Supramolecular luminescent system based on 2-cyano-3(4-(diphenylamino) phenyl) acrylic acid: Chiral luminescent host for selective CH3CN sensor

Article abstract of DOI:10.1039/c1ce05187c

New supramolecular luminescent host systems based on 2-cyano-3(4- (diphenylamino)phenyl) acrylic acid (CDPA), a triphenylamine based luminescent acid, and amines (propylamine (1), dimethylaminopyridine, DMAP (2) and (1S,2R)-2-amino-1,2-diphenylethanol (3)) were prepared using a supramolecular approach. For each, the inclusion of amines in the CDPA matrix led to blue shifts in the solid state luminescence. 1 forms a CH₃CN-selective, luminescent host and exhibits solvent dependent luminescent changes in the solid state. Crystallisation of CDPA-DMAP from EtOAc (2a) and CH₃CN (2b) produces two different solid forms which exhibit slight differences in luminescence (λ_max at 522 nm and 529 nm, respectively). The chiral luminescent host system (3a) obtained from CH₃CN shows robust, reversible CH₃CN-selective luminescent sensing (λ _max at 523 nm (with CH₃CN) and 553 nm (without CH ₃CN)). In this case the luminescence changes with the crystallising solvent (MeOH (3b) and EtOH (3c)). The Royal Society of Chemistry 2011.

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PAPER
Supramolecular luminescent system based on 2-cyano-3(4-(diphenylamino)
phenyl) acrylic acid: Chiral luminescent host for selective CH3CN sensor†
a
a
a
a
Savarimuthu Philip Anthony,ab Colm Delaney, Sunil Varughese, Longsheng Wang and Sylvia M. Draper
*
Received 9th February 2011, Accepted 11th August 2011
DOI: 10.1039/c1ce05187c
New supramolecular luminescent host systems based on 2-cyano-3(4-(diphenylamino)phenyl) acrylic
acid (CDPA), a triphenylamine based luminescent acid, and amines (propylamine (1),
dimethylaminopyridine, DMAP (2) and (1S,2R)-2-amino-1,2-diphenylethanol (3)) were prepared using
a supramolecular approach. For each, the inclusion of amines in the CDPA matrix led to blue shifts in
the solid state luminescence. 1 forms a CH3CN-selective, luminescent host and exhibits solvent
dependent luminescent changes in the solid state. Crystallisation of CDPA-DMAP from EtOAc (2a)
and CH3CN (2b) produces two different solid forms which exhibit slight differences in luminescence
(lmax at 522 nm and 529 nm, respectively). The chiral luminescent host system (3a) obtained from
CH3CN shows robust, reversible CH3CN-selective luminescent sensing (lmax at 523 nm (with CH3CN)
and 553 nm (without CH3CN)). In this case the luminescence changes with the crystallising solvent
(MeOH (3b) and EtOH (3c)).
viewpoint, although the prediction of the supramolecular
structure is difficult as it often results in host structures with
included solvent molecules.8–13 Nevertheless, the supramolecular
approach offers a wealth of opportunity for simple variation (by
changing one of the co-crystallisation components) and excellent
scope for tuning the solid-state luminescence by control of the
solid-state structure.12 Despite its simplicity a supramolecular
approach has not been widely used in generating porous or host–
guest luminescent systems. An exception is the work of Imai et al.
where they report supramolecular luminescent host systems
derived from mixing luminescent organic acids and amines and
demonstrate their solvent-dependent, solid-state optical proper-
ties.9,10,12 Recently we reported the switching and tuning of
organic solid-state luminescence in 2-cyano-3(4-(diphenylamino)
phenyl) acrylic acid (CDPA) by forming unusual intermolecular
H-bond interactions with amines.11 The unusual intermolecular
interactions of amines (pyridine, piperidine, pyrrolidine and
morpholine) with CDPA leads to the gradual blue shift of CDPA
solid state luminescence from 587 nm to 496 nm and the crystalline
host system of CDPA-piperidine displays selective CH3CN
luminescence switching. This unusual attribute of CDPA
prompted us to investigate the formation of supramolecular
luminescent host systems of CDPA with chiral amines. Changes in
the fluorescence of such systems, on interacting with chiral guests,
can provide time-efficient and sensitive enantiomer determination
of chiral reagents e.g. catalysts, natural products and drugs.14
In this manuscript, we report supramolecular luminescent
hosts generated from CDPA and amines, which exhibit selective
CH3CN-dependent, solid-state luminescence (Scheme 1). Co-
crystallisation of CDPA with propylamine produces a lumines-
cent host system (1) with included CH3CN solvent molecules in
Introduction
Luminescent materials find application in fields from environ-
mental monitoring to biomedical diagnostics, because of their
high sensitivity.1 Hence several efficient organic luminophores
with strong luminescence in solution have been developed for use
in pH, metal ion and anion sensing, and bio-imaging.2 However,
the development of functional materials based on solid-state
organic luminescence is rare due to quenching by molecular
aggregation or strong H-bonding.3 The potential application of
solid-state luminescent materials in organic electroluminescence
(EL), optoelectronic devices and sensors, accounts for recent
interest in this area.4 Chiral luminescent materials, in particular,
can exhibit circularly polarized luminescence (CPL).5 Porous or
host–guest luminescent organic materials, are interesting candi-
dates in analytical chemistry because of their guest dependent
optical properties which can be exploited for sensor applica-
tions.6,7 The unpredictable nature of the formation of such
luminescent, porous or host–guest structures has limited their
development in robust sensor applications.
