Excited State Intramolecular Proton Transfer Plus Aggregation

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Excited state intramolecular proton transfer plus aggregation-induced emission based diketopyrrolopyrrole luminogen: photophysical properties and simultaneously discriminative detection trace water in three organic solvents Fuyong Wu, Lingyun Wang, Hao Tang, and Derong Cao Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.9b00032 • Publication Date (Web): 14 Mar 2019 Downloaded from http://pubs.acs.org on March 14, 2019

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Analytical Chemistry

Excited state intramolecular proton transfer plus aggregation-induced emission based diketopyrrolopyrrole luminogen: photophysical properties and simultaneously discriminative detection trace water in three organic solvents Fuyong Wu, Lingyun Wang *, Hao Tang, Derong Cao Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, China, 510641 *Corresponding

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Analytical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract: Developing solid state NIR emitters and simultaneously discriminative detection trace water in organic solvents has long been a significant challenge. In this work, a novel diketopyrrolopyrrole -based luminogen (DPP1) with excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) characteristics has been designed and synthesized. Its amorphous and crystal solids show red and NIR-emissive fluorescence at 625 nm and 675 nm, respectively. When DPP1 reacted with fluoride anion, the resulting system (DPP1.F) can discriminatively detect water content in aprotic solvents with colorimetric and fluorescent dual-modes. Distinct fluorescent responses of “turn on”, “ratiometric turn off”, “ratiometric turn on” and low limit of detection of 0.0064 v%, 0.042 v% and 0.192 v% in THF, acetone, and acetonitrile were obtained, respectively. The water-induced sensitive and fast change in THF was applied to the determination of water in foodstuffs in practical solid-state indicator paper strips.

Keyword: Diketopyrrolopyrrole, Excited state intramolecular proton transfer (ESIPT), Deprotonation, Moisture, Fluorescent sensor, Aggregation-induced emission (AIE)

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Introduction Trace water in organic solvents is disadvantageous in many chemical organic reactions and give rise to low yield and poor selectivity of the final product. In pharmaceuticals and foodstuffs field, it is also necessary to control and analyze moisture level of products. The sensitive detection of trace water becomes urgent and important in these fields.1 To this end, traditional Karl Fischer titration method and other detection protocols

(electrochemistry, gas chromatography and nuclear

magnetic resonance, etc) have been utilized for trace water detection.2-8 Meanwhile, as a novel and useful spectroscopic tool, aquaphotomics based on near infrared spectroscopy study for water detection have received more attentions.9-12 However, lack of continuous monitoring, expensive cost, and long time consuming limit their application. Therefore, it is desirable to design and synthesize highly sensitive probes with superior performance to satisfies the practical application. Many fluorescent-based moisture sensors are available in the literatures based on different kinds of mechanisms such as fluorescence intensity change,13-16 ratio fluorescence,7-20 solvatochromism,21 and so on.22-25 Besides organic probes, some luminescent nanomaterials based sensors for water detection have also been developed.26 For example, covalent organic frameworks (COFs),27 carbon quantum dots,28 metal–organic frameworks (MOFs),29 copper nanoclusters,30 and other nanomaterials31 have been reported for sensing water in organic solvents. However, these systems have drawbacks such as aggregation caused quenching (ACQ) effect, small Stokes shifts, low sensitivity. More importantly, they fail to discriminatively 3



detect water content in different solvents. It is of great interest to develop multifunctional water probes with large Stokes shift and anti- ACQ effect. Excited state intramolecular proton transfer (ESIPT) fluorophores have many potential applications such as molecular logic gates, fluorescence imaging, optoelectronic devices, etc.32-34 The photophysical properties of ESIPT dyes are sensitive to surrounding medium such as solvent polarity, solvent type, acidity/basicity, hydrogen bonding, etc.

