Multifunctional Material with Efficient Optoelectronic Integrated

Nov 13, 2017 - The preparation process of the thin film could be described as ... 293 and 433 K on a Rigaku Saturn 724 diffractometer with Mo Kα radi...
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Multifunctional Material with Efficient Optoelectronic Integrated Molecular Switches Based on a Flexible Thin Film/Crystal Chang Xu, Wan-Ying Zhang, Qiong Ye,* and Da-Wei Fu* Ordered Matter Science Research Center, Jiangsu Key Laboratory for Science and Applications of Molecular Ferroelectrics, Southeast University, Nanjing 211189, P. R. China

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S Supporting Information *

ABSTRACT: Switchable materials, due to their potential applications in the fields of sensors, photonic devices, digital processing, etc., have been developed drastically. However, they still face great challenges in effectively inducing multiple molecular switching. Herein organic− inorganic hybrid compounds, an emerging class of hydrosoluble optoelectronic-active materials, welcome a new member with smart unique optical/electrical (fluorescence/dielectric) dual switches (switching ON/OFF), that is, [C5H13NBr][Cd3Br7] (1) in the form of both a bulk crystal and an ultraflexible monodirectional thin film, which simultaneously exhibits fast dielectric/fluorescent dual switching triggered by an optical/thermal/electric signal with a high signal-to-noise ratio of 35 (the highest one in the known optical/dielectric dual molecular switches). Additionally, the exceptional stability/fatigue resistance as well as the fantastic extensibility/compactness of thin films (more than 10000 times folding over 90°), makes 1 an ideal candidate for single-molecule intelligent wearable devices and seamlessly integrated optoelectronic multiswitchable devices. This opens up a new route toward advanced light/ electric high-performance switches/memories based on organic−inorganic hybrid compounds.

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INTRODUCTION Switchable materials, which undergo a convertible transition between high and low states (switching ON/OFF) under external stimuli (thermal/optical/electric), have captured increasing interest.1−6 Among them, the multifunctional switching materials, which enable the realization of a seamless integration of electricity, photoelectricity, and magnetoelectricity on a single device, have enormous potential to be applied in electronic devices that are used for sensors, switches, signal processors, photoelectronic devices, etc.7−18 However, owing to the serendipity and complexity of the preparation process, the realization of the light-emitting characteristic in a multifunctional switch is a really big challenge, particularly those that can be prepared as ultraflexible thin films.19−22 Accordingly, enormous previous studies on multifunctional switching have recently been extended to optoelectronic-active materials based on organic−inorganic hybrid compounds. Molecule-based optoelectronic-active materials have the ability to be single-molecule intelligent ultraflexible wearable devices and seamlessly integrated optoelectronic multiswitchable devices for future applications.23−27 It must be noted, nevertheless, that most researches on photoelectric materials based on organic−inorganic hybrid compounds focused on a lead-based series, which possess prominent advantages over traditional inorganic ceramics (such as efficient energy, controllability, flexibility, easiness in the fabrication of thin films, large crystals, and so on).28−34 Nevertheless, in spite of these fascinating prospects, the lead-based series still suffers from high toxicity and environmental contamination.35−39 Undoubtedly, the lead-free photoelectric/thermal materials © 2017 American Chemical Society

turn out to be the global research focus in this interesting and challenging frontier field. Recently, our group has carried out a series of work to fabricate lead-free photoelectric switchable materials, such as a dielectric/fluorescent switch, a thermal sensor switch, a photoelectric/thermal functional switch, and so on.40−45 In comparison, the switchable materials with switchable optical and dielectric behavior at high temperatures are rarely reported, especially those with a typical two-dimensional (2D) hybrid structure. Herein, the molecular switchable material with high Tc (phase transition Tc = 414 K) was successfully synthesized and prepared as an ultraflexible and monodirectional thin film and bulk crystal. It exhibits film-forming characteristics and rapidly tunable optoelectronic activity. What is more, by doping a certain amount of relatively low toxicity Mn2+ ions, we successfully make 1 exhibit novel dielectric luminescent multifunction−integration characteristics, which displays unique simultaneously switchable bistability in double channels of dielectric and fluorescence. This mechanism is dissimilar to that of the precedent switching materials, which affords a potential avenue to design the new multifunctional optoelectronic devices. In summary, our pioneering work, which combined the dual switchable properties (dielectric and luminescence) and structural phase transition into a single unit, opens up a new route toward advanced light/electric highperformance switches/memories based on organic−inorganic hybrid compounds. Received: August 10, 2017 Published: November 13, 2017 14477

