Visual sensing of CO2 in air with a 3-position modified naphthalimide-derived organogelator based on a fluoride ion-induced strategy

Accepted Manuscript Visual sensing of CO2 in air with a 3-position modified naphthalimide-derived organogelator based on a fluoride ion-induced strategy Xin Zhang, Yuanyuan Song, Meng Liu, Haimiao Li, Helue Sun, Mengmeng Sun, Haitao Yu PII:

S0143-7208(18)31717-0

DOI:

10.1016/j.dyepig.2018.09.010

Reference:

DYPI 6992

To appear in:

Dyes and Pigments

Received Date: 3 August 2018 Revised Date:

1 September 2018

Accepted Date: 5 September 2018

Please cite this article as: Zhang X, Song Y, Liu M, Li H, Sun H, Sun M, Yu H, Visual sensing of CO2 in air with a 3-position modified naphthalimide-derived organogelator based on a fluoride ion-induced strategy, Dyes and Pigments (2018), doi: 10.1016/j.dyepig.2018.09.010. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Graphical Abstract

Visual sensing of CO2 in air with a 3-position modified

ion-induced strategy

RI PT

naphthalimide-derived organogelator based on a fluoride

Xin Zhang, Yuanyuan Song, Meng Liu, Haimiao Li, Helue Sun, Mengmeng Sun, and

SC

Haitao Yu*

AC C

Highlights

ir in a

EP

TE D

M AN U

in air

A new naphthalimide-based organogelator bearing a naphthyl group at the 3-position is prepared which can form stable gels in some organic solvents. Real-time detection of CO2 stream has been realized with the synthesized gelator based

on an anion-induced strategy. The synthesized gelator can particularly provide the visual sensing means for CO2 in air via the solution-to-gel transition by the activation of fluoride anions.

ACCEPTED MANUSCRIPT

Visual sensing of CO2 in air with a 3-position modified naphthalimide-derived organogelator based on a fluoride ion-induced strategy

RI PT

Xin Zhang, Yuanyuan Song, Meng Liu, Haimiao Li, Helue Sun, Mengmeng Sun, and Haitao Yu*

National Demonstration Center for Experimental Chemistry Education, College of Chemistry and Materials Science, Hebei Normal University, Shijiazhuang, 050024, China

SC

[email protected] (H. Y.)

M AN U

Abstract: A new low-molecular-weight organic gelator derived from butyl naphthalimide having a naphthyl group attached at the 3-position with the amido linkage was synthesized. The synthesized gelator could form stable gels in several organic solvents. Scanning electron microscopy (SEM), temperature-dependent 1H NMR spectra, UV-vis spectroscopy, and PXRD were involved in the characterization of the obtained gels. Furthermore, the solution derived from the stimuli of fluoride ions to the DMSO gel were found to allow a naked-eye sensing of

TE D

CO2 stream through the solution-to-gel transition, as well as the quantitative analysis via fluorescence enhancement. Moreover, the present sensing system could also detect CO2 directly in air via the phase transformation which could provide a visual means for CO2 sensing in a confined space.

1. Introduction

EP

Keywords: naphthalimide-derived gelator, fluoride ion, CO2 sensing, naked-eye sensing, solution-to-gel transition

AC C

In recent decades, a great deal of attention has been paid to organogels based on low-molecular-weight organic gelators (LMWOGs) in various research areas due to their unique functions [1]. These soft materials, also called as supramolecular or physical gels, are formed by the self-assembly of LMWOG molecules through some weakly noncovalent interactions, including hydrogen bondings, van der Waals forces, electrostatic attractions, and π-π stacking interactions, etc., which can give rise to an entangled three-dimensional (3D) network to entrap a large number of organic liquid molecules by the surface tension, further leading to the formation of a semi-solid substance [2]. In particular, such solid-like materials can display multiple responses to external stimuli like heat, pH, light, ultrasound, ions, and so forth, usually resulting in a reversible gel-solution phase transition [3]. In recent years, reversible gelation-based phase transition, capable of permitting a visible sensing output to the naked eye, 1

ACCEPTED MANUSCRIPT has been receiving increasing interest in the development of visually analytical tools for important substrates [4]. Monitoring of carbon dioxide (CO2) is of vital importance since global warming has been becoming more and more severe due to the excessive emission of CO2 which is terribly threatening the global living environment [5]. Although there are some analytical techniques reported for CO2, the visual sensory systems based on the reversible gel-to-solution transition are not many available in the literature related to the CO2 assay [6]. Especially,

RI PT

the gelation-based sensing systems that can directly detect CO2 in relatively confined spaces such as mines, wells, ships, submarines, tunnels, and so on, are more rarely reported [7].