Supramolecular luminescent systems composed of two or
more organic components are desirable from a synthetic
aSchool of Chemistry, Trinity College Dublin, Dublin 2, Ireland. E-mail:
smdraper@tcd.ie; Fax: +353 16712826; Tel: +353 18962026
bPresent address: School of Chemical
University, Thanjavur-613401 Tamil Nadu, India
& Biotechnology, SASTRA
† Electronic supplementary information (ESI) available: Alternative
representation of crystal packing in 1, TGA for 1, 2a/2b and 3,
Circular dichroism spectrum of 3a, Comparison of solid state
luminescent intensity of CDPA, 1, 2a and 3a. CCDC reference
numbers 797566 and 797567. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c1ce05187c
6706 | CrystEngComm, 2011, 13, 6706–6711
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2: A mixture of CDPA (100 mg, 0.29 mmol) and dimethylami-
nopyridine (0.3 mmol) was dissolved in acetonitrile (15 mL) or
ethyl acetate (15 mL) as two separate experiments. Acetonitrile
solutions produced crystalline flakes of 2b on standing at room
temperature for12h. C29H26N4O2 (462.54):calcd. C 75.30, H 5.67,
N 12.11;foundC75.15, H 5.64, N11.99. Ethyl acetategave an85%
yield of single crystals of 2a after 8 h. C29H26N4O2 (462.54): calcd.
C 75.30, H 5.67, N 12.11; found C 75.06, H 5.58, N 11.99.
3: A mixture of CDPA (100 mg, 0.29 mmol) and (1S,2R)-2-
amino-1,2-diphenylethanol (0.3 mmol) was dissolved in aceto-
nitrile (15 mL), methanol (15 mL) and ethanol (20 mL) as three
separate reactions. Acetonitrile and methanol solutions produce
crystalline fibres of 3a and 3b respectively within 1 day. Ethanol
solutions gave crystalline thin plates (3c) after standing at room
temperature for one week. In all three solvents the crystalline
product yield was 85%. C36H31N3O3$H2O (571.65). calcd. C
75.64, H 5.82, N 7.35; found in 3a, C 75.77, H 5.50, N 7.18; 3b, C
75.35, H 5.78, N 7.25; 3c, C 75.22, H 5.76, N 7.23.
Scheme 1 CDPA-amine supramolecular luminescent systems.
the crystal lattice. The chiral supramolecular system prepared
from CDPA and the chiral amine (1S,2R)-2-amino-1,2-diphe-
nylethanol (3a) exhibits robust CH3CN-dependent luminescent
sensing as well as luminescent properties that differ depending on
the crystallising solvent. Co-crystallization of CDPA with
dimethylaminopyridine (DMAP) produces two different solid
forms (2a, 2b) for which the solid-state luminescence changes
with the crystallising solvent.
Details of UV-visible, circular dichroism and luminescence studies
Absorption and luminescence spectra were recorded using
a Perkin Elmer Lambda 1050 and Horiba Jobin Yvon Fluorolog
instrument. Solid state luminescence was measured by spreading
the powdered samples on a glass plate. To compare the intensity
of the solid state luminescence with CDPA in CH2Cl2 solution,
transparent KBr pellets of CDPA, 1–3 were prepared and the
concentration of the compounds in solution as well as in the solid
matrix were adjusted to keep the optical density (OD) around
0.5. KBr pellets of these samples show similar luminescence lmax
as their pure solid samples. Circular dichroism studies used
a Jasco J-810 Spectropolarimeter.