DOI: 10.1021/acs.inorgchem.7b02055 Inorg. Chem. 2017, 56, 14477−14485

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Figure 1. (a) Photograph of the transparent flaky crystal 1. (b) DSC curves of heating−cooling cycles from RTP to HTP. (c) XRD patterns of the ITO substrate and a thin film deposited on the ITO substrate at 293 K. The strong diffraction peaks at (0, 1, −1), which match well with the simulated crystal diffraction, disclosed the uniaxiality of these thin films. (d) Four-layer dense thin films successively deposited on the substrates layer-by-layer, with each layer deposited separately with a uniform thickness of 10 nm. (e) AFM scanning, as strong evidence of uniform morphology and controllable fabrication of a thin film. (f) Flexible thin film on the PET substrate under an external force.

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anisotropically using all reflections with I > 2σ(I). All H atoms were generated geometrically and refined using a “riding” model with Uiso(H) = 1.2Ueq(C or N). The CrystalClear software package (Rigaku, 2005) was used for data processing including empirical absorption corrections. The asymmetric units and packing views were drawn with DIAMOND. The selected bond distances and angles were calculated by DIAMOND and SHELXLTL. Crystallographic data and structure refinements at 293 and 433 K are listed in Table S1. Differential Scanning Calorimetry (DSC) and Dielectric Measurements. DSC measurements were performed on a PerkinElmer Diamond DSC instrument by heating and cooling the polycrystalline samples in the temperature range 340−440 K under nitrogen at atmospheric pressure in aluminum crucibles with a heating rate of 5 K min−1. The powder-pressed pellets with carbon glue painted as electrodes were used for dielectric studies. The dielectric permittivity ε (ε = ε′ − iε″) of 1 was measured on a Tonghui TH2828 instrument over the frequency range from 1 kHz to 1 MHz in the temperature range from 350 to 430 K with an applied alternatingcurrent (ac) electric field of 1 V. IR Spectrum and Powder XRD (PXRD) Measurement. IR measurement was performed on a Shimadzu model IR-60 spectrometer at room temperature, with the sample prepared as KBr diluted pellets (Figure S1). The variable-temperature PXRD data of 1 were measured with a PANalytical X’Pert PRO X-ray diffractometer over the temperature range of 293−443 K. The diffraction pattern was collected in the 2θ range of 5−50° with a step size of 0.02°. At roomtemperature phase (RTP) and high-temperature phase (HTP), the PXRD patterns of 1 and Mn-doped 1 coincide fairly well with the patterns simulated from single-crystal structures, which indicates phase purity (Figure S4).

EXPERIMENTAL SECTION

Preparation of Crystals and Thin Films. All of the analyticalgrade chemicals and solvents were purchased from Aladdin and used as received. For the synthesis of [C5H13NBr][Cd3Br7] (1), CdBr2· 4H2O (6.0 mmol) was added to a mixed solution of (2-bromoethyl)trimethylammonium bromide (1.0 mmol) and 40% HBr (1.0 mL) in water and acetonitrile (1:1) under stirring. Colorless crystals appropriate for X-ray crystal structural analysis were easily obtained by slow evaporation of the mixed solution at room temperature within 2 months. For the doping product, CdBr2·4H2O (5.0 mmol) and MnBr2·4H2O (1.0 mmol) were added to a mixed solution of (2bromoethyl)trimethylammonium bromide (1.0 mmol) and 40% HBr (10.0 mL) under stirring. Pink crystals that are appropriate for X-ray crystal structural analysis were easily obtained by slow evaporation of the mixed solution at 323 K in an oven within 1 month. Transparent thin films of 1 were successfully prepared by a convenient and inexpensive spin-coating method with a rotary speed of 6000 rpm. The preparation process of the thin film could be described as follows: first, the pure flaky crystals were dissolved in N,N-dimethylformamide via a microwave to form a solution with a concentration of 0.0765 mol L−1. Then, the above-mentioned solution was carefully repeatedly deposited on an indium−tin oxide (ITO)/ poly(ethylene terephthalate) (PET) substrate to form four-layer thin films. Finally, for further measurements, the grown films were dried at 60 °C.42,46 Crystallography. Variable-temperature single-crystal X-ray diffraction (XRD) data of compound 1 were collected at 293 and 433 K on a Rigaku Saturn 724 diffractometer with Mo Kα radiation (λ = 0.71073 Å). Crystal structures were solved by direct methods and refined with a full-matrix method based on F2 by means of the SHELXLTL software package. All non-H atoms were refined 14478

