D–A–D Structured Bis-acylhydrazone Exhibiting Aggregation-Induced

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Cite This: J. Org. Chem. XXXX, XXX, XXX−XXX

D−A−D Structured Bis-acylhydrazone Exhibiting Aggregation-Induced Emission, Mechanochromic Luminescence, and Al(III) Detection Kuppusamy Santhiya,† Shovan K. Sen,‡ Ramalingam Natarajan,‡ Ramasamy Shankar,§ and Balasubramanian Murugesapandian*,† †

Department of Chemistry, Bharathiar University, Coimbatore 641 046, India Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical Biology 4 Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India § Department of Physics, Bharathiar University, Coimbatore 641 046, India

J. Org. Chem. Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 09/06/18. For personal use only.

‡

S Supporting Information *

ABSTRACT: A readily accessible D−A−D triad molecule 1 was synthesized through acylhydrazone bond formation using carefully chosen building blocks. The molecule 1 exhibits emission through charge-coupled proton transfer and enhanced emission induced through aggregation and mechanochromic luminescence. Further, it detects Al(III) selectively among other cations in an efficient manner.

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INTRODUCTION Tremendous interest has been devoted to developing novel luminescent materials with diverse functionalities in recent years.1−4 These materials have been associated with a major problem, aggregation caused quenching (ACQ). In 2001, Tang’s group first discovered a contrasting phenomenon, compared to characteristics of ACQ effect, called aggregationinduced emission (AIE). AIE materials display less or weak emission in the solution state, whereas they show intense emission in the aggregated state.5−7 Mechanochromic luminescent materials are molecules that undergo morphological changes with concomitant change in photophysical properties while applying the external stimuli such as pressure or grinding. Recently, the research community has put more effort toward the synthesis of new AIE-active mechanochromic materials due to their practical application in various fields.7−10 Al3+ ions play a crucial role in day-to-day life. Because of their widespread applications, a considerable amount of Al3+ ions have been accumulated in environment, causing water contamination. Detection and monitoring of the concentration of Al3+ ions in the biosphere is an essential task. Furthermore, designing a multifunctional molecule with AIE characteristics that also displays fluorescence responses for Al3+ is of current interest.11−13 In this regard, we designed and synthesized a new (diethylamino)phenol-functionalized pyridine-2,6-bisacylhydrazone (1) with a donor−acceptor−donor configuration and examined its photophysical properties. The results show that 1 has mechanochromic and AIE characteristics and can function as a “turn-on” fluorescent sensor for Al3+ ion. © XXXX American Chemical Society

RESULTS AND DISCUSSION The luminophore 1 was designed and synthesized by the condensation reaction between pyridine-2,6-dicarbohydrazide and 4-(N,N-diethylamino)salicylaldehyde in quantitative yield (Scheme 1). Scheme 1. Synthesis of 1

Photophysical Properties. The newly synthesized compound 1 contains strong donor−acceptor−donor (D−A−D) unit as well as a proton transfer moiety, and the emission behavior of this kind of molecules is dominated by combination of three states such as locally excited state (LE), intramolecular charge-transfer state (ICT), and excited-state intramolecular proton transfer (ESIPT). To validate the emission mechanism in 1, the photophysical properties were measured in different solvents with varying polarities, and the results are shown in Figures S4 and S5. The molecule exhibits dual fluorescence emission in different solvents [10 μM] Received: June 1, 2018

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DOI: 10.1021/acs.joc.8b01377 J. Org. Chem. XXXX, XXX, XXX−XXX

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The Journal of Organic Chemistry

The lifetime was measured for aggregate in THF/water [10 μM] (fw = 30%), and it displayed two lifetimes, i.e., τ1 = 0.94 (90.96) and τ2 = 4.46 (9.04). These lifetimes are longer than those observed in neat THF. Finally, in the aggregated state, the possibilities of ICT/ESIPT become more favorable, and as a result, the intensity of CPT band increases upon aggregation. In the CH3CN/water mixture also, 1 undergoes AIE behavior (Figure S10). The photographic images of 1 in THF/water and CH3CN/water mixture under a UV lamp also confirm the AIE characteristics of 1 (Figure 1C and Figure S10). In highly soluble solvents, 1 exhibits weak emission in the longer wavelength region due to the presence of a free rotatable N−N single bond in 1, which obliterates the excited state by nonradiative emission and leads to weak or nonemissive behavior. In a higher water fraction, 1 starts to form aggregates which restrict the intramolecular rotations (RIR) about the N−N single bond and shows intense emission.18 The above results reveal that the RIR process may be responsible for AIE effects in 1 in addition to the CPT process in the aggregated state. Further, emission measurements in glycerol/THF and water/ THF mixtures (Figure S11) confirm that the RIR mechanism is present in this compound. In addition, aggregate formation was affirmed by dynamic light scattering (DLS) and FESEM measurements. DLS results reveal that the particle size of aggregates increases with increasing water fractions in the THF/ water mixture (Figure S12). FESEM images of 1 (Figure S13) clearly indicate the morphological changes occurring between crystalline and aggregates state of 1. Mechanochromic Luminescent Behavior of 1. Mechanochromic luminescent properties of 1 were scrutinized for the crystal in the pristine and ground states. The solid-state emission spectra of the single-crystal and pristine states exhibit peaks at 496 and 515 nm, respectively, with weak intensity.22 On the contrary, grinding of the pristine sample with a mortar and pestle produces a highly fluorescent yellowish green solid (Figure 2), and the emission spectrum of the ground sample