The large Stokes shift and dual emission are

remarkable properties of the ESIPT fluorophores. Especially, solid state emitters based on ESIPT coupled with aggregation-induced emission (AIE) processes receive considerable attention in functional materials.35-37 However, the examples emit at the red or NIR region with large Stokes shift are still rare. It would be an efficient way to obtain solid state emissions for ESIPT chromophores though AIE -based aggregation effect because non-radiative decay pathways in the excited state are largely suppressed. Inspired by this design strategy, we covalently linked a AIE group triphenylamine (TPA) and a popular ESIPT moiety (2-(2’-hydroxyphenyl)benzothiazole, HBT)

to diketopyrrolopyrrole core, resulting

in a novel solid state ESIPT emitter (DPP1) at red /NIR region with large Stokes shift. Moreover, by taking advantage of the fluorescence tunability and environmental sensitivity of ESIPT-active molecules, when DPP1 reacted with fluoride anion, the resulting system (DPP1.F) for the discriminative sensing water content in three solvents was achieved with colorimetric and fluorescent dual-modes.

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EXPERIMENTAL SECTION Chemicals and Instruments. All chemical reagents and starting materials are commercially available and were used without further purification, unless otherwise noted. 1H and

13C

nuclear magnetic resonance spectra were measured on Bruker

Avance III 400 MHz. The chemical shifts are expressed in ppm using (tetramethylsilane) TMS as an internal standard. The UV–vis absorption spectra were recorded using a Helios Alpha UV–vis scanning spectrophotometer with a 1cm quartz cell. Fluorescence spectra were obtained with a Hitachi F-4500 FL spectrophotometer with quartz cuvette (path length=1 cm). Compounds 2 and 3 were synthesized according to the literature methods.38,39 Synthesis of DPP1 Under N2 atmosphere, compound 2 (187 mg, 0.24 mmol), compound 3 (103 mg, 0.29 mmol), Pd(PPh3)4 (30 mg, 0.024 mmol), K2CO3 (353 mg, 2.4 mmol) and in 20 mL of toluene, 5ml of ethanol and 1.3 mL of H2O were heated at 60 oC for overnight. After cooling to room temperature, the mixture was concentrated and extracted with 50 mL of CH2Cl2. The organic portion was combined and the solvent was removed, , followed by column chromatography on silica (ethyl acetate/petroleum ether, 1/15, v/v) to give 104 mg DPP1 (yield 47%) 1H NMR (400 MHz, CDCl3): 12.68 (s, 1H), 8.03 (d, J=8.0 Hz, 1H), 7.91-7.971 (m, 6H) ,7.78 (d, J=8.4 Hz, 4H),7.74 (d, J=8.4 Hz, 2H), 7.69 (dd, J1=8.4 Hz, J2=6.0 Hz, 1H), 7.52-7.56 (m, 3H), 7.45 (d, J=8.0 Hz,1H), 7.29 (d, J=8.0 Hz, 4H), 7.23 (d, J=8.4 Hz, 1H), 7.16 (d, J=7.6 Hz, 6H), 7.07 (d, J=11.2 Hz,2H), 3.81-3.85 (m, 4H), 1.21-1.32 (br, 14H), 0.83-0.87 (m, 8H). 13C NMR 5



(100 MHz, CDCl3) δ 169.06, 162.89, 162.82, 158.13, 151.81, 148.29, 148.05, 147.72, 147.47, 143.27, 142.56, 133.27, 132.64, 131.60, 131.48, 129.39, 129.29, 127.79, 126.93, 126.84, 126.76, 126.44, 125.75, 124.83, 123.35, 123.29, 122.29, 121.63, 118.65, 117.17, 109.99, 109.76, 42.15, 31.29, 29.52, 26.46, 22.51, 14.00. TOF-MS m/z calcd for C61H56N4O3S: 924.41; Found: 925.18 [M+H]+.

