Structurally simple thienodipyrandione-containing reversible fluorescent switching piezo- and acido-chromic materials

Article abstract of DOI:10.1039/c3tc31504e

We report here the structure-property correlations of a series of anthracene/pyrene derivatives grafted on a rigid, planar, and well conjugated endo-cyclic alkenyl lactone (thienodipyrandione) that exhibited aggregation induced emission. Unlike typical vinylene based solid-state fluorescence materials, rigid thienodipyrandione moieties can bestow a higher order of conformational twist as well as enhanced intermolecular interactions by C-H...O interactions due to the presence of a carbonyl group that leads to enhanced thermal stability. Compounds TDAn and TDAnPh exhibit distinct piezofluorochromic properties in which emission colors can be switched by grinding and heating. Based on a variety of spectroscopic techniques including XRD, DSC, and NMR, the observed piezochromic emission is attributed to the result of phase transition from structural crystalline (order) to amorphous (disorder) state or vice versa. Most uniquely, one of the anthracene derivatives, TDAn, displayed specific acido-fluorochromism whereas the other congener, TDAnPh, did not, even though they are structurally very similar. Crystal structure analysis revealed that a combination of various secondary interactions such as C-H...O, π-π and C-H...π interactions all play key roles in the supramolecular assemblies to display such distinctive features. The current study has disclosed a class of new stimuli-responsive materials with great potential in applications for micro-environmental sensing, optical switching and recording.

Full text of DOI:10.1039/c3tc31504e

Journal of
Materials Chemistry C
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PAPER
Structurally simple thienodipyrandione-containing
reversible fluorescent switching piezo- and acido-
chromic materials†
Cite this: J. Mater. Chem. C, 2013, 1,
6386
*
Rajeswara Rao M, Chia-Wei Liao and Shih-Sheng Sun
We report here the structure–property correlations of a series of anthracene/pyrene derivatives grafted on
a rigid, planar, and well conjugated endo-cyclic alkenyl lactone (thienodipyrandione) that exhibited
aggregation induced emission. Unlike typical vinylene based solid-state fluorescence materials, rigid
thienodipyrandione moieties can bestow a higher order of conformational twist as well as enhanced
intermolecular interactions by C–H/O interactions due to the presence of a carbonyl group that leads
to enhanced thermal stability. Compounds TDAn and TDAnPh exhibit distinct piezofluorochromic
properties in which emission colors can be switched by grinding and heating. Based on a variety of
spectroscopic techniques including XRD, DSC, and NMR, the observed piezochromic emission is
attributed to the result of phase transition from structural crystalline (order) to amorphous (disorder)
state or vice versa. Most uniquely, one of the anthracene derivatives, TDAn, displayed specific acido-
fluorochromism whereas the other congener, TDAnPh, did not, even though they are structurally very
similar. Crystal structure analysis revealed that a combination of various secondary interactions such as
C–H/O, p–p and C–H/p interactions all play key roles in the supramolecular assemblies to display such
distinctive features. The current study has disclosed a class of new stimuli-responsive materials with
great potential in applications for micro-environmental sensing, optical switching and recording.
Received 1st August 2013
Accepted 5th August 2013
DOI: 10.1039/c3tc31504e
www.rsc.org/MaterialsC
excellent PL properties. One of the recent goals for practical
applications is the control of the molecular packing mode
Introduction
instead of chemical alteration of the molecules.7 Since lumi-
nescence properties of organic solids greatly depend on the
molecular packing and intermolecular interactions, tunable
solid-state emission could be realized through an external
stimulus affecting the mode of molecular packing. In this
regard, stimuli-responsive uorescence switching, such as pie-
zochromism,8 vapochromism,9 light,10 thermo-11 and acid-
dependent12 luminescence, of smart materials has received
unprecedented attention.