(Figure S5). The shorter wavelength peaks were assigned to the locally excited state, which is due to fast decay and vibrational signatures of molecule. The broad longer wavelength peak may be due to the ICT or ESIPT or both processes, since this molecule contains both a charge donor −N(C2H5)2 group (can contribute ICT) and an −OH group (can contribute ESIPT). In general, positive solvatochromism with high Stokes shift (Figure S6) supports ICT behavior, whereas a change in intensity (high to low) of tautomer band in nonpolar/aprotic to protic solvents supports the presence of ESIPT behavior (Figure S5b), and this behavior is due to the disruption of intramolecular hydrogen bonding through intermolecular hydrogen bonding using protic solvents.14−16 We observed both scenarios in the longer wavelength region, and it supports the presence of ICT and ESIPT in 1. It is also well-known that presence of ICT group facilitates the proton-transfer process. In addition, fluorescence lifetime measurement yielded biexponential decay with two lifetimes (Table S1). Therefore, we reason that the broad fluorescence emissions in all solvents are due to the charge-coupled proton transfer (CPT) phenomenon. The shorter lifetime is due to the intense LE emission, and the longer lifetime (∼3.5−4.6 ns, Table S1) is due to the weak CPT emission. The large energy gap of 3.168 eV was observed due to the distinction of electron distribution in the HOMO and the LUMO (Figure S7). AIE Characteristics of 1. The AIE behavior of compound 1 was studied by emission and UV−vis spectral measurements in THF/water (two different concentrations) and a CH3CN/ water solvent mixture with varying (0−90%) water fraction, and the results are shown in Figure 1 and Figures S8−S10.

Figure 2. Fluorescent photographs of pristine and ground sample under UV lamp.

Figure 1. (A) Emission spectra of 1 in THF/water mixtures [100 μM] λex = 375 nm. (B) Plots of the (I − Io)/Io value versus THF/water fraction. (C) Fluorescence photo of 1 with increasing water fractions (0−90%) under UV lamp.

shows a high intensity peak at 545 nm with a bathochromic shift of (515−545 nm) 30 nm from pristine sample (Figure S14). The quantum yield also increased from 1.2% to 18.5% upon grinding. This observation was clearly witnessed by the naked eye (Figure 2). In solid-state absorbance measurements, 30 nm wavelength shifts was observed from the pristine sample (409 nm) to the ground sample (439 nm) (Figure S15). Both pristine and ground samples show identical melting points at ∼260 °C. The stability of the ground samples was checked, and the results show that the emission behavior of the ground sample remained the same for a long time (above 10 days) and irreversible in nature. Further, the recrystallization process regenerates the original state from the ground sample. The application of shear force made a permanent deformation in the

Upon excitation at 375 nm, the compound exhibits weak emission as a broad peak around 532 nm in pure THF. When the water content was above 60%, an almost 15-fold increase in emission intensity was observed, and this enhancement of emission intensity is due to the aggregate formation (Figure 1A,B). The AIE characteristics of 1 were further confirmed by increasing the quantum yield from 0% (ϕ = 3.9%) to 80% (ϕ = 89.2%) water content in a THF/water mixture [100 μM]. The UV−vis absorption spectrum of 1 was measured in a THF/water mixture (Figure S8), and the level-off tail started to appear in the longer wavelength region when the water content exceeded 50%, confirming the formation of aggregates.17−21 B