RESULTS AND DISCUSSION Photophysical properties of DPP1. 2-(2’-hydroxyphenyl)benzothiazole (HBT) is a well-known ESIPT characteristic dye that usually shows large Stokes shift and dual emission.39 The nonplanar propeller-like molecular conformation of triphenylamine (TPA) can effectively preclude the intermolecular π- π stacking,40-41 thereby avoiding the severe self-quenching of fluorescence. As a class of excellent red fluorescent emission dyes, DPP has wide applications

in sensing and detection due to their

brilliant light, weather, and heat stability.42-45 Thus, DPP1 consisting of TPA, DPP, HBT units was designed and synthesized. Suzuki cross-coupling reaction was mediated by Pd(PPh3)4 between the dibromodiketopyrrolopyrrole 1 and TPA-boric acid to yield the pivotal intermediate 2. Suzuki cross-coupling reaction of 2 with HBT-boric acid ester 3 generated DPP1. The molecular structure of DPP1 was assigned by 1H NMR, 13C NMR and MALDI-TOF MS (Figure S1-S3). The 1H NMR spectrum supports the formation of intramolecular hydrogen bonding between the OH and the neighboring benzothiazole N atom because of presence of a singlet signal at 12.68 ppm. 6


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DPP1 showed two maximum absorption bands at about 500 nm and 300 nm as well as a shoulder band at 350 nm, which is nearly the same regardless of the solvent polarity and indicative of the rigidity of the molecular framework (Figure S4). Interestingly, the appearance of a red-shift band at 317 nm and a weak absorption band at 593 nm in DMF are present, which can be ascribed to the presence of small amounts of deprotonated ground-state anion. The acidic property of OH in DPP1 has made it easy to be deprotonated by DMF with strong basicity. The fluorescence spectral data of DPP1 also measured in different solvents. Single keto tautomer emission peak ranged at 559-581 nm is observed in different solvents when the excitation wavelength is 500 nm. With the increase of the polarity and hydrogen-bonding capacity of the solvents, the band maxima of the tautomer emissions become blue shifted (Figure S5). When the excitation wavelengths change from 500 nm to 350 nm, dual emissions are observed in THF, acetone and acetonitrile: the normal emissions ranged from 443 nm to 470 nm and the large Stokes-shifted tautomer emissions ranged from 550 nm to 572 nm. The corresponding data are shown in Table S1. As shown in Figure S6, DPP1 gives a maximum fluorescence intensity in a low polarity solvent like THF, while the minimum value for DPP1 is observed in a high polarity solvent like acetonitrile. The photophysical properties of DPP1 in THF–water mixtures were investigated with different water fractions. As shown in Figure S7, DPP1 showed strong yellow emission at 573 nm. With an increase in the water fraction from 0 to 60%, the emission intensity of DPP1 significantly decreased. Upon further increasing the water 7



fraction from 60% to 90%, a slight increase in the emission intensity was observed along with a red-shift in the PL maximum from 573 nm to 591 nm. This can be ascribed to the twisted intramolecular charge transfer (TICT) effect caused by the electron donor–acceptor (D–A) structural feature of DPP1, which contained rotatable and propeller shaped triphenylamine group and electron withdrawing DPP group. Due to higher polarity of mixed solvents than THF, DPP1 can be dominated by TICT state in THF–water mixtures and resulted in red-shifted and quenched emission. In presence of water fraction between 70% and 90%, DPP1 was in the aggregated state, as confirmed by the DLS results (Figure S8), and the restricted intramolecular rotation (RIR) process endowed it with a red AIE fluorescence. Accordingly, the emission color changed from yellow to red with the increase of fw. The traditional DPP compounds usually have Stokes shifts smaller than 50 nm, but the large Stokes shift (82 nm) of DPP1 herein may be promising characteristics for practical application. We then studied the concentration effect on the emission of DPP1 in THF. As shown in Figure S9, the emission spectrum is progressively intensified with almost no shift in the emission peak when the concentration increased from 0.1 μM to 100 μM. Such a concentration effect has commonly been observed in typical AIE systems.24 The solid state fluorescence properties of DPP1 powder was investigated. As shown in Figures 1a-b, a red emission at 625 nm and a fluorescence quantum yield of 2.9% was observed in the case of amorphous sample. The emission maxima for DPP1 solids were red-shifted compared to its dilute solution, which can be assigned to better conjugation in the solid state. Crystallization is a process where the molecules are 8