DOI: 10.1021/acs.inorgchem.7b02055 Inorg. Chem. 2017, 56, 14477−14485

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Figure 2. (a) Molecular structures of compound 1 at RTP and HTP. At HTP, the C5H13NBr+ cations displayed a disordered feature (in the red circle), while at RTP, the disordered C5H13NBr+ cations were frozen (in the blue circle). All H atoms were omitted for clarity. (b) Twisted inorganic anion/metal skeleton basic unit at RTP and HTP. The four quadrilateral voids formed by four neighbor bridging Cd atoms, while other atoms were omitted for clarity. (c) Perforated network of 1. The elliptical part shows the location of a single disordered cation, while other atoms were omitted for clarity. (d) At HTP, the flexible bromoethyl of the cation that undertook the arduous task of interesting pendulum-like motions, which may be the main driving force of a switchable phase transition. The disordered organic cation embedded in the free space between two consecutive inorganic [Cd3Br7]−n layers. Other atoms were omitted for clarity. The pendulum is the original and does not involve any copyright issues.

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RESULTS AND DISCUSSION Thermal Properties of 1. To confirm the temperaturetriggered phase-transition behavior, thermal analysis was a very efficient way. The DSC curve of 1 displayed double peaks of reversible heat anomalies at 414 and 391 K upon heating and cooling processes, respectively, indicating the existence of a reversible phase transition with a high Tc of 414 K (Figure 1b). The sharp shape of the anomalous peaks with wide thermal hysteresis (about 23 K) shows that this phase transition was more in line with the first-order type.47−49 On the basis of the DSC curves of compound 1, the average enthalpy change ΔH (1) was estimated to be 1.068 kJ mol−1. According to the entropy change ΔS = ΔH/Tc, ΔS (1) was determined to be 2.579 J mol−1 K−1. On the basis of the Boltzmann equation ΔS = R ln(N), where R is the gas constant and N is the ratio of the number of respective geometrically distinguishable orientations, the calculated value of N (1) was 1.36, which was consistent with the ordered/disordered-type character of the transition. For a convenient description, we label the phase of 1 above 414 K as the HTP and the phase below 414 K as the lowtemperature phase (LTP). Controlled Preparation of Thin Films. In Figure 1d, fourlayered dense thin films were successively deposited on the substrates layer-by-layer, and each layer can be deposited separately with a uniform thickness of 10 nm. The thin film with ideal film-forming controllability and advanced properties, likely, is a thoroughly reliable material to show the sign of its

true genius as a miniaturized integrated ultraflexible device. This may provide a quick and accurate way of controlling and monitoring the desirable features in the preferred thickness on the basis of variable device requirements. As strong evidence that testifies to the uniform morphology and controllable fabrication of thin films, both atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements were implemented. After each layer was deposited, the uniform film thickness was clearly captured by AFM scanning. Eventually, each layer can be controllably prepared and shown the same thickness of 10 nm and uniform morphology (Figures 1e and S3b) What is more, the XRD results indicated that the thin film shows only the apparent (0, 1, −1) reflection located at around 10°, which matches fairly well with the simulated results from single-crystal data (Figure 1c). We slightly smoothed the XRD curves because of the large fluctuation of the baseline. Hence, we could explicitly conclude that we obtained a highly oriented thin film.42,50 Also, this unidirectional and compact thin film retains the structural retention characteristics after at least 10000 times folding over 90°, which signifies its potential in ultraflexible devices (the ultraflexibility is shown in Figure 1f). Structure Analysis of Compound 1. For single crystals with the optoelectronic-switch characteristic, a bistable structural transformation between ordered (switching OFF) and disordered (switching ON) states was usually one of the preliminary requirements. Therefore, in order to explore the 14479

