A stimuli-responsive and chemically tunable organic microcrystal laser switch

Article abstract of DOI:10.1039/C8CC08298G

We demonstrated a stimuli-responsive and chemically switchable organic microbelt laser through reversible protonation-deprotonation reactions. The parent microbelt cavity together with the optically allowed 0-1 transition of H-aggregates enables a microlaser to operate at 585 nm. Upon HCl vapor treatment, the protonation of surface molecules shifts the lasing wavelength to 560 nm, generating an intensity contrast ratio >10⁵, accompanied by a sharp color change from orange (deprotonated) to green (protonated). When treated with HCl-NH₃ vapor, the protonation-deprotonation reactions lead to a reversible microlaser switch between 585 nm and 560 nm with good reproducibility and photostablity, making them attractive in high-throughput chemical and biological sensing applications.

Full text of DOI:10.1039/C8CC08298G

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A stimuli-responsive and chemically tunable
organic microcrystal laser switch†
Cite this: Chem. Commun., 2019,
5, 814
5
a
a
a
a
b
b
Xin Cai, Zhenzhen Xu,* Xiaolin Zheng, Chenhui Ran, Peng Liu, Xianxiong He,
b
a
ab
Received 3rd November 2018,
Accepted 13th December 2018
Xue Jin, Qing Liao and Hongbing Fu
*
DOI: 10.1039/c8cc08298g
rsc.li/chemcomm
We demonstrated a stimuli-responsive and chemically switchable soluble in organic solvents which are well suitable for low-cost,
1
3
organic microbelt laser through reversible protonation–deprotonation low-temperature processing. On the one hand, self-assembled
reactions. The parent microbelt cavity together with the optically organic microcrystals provide well-defined crystal facets to
allowed 0–1 transition of H-aggregates enables a microlaser to form built-in cavities for laser applications, such as nanowire
1
4,15
operate at 585 nm. Upon HCl vapor treatment, the protonation of Fabry–P ´e rot (FP)
and microdisk whispering-gallery mode
microlasers. On the other hand, organic semiconductors
an intensity contrast ratio 410 , accompanied by a sharp color change exhibit rich excited-state dynamics, such as excited-state intra-
16–19
surface molecules shifts the lasing wavelength to 560 nm, generating (WGM)
5
20–22
from orange (deprotonated) to green (protonated). When treated with molecular proton transfer (ESIPT)
HCl–NH vapor, the protonation–deprotonation reactions lead to a charge transfer (CT) processes,
and twisted intramolecular
which provide great opportu-
23–28
3
reversible microlaser switch between 585 nm and 560 nm with good nities to realize tunable laser performances. Nonetheless, reversible
reproducibility and photostablity, making them attractive in high- switch between different outputs from a single laser device upon
throughput chemical and biological sensing applications.
exposure to external stimuli is still a challenge.
Many fluorescent molecules can reversibly interact with
Microlasers that can generate intense coherent light on the external stimuli through chemical reactions, such as protonation–
micro/nanoscale have attracted extensive research interest, because deprotonation, complexation–decomplexation, and reduction–
2
9
of their applications in high-throughput chemical and biological oxidation reversible reactions. Following our interest in the
1–6
sensing, on-chip data communication and color laser displays.
design of reversibly switchable microlasers, we chose 4-(4-(4-(4-
Output wavelength tunability is an important figure-of-merit for (4-(dimethylamino)styryl)-2,5-dimethoxystyryl)-2,5-dimethylstyryl)-
developing microlasers. To integrate wavelength-tunable multicolor 2,5-dimethoxystyryl)-N,N-dimethylbenzenamine (OPV-DMBA) as
lasers, several gain media with different bandgaps have to be the model compound, which can undergo reversible protonation–
7–12
assembled on a single photonic circuit.
This, however, remains deprotonation reactions. (i) Self-assembly of OPV-DMBA generates
difficult, because monolithic growth and patterning of II–VI and single-crystalline microbelts (MBs), which constitute a high-quality
III–V semiconductors onto a silicon substrate are not easy tasks built-in FP microresonator. Together with the emissive H-aggregates
because of material lattice mismatch and incompatible growth as a superior gain medium, low-threshold microlasers were realized
temperatures.
with a narrow output at 585 nm (full width at half maximum,
As compared with inorganic counterparts which are usually FWHM = 8 nm). (ii) The chemo-reactive OPV-DMBA molecules on
hard and fragile and difficult to process in solution, organic the surface layers of microbelts can be protonated upon exposure to
semiconductors are soft materials with a low melting point and HCl vapor, providing a different gain medium for microlasers,
shifting the lasing wavelength to 560 nm. (iii) When treated with
the HCl–NH
to a reversible microlaser switch between 585 (orange) and 560 nm
green). With good reproducibility and photostability, our chemi-
cally tunable microlasers provide guidance for high throughput
chemical and biological sensing applications.