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organized regularly into a structure. DPP1 crystals were obtained by slowly volatilization of its THF solution under room temperature. XRD data indicate DPP1 crystals have obvious diffraction peaks at 5.3o, 6.9 o, 10.8 o, 16.4 o, 17.6 o, 19.1

o

(Figure 1c). SEM photographs further demonstrate the regular and rectangular shape of DPP1 crystals is present (Figure 1d). Surprisingly, DPP1 crystals showed NIR emission at 675 nm with a fluorescence quantum yield of 4.9%, which was bathochromic as compared with its amorphous state. This observation can be ascribed to effective suppressing non-radiative pathways by TPA group in DPP1 and its crystalline packing. DPP1 failed to show AIE effect in THF–water mixtures, but its solids are emissive. These observations can be ascribed to as follows. (1) The effect of suppressing non-radiative pathways by TPA group is much stronger in the solid state than that in solvent. (2) The inter-/intramolecular H-bonds between -OH groups in the solid state for DPP1 are beneficial to prevent quenching, which is helpful to develop highly emissive NIR fluorescent materials based on ESIPT chromophores. Spectral properties of DPP1 with F-. UV−vis absorption spectra of DPP1 with and without [(n-Bu4)N]F were monitored in three dry solvents. When excess of F- was added to the solution of DPP1 in dry THF and acetone, prominent changes were observed (Figure 2a-b). The color changes in the presence of F- were observed (Figure 2a-b), accompanied by a decrease at ∼500 nm and appearance of new absorption band at ∼568 nm with three isosbestic points. Meanwhile, another new peak appeared at 426 and 433 nm, respectively. There are 68 and 78 nm red shifts in both cases. In acetonitrile, only 44 nm red shift, a decrease at 490 nm and appearance of new 9



absorption band at 534 nm with three isosbestic points were found (Figure 2c). The resulting isosbestic points inferred presence of new species for DPP1 with F- in three organic solvents. The color changes from yellow to dark purple, light purple and pink can be observed by naked eyes, respectively (Figure 2e). The corresponding data have been summarized in Table S2. As we know, F- ions are easy to participate in F-based hydrogen bond and deprotonation process (even formation of HF2-)46-49 In our case, UV−vis spectra for DPP1 in presence of [(n-Bu4N)]OH in THF and acetone are very similar to those of DPP1 plus F− system (Figure S10a, b). This inferred the deprotonation of DPP1 by Fion in THF and acetone was present. The 1H NMR spectrum DPP1 in presence of [(n-Bu4N)]F was investigated.. It was easy to find out that the hydroxyl group of DPP1 at 12.7 ppm disappeared completely with excess F- ion, meanwhile, the signals of other aromatic protons moved to high field (Figure S11). These results indicated that the deprotonation of phenol group of DPP1was involved. However, in acetonitrile, UV−vis spectrum for DPP1 in presence of [(n-Bu4N)]OH is different from that DPP1 plus F− system

(Figure S10c). This infers that deprotonation

process is not involved. The fluorescence responses of the DPP1 with F- were investigated. DPP1 shows strong emission at 575 nm in THF. It is interesting that this deprotonation by Finduces a great fluorescence quenching (Figure 3a). When 40 μM F- anions were added, 98% emission was quenched. It can be explained that ESIPT process is inhibited by deprotonation, resulting in a significant quenching of the keto tautomer 10