The rst uorescence color switching compound based on a
pressure stimulus with aggregation induced emission (AIE)
property was reported by Park in 20108a and followed by a
number of new uorescence color switching compounds
synthesized by many others.8b–m Nevertheless, few examples of
stimuli-responsive uorescent materials with AIE properties
have been successfully developed to date.8–12 These materials
are currently still in the initial stage of investigation and an in-
depth understanding of the structure–property relationships of
solid-state emission behavior is mandatory in order for better
design and development of materials with intriguing proper-
ties. In particular, multi-stimuli responsive materials are
extremely rare.12a,13 Thus, there is a great demand to exploit new
stimuli-responsive materials such as piezochromic uorescent
The fundamental and essential issue in materials chemistry is
to understand the electronic interactions and self-assembly in
molecular solids which play a crucial role in determining the
ultimate optoelectronic properties. The design and synthesis of
solid-state luminophoric materials have received tremendous
attention in both scientic research and practical aspects owing
to their potential applications in the eld of optical and opto-
electronic devices.1 Especially, the correlations between the
molecular stacking mode and modulated optical properties in
order to improve and rene the design concept to develop
materials with desired properties. The ability to manipulate the
photoluminescence (PL) of organic materials is an important
aspect due to the diverse applications such as sensors,2 security
inks,3 re-healable materials,4 shape memory materials,5 and
light-emitting diodes.6 A great deal of synthetic effort has been
devoted to develop these materials to achieve color tuning and
Institute of Chemistry, Academia Sinica, 115 Nankang, Taipei, Taiwan, Republic of
China. E-mail: sssun@chem.sinica.edu.tw; Fax: +011-886-2-27831237; Tel: +011-
886-2-27898596
† Electronic supplementary information (ESI) available: Characterization data,
UV-vis, uorescence spectra, and photographs. CCDC 919160 and 919162. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3tc31504e
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(PCF) materials and the investigation of their properties is switching processes. Moreover, TDAn exhibits a unique acido-
highly desirable. uorochromism based on a combination of subtle intermolec-
Within this line of idea, various 9,10-distyrylanthracene ular interactions.
derivatives have been investigated as piezochromic uorescent
materials.14 Interestingly, in most of the anthracene based PCF
Results and discussion
materials, a common structural design is merely to change the
substituents at the styryl positions. In the pursuit to gain deeper
insights and to establish in-depth structure–property correla-
tions as well as for more potential practice applications, it is
highly desirable and indeed indisputable to extend the scope of
advanced material designs exhibiting PCF behavior. By keeping
these in mind, through a judicious structural design, we have
prepared a new building block, thienodipyrandione (TDP),
which is a rigid, planar, and well-conjugated endo-cyclic alkenyl
lactone. The TDP moiety has been introduced between two
anthracene or pyrene groups to explore the PCF properties. We
envisaged that a rigid TDP moiety would bestow a higher order
of conformational twist compared to simple vinylene moiety as
well as to induce unique supramolecular stacking architectures
associated with various secondary intermolecular interactions.
In addition, these cooperative supramolecular interactions can
further increase the thermal stability of the resulting PCF
materials, which is also an issue of concern for practical
applications.14a
We report herein the structure–property correlations of
aggregation-induced emission (AIE) and PCF behavior of
phenyl anthracene (TDAnPh), and pyrene (TDPy) molecules
(Scheme 1). The photophysical properties and AIE property of
these molecules induced by the intermolecular interactions
were rationalized by their X-ray crystal structures and theoret-
ical calculations (B3LYP/6-31G(d)). In particular, the TDAn and
TDAnPh exhibited an interesting piezo-uorochromism, and
the color changes in solid-state emission could be repeated
many times, indicative of an excellent reversibility in the
Synthesis
The three target compounds TDAn, TDAnPh, and TDPy were
synthesized by palladium catalyzed cross-coupling of 2,5-
dibromo-3,4-diethylcarboxylthiophene 4 with corresponding
aromatic alkynes followed by acid catalyzed cyclization
(Scheme 1). All compounds were puried by column chroma-
tography and re-crystallization process and the puried
materials were fully characterized by various spectroscopic
techniques. Full synthetic details are given in the experimental
section.
Optical properties
The absorption spectra of TDAn and TDAnPh in dilute toluene
solution exhibited absorption bands at 391 and 398 nm,
respectively, with characteristic anthracene vibrational features,
while TDPy (420 nm) displayed a broad spectral prole (Fig. S23,
S24, and S25 ESI†). The bathochromic shi in the absorption
spectrum of TDPy to its anthracene congener suggests
enhanced conjugation in the p framework of TDPy. Further-
more, all compounds in their dilute solutions, regardless of the
solvents used, were weakly uorescent with broad structureless
emission proles (Fig. 1). Interestingly, the Stokes shis for all
compounds were large, i.e. 8128 cmꢀ1, 8205 cmꢀ1, and 5222
cmꢀ1 in toluene solutions for TDAn, TDAnPh, and TDPy,
respectively, indicative of large geometrical changes between
the ground- and excited-state conformations. A large Stokes
shi typically indicates a change in geometry from the highly
twisted ground state to the more planar excited state or vice
Scheme 1 Synthetic scheme of TDP based AIE molecules TDAn, TDAnPh and TDPy.
