locally excited state.
Figure 3. Solid state emission spectra of
1
-
6
( λex = 350 nm). Images of compound
under UV light illumination (bottom, λex = 365 nm).
Structural Characterization-Polymorphism
Figure 2. Calculated frontier molecular orbitals and the orbital energies (eV) of
(energy levels are not to scale). (Atom colour codes: B: orange, N: blue, C:
black, hydrogen atoms are omitted for clarity).
1-
6
In the solid state, compounds
1-6 showed unstructured
emission peaked at ~ 446, ~ 433, ~ 469, ~437, ~452 and ~504
nm respectively upon excitation at 350 nm (Figure 3).
Compounds
solution state. The absolute fluorescence quantum yields
determined for pristine solid powders of and are
1-6 followed the similar trend as observed in
Figure 4. Molecular structures of
(bottom right), (H atoms except those coordinated to N atom of
for clarity).
1
(top left),
4
(top right),
5
(bottom left), and
6
1
are omitted
1
,
2
,
3
,
4
,
5
6
10.7, 22.2, 40.3, 29.9, 31.0 and 38.6 % respectively. The
fluorescence decay rate constants (kr) and non-radiative decay
rate constants (knr) are calculated by using the average
fluorescence lifetimes and quantum yields. The higher solid
state quantum yields observed for 3 and 6 are due to relatively
small knr values resulting in suppression of non-radiative
To gain a molecular level understanding of the luminescence
characteristics of compounds , crystallization of these
compounds were carried out. Single crystals suitable for X-ray
diffraction were obtained by slow evaporation of from
solutions of EtOAc, and from DCM solutions (Figure 4,
Table S9). Interestingly, compound forms polymorphs, by
1-6
1
4
,
5
6
3
relaxation. (Table S6).
slow evaporation of hexane (3GP) and DCM (3BP) solutions,
respectively (Figure 6, 7 and Table S7). The boron atom in
compounds 1, 3BP and 3GP, 4, 5 and 6 has a trigonal planar
configuration with the sum of angles around boron being 360o.
However, the nitrogen centre(s) adopt slightly pyramidal
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geometry; the sums of angles around N add up to ~ 342-350°. the crystal data revealed that 3BP crystallized iVniewmAortnicloecOlninlinice
In the solid state, compound
showed unique N −H…π crystal lattice in P21/c space group, whiDleOI3: G10P.10c3r9y/sCt7aTllCiz0e16d76inJ
1
interactions (π system of duryl moiety) and forms a one triclinic (P-1) crystal lattice. Two crystallographically distinct
dimensional zig-zag chain with a N−H…π distance of 2.49 Å molecules were present in the asymmetric units of 3BP (Figure
(Figure 5). The N−H…π interaction observed in 1 (2.49 Å) is 6, left) and 3GP (Figure 7, left); these are labelled as molecule
quite stronger compared to recently reported 4- A and molecule B respectively and the metric parameters for A
(dimesitylboryl)aniline (3.02 Å), 4-(dimesitylboryl)-3,5- and B differ significantly (Table S8).
dimethylaniline (4.08 Å).15a
To understand the distinct emission characteristics of the
polymorphs 3BP and 3GP, their solid state packing in the
crystal lattice was examined. Both 3BP and 3GP polymorphs
form strong intermolecular N-H…N and N-H… interactions at
several positions. Three neighboring molecules of 3BP form an
intermolecular trimer via N-H…N interactions (Figure 6,
middle). One of the two –NH2 groups of diaminophenyl unit is
involved in the formation of intermolecular trimer. The second
NH2 group connects the neighbouring trimers via
intermolecular N-H…N interactions and generates 3D
supramolecular network structure (Figure 6, right). In case of
3GP, the intermolecular N-H…N interaction between four of
(H the adjacent molecules generate a tetramer (Figure 6, middle).
Further intermolecular N-H…N interaction between the
neighbouring tetramers generated 3D supramolecular
structure (Figure 7, right). The hydrogen bonds play an
important role in fixing the orientation of the donor aniline
and acceptor boryl units. The dihedral angle between the BC2
(mesityl carbon) plane and donor aniline in 3BP and 3GP were
found to be ~ 38 ° and ~22 ° respectively. The smaller dihedral
angle in 3GP indicates that the donor (aniline) and acceptor
(boryl) interactions in 3GP is stronger than in 3BP, in support
Figure 5. Intermolecular (N-H…π) interaction in the molecular structure of
1
atoms except those coordinated to N atom are omitted for clarity).
of the red shifted emission of 3GP compared to 3BP
.