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emission during the F- titration. Secondly, the fluorescence response of DPP1 in acetone in the presence of F- were followed. It was found that DPP1 weakly emitted at 579 nm. This band began to decay and a new and substantially blue-shifted emission at 487 nm was dramatically enhanced with increasing F- concentration (Figure 3b). The ratio of I487/I579 changed from 0.05 to 9.40. Surprisingly, the fluorescence spectra of DPP1 for fluoride titration in acetonitrile displays different response as compared with both cases mentioned above (Figure 3c). DPP1 emitted a weak emission at 547 nm. Upon addition of F-, emission at 547 nm quenched and a new and substantially blue-shifted emission appeared at 484 nm upon addition of Fand was slowly enhanced with increasing F- concentration. The ratio of I484/I547 changed from 0.02 to 3.1. The distinct fluorescent response of DPP1 in different organic solvents in presence of F- are summarized in Figure 3d. Moreover, distinct emission color changes can be found by naked eyes (Figure 3e). As discussed above, DPP1 in three different organic solvents show distinct UV-vis and emission response in presence of F-. These observations can be ascribed to as follows. (1) There are coexisted interconvertible isomers in solutions, which is easily disturbed in presence of fluoride ions. Some hydrogen bonds complexes or deprotonation products maybe form. (2) Two types of hydrogen atom in DPP1 are likely to bind with fluoride to form N-H···F or O-H···F hydrogen bond due to the two coexisting enol and keto isomers. However, compared to O-H···F, N-H···F is more difficult to further bind another fluoride and then the deprotonation process cannot proceed. (3) The solvation effect on THF and acetone can’t be neglected. However, 11



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some differences exist in two types of intermolecular hydrogen bonding through solvation effect due to different directionalities between sp3 and sp2 hybridization state oxygen atoms. The strength of hydrogen bonds to ether and ketone groups in their optimum geometries turns out to be similar, but hydrogen bonds to the ketone carbonyl oxygens are marginally stronger.50 These factors result in different absorption and emission spectra of DPP1 in presence of F- in three solvents. The proposed binding mechanism and deductive structure was shown in Scheme 1. DPP1 in THF did not show any significant response to other anion species (Cl-, ClO4-, NO3-, AcO-, I, - Br, - HSO4-, H2PO4-) (Figure S12). The anion’s ability to form hydrogen bonding maybe the origin of observed selectivity, because only fluoride anion was strong enough to compete with the existing intramolecular hydrogen bonding, resulting in deprotonation of DPP1. It is well known that water is able to disturb H-bond interaction

−

or deprotonation progress between F- and analytes

because of high solvation of F− in water. It is promising to apply DPP1 plus F− system (DPP1.F) as a water sensor. In our case, the solution of DPP1.F in THF, acetone, acetonitrile in presence of trace water resulted in obvious color changes (Figure 3e). Colorimetric and fluorescent detection of water with DPP1.F. As shown in Figure 4a, two bands at 426 and 568 nm disappeared and original bands at 350 and 500 nm regenerated when water was added to

DPP1.F in anhydrous THF.

Simultaneously, quenched emission at 579 nm is recovered and emission color of the solution restored to the original yellow (Figure 5a). These changes were due to the regeneration of DPP1 by interaction of DPP1.F and water molecules and gave out 12


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fluorescence “turn on” response. On the other hand, different UV-vis and fluorescence response was found after the addition of water to DPP1.F in anhydrous acetone. The whole spectrum blue-shifted from 569 to 527 nm and from 433 to 420 nm without peak shape change, but had a leveled-off tail in the visible region due to the Mie effect of the nanoparticles