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the other hand, TDPy showed very weak emission at 505 nm in
2-methyl THF–toluene glass at 77 K with a modest shi in the
band position compared to its emission at 538 nm in solution
(Fig. S29 ESI†). Noticeably, the Stokes shis for TDAn
(3370 cmꢀ1), TDAnPh (2917 cmꢀ1) and TDPy (3895 cmꢀ1) in a
2-methyl THF glass were signicantly small compared to their
solution state, strongly emphasizing that the structural relaxa-
tion in the excited state was prohibited. On the other hand, as
anticipated, the uorescence quantum yields in 2-methyl THF
glass were quite high compared to their corresponding solu-
tions and were 49%, 60% and 42% for TDAn, TDAnPh and
TDPy, respectively. Similar to the emission properties in the
solid state, the substantial blue shi of TDAn and TDAnPh in
glassy state suggests a highly conformational twist in molecular
structure compared to the one in solution. In the case of TDPy,
the minor blue shi of the emission in the glassy state strongly
intimates minor conformational change of the molecule.
Fig. 1 The normalized PL spectra of TDAn (a) and TDAnPh (b) at various states
and conditions.
versa.15 It is worth mentioning that no concentration (1 ꢁ 10ꢀ4
to 1 ꢁ 10ꢀ7 M) dependent emission spectra were observed for
any of the compounds, which precludes excimer formation.
TDP derivatives displayed a minor red shi in the solid-state
absorption spectra compared to the absorption spectra in
solution. In contrast, the emission maxima in the solid state are
very different from those in solution. Relatively strong green
and bluish green uorescence were observed for TDAn and
TDAnPh with maxima at 507 (Ff ¼ 12.7%) and 491 nm (Ff ¼
21.6%), respectively, which are blue shied 64 and 100 nm,
respectively, with respect to the emissions in toluene solutions
(Ff ¼ 8.3% for TDAn and Ff ¼ 6.2% for TDAnPh) (Fig. 1a and b).
The signicant blue shi of the solid-state emission implies a
distorted and highly twisted arrangement in the solid state
which limits effective conjugation and results in blue-shied
emission to that in solution. In the case of TDAnPh, further
blue-shi can be ascribed to the increased structural twist by
the additional phenyl substitution. The increased emission
intensity could be attributed to the aggregation induced emis-
sion (AIE) enhancement. Surprisingly, unlike TDAn and
TDAnPh, TDPy showed no solid-state emission (Fig. S26 ESI†).
TDP derivatives render no change in the glassy-state
absorption spectra compared to the absorption spectra in
solution indicating that compounds in both solution and glassy
state possess similar rigid ground state conformations (Fig. S27
ESI†). In contrast, like in the solid-state, the emission maxima
in glassy state are different from those in solution. Both TDAn
and TDAnPh emitted intense blue uorescence in toluene or 2-
methyl THF glass at 77 K (Fig. 2) with an emission band
centered at 463 nm, which was signicantly blue-shied from
their room-temperature solution emission maxima at 571 and
591 nm for TDAn and TDAnPh, respectively. Moreover, TDAnPh
exhibited a structured emission spectrum (Fig. S28 ESI†). On
Geometry optimized structures
The optimized geometry structures by Gaussian 09 at B3LYP/
6-31G(d) level revealed that all three TDP derivatives adopt a
twisted spatial conformation. The dihedral angles of the TDP
core and the peripheral aromatic moieties differed among each
compound with 61.99ꢂ, 64.89ꢂ and 40.43ꢂ, respectively, for
TDAn, TDAnPh and TDPy (Fig. 3). The relatively small torsional
angle in the case of TDPy is attributed to the reduced internal
steric hindrance. Even though the optimized structure of TDPy
in the gas phase shows some structural distortion, the obser-
vations of minor blue shi in the emission of TDPy in glassy
state at 77 K and no emission in solid state indicate that the
quenching of emission in solid state is likely due to the prom-
inent intermolecular interactions through the pyrene moieties.
