Reversible and hydrogen bonding-assisted piezochromic luminescence for solid-state tetraaryl-buta-1,3-diene

Article abstract of DOI:10.1039/c3cc42644k

Reversible piezochromic luminescence and aggregation induced emission properties of 4,4′-((Z,Z)-1,4-diphenylbuta-1,3-diene-1,4-diyl)dibenzoic acid are reported. The photoluminescent color of it changes from blue to yellow-green upon grinding, which can be

Full text of DOI:10.1039/c3cc42644k

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Reversible and hydrogen bonding-assisted
piezochromic luminescence for solid-state
tetraaryl-buta-1,3-diene†
Cite this: Chem. Commun., 2013,
49, 7049
Received 11th April 2013,
Accepted 13th June 2013
a
a
Ting Han,z Yijia Zhang,z Xiao Feng,*ab Zhengguo Lin,b Bin Tong,a Jianbing Shi,a
Junge Zhib and Yuping Dong*a
DOI: 10.1039/c3cc42644k
www.rsc.org/chemcomm
Reversible piezochromic luminescence and aggregation induced formation of p–p stacking interactions, but can also efficiently
emission properties of 4,40-((Z,Z)-1,4-diphenylbuta-1,3-diene-1,4-diyl)- obstruct the rotation of the phenyl groups and permit deactivation
dibenzoic acid are reported. The photoluminescent color of it changes by fluorescence in the aggregation state.8 On the other hand,
from blue to yellow-green upon grinding, which can be restored upon although the atoms within crystals can move, the movement is
exposure to a solvent. Intermolecular hydrogen bonding plays a key severely constrained. We suppose that the introduction of another
role in the altered emission.
stimuli-responsive part is preferred to produce some remarkable
changes by mechanical force.
Piezochromic materials, which change the color of their
Herein, we designed and synthesized a novel piezochromic
luminescence in response to mechanical stimuli, are of practical material 4,40-((Z,Z)-1,4-diphenylbuta-1,3-diene-1,4-diyl)dibenzoic
importance for mechano-sensors, optical recording, security acid (TABD–COOH), which exhibits high solid-state fluorescence
papers and optoelectronic devices.1 They possess significance quantum yield (69.60%) with characteristic AIE properties as
in fundamental research to establish the remarkable influence well as reversible mechano-responsive abilities. A drastic change
of the subtle interplay of molecular and supramolecular level in fluorescence of TABD–COOH occurred upon grinding and can
structures on the tuning and altering of the luminescence of be fully restored to its original color upon exposure to solvents or
fluorophores in the solid state (SS).2 Although a variety of their vapors. The destruction of intermolecular hydrogen bonding
mechano-sensitive organic molecules,3 metal complexes4 and (H-bonding) interactions by applying high pressure, leading to
polymers5 have been developed recently, the rational molecular the state where close packing is the overriding factor governing
design of such materials and an effective mechanism explana- molecular packing, is responsible for the altered emission of
tion still need to be explored.
the ground samples.
In order to access piezochromic materials with high perfor-
TABD–COOH was prepared in three simple steps with an
mance, chromophores that can emit high fluorescence in the solid overall yield of 51% (Scheme 1). A full description of the
state with stimuli-responsive units are expected to be incorporated. synthetic approach and the characterization of the corresponding
Aggregation induced emission (AIE) molecules, discovered in 2001 compounds are provided in the ESI.† Compared with iconic
by Tang’s group,6 are a class of materials that show no emission or AIE-fluorophores, tetraphenylethylene (TPE) derivatives, that
little emission in dilute solutions but are brightly fluorescent in were synthesized through McMurry coupling reaction,7d the
their aggregation state.7 Unlike typical luminophores that usually product of which is commonly a mixture of E and Z stereo-
quench their fluorescence in SS resulting from undesirable inter- isomers, TABD derivatives can be easily obtained symmetrically
molecular interactions (e.g. p–p stacking, the formation of exci- with high stereoselectivities. Meanwhile, TABD–COOH is thermally
mers), AIE luminophores generally contain short intermolecular
interactions (e.g. C–Hꢀꢀꢀp) in SS, which can not only prevent the
a College of Materials Science & Engineering, Beijing Institute of Technology,
5 South Zhongguancun Street, Beijing, 100081, China.
E-mail: fengxiao86@bit.edu.cn, chdongyp@bit.edu.cn
b College of Chemistry, Beijing Institute of Technology,
5 South Zhongguancun Street, Beijing, 100081, China
† Electronic supplementary information (ESI) available: Experimental details, TGA,
UV, IR, XRD, DSC and single crystal data. CCDC 933576. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c3cc42644k
‡ T. Han and Y. Zhang contributed equally to this work.