DOI: 10.1021/acs.inorgchem.7b02055 Inorg. Chem. 2017, 56, 14477−14485

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Figure 3. (a) View of the parallel-plate capacitor electrode and schematic illustration of the dielectric measurement mechanism. (b) Real (ε′) and imaginary (ε″) parts of the dielectric permittivity at 1 MHz on the heating−cooling cycle for the polycrystalline sample. (c) Temperature dependence of the real part (ε′) of the polycrystalline samples of 1 at 5 kHz, 10 kHz, 100 kHz, and 1 MHz upon cooling. (d) ε′ switching of compound 1, which is completely reversible without any fatigue after several ON/OFF cycles at 1 MHz. Only six cycles are shown for clarity.

84.54(4)° to 178.35(3)° (Table S2). These values are in good agreement with those reported for Cd−Br-containing compounds.51−55 The asymmetric unit of 1 at 433 K contained one independent (2-bromoethyl)trimethylammonium cation, three Cd atoms, and seven Br atoms, the same as that in the RTP. The Cd1−Br bond lengths were in the range of 2.539(2)− 3.211(3) Å and the bond angles of Br−Cd−Br varied from 84.13(4)° to 178.81(3)°, while the Cd2 and Cd3 atoms with the Cd−Br distances ranged from 2.717(2) to 2.948(2) Å and the bond angles of Br−Cd−Br varied from 83.36(5)° to 174.27(3)°, which shows slight changes. Different from the case for an inorganic layer, the motional state of (2-bromoethyl)trimethylammonium cations showed an obvious change compared to that of the RTP. They became orientationally disordered over two positions with 0.5 occupancies for the C4− C5−Br1 chain in the cation. In addition, the bond lengths and angles of the cation also changed significantly; for example, the bond angles were 117.7(11)°, 99.9(8)°, 120.4(7)°, and 112.3(7)° for N1−C4−C5, C4−N1−C3, C4−N1−C1, and C2−N1−C3, respectively. Except for the disorder of the cation, the alternating inorganic−organic-layered structure was preserved at the HTP (Figure S6). What is more, the idiographic structure of 1 was based on ribbons comprised of two infinite chains of corner-sharing CdBr6 octahedra, and the edges of these ribbons had “fringed” edges consisting of a CdBr5 trigonal bipyramid, giving rise to a rarely seen perforated 2D network (Figure 2c). Besides, one layer of cations was embedded in the free space between two consecutive inorganic [Cd3Br7]−n layers, forming an alternating organic−inorganic-layered structure (Figure S6). Origins of Phase Transitions of 1. The switching materials usually possess a bistable molecular motion between

mechanism of molecular-based switching as well as adjust and optimize the switching performance accordingly, precise analysis of the bistable structure at 293 and 433 K was performed according to the results of variable-temperature Xray structure determinations (Table S1). Fortunately, the ordered/disordered state of the pendulum-like motion of the cation was confirmed to match well with the optical/electric switching ON/OFF states and DSC measurement results. Like the characteristics of the switch material, 1 exhibits two structural phases, that is, RTP below Tc and HTP above Tc. At 293 K (RTP), 1 crystallized in the triclinic crystal system P1̅ (No. 2). Crystallographic data are given in CCDC 1544419. Upon heating to 433 K (HTP), the space group of 1 was maintained, but the cell parameters displayed a difference from those in the RTP (Table S1). Crystallographic data are given in CCDC 1544420. The asymmetric unit of 1 at 273 K consisted of one independent (2-bromoethyl)trimethylammonium cation, three Cd atoms, and seven Br atoms (the molecular structures are shown in Figure 2a). For the cation, because of the decline of thermal perturbation, the bistable pendulum-like motions of the cation were frozen, with bond angles of 113.3(8)°, 97.1(6)°, 114.3(7)°, and 113.8(8)° for N1−C4−C5, C4−N1−C3, C4−N1−C1, and C2−N1−C3, respectively. The Cd atoms show two coordination modes: for Cd1, a distorted trigonal bipyramid is presented, while both Cd2 and Cd3 are distorted octahedra. The octahedra surrounding Cd2 and Cd3 were connected through the Br bridge, with the Cd−Br distances ranging from 2.7065(14) to 2.9308(12) Å and the bond angles of Br−Cd−Br varying from 83.52(4)° to 174.01(4)°. Each Cd1 bipyramid was connected to Cd2 and Cd3 octahedral chains at the Br1−Br3 edge to give a layered structure, with Cd−Br distances ranging from 2.5491(12) to 3.1649(15) Å and bond angles of Br−Cd−Br varying from 14480