Figure 6. Asymmetric unit content (top left) of 3BP. Representation of formation
of intermolecular trimer in solid state of 3BP (top right). Representation of the
intermolecular N-H…N interactions between the neighbouring trimers in 3BP
(bottom). All the hydrogen atoms (except -NH2 unit) are omitted for clarity.
Figure 7. Asymmetric unit content (top left) of 3GP. Representation of formation
intermolecular tetramer in solid state of 3GP (top right). Representation of the
intermolecular N-H---N interactions between the neighboring tetramers in 3GP
(bottom). All the hydrogen atoms (except -NH2 unit) are omitted for clarity.
Interestingly, the polymorphs of
3 showed different emission
colours under UV light illumination. 3BP crystal showed blue
colour emission (~450 nm) while 3GP crystal showed green
colour (~ 505 nm) emission (Figure 8). Careful examination of
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100 °C for about 30 min. It has been found thaVtietwhAertigclreoOunnlinde
form of and
showed a higher averageDeOxcI:it1e0d.10s3t9a/tCe7TliCfe01t6im76eJ
1
3
compared to the pristine sample (Table S11). The absolute
fluorescence quantum yields of 1G and 3G are 12.2 and 36.5 %
respectively. These values indicate that fluorescence quantum
yield of ground samples 1G and 3G are comparable to the
pristine samples of
1 and 3, respectively. This result is
noteworthy in the field of smart materials; only a few
materials have been reported to show higher fluorescence
quantum yield for unground sample than the ground sample.18
The pristine and ground samples of
1 and 3 were examined by
Figure 8. Luminescence spectra of polymorphs 3BP and 3GP of compound
3
FT-IR spectroscopy (Figure S30). The pristine sample of
1
(right, λex = 350 nm). Images of single crystals under UV light illumination (left, λex
showed the NH stretching vibrations around 3383 cm-1 and
= 365 nm).
3476 cm-1, while the ground form (1G) displayed peaks at
3401 cm-1 and 3482 cm-1. In case of
3
, the peaks corresponding
to N-H stretching were observed around 3383 cm-1 and 3476
prompted us to study their solid state PL features under cm-1 for pristine form, and 3401 cm-1 and 3482 cm-1 are for the
mechanical force. Compounds and only showed altered ground form (3G). From these data, the ground forms of and
emission upon mechanical grinding (Figure 9). The emission have shown slightly higher N-H stretching vibrations
features of ground samples of and were significantly red compared to respective pristine forms clearly indicating that
Mechanochromism
The bright solid state luminescence characteristics of
1-6
1
3
1
3
1
3
shifted from 445 to 465 nm (blue to cyan blue) and 468 to 493 the hydrogen bonds were weakened; that could be due to
nm (cyan blue to green) respectively. The energy difference in partial perturbation from the ordered structure upon
the bathochromic shift sums to 966 and 1083 cm-1. The ground mechanical force.
form of 1 and 3 reverted back to original colour by heating at
Figure 9. Solid state emission spectra of different samples of
under UV-light illumination (λex = 365 nm).
1 (left) and 3 (right) obtained after mechanical grinding (ex = 350 nm). Images of compounds 1 and 3
Figure 10. PXRD pattern of different samples of
1
(left) and
3
(right) obtained after mechanical grinding.
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The strong H-bonding interactions observed in the solid states Highly ordered crystalline aggregates were observed in the
were disturbed by mechanical force and affected the morphological pattern of pristine sample whereas the bigger
electronic energy levels of the compound. The above inference crystals of
was further validated by the insensitivity of corresponding upon grinding (Figure 11).
methylated derivatives and towards mechanical stress.
Compounds and showed only weak Van der Waals
3 were broken into highly disordered aggregates,
4
6
4
,
5
6
Conclusion
interactions in the solid state (Figure S29). We also checked
the luminescence characteristics of previously reported 4-
(dimesitylboryl)aniline
dimethylaniline under mechanical pressure and found that
those are insensitive despite having H-bonding interactions in
the solid state. The possible reason may be the strength of
hydrogen bond in above mentioned borylanilines relative to
and 3 15a
Evidently, the changes in intermolecular interactions
and conformational planarization of and by applied force
A
series of borylated aryl amines were conveniently
and
4-(dimesitylboryl)-3,5-
synthesised and structurally characterised. The optical data
clearly demonstrated that the ICT can be controlled by steric
and electronic factors. Compounds
altered emission in response to the external stress and
controlled experiments demonstrated that non-covalent
intermolecular hydrogen bonds (N-HN and N-H) played a
pivotal role for the mechanoluminescent response.