The model compound of OPV-DMBA was synthesized by a
classical Horner–Wadsworth–Emmons coupling reaction with a yield
of 58% (Scheme S1, ESI†) OPV-DMBA is an oligo(phenylenevinylene)
derivative with two N,N-dimethyl end-groups as chemical
3
vapor, the protonation–deprotonation reactions lead
a
Beijing Key Laboratory for Optical Materials and Photonic Devices, Department of
Chemistry, Capital Normal University, Beijing 100048, People’s Republic of China.
E-mail: xuzhenzhen@cnu.edu.cn, hbfu@cnu.edu.cn
(
b
Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Department of
Chemistry, School of Sciences, Tianjin University, Collaborative Innovation Center
of Chemical Science and Engineering, Tianjin 300072, People’s Republic of China.
E-mail: hongbing.fu@tju.edu.cn
†
Electronic supplementary information (ESI) available: Details of synthetic
procedures and additional data. CCDC 1845245. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c8cc08298g
8
14 | Chem. Commun., 2019, 55, 814--817
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+
ꢁ
Fig. 1 (a) The reversible chemical reaction between molecule OPV-DMBA and OPV-DMBA ꢀHCl . (b) Theoretically calculated frontier orbitals.
c) Normalized UV-Vis absorption and PL spectra of OPV-DMBA in THF solution (upper panel) and then adding with excess HCl (lower panel). The
(
ꢁ5
concentrations of dyes are all 1.0 ꢂ 10 M.
reaction sites, which can undergo reversible protonation/deprotona-
tion reactions (Fig. 1a). We calculated the frontier molecular orbitals
+
ꢁ
of parent OPV-DMBA and protonated OPV-DMBA ꢀHCl forms by
Gaussian 03 programs at the B3LYP/6-31g* level. As shown in
Fig. 1b, the HOMO (ꢁ4.29 eV) of OPV-DMBA is distributed on the
whole molecule, while the LUMO (ꢁ1.66 eV) is concentrated on the
+
ꢁ
distyrylbenzene core. Upon protonation by HCl, OPV-DMBA ꢀHCl
possesses a deeper HOMO at ꢁ5.06 eV and a LUMO at ꢁ2.32 eV.
Different from most investigations on the decreased band gap of
functional chromophores containing nitrogen atoms under the
30
proton trigger, the calculation results predict that the band gap
+
ꢁ
increases from OPV-DMBA (2.63 eV) to OPV-DMBA ꢀHCl (2.74 eV).
0
This case is similar to the reported 1,1 -(2,5-distyryl-1,4-phenylene)-
31
dipiperidine molecule.
Fig. 1c presents the UV-Vis absorption (dashed) and fluorescence
(solid) spectra. The maximum absorption peak of the OPV-DMBA
monomer is at 444 nm with a molar extinction coefficient of
ꢁ1
ꢁ1
e = 107 200 M cm , while its emission spectrum exhibits a
vibronic progression with the maximum at 541 nm (CIE: 0.40,
0
.57, Fig. S1, ESI†) and a fluorescence quantum yield of F = 0.80.
+
ꢁ
Upon protonation, the absorption band of OPV-DMBA ꢀHCl
ꢁ1
ꢁ1
was shifted to 432 nm with e = 55000 M cm . Meanwhile, its
Fig. 2 (a) SEM images of ensemble MBs placed on a glass substrate.
b) The SAED pattern of a single microbelt. (c) XRD profiles of MBs and the
emission maximum was blue-shifted to 500 nm (CIE: 0.25, 0.58,
(
Fig. S1, ESI†) with F = 0.90. The blue-shift observed in the emission simulated powder spectrum using MECURY software. (d) The molecular
+
ꢁ
maxima from OPV-DMBA to OPV-DMBA ꢀHCl is consistent with arrangement in the MBs. (e) Intensity normalized absorption (dashed lines)
and PL (solid lines) spectra of random MBs mat on the glass substrate.