DOI: 10.1021/acs.joc.8b01377 J. Org. Chem. XXXX, XXX, XXX−XXX

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intramolecular hydrogen bond with the imine nitrogen (CONHN), which facilitates the intramolecular proton transfer in the excited state. The two amide N−H protons involve weak intramolecular interaction with pyridine nitrogen in the solid state. In addition, 1 crystallized along with a water molecule, which is located in the cleft of 1. The water− oxygen forms hydrogen bonding with the amide N−H groups (Figure 4A). All three aromatic rings are not present in a single plane, and both (diethylamino)phenol B and C moieties are twisted to the pyridine A unit. The dihedral angle between the planes A and B is 13.743°, between A and C is 13.743°, and between B and C 26.004°. As a result, whole molecule adopts the twisted conformation in the solid state. The presence of a water molecule in the molecular structure and a free rotatable N−N single bond between the pyridine and (diethylamino)phenol moieties plays an important role for the adaptation of the twisted conformation of 1 (Figure S19). Further, the hydrogen atoms of the water molecule were involved in hydrogen bonding with carbonyl groups of symmetryrelated neighboring molecules of 1 (Figure 4B). In the crystal lattice, the (diethylamino)phenol rings B and C show the slipped stacking interaction and interplanar distance between the adjacent B rings is 3.3344 Å (Figure S20), and the distance between the centers of the adjacent ring is 7.170 Å. Further, the twisted conformation of 1 is advantageous to avoid the aggregation caused quenching by suppressing the effective π−π stacking interaction between the aromatic rings.22−24 Here, the twisted conformation of 1 and intramolecular and intermolecular hydrogen bonding play a very important role for CPT, AIE, and mechanochromic luminescent behaviors. When the external force is applied to the pristine sample, H-bonding gets ruptured in 1, as a result, emission intensity was drastically increased with a turn-on emission, and it may be due to the planarization of phenol and pyridine rings by release of twist strain, which is associated with the change in emission wavelength.25,26 Analytical Studies of 1. The metal-binding performance of 1 has been investigated by emission measurement toward Al(III), Cr(II), Fe(II), Cd(II), Zn(II), Pb(II), Ag(I), Co(II), Cu(II), Ni(II), Hg(II), and Na(I) ions. The studied were performed with their perchlorate and nitrate salts in DMF. Upon excitation at 378 nm, 1 (10 μM) exhibits broad peak around 563 nm. During the addition of different metal ions to 1, Al3+ ion shows selective sensitivity among all other metal ions (Figure 5A). Interestingly, during the Al3+ titration, 9.3-fold increments in emission intensity were observed (Figure 5B). The Job’s plot measurement reveals that 1:3 complex

regular arrangement of molecules in the ground samples.7−10,22,23 Extra support for the mechanochromic luminescent properties of 1 was acquired from powder X-ray diffraction (PXRD) and FESEM analysis in the crystalline state and ground state. The sharp and intense peaks are diminished by shear force, which is due to the demolition of ordered structure or weak interactions in the pristine sample upon grinding (Figure S16A,B). The SEM image distinctively differentiates the different morphology of 1 with and without shear force (Figure S16C,D). Both PXRD and SEM analyses confirm the mechanochromic luminescent behavior of 1. Fluorescence microscope images of 1 in crystal, pristine, and ground states (Figure 3) indicate that the ground sample

Figure 3. Fluorescence microscope images of (A) crystal, (B) pristine, and (C) ground sample.

exhibits very high yellowish green fluorescence compared to the other samples. In addition, when the edges of the single crystals were crushed or broken; astonishingly, highly emissive fluorescence was observed at the breaking corners of the crystals (Figure S16).24 Solid-State Structure of 1. The solid-state structure of the compound was carefully analyzed to correlate with the CPT, AIE, and mechanochromic luminescent behavior of 1. The molecular structure (Figure 4A and Figure S18) reveals that the (diethylamino)phenolic −OH group forms an

Figure 5. (A) Emission response of 1 (10 μM) toward different cations (10 equiv) in DMF. (B) Emission titration of 1 (10 μM) with Al3+ (1 mM stock; 0−20 equiv; each addition 40 μL = 1.3 equiv) (excitation wavelength: 378 nm). Inset: photograph of 1 before and after Al3+ addition under UV lamp.

Figure 4. (A) Molecular structure of 1. (B) Hydrogen-bonded onedimensional polymeric network. C

DOI: 10.1021/acs.joc.8b01377 J. Org. Chem. XXXX, XXX, XXX−XXX

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The Journal of Organic Chemistry formation occurs between 1 and Al3+ (Figure S21). Mass spectral analysis also confirms the 1:3 stoichiometric ratio, and it shows m/z values for [LAl3(NO3)7(CHCl3)] + 1 and [LAl3(NO3)7(CH3OH)] + 1 at 1178.7 and 1091.5 respectively (Figure S22). The comparison of the 1H NMR spectrum of 1 and 1−Al3+ (DMSO-d6) complex indicates that the phenolic −OH proton completely disappeared, and both the CO−NH amide proton and the CHN imine proton of 1 were downfield shifted as compared to the probe 1. Further, the broadening of the aromatic region in the 1−Al3+ complex indicates that the overall electron distribution occurs in the complex (Figure S23). Based on the linear plot relationship experiments, the detection limit of Al3+ was calculated and the value is 6.2164 × 10−9 M (Figure S24). This value is well below the permissible value for Al3+ based on USEPA. Additionally, potential binding affinity of 1 was checked for practical purposes, and it was found to be 4.6227 × 106. These values demonstrate efficient complex-forming behavior of receptor 1 selectively toward the metal ion Al3+. Further, competitive fluorescence measurement was carried out to access the selectivity of 1 toward Al3+ ion (Figure S25). The selective detection of Al3+ by 1 is due to the inhibition of ESIPT, restriction of isomerization around the CHN group and chelationenhanced fluorescence behavior (CHEF).11−13 The reversible characteristic of 1 toward Al3+ was monitored in emission measurements by using EDTA as a strong chelating ligand, and the results demonstrate the reusable nature of 1 (Figure S26A,B).