Relatively weak steric repulsive interactions between central
TDP and the peripheral pyrene moieties might escalate the
planarization of the molecule in the solid-state which in turn
favors the intermolecular interactions. The observation of
prominent red-shi in the absorption maxima of TDPy
compared to its anthracene congeners supports the notion. To
obtain further insights in the aggregation-induced emission of
TDAn, TDAnPh and TDPy, we have attempted to grow single
crystals. Single crystals of TDAn and TDAnPh, suitable for X-ray
diffraction analysis, were successfully obtained by slow cooling
of a hot DMSO solution of TDAn and slow evaporation of a
CHCl3 solution of TDAnPh, respectively. The molecular struc-
tures of TDAn and TDAnPh are presented in Fig. 3. Both crystals
are monoclinic with space groups of C2/c and C2/m for TDAn
and TDAnPh, respectively. Similar to the geometry optimized
structures, the crystal structures of the TDAn16 and TDAnPh16
also exhibited highly twisted non-planar conformations with
eminent torsional angles of 60.6ꢂ and 71.1ꢂ, respectively,
between TDP and anthracene moieties. Unfortunately, we were
not able to obtain single crystals with good quality for TDPy due
to its poor solubility in common organic solvents. Nevertheless,
with similar structural distortion parameters for TDAn and
TDAnPh obtained from their single crystal analysis and
computational results, the calculated structure for TDPy could
Fig. 2 Photographs of 2-methyl THF solutions (5 ꢁ 10ꢀ6 M) of TDAn (a),
TDAnPh (b) and TDPy (c) at ambient temperature (left) and 77 K (right).
6388 | J. Mater. Chem. C, 2013, 1, 6386–6394
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Fig. 3 Calculated optimized conformational structures (left) and crystal structures (right) of TDAn, TDAnPh and TDPy.
provide a good reference to rationalize its solid-state emissive aggregates (Fig. 4a and b).17 The PL spectra of the TDAn and
behaviors.
TDAnPh in the water–THF mixtures with different water
contents are illustrated in Fig. 4c and d. The PL intensities of
TDAn and TDAnPh in dilute THF solutions were weak and
decreasing in their intensities was observed as the water
content increased up to 50%. However, the emission abruptly
increased with a concomitant blue shi with a water fraction up
to 60–70%. Thus, the increase in PL intensity can be attributed
to the AIE effect caused by the formation of molecular aggre-
gates when water is added into the solution. The Ff of TDAn and
TDAnPh increases drastically to 13 and 21%, respectively, in
THF–water as the nano-aggregates formed. The increased
uorescence quantum yields in the aggregation state with
respect to the solution state could be attributed to the restricted
intramolecular rotations (RIR). In molecularly dissolved solu-
tions, the intramolecular torsional motion is relatively free
which facilitates the non-radiative relaxation pathways and
affords weak uorescence emission. However, in aqueous
media, the intramolecular vibration and rotations are restricted
due to the formation of aggregates to exhibit the aggregation-
induced emission enhancement. The colors of these
compounds in THF–water mixtures with different water frac-
tions are signicantly different (insets of Fig. 4c and d). This can
be attributed to the formation of various aggregation states of
the molecules such as crystalline and amorphous particles in
the mixed solvent.
Aggregation induced emission
To further conrm AIE properties of TDAn and TDAnPh,
absorption and photoluminescence in THF–water mixtures
were studied in detail. The absorption spectra of TDAn and
TDAnPh exhibited no signicant change until the water fraction
was increased to 70% where the absorption spectrum was broad
with levelling-off of the tail in the visible region due to Mie effect
or light scattering because of the formation of nanoscopic
Piezo-uorochromism
One common structural feature for the class of AIE compounds
is that multiple peripheral phenyl groups are linked to an
olenic core with examples including distyrylanthracenes, cya-
nodistyrylbenzene, silole, triphenylethylene, and tetraphenyl-
ethylene derivatives etc.14,18 Due to the large steric hindrance
between the phenyl rings the AIE molecules adopt a twisted
Fig. 4 Absorption and PL spectra of TDAn (a and c) and TDAnPh (b and d) in
various THF–water mixtures. The insets of (c) and (d) show the fluorescence
images of TDAn and TDAnPh with various water fractions (from left to right: 0%,
40%, 70%, and 90%) under UV light (365 nm).
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conformation which reduces the p–p interactions. In this scanning calorimetry (DSC) experiments were performed. The
regard, the weak molecular interaction leads to defects in the as-synthesized compounds for both TDAn and TDAnPh clearly
crystals and can be readily destroyed by applying an external exhibited sharp and intense reections in their XRD proles
pressure. The applied pressure induces planarization of the indicative of microcrystalline structures. In contrast, the ground
molecular conformation because of the release of the twist samples did not show any noticeable XRD patterns, which
stress and, thus, results in a red shi of the emission spectrum. suggests the ground samples are amorphous. Similar XRD
The original conformation can be recovered simply by heating. signals to those in the as-synthesized samples appeared when
The phenomena of uorescent switching by grinding and the ground samples were heated (Fig. 6a and b). Thus, the
heating can be termed as piezochromic aggregation induced transformation of green or blue-green uorescent to orange
emission (PAIE).14,18 Both TDAn and TDAnPh exhibited prom- emission is imputed to phase transition and is completely
inent PAIE properties. Upon grinding the as-synthesized reversible under treatment of grinding (or pressing) and
compounds with a pestle, the green (507 nm) and bluish green annealing (or re-crystallizing from solvent). No peak was
ꢂ
(491 nm) emissive solids of TDAn and TDAnPh changed to observed up to 300 C in the DSC diagram for as-synthesized
yellow emissive solids (Fig. 5a) and showed emission maxima at samples of both TDAn and TDAnPh. However, the correspond-
548 and 540 nm, respectively, for TDAn and TDAnPh (Fig. 1a ing ground samples exhibited a clear exothermic peak at 134
and b) and the quantum yields (Ff) of ground TDAn and and 250 ꢂC for TDAn and TDAnPh, respectively (Fig. 6c and d).