Experimental
Synthesis and characterization
Triphenylamine, cyanoacetic acid, POCl3, anhydrous dimethyl
formamide (99.8%), propylamine, dimethylaminopyridine, and
(1S,2R)-2-amino-1,2-diphenylethanol were obtained from
Aldrich and used as received. Elemental analyses were measured
with a Perkin-Elmer 2400 II CHN analyzer. Thermogravimetric
analyses (TGA) were carried out using a Perkin Elmer Pyris-1
TGA under both nitrogen and oxygen flow using a platinum
crucible (ca. 5 mg sample; heating rate of 10 ꢀC minꢁ1; range 25–
900 ꢀC). The instrument was calibrated to In and Ni standards in
air atmosphere. Co-crystallisations were performed in air under
ambient conditions, using HPLC grade solvents.
Details of powder X-ray diffraction (PXRD) and single crystal
studies
PXRD measurements were recorded using a Siemens diffrac-
tometer-D500 at room temperature.
Single crystals were immersed in oil and carefully chosen after
they were viewed through a polarizing microscope. The crystals
were glued to a thin glass fibre using an adhesive (cyano acrylate)
and mounted on a diffractometer equipped with an APEX CCD
area detector. The data collection was carried out at 150 K and the
crystals were smeared in NIH immersion oil to protect them from
ambient laboratory conditions. The intensity data were processed
using Bruker’s suite of data processing programs (SAINT), and
absorption corrections were applied using SADABS.15 The
structure solution of all the complexes was carried out by direct
methods, and refinements were performed by full-matrix least-
squares on F2 using the SHELXTL-PLUS16 suite of programs. All
the structures converged to good R factors. All the non-hydrogen
atoms were refined anisotropically, and the hydrogen atoms were
fixed on calculated positions using appropriate HFIX options in
SHELXTL and were refined isotropically. Intermolecular inter-
actions were computed using the PLATON program.17
2-cyano-3(4-(diphenylamino)phenyl)acrylic acid (CDPA). A 70
mL acetonitrile solution of 4-diphenylaminobenzaldehyde (1.0 g,
3.66 mmol), cyanoacetic acid (0.34 g, 4.0 mmol), and piperidine
(0.62 g, 7.32 mmol) was refluxed for 4 h under a nitrogen
atmosphere. Solvent removal by rotary evaporator followed by
solvent extraction (CH2Cl2 and aq. HCl (0.1 M)) yielded the
product as a dark purple solid, (1.05 g, 85%): Mp 213-214 ꢀC. 1H
NMR (400 MHz, CDCl3) d 8.15 (s, 1H), 7.90 (d, 2H), 7.39
(t, 4H), 7.23 (m, 6H), 6.98 (d, 2H). 13C NMR (125 MHz, CDCl3)
d 168.5, 155.0, 153.2, 145.1, 132.7, 129.6, 126.3, 125.5, 122.8,
118.2, 116.9, 95.5.
1: A mixture of CDPA (100 mg, 0.29 mmol) and propylamine
(0.3 mmol) was dissolved in acetonitrile (15 ml) and left to stand
at room temperature. Crystalline needles of 1 form after 4–5 h in
90% yield. C25H25N3O2 (399.48): calcd. C 75.16, H 6.31, N 10.52;
found C 74.95, H 6.34, N 10.42.
Results and discussion
Organic luminescent acid, CDPA, a triphenylamine derivative,
was synthesized following the literature procedure.18 CDPA
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exhibits strong luminescence in CH2Cl2 solutions with lmax at
603 nm and estimated quantum yield (Ff) 0.165 (on comparison
with coumarin 6). Solid CDPA luminesces with similar inten-
sity.11 Supramolecular luminescent organic systems were
prepared by crystallising CDPA with different amines in
CH3CN, EtOAc and alcohol (Scheme 1). The crystalline product
of 1 could be obtained from CH3CN solvent only. Ethyl acetate,
methanol, ethanol, methylene chloride and toluene were the
other solvents tested for the preparation of CDPA supramolec-
ular luminescent systems.