Nano. Surface morphology of 1 material was investigated by means of FESEM-FEI Quanta 250 FEG scanning electron microscope (SEM). Fluorescence microscope images were captured in CKX 41 (Olympus). Synthesis of 1. Diethyl pyridine-2,6-dicarboxylate and pyridine2,6-dicarbohydrazide were synthesized by the reported procedures.27,28 Pyridine-2,6-dicarbohydrazide (0.166 g, 0.85 mmol) was taken in a 50 mL round-bottomed flask and dissolved in 20 mL of ethanol and stirred for 30 min. 4-(N,N-Diethylamino)salicylaldehyde (0.412 g, 2.13 mmol) was added in portions to the aforesaid solution of pyridine-2,6-dicarbohydrazide. To this, 2 drops of concd H2SO4 was added and the solution refluxed for 4 h. The mixture was allowed to cool, and the crystalline yellowish precipitate settled, which was then filtered and finally washed two times with cold methanol. Mp: 259−260 °C. The compound was characterized by 1H NMR, 13 C NMR, and HR-MS. Yield: 0.318 g (70%). 1H NMR (400 MHz, DMSO-d6): δ = 12.12 (s, 1H), 11.24 (s, 1H), 8.64 (s, 1H), 8.31−8.17 (m, 3H), 7.29 (d, J = 8.8 Hz, 2H), 6.27 (dd, J = 8.8, 2.4 Hz, 2H), 6.11 (d, J = 2.4 Hz, 2H), 3.33 (q, J = 7.0 Hz, 8H), 1.07 (t, J = 7.0 Hz, 12H) ppm. 13C NMR (101 MHz, DMSO-d6): δ = 160.4, 159.2, 152.2, 151.0, 148.7, 140.4, 132.0, 125.6, 106.9, 104.4, 98.0, 44.4, 13.1 ppm. HR MS: m/z calcd 546.2823, found 546.2826. X-ray Crystallographic Study. Single-crystal X-ray data were collected at 296 K on a Bruker Kappa APEX2 CCD diffractometer with Mo Kα radiation.29 Preliminary lattice parameters and orientation matrices were obtained from three sets of frames. Then full data were collected using the ω and ϕ scan method with a frame width of 0.5°. Data were processed with the SAINT+ program for reduction and cell refinement.30 Multiscan absorption corrections were applied by using the SADABS program for area detection.31 The structure was solved by SHELXT31 and refined with SHELXL32 using the Olex2 program.33 CCDC data (1832889, Table S1) can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/datarequest.cif.

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CONCLUSION In summary, a versatile diethylamino-functionalized D−A−D bis-acylhydrazone compound has been designed and readily synthesized. Molecule 1 shows emission through charge-coupled proton transfer, aggregation induced emission, and mechanochromic luminescence upon grinding. In addition, compound 1 acts as turn-on fluorescent sensor for Al(III) selectively over the other cations in an efficient manner.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.8b01377. NMR spectra, HRMS, absorbance and fluorescence spectra, computational data, and additional data (PDF) X-ray data for compound 1 (CIF)

EXPERIMENTAL SECTION

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General Information. All of the materials for synthesis were purchased from commercial suppliers. Pyridine-2,6-dicarboxylic acid, 4-(N,N-diethylamino)salicylaldehyde, and hydrazine hydrate were purchased from Sigma-Aldrich and were used without further purification. Single-crystal X-ray diffraction data were collected on a Bruker APEX2 CCD diffractometer at 296 K. 1H NMR and 13C NMR were recorded on a Bruker Avance III HD Nanobay 400 MHz FT-NMR spectrometer, and chemical shifts are expressed in parts per million using TMS as internal standard. HRMS was recorded on a JEOL JMS 600H mass spectrometer or Thermo Fisher LTQ Orbitrap (ESI). The absorption spectra, titrations, and other related experiments were conducted in the wavelengths range 250−700 nm by using a JASCO V-630 UV−vis spectrophotometer in quartz cuvettes with a path length of 1 cm. Fluorescence spectra were recorded on a Quanta Master 40 spectrophotometer from Photon Technology International (slit width of 2.0 nm) and JASCO FP-6600 spectrophotometer. HORIBA Fluoromax was used for solid-state emission measurement. The fluorescence spectra and time-resolved fluorescence (TRF) decay measurements were recorded on a FLS-980 EDINBURGH spectrometer. A 375 nm laser was used as an excitation light source for TRF measurements, and the data were collected at an emission wavelength ∼450 nm. The goodness of fit to the decay curves was determined by the reduced χ2 values. The values of χ2 in all cases were close to unity, and weighted residuals were between ±4. DFT studies were performed on the B3LYP/6-311++G* basis set. Powder X-ray diffraction was carried out in XRD-Rigaku smart lab-Xray Diffractometer. DLS studies were done in Malvern Zeta sizer