51, 52

DLS confirmed aggregates of DPP1.F in presence of water. DPP1.F in anhydrous acetone was homogeneous, but DPP1.F formed approximately 30 nm size aggregates after addition of 2.5% water (Figure S13). The aggregation mechanism is unclear. The great fluorescence quenching from emission at 487 nm was present, meanwhile, a weak keto emission at 547 nm appeared. In the end, two weak emission at 487 and 547 nm co-exist and showed fluorescence “ratiometric turn off” characteristics (Figure 5b). Finally, DPP1.F has a weak emission around 484 nm in acetonitrile. After the gradual addition of water, this emission band starts to decrease and a new band around 546 nm starts to generate (Figure 5c). At last, only keto form emission at 546 nm was present. So, simultaneous monitoring of the changes of fluorescence intensity at 546 nm and 484 nm to generate a “ratiometric turn on” fluorescent probe, enabling us to use DPP1.F for detection of trace water in acetonitrile. Accordingly, as shown in Figures 6 and 7, the shift in the UV-vis and emission profile resulted in distinct color and emission changes under irradiation (365 nm), depending on addition of amount of water in THF, acetone and acetonitrile. As shown in Movies in Supporting Information, 5 s was enough to complete the reaction. From the results discussed 13



above, one can assume the formation of intermolecular hydrogen bonds between DPP1 and the water molecules. Moreover, it is possible mono- and polyhydrate species are formed between DPP1 and water by successively solvated process and hydrogen bonding, as shown in Scheme 2. Good linear relationships between fluorescence intensities change and the water content were obtained (Figure S14). The detection limit (LOD) for water using DPP1.F were calculated as 0.0064 v% in THF, 0.042 v% in acetone and 0.192 v% in CH3CN based on a 3σ/slope. The LODs have been summarized in Table 1, which is compared with various sensing materials based on different detection mechanism. Practical applications for water detection. Since detection system (DPP1.F) showed lowest limit of detection (0.0064%) for trace water in THF among three organic solvents, THF-water mixture was selected as practical application. DPP1-based test strip was firstly fabricated due to its handy, disposable and visualized characteristics. As shown in Figure 8, colorimetric changes were found by immersing this test strips in THF or acetone solution of F-. At the same time, the bright fluorescence of DPP1 test strip being quenched was clearly visualized. The colored test paper was further used for trace water detection in THF. The color changed from purple to the reddish-brown and the emission recovered when they are dipped into commercially available THF solvent. The detection process was simple and rapid. Since the moisture content of raw products affects the quality and stability of the final product, determination of the water content is important and challenging in the 14


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food industry. DPP1.F for the possible detection of water content in honey and salt was carried out. When sample was added into DPP1.F (10 μM) in THF, the emission intensity at 579 nm was enhanced. On the basis of the relationship of between the fluorescence intensity at 579 nm and content of water in Figure 5a, we found that honey has more moisture content as compared to salt (0.25% vs 0.01%). The naked-eye detection of water content among different commercial products can also be achieved, as shown in Inset of Figure 8. In order to confirm the observed emission enhancement at 579 nm was due to presence of water in honey and salt, a known content of water was added into the same solution. It can be found more emission enhancement at 579 nm was present (Figure 9). These fluorescence studies show that DPP1.F has potential to detect low water content in the commercial raw sample materials.

CONCLUSIONS In summary, a TPA and HBT decorated diketopyrrolopyrrole compound (DPP1) was designed and prepared. DPP1 showed both ESIPT and AIE characteristics with large Stoke shifts. In solid, DPP1 crystals showed a NIR fluorescence emission at 675 nm, but its amorphous powder emitted at 625 nm. The DPP1.F system for trace water detection in three organic solvents with colorimetric and fluorescent dual modes and good naked-eye visual detection was successfully achieved. DPP1.F have high sensitivity for water in THF with low LOD up to 0.0064%. Test papers incorporated with DPP1.F are rapid, portable, naked-eye detection water content of commercial 15



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products. It will be a very useful to design more delicate ESIPT-based water chemosensors.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Experimental section, UV−vis, fluorescence, 1H NMR,

13C

NMR, MALDI-TOF-MS

and additional spectroscopic data (PDF).