Scheme 1 Synthesis route of TABD–COOH. (a) PdCl2, CuBr2, r.t.; (b) 4-methoxy-
carbonylphenylboronic acid, Pd(PPh3)4, Na2CO3 (aq), reflux; (c) (1) NaOH (aq),
reflux (2) HCl (aq).
c
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stable up to 320 1C as indicated by thermal gravimetric analysis
(Fig. S1, ESI†), which is important for further device applications.
AIE features of TABD–COOH were indicated by a 55-fold
increase in quantum yield when going from its THF solution
(FF = 1.28%) to SS (FF = 69.60%). It was further verified by the
trajectory of the change in its fluorescence intensity in the
THF–hexane mixtures (Fig. 1). The fluorescence intensities
of its solutions with a hexane fraction ( fH) lower than 60%
were negligibly small. This contributes to the non-radiative
de-excitation caused by the free rotation of the s bonds. The
emission started to drastically increase until the fH reached
70%, at which point, the aggregates started to form (Fig. S2,
ESI†) and the free rotations were restricted. With a fH of 90%,
the FF value increased to 43.1%.
Fig. 3 (a) Normalized FL spectra of the TABD–COOH powder upon fuming–
grinding. (b) Maximum emission wavelength change versus repeating cycles.
(c) Photographs of TABD–COOH cast filter paper upon piezowriting–erasing
under UV-light (365 nm).
The addition of hexane to a THF solution of TABD–COOH
resulted in precipitation of a white powder (F-form, Fig. S3a,
ESI†), which exhibited strong blue luminescence under irradia-
tion of UV-light (Fig. S3d, ESI†). Upon gentle grinding of TABD–
COOH using a spatula or mortar, this blue-emitting white solid a characteristic piezochromic effect. Meanwhile, TABD–COOCH3
was converted to a yellowish solid (G-form, FF = 34.76%, Fig. 2a exhibits a similar AIE phenomenon, but its piezochromic change
and Fig. S3c in ESI†) showing yellow-green luminescence (Fig. 2b is not as significant as that of TABD–COOH.
and Fig. S3f in ESI†), and this change occurred only at the pressed
The reversibility of piezochromic behaviour was confirmed
area (Fig. 2a and b). Attractively, it can be reverted to its original (Fig. 3). The yellow-green emission color obtained after grinding
color upon adding a drop of polar solvent (e.g. MeOH, EtOH, THF, (G-form) could be fully restored to its initial state (F-form) upon
Fig. 2c). Absorption and emission spectra of TABD–COOH in two simply wetting or fuming with polar solvents, such as MeOH,
forms are shown in Fig. S4 in ESI† and Fig. 3(a), respectively. A red EtOH and THF, and this piezochromic change could be repeated
shift of 11 nm in UV-vis absorption spectra was observed from the many times without any deterioration (Fig. 3a and b). As a
F-form powder (l = 363 nm) to the G-form powder (l = 374 nm), practical fast-responding demonstrator for piezochromic lumines-
whereas the maximum emission wavelength shifted from 448 to cence tuning, we prepared a blue-emitting film by casting THF
478 nm. This remarkable change in fluorescence upon grinding is solution of TABD–COOH on a filter paper. As shown in Fig. 3c,
three distinct yellow-green luminescent letters ‘‘BIT’’ were
written on the filter paper with a spatula in contrast to the
blue surrounding regions. This piezowriting could be erased
upon exposure to organic vapor (several minutes) as well as
upon adding polar solvents on it (within 1 second). Thus,
various kinds of patterns can be recorded simply by hand-
writing and subsequently be erased with solvents.
FT-IR, single crystal X-ray diffraction, powder X-ray diffraction
(PXRD) and differential scanning calorimetry (DSC) measurements
were applied to gain insight into the origin of the piezochromic
properties of TABD–COOH.