TDAnPh samples were found to be 4.1% and 5.3% respectively. This thermal behavior is ascribed to a solid–solid trans-
Obviously, the appearance of pressure induced emission formation, i.e. the meta-stable state of the ground samples to a
changes in TDAn and TDAnPh indicates that these compounds more stable state by annealing.19 On the basis of PXRD, as well as
1
behave as piezochromic materials. The precise matching of H solid and frozen state emission data, it can be rationalized that
NMR and MALDI-TOF mass spectra of the ground samples of both TDAn and TDAnPh possess a highly twisted conformation
TDAn and TDAnPh to their corresponding as-synthesized in the solid state which is stabilized by various secondary
samples implies that no chemical reactions occurred during the bonding interactions. However, the molecular conformation
grinding process and the different luminescence properties are becomes planar to some degree in the amorphous state which
truly ascribed to the physical processes such as change in the leads to close packing and stronger intermolecular interactions.
intermolecular packing and phase transition. The orange The increased intramolecular conjugation caused by the
emissive ground solids can be reverted back to the as-synthe- planarity in amorphous samples might induce red shis in the
ꢂ
sized materials upon annealing the ground samples at 140 C PL spectra relative to crystalline samples. On the other hand,
for TDAn and 250 ꢂC for TDAnPh for about 5 min or recrys- these increased intermolecular interactions might propagate a
tallizing from a dichloromethane solution. The reversible photo-induced electron transfer process which effectively deac-
switching of the emission wavelengths can be realized by the tivates the emitting state and decreases Ff signicantly, as
repeated process of grinding and heating without decomposi- evident by the Ff of the ground samples.
tion of the samples (Fig. 5b and c). The switchable color change
feature of the compounds may render them promising candi-
dates for temperature or pressure sensing as well as optical
Acido-uorochromism
recording materials.
Another interesting phenomenon of the current system is that
To obtain insights into the phase transition and molecular
packing, powder X-ray diffraction (XRD) and differential
TDAn exhibits selective and pronounced acido-chromic
Fig. 5 Photographs of the ground (or acid-fumed) and the annealed samples of
TDAn under UV light (365 nm) (a); emission wavelengths of the repeated
grinding and annealing treatments of TDAn (b) and TDAnPh (c).
Fig. 6 XRD (top) and DSC (bottom) profiles of TDAn (a and c) and TDAnPh
(b and d).
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luminescence. As shown in Fig. 5a, aer exposure of the as- interactions such as p–p, C–H/p and C–H/X (X ¼ F, O, N, S
synthesized TDAn to triuoroacetic acid (TFA) vapor for 2 min etc.) that can be used to tune the solid-state molecular
or longer, the bluish green emission changed to yellow emis- arrangements and plays a crucial role in the stability of the
sion. The vapor chromic experiments have also been tested with crystal packing. The crystal structure of TDAn adopts a so-called
different acids such as BF3$Et2O, POCl3, and SOCl2, which sandwich herringbone type20 of pattern in which dimers of
showed similar phenomena to TFA (Fig. 7a). The resulting TDAn are arranged in a herringbone manner by the coexistence
yellow emissive sample appeared virtually the same to the of two types of interactions (Fig. 8a). A face-to-face p stacking
˚
ground sample in both color and the emission maxima interaction to form dimer (3.56 A) and two face-to-edge inter-
˚
(544 nm) and the emission was readily switched back to its dimer C–H/O (2.87 A) interactions result in the sandwich
original bluish green emission at 507 nm by heating the sample herringbone. Two monomeric units in the TDAn dimer overlap
at 140 ꢂC for 5 min. It is worth mentioning that approximately perfectly in their long molecular axis while an ꢃ80% of
70% of the TDAn sample turned to yellow emissive solid upon convergence was noticed in the short-molecular axis. Moreover,
acid-exposure while a thin-lm displayed complete conversion. two TDAn molecules form an anti-parallel arrangement in the
Similar to TDAn ground sample, the acid-fumed sample (Ff ¼ dimer and two solvent DMSO molecules also co-crystallized per
3.2%) also exhibited a lower quantum yield due to acid induced unit of the TDAn dimer. These two kinds of intermolecular