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Figure 4. (a) Crystals and powder of Mn-doped 1 under sunlight and UV light, showing a strong red-light emission. (b) Emission spectra of 1 at 303 K (switch “ON” at room temperature) and 463 K (switch “OFF” at high temperature) under an excitation wavelength of 370 nm. (c) Bistable PL switch triggered by the temperature (switch “ON” for the high-intensity state/room temperature state and switch “OFF” for the low-intensity state/ high temperature state). (d) Schematic diagram of the luminescent intensity switching “ON”/“OFF” cycles based on compound 1, which crisply indicates that the PL intensity of 1 can recover rapidly without any obvious fatigue after several continuous cycles.

transition of this photoelectric multifunctional switch from the RTP to the HTP. PXRD measurements were performed from 303 to 443 K, which also indicates the existence of a structural transition (Figure S5). Dielectric Properties of 1. The characteristic of dielectric switching is just electric-dipole bistability (high dielectric state ON/1 and low dielectric state OFF/0) triggered by a thermal/ electric signal. In order to fully express the switching mechanism of the dielectric switch and further confirm the occurrence of a phase transition, variable-temperature dielectric permittivity measurements were performed on pressed-powder polycrystalline samples at select frequencies. As shown in Figure 3b, the real part (ε′) of the dielectric permittivity of 1 shows two obvious reversible steplike anomalies at around 414 K (heating mode) and 391 K (cooling mode) in the temperature range of 350−425 K. In the heating mode at 1 MHz, the dielectric constant remains stable with a value of 6.4 from 350 to 414 K, which represents the low dielectric state. As the sample is heated further, ε′ displays striking increases to a maximum value of about 15 at 413 K and thereafter exhibits a plateau with a slight increase, which represents the high dielectric state. The dielectric loss (ε″) also displays clear steplike anomalies during the heating and cooling processes at 1 MHz, which further confirms the occurrence of a phase transition. In addition, the temperature-dependent measurements of ε′ upon cooling at 5, 10, 100, and 1000 kHz are shown in Figure 3c, which also displays steplike anomalies in the vicinity of 391 K. It is obvious that 1 was sensitive to the external frequencies and gradually exhibited a frequency-

the ordered and disordered states. Thus, with the purpose of finding a compound exhibiting the switching characteristic, through the deliberate selection of flexible organic cations, we successfully designed a smart optielectric integrated switch, [C5H13NBr][Cd3Br7], which owns optical/electric dual switching. According to our previous work,19−21 the organic cations own a flexible bromoethyl chain, which could make interesting pendulum-like motions at the HTP (Figure 2d). More specifically, the motional state of the (CH3)3NCCBr cation exhibits a notable difference between the RTP and HTP. At the HTP, the (CH3)3NCCBr cation was orientationally swung over two positions. With the temperature decreasing, the dynamic pendulum-like thermal motion of the (CH3)3NCCBr cation was frozen, and every (CH3)3NCCBr cation was totally ordered56 (Figure 2a). This motion mode matched well with the optical/electric switching ON/OFF states. Besides, the comparatively weaker hydrogen-bonding interactions unlock more freedom for the dynamical motion of the cations.48,57 Through precise analysis of the main packing and structural differences between the RTP and HTP, we found that the degrees of distortion for [CdBr6] octahedra and [CdBr5] bipyramids at the two temperatures were different and the distances between adjacent layers also changed from 9.1726(27) Å (RTP) to 9.3293(59) Å (HTP), which indicates a slight distortion in the [Cd3Br7]−n network (both the Br− Cd−Br and Cd−Br−Cd angles were changed; Figures 2b and S6). Thus, we could conclude that the ordered/disordered transition of the cations as well as distortion of the [Cd3Br7]−n network might be the main driving force for the phase 14481