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +91-422-2422387. Tel: +91-422-2428312. ORCID

Balasubramanian Murugesapandian: 0000-0002-7096-9816 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS B.M. thanks SERB, New Delhi, India (YSS/2015/000037), for financial support and UGC, New Delhi, for a start-up grant and UGC FRP faculty award (F.4-5(94-FRP)/2014(BSR). R.N. thanks SERB, New Delhi, India (SR/S2/RJN-62/2012), for funding. B.M. thanks Dr. Santosh Kumar Behera, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, for fruitful discussions regarding CPT and lifetime measurements.

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DEDICATION This paper is dedicated to Prof. Vadapalli Chandrasekhar on the occasion of his 60th birthday. D

DOI: 10.1021/acs.joc.8b01377 J. Org. Chem. XXXX, XXX, XXX−XXX

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The Journal of Organic Chemistry

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Wang, Y.; Liu, X.; Han, A.; Zhang, C.; Zang, L. Twisted Donor− Acceptor Cruciform Luminophores Possessing Substituent-Dependent Properties of Aggregation-Induced Emission and Mechanofluorochromism. J. Phys. Chem. C 2018, 122, 2297−2306. (d) Zhao, J.; Chi, Z.; Zhang, Y.; Mao, Z.; Yang, Z.; Ubba, E.; Chi, Z. Recent progress in mechanofluorochromism of cyanoethylene derivatives with aggregation-induced emission. J. Mater. Chem. C 2018, 6, 6327− 6353. (e) Gao, H.; Xu, D.; Liu, X.; Han, A.; Zhou, L.; Zhang, C.; Yang, Y.; Li, W. Tetraphenylethene modified β-ketoiminate boron complexes bearing aggregation-induced emission and mechanofluorochromism. RSC Adv. 2017, 7, 1348−1356. (f) Gao, H.; Xu, D.; Wang, Y.; Wang, Y.; Liu, X.; Han, A.; Zhang, C. Effects of alkyl chain length on aggregation-induced emission, self-assembly and mechanofluorochromism of tetraphenylethene modified multifunctional βdiketonate boron complexes. Dyes Pigm. 2018, 150, 59−66. (g) Wang, Y.; Xu, D.; Gao, H.; Wang, Y.; Liu, X.; Han, A.; Zhang, C.; Zang, L. Mechanofluorochromic properties of aggregation-induced emissionactive tetraphenylethene-containing cruciform luminophores. Dyes Pigm. 2018, 156, 291−298. (h) Xu, D.; Hao, J.; Gao, H.; Wang, Y.; Wang, Y.; Liu, X.; Han, A.; Zhang, C. Twisted donor−acceptor cruciform fluorophores exhibiting strong solid emission, efficient aggregation-induced emission and high contrast mechanofluorochromism. Dyes Pigm. 2018, 150, 293−300. (i) Gao, H.; Xu, D.; Liu, X.; Han, A.; Zhou, L.; Zhang, C.; Li, Z.; Dang, J. Tetraphenylethene-based β-diketonate boron complex: Efficient aggregation-induced emission and high contrast