enhanced intermolecular interactions. The low quantum yield interactions play a substantial role in TDAn to form the
of the acid-fumed solid could also be attributed to a similar herringbone arrangement and the molecules with herringbone
mechanistic process occurring in the ground samples. The stacking structure are known to possess minimal p–p stacking
phase transition from the crystalline powder to amorphous interactions.21 On the other hand, the additional phenyl
solid can be realized by exposure to the acid vapor. Thermal substituents in TDAnPh heavily inuenced the crystal packing
annealing of the acid-exposed solid reverts to its original crys- to form a one-dimensional slipped p-stacking along the
talline state. It is worth noting that only a 5 nm bathochromic molecular long axis. The adjacent anthracene planes over-
shi in the PL spectrum in a toluene solution of TDAn was lapped with each other by about 33% and the vertical average
˚
observed in the presence of acid, indicative of the substantial intermolecular distance of 3.60 A suggests prominent p–p
effect in the solid state due to the phase transition from crys- interactions between the molecules (Fig. 8b). Besides the strong
talline to amorphous state. The reversibility of the emission was p–p interactions, there were also eight C–H/p interactions
conrmed by a repeated process of acid exposure and heating between the anthracene and phenyl substituents with four
treatments (Fig. 7b). In contrast, the acidochromic modulation adjacent molecules along the short molecular axis (Fig. 8c).
was not observed for TDAnPh even aer prolonged exposure to From the above ndings, it can be rationalized that the acid will
acid vapor. The XRD pattern for acid-fumed TDAn showed very protonate the carbonyl oxygen upon acid vapor exposure and
weak and broad diffraction signals indicating the structural diminish the relatively weak intermolecular interactions in
changes in molecular aggregation from crystalline to amor- TDAn, whereas the strong synergetic intermolecular p–p and
phous state (Fig. 6a). As expected, acid-fumed TDAn showed an C–H/p interactions in TDAnPh override the effect of acid.
exothermic peak at 134 ꢂC in its DSC diagram, which exactly
matches the phase transition temperature of TDAn ground
sample (Fig. 6c). Intense and sharp XRD reection peaks are
Conclusions
In summary, we have demonstrated two new TDP graed
anthracene derivatives exhibiting AIE and piezochromic
also similar to its as-synthesized compound and the absence of
DSC phase transition signal suggests no effect of acid on its
molecular packing in TDAnPh (Fig. 6b and d).
In order to understand the structure–property relationship
of specic acido-chromic characteristics of TDAn over TDAnPh,
a comparison of the molecular arrangements in the crystal
structures by X-ray structural analysis has been performed. The
molecular packing is certainly driven by the intermolecular
Fig. 7 (a) Overlay of solid-state PL spectra for as-synthesized and various acid-
fumed TDAn; (b) The PL spectra of TDAnPh in repeated conversions between
acid fuming and heating treatments.
Fig. 8 Crystal packing modes of (a) TDAn (b) & (c) TDAnPh. The co-crystallized
DMSO molecules in TDAn were omitted for clarity. The central TDP core showed
severe crystallographic disorder in the TDAnPh crystal structure.
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properties in which emission colors can be switched by under a nitrogen atmosphere. Aer cooling to room tempera-
grinding and heating. Based on XRD, DSC, and NMR studies, ture, brine (50 mL) was added and the reaction mixture was
the PL change is attributed to a result of structurally ordered to extracted with CH2Cl2 and dried over Na2SO4. The solvent was
disordered phase transition. We also found that one of the evaporated under reduced pressure and the residue was puri-
anthracene derivatives, TDAn, displayed specic acido-chrom- ed by column chromatography on silica gel to furnish the
ism, whereas the other congener, TDAnPh, did not. On the basis corresponding products.
of crystal structure analysis, we concluded that the change of
crystalline to amorphous state was due to the lack of strong
intermolecular interactions. The current study has disclosed a
class of new stimuli-responsive materials with great potentials
in applications for micro-environmental sensing, optical
switching and recording.