Acknowledgements The supports by the Natural Science Foundation of Guangdong Province (2015A030313209, 2016A030311034) and the Fundamental Research Funds for the Central Universities (2017ZD075) are gratefully acknowledged.

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Massue,

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Retailleau,

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2-(4‘-N,N-diethylamino-2‘-hydroxyphenyl)benzimidazoles:

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S

N

S

N-

O-

O

Flu

Flu

F- induced deprotonation

S

S

Excitation

NH

F- induced H-bond

N H

S

O

N H

O

Flu

Flu

S

N H F

O

Flu

Enol form

F

O

Flu

Keto form

Solvation (only exsit in THF and acetone)

S

sp2

N H

O

S

Or

N H

O

sp3 O

O

Flu

Flu C6H13 N

O N

Flu

N

O

C6H13

Scheme 1 Possible structures of DPP1 from fluoride interaction and solvation.

C6H13 C6H13 O

N

N

S

N

H2O

H

N

S

O

N

N O H

O O

O

N C6H13

N

N

O

S

C6H13 H N

H2O

N

N

H

S

N H

O H

O

O

H O

H

O

O N C6H13

O H

H

H O C6H13 H

N C6H13

O

H

H

H

O H

O

O H

H

Scheme 2 Possible DPP1-water hydrogen bond complex.

21


N C6H13

O H

H

O H

H


Figure 1. (a) The emission spectra sand (b) fluorescent photographs of DPP1 in the amorphous and s crystalline state. (c) SEM photo of DPP1 crystal. (d) XRD spectra of DPP1 in the amorphous and crystal state.

22


Page 22 of 31

Page 23 of 31

0.4 0.45

(a) THF

-

0.30

Absorbance

Absorbance

(b) Acetone

5.0 eqv. [F ] 0 eqv.

0.15

5.0 eqv.

0.3

-

F 0.2

0 eqv.

0.1

0.00

0.0 300

400

500 600 Wavelength (nm)

(c) Acetonitrile

0.4

700

400


700

0.5

5 eqv.

(d)

THF Acetone Acetonitrile

0.4

-

Absorbance

F

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0 eqv.

0.2

0.3

567 nm

531 nm

0.2 0.1

0.0

0.0 300

400


400

700


700

Figure 2. UV-vis titration spectra of DPP1 (10 μM) in presence of varying amount of [(n-Bu4)N]F in (a) dry THF, (b) dry acetone and (c) dry acetonitrile, (d) UV-vis spectra of DPP1 (10 μM) in presence of [(n-Bu4)N]F (50 μM) in dry THF, acetone and acetonitrile. (e) Color changes of DPP1 in dry THF, acetone and acetonitrile after the addition of F- ion and subsequent addition of a trace amount of water.

23



1000

(a) THF

4000

0 eqv.

3000

[F ]

-

2000

4 eqv.

8.0 eqv.

600

-

F 400

0 eqv.

200

1000 0

0 550

210

(b) Acetone

800

FL Intensity

FL Intensity

5000


700

750

500

1000

(c) Acetonitrile

550 600 650 700 Wavelength (nm)

(d)

FL Intensity

140

20.0 eqv. -

F 70

0 eqv.

750


487 nm

FL Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 31

572 nm

0

0 500

550


700

750

500

550

600 650 700 Wavelength (nm)

750

Figure 3. The emission titration spectra of DPP1 (10 μM) in presence of varying amount of [(n-Bu4)N]F in (a) dry THF, (b) dry acetone and (c) acetonitrile, (d) The emission spectra of DPP1 (10 μM) in presence of [(n-Bu4)N]F (50 μM) in dry THF, acetone and acetonitrile. (e) Color changes of DPP1 in dry THF, acetone and acetonitrile after the addition of F- ion and their color changes upon addition of a trace amount of water content taken under 365 nm UV irradiation.