mechanofluorochromism. Dyes Pigm. 2017, 139, 157−165. (11) Shyamal, M.; Mazumdar, P.; Maity, S.; Sahoo, G. P.; SalgadoMoran, G.; Misra, A. Pyrene Scaffold as Real-Time Fluorescent Turnon Chemosensor for Selective Detection of Trace-Level Al(III) and Its Aggregation-Induced Emission Enhancement. J. Phys. Chem. A 2016, 120, 210−220. (12) (a) Han, T.; Feng, X.; Tong, B.; Shi, J.; Chen, L.; Zhi, J.; Dong, Y. A novel “turn-on” fluorescent chemosensor for the selective detection of Al3+ based on aggregation-induced emission. Chem. Commun. 2012, 48, 416−418. (b) Wang, Q.; Wen, X.; Fan, Z. A Schiff base fluorescent chemosensor for the double detection of Al3+ and PPi through aggregation induced emission in environmental physiology. J. Photochem. Photobiol., A 2018, 358, 92. (13) (a) Samanta, S.; Goswami, S.; Hoque, M. N.; Ramesh, A.; Das, G. An aggregation-induced emission (AIE) active probe renders Al(III) sensing and tracking of subsequent interaction with DNA. Chem. Commun. 2014, 50, 11833−11836. (b) Gui, S.; Huang, Y.; Hu, F.; Jin, Y.; Zhang, G.; Yan, L.; Zhang, D.; Zhao, R. Fluorescence TurnOn Chemosensor for Highly Selective and Sensitive Detection and Bioimaging of Al3+ in Living Cells Based on Ion-Induced Aggregation. Anal. Chem. 2015, 87, 1470−1474. (14) (a) Behera, S. K.; Karak, A.; Krishnamoorthy, G. Photophysics of 2-(4’-Amino-2’-hydroxyphenyl)-1H-imidazo-[4,5-c]pyridine and its Analogues: Intramolecular Proton Transfer versus Intramolecular Charge Transfer. J. Phys. Chem. B 2015, 119, 2330−2344. (b) Behera, S. K.; Murkherjee, A.; Sadhuragiri, G.; Elumalai, P.; Sathiyendiran, M.; Kumar, M.; Mandal, B. B.; Krishnamoorthy, G. Aggregation induced enhanced and exclusively highly Stokes shifted intramolecular proton transfer exhibiting molecule. Faraday Discuss. 2017, 196, 71−90. (15) (a) Kothavale, S.; Sekar, N. A New Series of Highly Fluorescent Blue-Green Emitting, Imidazole-Based ICT-ESIPT Compounds: Detail Experimental and DFT Study of Structural and Donating Group Effects on Fluorescence Properties. Chemistry Select 2017, 2, 7691−7700. (b) Jana, S.; Dalapati, S.; Guchhait, N. Proton Transfer Assisted Charge Transfer Phenomena in Photochromic Schiff Bases and Effect of − NEt2 Groups to the Anil Schiff Bases. J. Phys. Chem. A 2012, 116, 10948−10958. (16) (a) Padalkar, V. S.; Seki, S. Excited-state intramolecular pronttransfer (ESIPT)-inspired solid state emitters. Chem. Soc. Rev. 2016, 45, 169−202. (b) Kwon, J. E.; Park, S. Y. Advanced Organic Optoelectronic Materials: Harnessing Excited-State Intramolecular Proton Transfer (ESIPT) Process. Adv. Mater. 2011, 23, 3615−3642.