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compound 1 was also estimated, and a result of 9% was confirmed. Besides, as shown in Figure 4d, the luminescent intensity switching was also performed to test the reversibility of the powder sample 1. After several “ON”/“OFF” cycles, the luminescent intensity of 1 can remain stable and no valuable damping appears on the measurement process, which is consistent with the dielectric constant (ε′) switching process. The perfect features of reversibility/antifatigue as well as a higher signal-to-noise ratio of luminescent and dielectric switching further demonstrate that 1 is a promising optoelectronic simultaneous multifunctional switching material, which would ameliorate the current shortage of optical coatings and semiconductor devices. Molecular Photoelectric Multifunctional Switch and Mechanism. The optical/electric dual switching mechanism of this molecular-based optoelectronic multifunctional material under an external signal is simulated in Figure 5a. Specifically, under continuous thermal stimulation, the optical/electric signals would reach a critical point, and as a result, the switch would automatically receive and decode signals and convert

independent character with increasing frequencies. Furthermore, extrusive dielectric relaxation was not observed around the phase transition temperature, which could be interpreted as a relatively fast dipolar motion. Such a distinct dielectric change between the high- and low-temperature states makes 1 an excellent candidate for switchable dielectric materials. The reversibility of dielectric switching was also investigated on the single-crystal parallel-plate capacitors (Figure 3d). The dielectric switching ON/OFF (1/0) can be manipulated in the bulk crystal or unidirectional film capacitor by applying an external ac electric field, which shows a high signal-to-noise ratio of 35 and strong fatigue resistance (exceeding all of the known molecular switching materials). The switching characteristics and flexible thin films have been vested with significant power as promising switchable functional materials in the modern advanced information industry. Optical Switchable Properties of 1. Luminescence of solid-state materials is an important optical property that has many valuable applications.25,44,58−60 Also, because of the existence of a luminous activator Mn2+ (3d5) ion, the Mn compounds could give off red or green light depending on their coordination environment. What is more, the Mn2+ ions in octahedral coordination usually give off red light, while those with a tetrahedron tend to emit green light.41,45 However, the molecular optical (red fluorescence) switches caused by the structural phase transition are rarely reported, especially those simultaneously possessing striking dielectric switching. What is more, it can be controllably fabricated into thin films. So, in order to promote the applications of 1 in multifunctional optoelectronic materials by combining the merit of luminescence and dielectricity into a single molecule, we introduced luminescent ions by doping. Intriguingly, the Mn-doped pink powders emit red light when illuminated by an UV lamp (Figure 4a). As depicted in Figure 4b,c, the emission spectrum of 1 shows an evident bistable characteristic between the RTP (switching ON) and the HTP (switching OFF). After excitation of the powders at 370 nm, the emission spectrum of the powder sample changed significantly between the RTP (303 K) and the HTP (463 K). At the RTP (303 K), one relatively strong emission could be observed at 530 nm, which is associated with the transition of Mn2+ ions, while at the HTP (463 K), no obvious emission peak was detected and the photoluminescence (PL) intensity was almost the same as that of the noise. Also, because of fluctuation of the baseline, the PL emission curve at 463 K is slightly smoothed. Moreover, the PL intensity at 303 K is about 35 times higher than that at 463 K. The huge intensity differences indicate evident molecular optical bistable switches accompanied by the occurrence of a structural phase transition, which could further be confirmed by peak value changes of the PL intensity in the heating process shown in Figure 4c. With an increase of the temperature, the PL intensity decreases and also displays a steplike switch at around 413 K, which is consistent with the dielectric switch and shows its optical bistable property in the two phases (switch “OFF” for the low emission peak intensity and switch “ON” for the high emission peak intensity). In detail, the optical switching can be attributable to the cations’ movement. At the HTP, the energy loss of the vigorous cations’ thermal motion weakened the intensity of the emission spectrum, which represents the switch “OFF” states, while the disordered cations are frozen into ordered states at the RTP, which represents the switch “ON” states. The luminescence quantum yield of