Single crystal X-ray diffraction data provided insight into the
structural organization and guest-inclusion processes of these
supramolecular luminescent solids. The crystal lattice of CDPA
exhibits a helical network generated via O–H/NC interactions
involving the carboxyl and cyano groups.11 In 1, the amine
deprotonates CDPA to form ionic N+–H/Oꢁ interactions in the
crystal lattice (Fig. 1a, Table 1). The –NH3+ interacts with three
different CDPA molecules, forming a one-dimensional network
structure along the b-axis. In addition, lateral molecules are
stabilized by weak C–H/p interactions. The guest CH3CN
molecules are included in the space created between two adjacent
one-dimensional chains however they are not involved in any
significant interaction with the host framework (Fig. 1b and Fig
S1) and as a consequence are responsible for the first mass loss
observed in the TGA (Fig. S2).
Single crystals of CDPA-DMAP (2a) were obtained from
EtOAc. As a strong base, DMAP deprotonates CDPA (Fig. 2a,
Table 1). The carboxylate oxygen atoms form an interaction with
the protonated nitrogen and weaker interactions with the ortho
and meta hydrogen atoms of neighbouring protonated DMAP
molecules (Fig. 2b), giving a cyclic interaction with the proton-
ated heteroatom and the ortho hydrogens with a R3 (10) graph
4
set. The result of this multiple hydrogen bonding is the formation
of a charged 2-D network structure (Fig. 2b). Crystallization of
CDPA-DMAP from CH3CN (2b) produces crystalline flakes
which are not of sufficient quality for single crystal X-ray anal-
ysis. Solid-state luminescence studies of EtOAc (2a) and CH3CN
(2b) (discussed later) show a red shift (lmax at 522 nm, 2a and 529
nm, 2b). The powder X-ray diffraction (PXRD) patterns of 2a
and 2b are different demonstrating that these systems have
different structural arrangements in the crystal (Fig. 3) and TGA
for 2b does not show CH3CN loss (Fig. S3).
Fig. 1 Selected H-bond interactions in the crystal lattice (a) and crystal
packing (b) of 1. C (grey), N (blue), O (red), H (white); H-bonds (broken
ꢀ
line). dH/A distances (A) are marked.
Compound 3 was crystallized from CH3CN (3a), MeOH (3b)
and EtOH (3c). 3a and 3b form crystalline fibrous materials
and 3c forms thin crystalline plates, none of which were suit-
able for single crystal X-ray analysis. 3a becomes dull on
exposure to ambient laboratory conditions. In contrast the
fibres (3b) filtered from MeOH and thin plates (3c) obtained
from EtOH do not show any colour change even on drying
under vacuum.
and 3b. Crystallites of 3 obtained from isopropyl alcohol were
found to have a similar PXRD pattern to that of 3c, implying
that an increase in the alcohol chain length does not affect the
crystal packing. The supramolecular luminescent system 3a,
taken as representative of 3 generally, was examined using
circular dichroism spectroscopy to confirm their chirality
(Fig. S5).
The PXRD patterns of 3a before and after the removal of
CH3CN, 3b and 3c are provided in Fig. 4. Although less intense,
the peak positions in 3a before and after CH3CN removal
remain the same, indicating that solvent loss has not induced
any structural change. The facile loss of CH3CN from 3a (Fig
S4) gives further support to the suggestion that this solvent is
not involved in strong interactions within this chiral host
framework. 3b exhibits a similar PXRD pattern to 3a but that
of 3c is different and appears to be a polymorphic form of 3a
The presence of amines in the CDPA matrix did not quench
the solid-state luminescence and all the supramolecular systems
were more intense luminescence than CDPA itself (Fig. S6). The
enhancement of the luminescence might be due to the de-aggre-
gation of CDPA in the solid matrix. Supramolecular fibres (3a)
exhibited the highest luminescent intensity of the three systems
investigated. The normalized solid-state luminescence spectra of
CDPA, 1 and 2b are shown in Fig. 5a. Powdered CDPA shows
solid-state luminescence at lmax 587 nm which blue shifts to 506
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Table 1 Crystallographic data for 1 and 2a
1
(CCDC-797567)
2a
(CCDC-797566)
Compounds
Formula
[C3H10N][C22H15N2O2] 0.5C2H3N
[C7H11N2] [C22H15N2O2]
Formula Wt.
Crystal system
Space group
420.01
Monoclinic
P21/c
20.497(8)
6.687(3)
20.628(8)
90
118.114(7)
90
2493.8(18)
4
1.119
150(2)
0.072
50.22
24686
4375
3394
311
1.083
0.0834, 0.2298
462.54
Monoclinic
P21/n
7.6459(15)
27.929(6)
11.311(2)
90
91.84(3)
90
2414.3(8)
4
1.273
150(2)
0.082
50.50
18765
4341
3723
320
1.105
0.0555, 0.1498
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
a (ꢀ)
b (ꢀ)
g (ꢀ)
3
ꢀ
V/A
Z
Dc/g cmꢁ3
T/K
m/mmꢁ1
2q range (deg)
Total Reflns.