Diethyl 2,5-bis(anthracen-9-ylethynyl)thiophene-3,4-
dicarboxylate (1)
1H NMR (400 MHz, CDCl3): 8.64 (d, J ¼ 8.8 Hz, 4H), 8.51 (s, 2H),
8.05 (d, J ¼ 8.4 Hz, 4H), 7.66 (t, J ¼ 7.4 Hz, 4H), 7.55 (t, J ¼ 7.4 Hz,
4H), 4.53 (q, J ¼ 14, 7.2 Hz), 1.43 (t, J ¼ 7.0 Hz); 13C NMR (125
MHz, CDCl3): 162.67, 135.17, 132.97, 131.09, 129.22, 128.77,
127.19, 126.51, 125.88, 115.70, 97.06, 91.20, 61.88, 14.20; HRMS
(MALDI): m/z calcd for C42H29O4S: 629.1786 [M + H]+; found:
629.1807.
Experimental section
All chemical reagents were commercially available and were
used without further purication unless otherwise noted. All
reactions were monitored using pre-coated TLC plates and
puried by column chromatography. Column chromatography
was performed on silica (60–120 mesh). 1H NMR and 13C NMR
spectra (d values, ppm) were recorded using Bruker AVANCE III
400 MHz, Ultra Shield 400 and 500 MHz NMR spectrometers.
Absorption and uorescence spectra were obtained with a Var-
ian Cary 300 UV-vis spectrophotometer and Jobin-Yvon FL3-21
Horiba uorolog uorimeter, respectively. Fluorescence
quantum yields were measured using 9,10-diphenylanthracence
(DPA) in cyclohexane as a standard reference. Solid-state
emission quantum yields were determined by the Jobin-Yvon
FL3-21 Horiba uorolog uorimeter equipped with an inte-
grated sphere.22 Thermal transitions were collected by a Perkin-
Elmer Thermal Analysis DSC7 under nitrogen at a heating rate
Diethyl 2,5-bis(10-phenylanthracen-9-ylethynyl)thiophene-3,4-
dicarboxylate (2)
1H NMR (400 MHz, CDCl3): 8.73 (d, J ¼ 8.8 Hz, 4H), 8.27–8.20
(m, 8H), 7.71–7.57 (m, 14H), 7.45–8.41 (m, 8H), 4.55 (q, J ¼ 14.4,
7.2 Hz, 4H), 1.44 (t, J ¼ 7.2 Hz, 6H); 13C NMR (125 MHz, CDCl3):
162.94, 140.25, 138.44, 135.41, 132.89, 131.20, 130.12, 128.60,
128.00, 127.76, 127.43, 127.12, 126.86, 125.99, 116.05, 97.59,
91.71, 62.13, 14.48; HRMS (MALDI): m/z calcd for C54H36O4S:
780.2333 [M + H]+; found: 780.2350.
Diethyl 2,5-bis(pyren-1-ylethynyl)thiophene-3,4-dicarboxylate
(3)
1H NMR (400 MHz, CDCl3): 8.68 (d, J ¼ 5.2 Hz, 2H), 8.27–8.20
(m, 8H), 8.15–8.13 (m, 4H), 8.08–8.04 (m, 4H), 4.54 (q, J ¼ 14.4,
7.2 Hz, 4H), 1.46 (t, J ¼ 7.2 Hz, 6H); 13C NMR (125 MHz, CDCl3):
162.90, 135.45, 132.53, 132.25, 131.36, 131.19, 129.86, 129.04,
128.98, 127.37, 126.68, 126.58, 126.20, 126.11, 125.53, 124.73,
124.57, 124.35, 116.40, 99.28, 86.01, 62.07, 14.48; HRMS
(MALDI): m/z calcd for C46H30O4S: 676.1708 [M]+; found:
676.1723.
10 C minꢀ1. Powder XRD patterns of the samples were recor-
ꢂ
ded on a Philips X'Pert XRD System. Compounds 3,4-dicyano-
thiophene (6),23 thiophene-3,4-di(ethylcarboxylate) (5)24,25
thiophene-2,6-dibromo-3,4-di(ethylcarboxylate)
synthesized by following the literature.
(4)26
were
Thiophene-2,6-dibromo-3,4-di(ethylcarboxylate) (4)
Bromine (15.04 g, 95.2 mmol) was added drop-wise to
compound 5 (2 g, 23.8 mmol) in chloroform (3 mL). On
completion of bromine addition, the temperature of the reac-
tion mixture was raised from room temperature to 60–70 ꢂC and
kept for 12 h. The reaction mixture was then poured into aq.
sodium hydroxide solution and extracted with dichloro-
methane. The organic layer was washed with water, saturated
NaHCO3 solution and brine. Removal of the solvent yielded
General procedure for preparation of TDAn, TDAnPh and
TDPy
Compounds 1–3 (0.7 mmol) were dissolved in triuoroacetic
acid (10 mL) and the mixtures were reuxed at 70 ꢂC. The
progress of the reaction was monitored by TLC. Aer 24 h, the
reaction mixture was poured into water (300 mL) and the ltrate
thereby formed was washed with aq. NaHCO3 solution to
remove excess of acid. The crude mixture was repeatedly
washed with diethyl ether and methanol to yield pure
compounds in 61–68% yields.