24


Page 25 of 31

0.6

0.8 (a) THF

Absorbance

Absorbance

0.6 0.4

(b) Acetone

0.4

0.2

0.2

0.0

0.0 300

0.6

400


400

700


700

0.6

(c) Acetonitrile


(d)

0.4

Absorbance

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.2

0.0

0.4

0.2

0.0

300

400


700

400


700

Figure 4. DPP1.F in (a) dry THF with 0−0.55% (v/v) of water content, (b) acetone with 0−0.70% (v/v) of water content, (c) acetonitrile with 0−0.55% (v/v) of water content and (d) The UV-vis spectra of DPP1.F (10 μM) in presence of water in dry THF, acetone and acetonitrile.

25



1200

579 nm

(a) THF

1500

FL Intensity

FL Intensity

2000

1000

(b)

Acetone

487 nm

900 600 547 nm

300

500

0

0 500

120


700

500

750

700


(d)

546 nm

90


2000

(c) Acetonitrile 484 nm FL Intensity

150

FL Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 31

60

1000

30 0

0

500

550


750

500

550


750

Figure 5. Fluorescence titration curves of DPP1.F (0.01 mM) upon addition of water content from 0 to 1.0% (v/v) in dry in dry THF (a), 0 to 2.5% (v/v) in dry acetone (b) and 0 to 1.25% (v/v) in dry acetonitrile (c) (λex=443 nm), (d) The collected emission spectra of DPP1.F in presence of water in dry THF, acetone and acetonitrile.

26


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Figure 6. Color changes of DPP1.F in (a) THF, (b) acetone and (c) acetonitrile with different water fraction.

Figure 7. Emission changes of DPP1.F in (a) THF, (b) acetone and (c) acetonitrile with different water fraction under 365 nm lamp.

27



Figure 8. Photographs of the paper strips adsorbed with DPP1.F in the presence of moisturized organic solvents in (a) THF and (b) acetone solvents at daylight and under 365 nm lamp.

28


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Page 29 of 31

80 60

F/F 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40 20 0

lt sa

3 2

y ne o h

1

Figure 9. Changes of emission intensities of DPP1.F (0.01 mM) in presence of commercial products in dry THF (λex = 443 nm). 1: free DPP1.F; 2: PP1.F+analytes; 3: PP1.F+analytes+H2O.

29



Page 30 of 31

Table 1 Comparison of the sensing features of DPP1.F and other examples. Materials

Response mode

LOD

Real samples

Ref.

DPP1.F

0.0064 v% (THF), 0.0042 v% (ACT), 0.192 v% (ACN)

Salt, honey

This work

Copper complex

Turn-on (THF), Ratiometric Turn-off (ACT), Ratiometric Turn-on (ACN) Turn-on

Wheat, salt, sugar

53

BODIPY derivative

Ratiometric

Grapeseed oil, honey

24

N-Heteroaryl-1,8-nap hthalimide

Turn-off

Copper nanoclusters

Turn-off

Carbon quantum dots

Turn-on

0.003 wt% (THF), 0.033 wt% (MeOH), 0.052 wt% (ACT), 0.448 wt% (ACN) 0.003 v% (ACN, THF), 0.006 v% (ACT), 0.007 v% (DMSO), 0.008 v% (1,4-dioxane) 0.049 v% (1,4-dioxane) 0.021 v% (ACN) 0.016 v% (acetone) 0.020 v% (THF) 4.0 ×10−4 v% (DMF), 2.0 ×10−4 v% (ACN), 1.6 × 10−4 v% (THF) 0.1 v% (EtOH)

Covalent frameworks

Ratiometric

CH3NH3PbBr3

organic

Turn-off

0.022 wt% (ACT), 0.026 wt% (THF), 0.034 wt% (EtOH) 0.04 % (Relative humidity)

Abbreviation: ACT for acetone, ACN for acetonitrile.

30


—

—

—

18

30

28

—

27

—

54

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for TOC only

31


Excited State Intramolecular Proton Transfer Plus Aggregation

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