1 and 3 displayed an
1
.
1
3
can permit a more in-plane arrangement of donor and
acceptor units and possibly better intermolecular charge
transfer interactions, leading to a bathochromic shift in
luminescence.
Substituted amine derivatives (
above inference. Compound
4
,
5
and
6) further validated the
3
crystallized in the two different
polymorphic forms which exhibited different emission
characteristics due to their distinct supramolecular
interactions in the solid state. Owing to strong solid emission
and stimuli responsive luminscence these molecules may find
applications in smart materials and optoelectronic devices.
Experimental Section
Methods and equipment
All the precursors were purchased from commercial suppliers
(Sigma-Aldrich, USA; Merck, Germany; SDFCL, India), and used
as received, unless otherwise mentioned. All reactions were
carried out under argon atmosphere using standard schlenck-
line techniques. THF was dried over sodium and distilled out
under argon atmosphere. DCM and chloroform were dried
using CaH2 and stored over 4Å molecular sieves. DMSO was
Figure 11. Scanning Electron Microscope (SEM) images of as prepared (left) and
ground (right) samples of 3.
To get further insight into the mechanofluorochromic
characteristics of and in the solid state, powder X-ray
diffraction (PXRD) analysis were carried out for different
samples of and obtained after mechanical treatment
(Figure 10). The PXRD pattern of pristine samples of and
1
3
1
distilled and stored over 4Å molecular sieves. H and 13C NMR
spectra were recorded at 25 °C on a Bruker Avance 400 MHz
NMR Spectrometer operating at a frequency of 400 MHz for 1H
and 100 MHz for 13C. 1H NMR spectra were referenced to TMS
(0.00 ppm) as an internal standard. Chemical shift multiplicities
are reported as singlet (s), doublet (d), triplet (t), quartet (q),
and multiplet (m). 13C resonances were referenced to the
CDCl3 signal at ~77.6 ppm. High resolution mass spectra
(HRMS) were recorded on a Micromass Q-ToF High Resolution
Mass Spectrometer by electrospray ionization (ESI) method.
Melting points of the compounds were measured on a
1
3
1
3
exhibit sharp and intense reflection peaks indicative of
crystalline nature of these compounds. A visible change is
noticed in the PXRD pattern of the ground samples of
1 and 3.
The greater full width at half maximum (FWHM) and change in
the intensities of the ground samples compared to the pristine
ones point to possible deformation of the ordered structures.
In order to understand the morphological changes of
compounds taking place upon mechanical grinding, scanning
electron microscopic (SEM) images of pristine and ground
samples were recorded; unfortunately we could not get the
calibrated melting point apparatus (Analab),
Thermocal10.
Electronic absorption spectra and fluorescence emission
spectra were recorded on a Perkin Elmer LAMBDA 750
UV/visible spectrophotometer and Horiba JOBIN YVON
SEM images for
1 due to charging. The SEM images of 3
showed noticeable changes in the morphology upon grinding.