REFERENCES

(1) (a) Baldo, M. A.; O'Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.; Thompson, M. E.; Forrest, S. R. Highly efficient phosphorescent emission from organic electroluminescent devices. Nature 1998, 395, 151−154. (b) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Dos Santos, D. A.; Bredas, J. L.; Logdlund, M.; Salaneck, W. R. Electroluminescence in conjugated polymers. Nature 1999, 397, 121−128. (c) Saragi, T. P. I.; Spehr, T.; Siebert, A.; Fuhrmann-Lieker, T.; Salbeck, J. Spiro Compounds for Organic Optoelectronics. Chem. Rev. 2007, 107, 1011−1065. (2) Lin, G.; Peng, H.; Chen, L.; Nie, H.; Luo, W.; Li, Y.; Chen, S.; Hu, R.; Qin, A.; Zhao, Z.; Tang, B. Z. Improving Electron Mobility of Tetraphenylethene-Based AIEgens to Fabricate Nondoped Organic Light-Emitting Diodes with Remarkably High Luminance and Efficiency. ACS Appl. Mater. Interfaces 2016, 8, 16799−16808. (3) Sun, S.-K.; Wang, H.-F.; Yan, X.-P. Engineering Persistent Luminescence Nanoparticles for Biological Applications: From Biosensing/Bioimaging to Theranostics. Acc. Chem. Res. 2018, 51, 1131−1143. (4) Lochenie, C.; Schötz, K.; Panzer, F.; Kurz, H.; Maier, B.; Puchtler, F.; Agarwal, S.; Köhler, A.; Weber, B. Spin-Crossover Iron(II) Coordination Polymer with Fluorescent Properties: Correlation between Emission Properties and Spin State. J. Am. Chem. Soc. 2018, 140, 700−709. (5) Photophysics of Aromatic Molecules; Birks, J. B., Ed.; Wiley: London, 1970. (6) (a) Xiong, Y.-B.; Yuan, Y.-X.; Wang, L.; Sun, J.-P.; Qiao, W.-G.; Zhang, H.-C.; Duan, M.; Han, H.; Zhang, S.; Zheng, Y.−S. Evidence for Aggregation-Induced Emission from Free Rotation Restriction of Double Bond at Excited State. Org. Lett. 2018, 20, 373−376. (b) Desroches, M.; Morin, J.-F. Anthanthrene as a Super-Extended Tetraphenylethylene for Aggregation-Induced Emission. Org. Lett. 2018, 20, 2797−2801. (c) Sturala, J.; Etherington, M. K.; Bismillah, A. N.; Higginbotham, H. F.; Trewby, W.; Aguilar, J. A.; Bromley, E. H. C.; Avestro, A.-J.; Monkman, A. P.; McGonigal, P. R. Excited-State Aromatic Interactions in the Aggregation-Induced Emission of Molecular Rotors. J. Am. Chem. Soc. 2017, 139, 17882−17889. (7) (a) Mei, J.; Leung, N. L. C.; Kwok, R. T. K.; Lam, J. W. Y.; Tang, B. Z. Aggregation-Induced Emission: Together We Shine, United We Soar. Chem. Rev. 2015, 115, 11718. (b) Li, Y.; Ma, Z.; Li, A.; Xu, W.; Wang, Y.; Jiang, H.; Wang, K.; Zhao, Y.; Jia, X. A Single Crystal with Multiple Functions of Optical Waveguide, Aggregation-Induced Emission, and Mechanochromism. ACS Appl. Mater. Interfaces 2017, 9, 8910−8918. (8) (a) Dong, Y. Q.; Lam, W. Y. J.; Tang, B. Z. Mechanochromic Luminescence of Aggregation-Induced Emission Luminogens. J. Phys. Chem. Lett. 2015, 6, 3429−3436. (b) Wang, A.; Fan, R.; Wang, P.; Fang, R.; Hao, S.; Zhou, X.; Zheng, X.; Yang, Y. Research on the Mechanism of Aggregation-Induced Emission through Supramolecular Metal−Organic Frameworks with Mechanoluminescent Properties and Application in Press-Jet Printing. Inorg. Chem. 2017, 56, 12881− 12892. (c) Shin, S. W.; Oh, J. P.; Hong, C. W.; Kim, E. M.; Woo, J. J.; Heo, G.-S.; Kim, J. H. Origin of Mechanoluminescence from CuDoped ZnS Particles Embedded in an Elastomer Film and Its Application in Flexible Electro-mechanoluminescent Lighting Devices. ACS Appl. Mater. Interfaces 2016, 8, 1098−1103. (9) Butler, T.; Morris, W. A.; Samonina-Kosicka, J.; Fraser, C. L. Mechanochromic Luminescence and Aggregation Induced Emission of Dinaphthoylmethane β-Diketones and Their Boronated Counterparts. ACS Appl. Mater. Interfaces 2016, 8, 1242−1251. (10) (a) Chua, M. H.; Zhou, H.; Lin, T. T.; Wu, J.; Xu, J. Triphenylethylenyl-based donor−acceptor−donor molecules: studies on structural and optical properties and AIE properties for cyanide detection. J. Mater. Chem. C 2017, 5, 12194−12203. (b) Yang, Z.; Chi, Z.; Mao, Z.; Zhang, Y.; Liu, S.; Zhao, J.; Aldred, M. P.; Chi, Z. Recent advances in mechano-responsive luminescence of tetraphenylethylene derivatives with aggregation-induced emission properties. Mater. Chem. Front. 2018, 2, 861−890. (c) Wang, Y.; Xu, D.; Gao, H.; E

DOI: 10.1021/acs.joc.8b01377 J. Org. Chem. XXXX, XXX, XXX−XXX

Article

The Journal of Organic Chemistry

(29) APEXII, Program for Bruker CCD X-ray Diffractometer Control; Bruker AXS, Inc.: Madison, WI, 2006. (30) SAINT+ Program for Reduction of Data Collected on a Bruker CCD Area Detector Diffractometer; Bruker AXS, Inc.: Madison, WI, 2006. (31) Sheldrick, G. M. SADABS, Program for Empirical Absorption Correction of Area-Detector Data; Universität Göttingen: Göttingen, 2008. (32) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3−8. (33) Sheldrick, G. M. Acta Crystallogr. 2015, C71, 3−8.