the calculation results in Fig. 1b. Notably, upon addition of
+
ꢁ
NH
3
ꢀH
2
O into OPV-DMBA ꢀHCl solution in THF, the fluores-
cence emission color was recovered to yellow-green instantly
(Fig. S1–S4, ESI†). Moreover, the switch is reversible.
corresponding to crystal planes with k = 0, such as {002} and
The MBs of OPV-DMBA were prepared by drop-casting a high-order {004}, are observed (Fig. 2c). The OPV-DMBA molecules
0.5 M THF solution on the glass substrate at room temperature. stack in a face-to-face configuration along the crystal b-axis, leaving
The as-prepared MBs have a well-defined belt-like morphology the dimethylamino group exposed on the surface layers of
Fig. 2a), with a width (W) of 0.3–10 mm uniformly distributed microbelts which can be protonated upon exposure to HCl
along the entire length (L) of 5–50 mm. The thickness of the MBs vapor (Fig. 2d and Fig. S6, ESI†).
is about 170 nm (Fig. S5, ESI†). Triclinic OPV-DMBA crystals
Fig. 2e depicts the emission and absorption spectra of OPV-
CCDC no. 1845245†) belong to the space group of P1%, with cell DMBA MBs. Table S1 (ESI†) summarizes the related photo-
(
(
parameters of a = 5.97 Å, b = 8.15 Å, c = 20.83 Å, a = 81.491, physical parameters. As compared with monomers, the absorption
b = 88.641 and g = 79.851. Therefore, the squared and circled spectrum of these microcrystals exhibits a strongly blue-shifted
sets of spots in the SAED pattern are due to {100} and {020} maximum around 401 nm, suggesting that OPV-DMBA molecules
Bragg reflections. This is consistent with X-ray diffraction form H-aggregates in these crystals. This is consistent with the
12,16
(XRD) measurements, in which only the diffraction peaks face-to-face packing in the molecular arrangement (Fig. 2d).
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The PL spectrum of these microcrystals is dominated by the 0–1 of the microbelts through the chemical adsorption process (ESI†).
transition at 585 nm. The fact that the radiation transition rate However, the MB microlaser can still operate around 560 nm with
ꢁ
2
kr of the crystals is slower than that of the monomers is the a threshold at 14.3 mJ cm and a spacing of Dl = 1.11 nm, which
fingerprint of the H-aggregation model (Fig. S7 and S8, ESI†).
are both close to them without HCl vapors (Fig. 3d).
As reported previously, H-aggregated organic semiconduc-
Correspondingly, the PL-color of the microbelts below the
tors can be superior gain materials for laser applications, in threshold becomes a little greenish without an obvious change,
which the optically allowed 0–1 transitions naturally provide a owing to broad spontaneous emissions (FWHM 4 40 nm)
1
2,16
four-level scheme.
were performed by using our homemade PL setup in Scheme S2 when the optical pumping exceeds the threshold, a sharp
ESI†). Representative m-PL spectra of the selected microbelt colour change from orange (CIE = 0.54, 0.46) to green (CIE =
Optically pumped lasing measurements overlapping with each other (Fig. 3 and Fig. S9, ESI†). However,
(
with width W = 10.3 mm and L = 19.4 mm at different pump 0.39, 0.61) occurred, consistent with the strong laser emission
densities (P) are shown in Fig. 3c and Fig. S9 (ESI†). With the with FWHM o 10 nm centered from 585 nm to 560 nm.
increase of pump intensity, the PL intensity of the 0–1 transition Moreover, they all exhibit two impressive spots on the two end
at 585 nm was dramatically amplified and strong laser emissions facets along the length of the MBs, which is a typical characteristic
2
emerge as a set of multiple sharp peaks with a spacing of of FP type resonators with nearly all the electric field |E|
Dl = 1.18 nm. Simultaneously, the PL spectra become sharp intensities limited inside on the surface of four edges of MBs
peaks with FWHMs from 40 nm to 8 nm. The integrated (Fig. S10, ESI†). For the FP-type resonance, the mode spacing
2
intensities of the 0–1 peaks as a function of P show clearly a (Dl) at l is given by equation, Dl = l /2Lꢀ[n ꢁ l(dn/dl)], where
ꢁ
2
threshold at Pth = 12.8 mJ cm
.