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Fluoromax-4 spectrometer, respectively. Solutions of all the 3-(Dimesitylboryl)aniline (2): Step1:- To a soVluietwioArnticleoOfnli3ne-
DOI: 10.1039/C7TC01676J
compounds for spectral measurements were prepared using bromoaniline (2 g, 11.62 mmol) in THF (50 mL) at −78 °C was
spectrophotometric grade solvents, microbalance (± 0.1 mg added drop wise n- BuLi (14.50 mL of a 1.6 M solution in
precision) and standard volumetric glass wares. Quartz hexanes, 23.25 mmol), and the reaction mixture was stirred
cuvettes with sealing screw caps were used for the solution for 1 h at the same temperature. Trimethylsilyl chloride (2.90
state spectral measurements. Single-crystal X-ray diffraction g, 26.75 mmol) was added, and the reaction mixture was
studies were carried out with
a Bruker SMART APEX warmed to room temperature and stirred for 6 h. Volatiles
diffractometer equipped with 3-axis goniometer. The data were removed in vacuum, and the product (N-(3-
were integrated using SAINT, and an empirical absorption bromophenyl)-1,1,1-trimethyl-N-(trimethylsilyl)- silanamine)
correction was applied with SADABS. The structures were was distilled out (~ 120 °C) under reduced pressure. Yield:
1
solved by direct methods and refined by full matrix least- 90%. H NMR (400 MHz, CDCl3, 25 °C): δ (ppm) 7.25 (s, 1H),
squares on F2 using SHELXTL software.20 All the non-hydrogen 7.14-7.12 (m, 1H), 7.10 (s, 1H), 6.89 (d, J = 7.6 Hz, 1H), 0.14 (s,
atoms were refined with anisotropic displacement parameters, 18H). Step2:- To a solution of N-(3- bromophenyl)-1,1,1-
while the hydrogen atoms were refined isotropically on the trimethyl-N-(trimethylsilyl)silanamine (2.0 g, 6.40 mmol) in
positions calculated using
a riding model. Theoretical THF (50 mL) at −78 °C was added dropwise n-BuLi (4.40 mL of a
calculations were performed using the Gaussion 09 suite of 1.6 M solution in hexanes, 7 mmol), and the reaction mixture
quantum mechanical calculations. The hybrid Becke 3-Lee- was stirred for 1 h. Mes2BF (2 g, 7.20 mmol) in THF (10 mL)
Yang-Parr (B3LYP) exchange correlation functional was was added, and the reaction mixture was warmed to room
employed to predict the minimum energy molecular temperature over 12 h. The solvent was evaporated, and the
geometries of the compounds. Geometries were fully crude residue was dissolved in methanol and refluxed for 6 h.
optimized in the gas phase at the B3LYP level of theory by The reaction mixture was cooled to room temperature and
using the 6-31G(d) basis set for all the atoms. Frequency extracted using ethyl acetate. The combined extracts were
calculations were performed on each optimized structure stored over anhydrous Na2SO4, and the solvent was removed
using the same basis set to ensure that it was a minimum on under reduced pressure. The crude product was purified by a
the potential energy surface.21 Powder X-ray diffraction column chromatography over neutral alumina using a mixture
patterns of compounds were collected from a XD-D1 Shimadzu of petroleum ether and ethyl acetate (95:5 ratios) as eluent to
X-ray diffractometer. SEM micrographs were collected on a obtain the title compound as an off-white solid. Yield: 90%.
1
field emission scanning electron microscopy (FESEM, FEI M.P: ~ 178-180 °C. H NMR (400 MHz, CDCl3, 25 °C): δ (ppm)
Inspect F50), energy dispersive X-ray spectroscopy (EDS, 7.17 (t, J = 8 Hz, 1H), 6.96 (d, J = 6.8 Hz, 1H), 6.86 (d, J = 6.8 Hz,
Oxford instrument) attached with FESEM. Solid samples were 1H), 6.82 (s, 4H), 6.81 (s, 1H), 3.59 (s, 2H), 2.34 (s, 6H), 2.05 (s,
loaded on carbon tape prior to measurements.
Syntesis
12H); 13C NMR (100 MHz, CDCl3, 25 °C): δ (ppm) 146.4, 142.4,
141.3, 139.0, 129.3, 128.5, 127.3, 122.6, 119.2, 23.8, 21.7. 11B
NMR (376.5 MHz, CDCl3, 25 °C): δ (ppm) 74.2. ESI-MS (positive
ion mode): Mcalc. for C24H28BN = 341.23 Da; found: 342.23 Da
[M+H]+
4-(Dimesitylboryl)-2,3,5,6-tetramethylaniline (1)
: An oven
dried two neck round bottom flask was equipped with reflux
condenser connected to Schlenk line and another neck with
glass stopper. The reaction flask was evacuated and then
refilled with argon. The flask was charged with proline (225
mg, 1.50 mmol), sodium azide (150 mg, 2.50 mmol), CuI (220
5-(Dimesitylboryl) benzene-1,3-diamine (3): Compound
prepared following a procedure similar to that used for
compound . The quantities involved and characterization data
3 was
2
are as follows. 5-bromobenzene-1,3-diamine (2 g, 10.69
mmol), n-BuLi (1.6 M, 29.00 mL, 47.00 mmol) ClSiCH3 (5.80 g,
53.45 mmol). 5-bromobenzene-N, N, N, N-tetrasilyl-1,3-
diamine was distilled out (~ 150 °C) under reduced pressure,
Yield: 95%; 1H NMR (400 MHz, CDCl3, 25 °C): δ (ppm) 6.79 (d, J
= 1.6 Hz, 2H), 6.38 – 6.37 (m, 1H), 0.06 (s, 36H). Step2:- 5-
bromobenzene-N, N, N, N-tetrasilyl-1,3-diamine (2.00 g, 4.20
mmol), n-BuLi (2.90 mL, 4.60 mmol), Mes2BF (1.30 g, 5.04
mmol). The crude product was purified by column
chromatography over neutral alumina using a mixture of
petroleum ether and ethyl acetate (80:20 ratios) as eluent to
obtain the title compound as a pale brown solid. Yield: 80%.