1
compound 4 as a white crystalline solid in 85% yield. H NMR
(400 MHz, CDCl3): 4.37 (q, J ¼ 14.4, 7.2 Hz, 4H), 1.37 (t, J ¼ 7.6,
6H); 13C NMR (125 MHz, CDCl3): 161.29, 133.79, 115.60,
61.89,14.01.
3,7-Di(anthracen-9-yl)thieno[3,2-c:4,5-c0]dipyran-1,9-dione
General procedure for preparation of compounds 1–3
(TDAn)
Solutions of compound 4 (1.3 mmol) and the corresponding 1H NMR (400 MHz, DMSO): 8.90 (s, 2H), 8.26–8.23 (m, 4H),
alkyne (3.0 mmol, 2.2 equiv.) in dry THF–triethylamine (3 : 1) 8.10–8.08 (m, 4H), 7.75 (s, 2H), 7.68–7.62 (m, 8H); 13C NMR (125
were coupled in the presence of catalytic amounts of MHz, DMSO): 134.68, 132.17, 131.58, 131.50, 130.72, 129.96,
PdCl2(PPh3)2 (3 mol %) and CuI (2 mol %) at 50 ꢂC for 16 h 129.53, 128.89, 128.80, 127.60, 126.85, 125.92, 125.05; HRMS
6392 | J. Mater. Chem. C, 2013, 1, 6386–6394
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Journal of Materials Chemistry C
(MALDI): m/z calcd for C38H21O4S: 573.1160 [M + H]+; found:
573.1180.
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C. Zhang, Q. Peng, Q. Liao, Y. Wu, Z. Xu, Y. Zhao, H. Fu
and D. Zhang, Adv. Funct. Mater., 2012, 22, 4862; (l) B. Xu,
Z. Chi, J. Zhang, X. Zhang, H. Li, X. Li, S. Liu, Y. Zhang
and J. Xu, Chem.–Asian J., 2011, 6, 1470; (m) G. R. Krishna,
M. S. R. N. Kiran, C. L. Fraser, U. Ramamurty and
C. M. Reddy, Adv. Funct. Mater., 2013, 23, 1422; (n)
M. Rajeswara Rao, C.-W. Liao, W.-L. Su and S.-S. Sun, J.
Mater. Chem. C, 2013, 1, 5491–5501.
3,7-Bis(10-phenylanthracen-9-yl)thieno[3,2-c:4,5-c0]dipyran-
1,9-dione (TDAnPh)
1H NMR (400 MHz, CDCl3): 8.04 (d, J ¼ 8.4 Hz, 4H), 7.73 (d, J ¼
8.8 Hz, 4H), 7.65–7.52 (m, 10H), 7.47–7.39 (m, 8H), 7.15 (s, 2H);
13C NMR (125 MHz, CDCl3): 158.18, 155.53, 150.67, 141.14,
138.43, 131.17, 130.44, 129.98, 128.68, 128.06, 127.71, 127.07,
125.86, 125.63, 125.20, 120.21, 105.14; HRMS (MALDI): m/z
calcd for C50H29O4S: 725.1786 [M + H]+; found: 725.1795.
3,7-Di(pyren-1-yl)thieno[3,2-c:4,5-c0]dipyran-1,9-dione (TDPy)
1H NMR (400 MHz, CDCl3): 8.66 (d, J ¼ 9.2 Hz, 2H), 8.45–8.15
(m, 14H), 8.17 (t, J ¼ 7.6Hz, 2H), 7.89 (s, 2H); 13C NMR spectrum
was not acquired due to poor solubility in solvents; HRMS
(MALDI): m/z calcd for C42H25O4S: 621.1160 [M + H]+; found:
676.1175.
Acknowledgements
We are grateful to the National Council of Taiwan (Grant no.
100-2628-M-001-002-MY3) and Academia Sinica for support of
this research. R. R. M. thanks the postdoctoral fellowship
sponsored by the National Science Council of Taiwan (Grant no.
101-2811-M-001-181). Dr Yu-Sheng Wen at Institute of Chem-
istry, Academia Sinica and Mr Ting-Shen Kuo at National Tai-
wan Normal University are acknowledged for their help in
crystal structure renement.
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