[n ꢁ l(dn/dl)] is the group velocity refractive index. As shown in
Considering the sensitivity to the HCl molecule of OPV-DMBA, Fig. 3g and Fig. S11 (ESI†), two plots of the mode spacing Dl at
we study the chemically tunable microlasers utilizing a gas l = 585 nm for MBs (yellow line) and l = 560 nm for MB@HCl
flowing system based on a confocal dish (Fig. 3a). As shown in (green line) versus 1/L of the length of the MBs, respectively,
Fig. 3b, after adding a small amount of HCl vapor (Z10 ppm), the demonstrate a clear linear relationship. Moreover, the group
MBs on the glass substrate exhibit a maximum emission blue- refractive index [n ꢁ l(dn/dl)] at 585 nm and 560 nm were
shifted to 560 nm. The ion chromatography results show that the calculated to be 7.73 and 7.53, respectively. Moreover, the
+
ꢁ
mole fraction of OPV-DMBA ꢀHCl in MBs@HCl is B0.03, which morphology of the microbelts also remains the same after
+
ꢁ
verifies the formation of a unilayer of DMBA ꢀHCl on the surface exposure to HCl (Fig. S12–S14, ESI†). However, the laser switch
MBs might be achieved through the competition light amplifi-
cation from the two kinds of gain medium.
Fig. 4a exhibits the evolution of the laser emission spectra of
MBs above the threshold after a small amount of HCl vapor was
injected into the confocal dish. Initially, the orange MB shows a
periodic interference laser peak at 585 nm with a ratio of the
intensity at 560 nm and 585 nm I560/I585 = 0.0015 ꢃ 0.0002.
When the exposure time was increased to 1–3 s, the competition
between two gain media would happen, and two laser peaks can
simultaneously emerged. And, the band at 585 nm was quenched
with the increase of the laser peak intensity at 560 nm. Upon
increasing the exposure time to 5 s, the competition would
disappear and only a single 560 nm laser peak exists with
I
560/I585 = 400 ꢃ 50, which means that the much narrower laser
emissions above the lasing threshold generate an intensity
contrast ratio 410 . At the same time, the PL images of the
5
Fig. 3 (a) Schematic of the microlaser sensor measurement. (b) Relative
PL spectra of a single MB (orange line) and MB@HCl (green line) placed on
a glass substrate below the threshold. (c and d) PL spectra of a single MB (c)
and MB@HCl (d). (e and f) The integrated area of the 0–1 peak for MB (e)
and MB@HCl (f) as a function of pump density. (g) The mode spacing Dl
at l = 585 nm for MBs (orange) and 560 nm (green) for MB@HCl versus 1/L.
The scale bar is 10 mm.
Fig. 4 (a) Wavelength shift from to 585 nm to 560 nm of the microlaser
with the different exposure times after adding HCl vapor. The scale bar is
5 mm. (b) Cyclic switch of the microlaser wavelength.
8
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microbelts exhibit a gradual color change from orange to green Imaging Technology, the Ministry of Science and Technology of
Fig. 4a and Fig. S16, ESI†). Considering the change in the China (Grant No. 2013CB933500 and 2017YFA0204503).
(
I560/I585 ratio for PL spectra to be about 8 (Fig. 3b), the on–off
ratio of our tunable microlasers is 4 orders of magnitude greater
than that of the PL sensor.
Conflicts of interest
Using the Gaussian03 programs at the B3LYP/6-31G** level,
the energy change containing zero-point vibrational energy
There are no conflicts to declare.
+
ꢁ
in the OPV-DMBA + HCl - OPV-DMBA ꢀHCl gas phase is
ꢁ
1
Notes and references
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organic microcrystal laser switch is realized through a new
chemical reaction tunable mechanism based on OPV-DMBA
1
1
3
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2
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3
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under several continuous chemical gas treatments, making them
attractive in high-throughput chemical and biological sensing
applications.
This work was supported by the National Natural Science
Foundation of China (Grant No. 91333111, 21503139 and
2
2
2
2
(
1673144), the Beijing Natural Science Foundation of China
Grant No. 2162011), High-level Teachers in Beijing Municipal
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for Sci-Tech Innovation-Fundamental Scientific Research Funds
025185305000/210), Youth Innovative Research Team of Capital
Normal University, and Beijing Advanced Innovation Center for
(
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This journal is ©The Royal Society of Chemistry 2019
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