mg,
1.15
mmol)
and
(4-bromo-2,3,5,6-
tetramethylphenyl)dimesitylborane (250 mg, 0.38 mmol) and
then degassed dry DMSO (15 mL) was added. The reaction
mixture was slowly warmed to 100 °C (procedure is not
recommended for higher scales). During the course of the
reaction, the solution turned from colorless to dark green
color. After consumption of the starting material (confirmed
by TLC), the mixture was filtered through celite and compound
was purified by column chromatography over silica-gel, eluting
with hexane-ethyl acetate (1:1), gave the pale yellow color
1
solid. Yield: 80%. M.P: ~ 183-185 °C. H NMR (400 MHz CDCl3,
25 °C): δ (ppm) 6.71 (s, 4H), 3.70 (s, 2H), 2.25 (s, 6H), 2.03 (s,
6H), 2.00 (s, 6H) 1.97 (s, 6H), 1.91 (s, 6H); 13C NMR (100 MHz,
CDCl3, 25 °C): δ (ppm) 145.7, 143.6, 140.7, 140.7, 139.5, 138.6,
136.5, 128.7, 128.6, 117.7, 23.1, 23.0, 21.3, 20.4, 13.2. 11B
NMR (376.5 MHz, CDCl3, 25 °C): δ (ppm) 75.6. ESI-MS (positive
ion mode): Mcalc. for C28H36BN = 398.3019 Da; found:
398.3315 Da [M+H]+.
1
M.P: ~ 167-169 °C. H NMR (400 MHz, CDCl3, 25 °C): δ (ppm)
6.80 (s, 4H), 6.29 (d, J = 2 Hz, 2H), 6.17 (t, J = 2 Hz, 2H), 3.35 (s,
4H), 2.31 (s, 6H), 2.04 (s, 12H). 13C NMR (100 MHz, CDCl3, 25
°C): δ (ppm) 148.8, 147.3, 142.4, 141.3, 138.8, 128.4, 113.8,
106.0, 23.6, 21.6. 11B NMR (376.5 MHz, CDCl3, 25 °C): δ (ppm)
73.7. ESI-MS (positive ion mode): Mcalc. for C24H29BN2
=
357.2502 Da; found: 357.2505 Da [M+H]+. (Note: 5-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
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Journal of Materials Chemistry C
Page 8 of 10
ARTICLE
Journal Name
bromobenzene-1,3-diamine was prepared from m-
dinitrobenzene by following the reported procedure22).
Acknowledgements
P. Thilagar and P. Sudhakar thanks Science and Engineering
Research Board (SERB), New Delhi, India for financial support.
K. K. Neena thanks CSIR New Delhi for research fellowship.
View Article Online
DOI: 10.1039/C7TC01676J
4-(Dimesitylboryl)-N,N,2,3,5,6-hexamethylbenzenamine (4)
Sodium hydride (27 mg, 2.2 mmol) was added to THF (20 mL)
solution of (200 mg, 1 mmol) at 0 under stirring. After 30
minutes, MeI (69 L, 2.2 mmol) was added drop wise to the
reaction mixture at ~ . The reaction mixture was warmed
:
1
℃


0 ℃
Notes and references
to room temperature and the stirring was continued at room
temperature. The progress of the reaction was monitored by
TLC. After complete consumption of reactants, the reaction
mixture was quenched with saturated aqueous NH4Cl solution.
The organic layer was extracted with ethyl acetate and dried
over Na2SO4, and concentrated under reduced pressure. The
crude product was purified by column chromatography over
neutral alumina using a mixture of petroleum ether and ethyl
acetate (97:3 ratio) as eluent to obtain the title compound as
1
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Shan, K. D. Singer and C. Weder, Adv. Mater., 2011, 23
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colourless solid. Yield: 75 %. M.P: ~ 144-146 °C. H NMR (400
2425-2429; b) D. R. T. Roberts and S. J. Holder, J. Mater.