Unique Reflns.
Reflns. used
No. of Parameters
GOF on F2
Final R1, wR2
Fig. 3 PXRD patterns of 2a and 2b.
Fig. 2 Selected H-bond interactions in the crystal lattice (a) and crystal
packing (b) of 2a. Only H atoms involved in H-bond interactions are
shown; C (grey), N (blue), O (red), H (white); H-bonds (broken line).
ꢀ
dH/A distances (A) are marked.
nm in the presence of propylamine (1). The solvent dependent
change in the luminescence of 1 is shown in Fig. 5b. 1 with
CH3CN shows luminescence lmax at 506 nm, whereas on
removing CH3CN (on air-drying for 10 min) the solid-state
luminescence shifts to lmax 534 nm. Re-exposure to CH3CN
Fig. 4 Solvent dependent PXRD patterns of 3a and the PXRD patterns
of 3b and 3c.
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Fig. 5 Normalized solid state luminescence of (a) CDPA, 1, 2b and (b)
solvent and structural dependent luminescence of 1 and 2 (excitation l ¼
370 nm).
Fig. 6 Normalized solvent dependent solid state luminescence of 3a (a)
and structural dependent luminescence of 3a, 3b and 3c (b) (excitation
l ¼ 370 nm).
switches the luminescence back to lmax 506 nm. Exposure of
powdered 1 to other solvent vapours such as EtOAc, CH2Cl2,
CHCl3, MeOH, EtOH, toluene and H2O for 5–10 min did not
change the luminescence lmax significantly. This gives further
support to the selective sensing of CH3CN within the crystal
lattice of 1.
the analysis shows one included water molecule in each case. The
solvent dependency of 3a and 3b and polymorphism of 3c gives
rise to different solid state luminescence at lmax 522 nm, 535 nm
and 545 nm, respectively (Fig. 6b).
The different solid forms of 2a and 2b show luminescence lmax
at 522 nm and 529 nm, respectively (Fig. 5b). Chiral supramo-
lecular luminescent host system 3a, which changes colour on
drying in the air, exhibits selective CH3CN solvent dependent
solid-state luminescence (Fig. 6a). 3a with CH3CN luminesces at
Conclusion
In conclusion, a co-crystallizing approach was used to prepare
new supramolecular luminescent host systems, including a chiral
luminescent host, based on CDPA. CDPA-propylamine (1) and
CDPA with (1S,2R)-2-amino-1,2-diphenylethanol (3a) form
CH3CN-selective, supramolecular, luminescent host systems that
undergo reversible luminescence changes upon drying and re-
exposure to CH3CN. Interestingly, the crystallization of 3 in
different solvents produces species that differ in both structural
organization and solid-state luminescence. These results are of
interest in sensor applications where the chirality of 3 could be of
particular importance.
l
max 523 nm but on removal of CH3CN (air-drying 5–6 min) red
shifts to lmax 553 nm. Re-exposure to CH3CN vapour (6–8 min)
switches the solid-state luminescence back to lmax 522 nm. Since
the PXRD patterns of 3a with and without CH3CN are the same
(Fig. 4), the solid state luminescence switching could be attrib-
uted to solvent inclusion in the crystal lattice. The easy removal
of CH3CN from 3a suggests that CH3CN does not partake in
significant H-bonding interactions in the crystal lattice. Exposure
of powdered 3a to EtOAc, CH2Cl2, CHCl3, MeOH, EtOH or
acetone solvent vapour for 5–10 min, blue shifts the luminescence
lmax to 539–546 nm. The small blue shift of luminescence upon
exposure to other solvents might be due to adsorption effects.
This observation supports the suggestion of the selective inclu-
sion of CH3CN in the crystal lattice of 3a. The elemental analyses
for 3 clearly establish the 1 : 1 ratio of CDPA: (1S,2R)-2-amino-
1,2-diphenylethanol in these systems (3a, 3b and 3c). In addition
Acknowledgements
This material is based upon works supported by EU FP6
[MKTD-CT-2004]
and
Science
Foundation
Ireland
[05PICAI819]. The authors thank the technical assistance of
Materials Ireland.
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