A broad absorption peak near 3430 cmꢁ1 arising from
H-bonding interactions was observed in the FT-IR spectrum
Fig. 1 (a) FL spectra of TABD–COOH in the THF–hexane mixture with different
fH. TABD–COOH concentration: 10 mM; excitation wavelength: 360 nm. (b) Plot of
of the F-form TABD–COOH, whereas a relatively sharp peak at
3423 cmꢁ1 resulting from ‘‘free’’ O–H bands in the G-form solid
was detected (Fig. S5, ESI†). In addition, compared with the
G-form solid, the C–O stretching band shifted from 1205 to
1267 cmꢁ1 and the out-of-plane O–H band appeared at 932 cmꢁ1
for the F-form solid. These results indicated that H-bonding
interactions in TABD–COOH were generated upon fuming and
suffered a different extent of deformation by the applied pressure.
Upon crystallization from the THF–hexane mixture, a trans-
parent single crystal of TABD–COOH was obtained. The struc-
ture solved from the diffraction data confirmed that multiple
H-bonding interactions occurred (Fig. 4), for example, O–Hꢀ ꢀ ꢀO
interactions between the carboxylic acid group in TABD–COOH and
maximum intensity vs. fH. Inset picture: image of TABD–COOH in THF–hexane
mixtures with fH of 0 (left) and 90 (right) under illumination using a hand-held UV
lamp at 365 nm.
Fig. 2 (a) Photograph of the half-ground powder of TABD–COOH under ambient
light. (b) Photograph of the half-ground powder under UV irradiation (365 nm).
(c) Photograph of the entire-ground sample after treatment with a drop of MeOH. oxygen atoms in THF, C–Hꢀꢀꢀp interactions between TABD–COOH
c
7050 Chem. Commun., 2013, 49, 7049--7051
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(973 Program; 2013CB834704), the National Science Founda-
tion of China (51073026, 51061160500 and 21074011) and the
Major Project Seed Research Program of Beijing Institute of
Technology (Grant No. 2012CX01008).
Notes and references
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and THF and C–Hꢀ ꢀ ꢀp interactions between two adjacent
TABD–COOH molecules. With the aid of all of these H-bonding
interactions, the free rotation of s bonds was obstructed and
the close p–p interactions were avoided.
The PXRD pattern of the F-form solid showed clear reflec-
tion peaks, which suggested the formation of ordered structure.
It should be noted that this pattern is not similar to the
diffraction data simulated from single crystal structure. This is
because unlike the single crystal structure, for the F-form solid,
dimeric and even ‘‘polymeric’’ structures could be formed due to
strong H-bonding interactions between carboxylic acid groups in
two adjacent TABD–COOH molecules. On the other hand, the
PXRD intensity of the G-form solid was strongly weakened
(Fig. S6, ESI†), which is an indication of partial deformation of
the ordered structure. Meanwhile, although the heating profile
of the F-form solid showed no peak up to 250 1C, two clear
exothermic peaks at 133 and 151 1C were observed only in the
first heating curve of the G-form solid (Fig. S7, ESI†). These two
peaks were supposed to contribute to crystallization and crystal
transformation temperatures, respectively. It is observed that
after annealing, the sample can also convert to its original color
due to the formation of highly ordered structures (Fig. S6, ESI†).
Thus, these results confirmed the piezochromic nature of
the TABD–COOH solid. It originated from the changes in the
molecular packing. That is, the molecular arrangement in the
F-form solid is overridden by H-bonding interactions. Applying
high pressure can destroy these interactions and lead to the
formation of the G-form solid, where close packing governs the
molecular packing. Furthermore, the permeation of vapors of
polar solvents into the powder or film promotes the regeneration
of H-bonds and the rearrangement of TABD–COOH molecules
from the G-form state to the F-form state.
In summary, we have demonstrated AIE features and rever-
sible piezochromic behavior of TABD–COOH, which was easily
prepared symmetrically with high stereoselectivity. The photo-
luminescent color of TABD–COOH can be altered upon gentle
grinding and simply recovered upon exposure to solvents
within 1 s. It is shown to be effective in introducing both the
AIE core and hydrogen bonding sites for the design of piezo-
chromic material with high fluorescence quantum yield in the
solid state.
The work reported in this communication was partially
supported by the National Basic Research Program of China
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 7049--7051 7051