(17) (a) Sasaki, S.; Drummen, G. P. C.; Konishi, G.-i. Recent advances in twisted intramolecular charge transfer (TICT) fluorescence and related phenomena in materials chemistry. J. Mater. Chem. C 2016, 4, 2731−2743. (b) Han, J.; Sun, J.; Li, Y.; Duan, Y.; Han, T. One-pot synthesis of a mechanochromic AIE luminogen: implication for rewritable optical data storage. J. Mater. Chem. C 2016, 4, 9287−9293. (18) Mukherjee, S.; Thilagar, P. Molecular flexibility tuned emission in ‘‘V’’ shaped naphthalimides: Hg(II) detection and aggregation induced emission enhancement (AIEE). Chem. Commun. 2013, 49, 7292−7294. (19) (a) Tang, W.; Xiang, Y.; Tong, A. Salicylaldehyde Azines as Fluorophores of Aggregation-Induced Emission Enhancement Characteristics. J. Org. Chem. 2009, 74, 2163−2166. (b) Shyamal, M.; Mazumdar, P.; Maity, S.; Samanta, S.; Sahoo, G. P.; Misra, A. Highly Selective Turn-On Fluorogenic Chemosensor for Robust Quantification of Zn(II) Based on Aggregation Induced Emission Enhancement Feature. ACS Sens 2016, 1, 739−747. (20) (a) Chen, J.; Law, C. C. W.; Lam, J. W. Y.; Dong, Y.; Lo, S. M. F.; Williams, I. D.; Zhu, D.; Tang, B. Z. Synthesis, Light Emission, Nanoaggregation, and Restricted Intramolecular Rotation of 1,1Substituted 2,3,4,5-Tetraphenylsiloles. Chem. Mater. 2003, 15, 1535− 1546. (b) Qin, A.; Lam, J. W. Y.; Mahtab, F.; Jim, C. K. W.; Tang, L.; Sun, J.; Sung, H. H. Y.; Williams, I. D.; Tang, B. Z. Pyrazine luminogens with “free” and “locked” phenyl rings: Understanding of restriction of intramolecular rotation as a cause for aggregationinduced emission. Appl. Phys. Lett. 2009, 94, 253308. (c) Shi, J.; Chang, N.; Li, C.; Mei, J.; Deng, C.; Luo, X.; Liu, Z.; Bo, Z.; Dong, Y. Q.; Tang, B. Z. Locking the phenyl rings of tetraphenylethene step by step: understanding the mechanism of aggregation-induced emission. Chem. Commun. 2012, 48, 10675−10677. (d) Mei, J.; Hong, Y.; Lam, J. W. Y.; Qin, A.; Tang, Y.; Tang, B. Z. Aggregation-Induced Emission: The Whole Is More Brilliant than the Parts. Adv. Mater. 2014, 26, 5429−5479. (21) Cao, Y.; Yang, M.; Wang, Y.; Zhou, H.; Zheng, J.; Zhang, X.; Wu, J.; Tian, Y.; Wu, Z. Aggregation-induced and crystallizationenhanced emissions with time-dependence of a new Schiff-base family based on benzimidazole. J. Mater. Chem. C 2014, 2, 3686−3694. (22) An, B.-K.; Kwon, S.-K.; Jung, S.-D.; Park, S. Y. Enhanced Emission and Its Switching in Fluorescent Organic Nanoparticles. J. Am. Chem. Soc. 2002, 124, 14410−14415. (23) Wang, Z.; Nie, H.; Yu, Z.; Qin, A.; Zhao, Z.; Tang, B. Z. Multiple stimuli-responsive and reversible fluorescence switches based on a diethylamino functionalized tetraphenylethene. J. Mater. Chem. C 2015, 3, 9103−9111. (24) Xu, S.; Liu, T.; Mu, Y.; Wang, Y.-F.; Chi, Z.; Lo, C.-C.; Liu, S.; Zhang, Y.; Lien, A.; Xu, J. An Organic Molecule with Asymmetric Structure Exhibiting Aggregation-Induced Emission, Delayed Fluorescence, and Mechanoluminescence. Angew. Chem. 2015, 127, 888− 892. (25) Han, T.; Zhang, Y.; Feng, X.; Lin, Z.; Tong, B.; Shi, J.; Zhi, J.; Dong, Y. Reversible and hydrogen bonding-assisted piezochromic luminescence for solid-state tetraaryl-buta-1,3-diene. Chem. Commun. 2013, 49, 7049−7051. (26) Zhang, X.; Chi, Z.; Li, H.; Xu, B.; Li, X.; Zhou, W.; Liu, S.; Zhang, Y.; Xu, J. Piezofluorochromism of an Aggregation-Induced Emission Compound Derived from Tetraphenylethylene. Chem. Asian J. 2011, 6, 808−811. (27) Bremer, A.; Ruff, C. M.; Girnt, D.; Mullich, U.; Rothe, J.; Roesky, P. W.; Panak, P. J.; Karpov, A.; Müller, T. J. J.; Denecke, M. A.; Geist, A. 2,6-Bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine as a Ligand for Efficient Actinide(III)/Lanthanide(III) Separation. Inorg. Chem. 2012, 51, 5199−5207. (28) Duke, R. M.; McCabe, T.; Schmitt, W.; Gunnlaugsson, T. Recognition and Sensing of Biologically Relevant Anions in Alcohol and Mixed Alcohol−Aqueous Solutions Using Charge Neutral CleftLike Glycol-Derived Pyridyl−Amidothiourea Receptors. J. Org. Chem. 2012, 77, 3115−3126. F

DOI: 10.1021/acs.joc.8b01377 J. Org. Chem. XXXX, XXX, XXX−XXX