Figure 5. (a) Diagram of the optical/electric integrated bistable switching mechanism. The pendulum-like motion of the organic cations with the flexible bromoethyl chain arouses this optoelectronic switch to reach a switching ON or OFF state. (b) Simulated application of the optical/electric integrated multifunctional switch in a thermal sensor. The blue circle indicates the mechanism of the optical/electric integrated molecular-based switch. Under a thermal/ optical/electric stimulus, the switch would automatically identify external signals and rapidly reach switching “ON”/“OFF” states, so as to realize the integrated automatic control of a single channel or multiple channels. 14482

DOI: 10.1021/acs.inorgchem.7b02055 Inorg. Chem. 2017, 56, 14477−14485

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Inorganic Chemistry rapidly from an “ON”/“OFF” state to an “OFF”/“ON” state. Moreover, the potential application of the optical/electric integrated switch in a thermal sensor is also depicted in Figure 5b. In particular, this smart material, which exhibits intelligent dielectric/optical switching under integration of a singlemolecule module of optical/thermal/electric triple controllable modules, could be fabricated into an ultraflexible thin-film device. Furthermore, this multifunctional material, which combines the effect of thermosensitive/photosensitive/electroresponse into a single-molecule sensitive synchronous photoelectric signal-responsive mode and could switch to fully automatic depending on the different physical environments and execute single/dual-channel selective response according to different environmental stimuli, laid the foundation for singleand dual-channel conversion. For instance, various wavelength stimulations would produce various optical signals, and the change of the electrical stimulation frequency would lead to a change of the dielectric signal intensity; meanwhile, the optical/ electric signals can also be rapidly switched simultaneously by a temperature control system. Moreover, the ultraflexible and unidirectional thin film, fabricated by a convenient/inexpensive spin-coating method, corresponded well with the photoelectric property test, which provided practicability for the minimized and integrated production of module devices. Therefore, this molecular-based optoelectronic multifunctional material, which fully demonstrated its excellent character as a flexible photoelectric switching device, would play an increasingly prominent role in promoting the application of intelligent integrated optoelectronic devices.

Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Qiong Ye: 0000-0002-3532-5388 Da-Wei Fu: 0000-0003-4371-097X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by Project 973 (2014CB848800), the National Natural Science Foundation of China (21422101, 21673038, and 21511140093), the Jiangsu Province NSF (BK20140056), and a research fund of SEU. Also, we greatly appreciate the reviewers for their helpful discussion and constructive suggestions on the substantial improvement in the quality of this work.

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CONCLUSION In conclusion, we have successfully synthesized and characterized a unique 2D-switchable optical/electrical integrated material, [C5H13NBr][Cd3Br7] (1), which underwent a fluorescence/dielectric bistable switching (switching ON/ OFF) at around 413 K. On the basis of structural analysis at the HTP and RTP, the reversible phase transition of 1 originated from the ordered/disordered transition of the cations. Moreover, the ultraflexible and monodirectional transparent thin film of 1 was also prepared through a facial/ environmentally friendly spin-coating approach. Such a perfect optical/electrical switching performance of 1 indicated that it would be an excellent candidate for the switchable optoelectronic devices and bring light to the development of the newly multifunctional integrated optoelectronic materials.

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AUTHOR INFORMATION

Corresponding Authors

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02055. IR spectrum, TGA curves, phenogram of thin-film properties, PXRD patterns, and crystal-packing views (Figures S1−S6, respectively), crystallographic data and refinement parameters (Table S1), and bond lengths and angles (Tables S2 and S3) (PDF) Accession Codes

CCDC 1544419−1544420 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The 14483

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