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MHz, CDCl3, 25 °C): δ (ppm) 6.71 (br s, 4H), 2.81 (s, 6H), 2.25 (s,
6H), 2.08 (s, 6H), 1.94 (s, 18H). 13C NMR (100 MHz, CDCl3, 25
°C): δ (ppm) 150.7, 145.4, 145.0, 140.9, 140.8, 139.0, 136.4,
132.6, 128.8, 128.7, 43.1, 23.2, 22.8, 21.3, 20.3, 15.2. 11B NMR
(376.5 MHz, CDCl3, 25 °C): δ (ppm) 75.9. ESI-MS (positive ion
mode): Mcalc. for C30H40BN = 425.4563 Da; found: 426.3461
Da [M+H]+.
Jiang, ACS Appl. Mater. Interfaces, 2015, 7, 23650-23659; e)
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Otera, Organometallics, 2017, 36, 556-563.
3-(Dimesitylboryl)-N,N-dimethylbenzenamine (5): Compound
5
was prepared following a procedure similar to that used for
compound . The quantities involved and characterization data
are as follows. Compound (200 mg, 1 mmol), sodium hydride
(31 mg, 2.2 mmol), MeI (80 L, 2.2 mmol). The crude product
3
4
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2

was purified by column chromatography over neutral alumina
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as a pale green solid. Yield: 83 %. M.P: ~ 141-143 °C. H NMR
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(400 MHz, CDCl3, 25 °C): δ (ppm) 7.23-7.20 (m, 1H), 6.93 (br s,
1H), 6.89-6.86 (m, 2H), 6.79 (br s, 4H), 2.85 (s, 6H), 2.29 (s, 6H),
2.01 (s, 12H). 13C NMR (100 MHz, CDCl3, 25 °C): δ (ppm) 150.7,
142.4, 141.2, 138.7, 129.0, 128.4, 125.7, 121.0, 116.8, 41.3,
23.8, 21.7. 11B NMR (376.5 MHz, CDCl3, 25 °C): δ (ppm) 73.8.
ESI-MS (positive ion mode): Mcalc. for C26H32BN = 369.3500
Da; found: 370.2756 Da [M+H]+.
5-(Dimesitylboryl)-N1,N1,N3,N3-tetramethylbenzene-1,3-
5
a) T. Mutai, H. Satou and K. Araki, Nat. Mater., 2005, 4, 685-
diamine (6): Compound
similar to that used for compound
quantities involved and characterization data are as follows.
Step 1: Compound (200 mg, 1 mmol), sodium hydride (27
mg, 2.0 mmol), MeI (70 L, 2.0 mmol). Step 2: sodium hydride
(27 mg, 2.0 mmol), MeI (70 L, 2.0 mmol). The crude product
6
was prepared following a procedure
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, in two steps. The
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Ding, C. Wang, Z. Liu and Y. Xie, J. Mater. Chem. C, 2013, 1,
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7409-7417; e) S. Yagai, T. Seki, H. Aonuma, K. Kawaguchi, T.
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
was purified by column chromatography over neutral alumina
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1
Yield: 52 %. M.P: ~ 150-152 °C. H NMR (400 MHz, CDCl3, 25
6
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°C): δ (ppm) 6.77 (s, 4H), 6.42-6.41 (m, 2H), 6.29 (br s, 1H),
2.85 (s, 12H), 2.29 (s, 6H), 2.03 (s, 12H). 13C NMR (100 MHz,
CDCl3, 25 °C): δ (ppm) 151.5, 147.0, 142.4, 140.9, 138.1, 128.0,
111.2, 102.0, 41.2, 23.5, 21.3. 11B NMR (376.5 MHz, CDCl3, 25
°C): δ (ppm) 73.4. ESI-MS (positive ion mode): Mcalc. for
C28H37BN2 = 412.4178 Da; found: 413.4256 Da [M+H]+.
5
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Journal of Materials Chemistry C
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Journal of Materials Chemistry C
Page 10 of 10
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DOI: 10.1039/C7TC01676J
Bright tunable solid state emission, intriguing mechanochromism and polymorphism
dependent optical features of a series of borylated aryl amines were demonstrated.