Recently, some naphthalimide-based organogelators have been developed in combination with an anion-induced strategy for the analysis of CO2 stream via the solution-to-gel transformation [8]. However, the

SC

reported gelators failed to directly sense the CO2 in air. Following our continued pursuit of developing such CO2 sensing systems, we report herein a new napthalimide-derived organogelator with the naphthyl group at 3-position

M AN U

of naphthalimide. We expect that not only could this gelator visually sense CO2 in air via gelation-based phase transition but it also could quantitatively analzye CO2 by fluorescence changes.

O

O

O

O

O

O

NO2

NO2

EP

O

NH2

2

O

AC C

iii)

N

ii)

TE D

i)

N

3

N

O O N H Nap-but 1

Scheme 1. i) Butylamine, ethanol, microwave, reflux for 10 min, 60%; ii) hydrazine hydrate and 10% Pd/C, ethanol, reflux for 1h, 65%; iii) 2-naphthoyl chloride, 1, 4-dioxane, microwave, reflux for 15 min, 75%. 2. Experimental section 2.1. General information of materials and instrument Tetrabutylammonium salts which were utilized for anion titration experiments were purchased from 2

ACCEPTED MANUSCRIPT Sigma-Aldrich. All the chemicals for synthesis were commercially available at analytical grade and used without further purification. Microwave-assisted reactions were carried out in a XH-300B microwave reactor (2450 MHz, AC220V ± 10%). Thin-layer chromatography (TLC) with 0.25-mm Merck silica gel plates (60F-254) were utilized for the track of the reaction process under irradiation by UV-lamp (254 nm). Merck Millipore silica gel (300-400 mesh) was used in the column chromatography purification. 1H NMR and

13

C NMR spectra were

RI PT

recorded on a Bruker Avance AVIII-500Q spectrometer (500 MHz). 1H chemical shifts were recorded in ppm with tetramethylsilane (TMS) as an internal standard. Mass spectra were recorded on an AB SCIEX 3200Q TRAP LC/MS/MS system united with Agilent 1260 Infinity HPLC. An Elemerlar Vario EL III elemental analyzer (Germany) was utilized for elemental analyses of the synthetic compounds. Melting points were determined on a

SC

X-5 melting point apparatus. The morphologies of the xerogels were characterized by a Hitachi S4800 FE-SEM microscope. The samples were prepared by dropping the hot solution of the gelator in DMSO at its MGC

M AN U

(minimum gelation concentration) on a glass sheet where gel could be formed on site, and then evaporation of the solvent was implemented for 48 h at room temperature under vacuum. The XRD patterns of xerogels, which were prepared by drying the resultant gels on the glass plates for 48 h at room temperature under vacuum, were recorded on a Bruker D8 ADVANCE high resolution diffractometer (Cu Ka radiation, l = 1.546 Å). Fluorescence spectra were obtained on a Hitachi F-4500 fluorescence spectrophotometer in quartz cells with a pathlength of 1

TE D

cm. UV-vis absorption spectra were determined on a Perkin-Elmer Double Beam UV/vis Spectrometer in quartz cells with a pathlength of 1 cm. CO2 stream was controlled and detected by a V10FD-XS flow controller which was connected to a high-pressure CO2 cylinder with a hose. The controller can detect the follow velocity ranging

EP

from 0 to 10 mL min-1. 2.2. Synthesis Procedures

AC C

Synthesis of 3-nitro-N-butyl-1,8-naphthalimide (2) 3-Nitro-1,8-naphthalic anhydride (0.24g, 1 mmol) was dissolved in the ethanol (30 ml). Then, n-butylamine (0.08 g, 1.1 mmol) was added slowly under magnetic stirring. The resulting solution was heated to reflux at 78 oC for 10 min under microwave. The obtained solid was filtered and dried in vacuum to give a light yellow solid of 179 mg, yield: 60%. M.p.182.4-184.3oC。 1H NMR (500 MHz, CDCl3): δ 9.32 (d, J = 2.0 Hz, 1H), 9.13 (d, J = 2.0 Hz, 2H), 8.78 (d, J = 7.5 Hz, 1H), 8.42 (d, J = 8.0 Hz, 1H), 7.94 (t, J = 7.5 HZ, 2H), 4.21 (t, J = 7.5 Hz, 2H), 1.76-1.50 (m, 2H), 1.48-1.42 (m, 2H), 0.99 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ 163.1, 162.6, 146.2, 136.6, 134.3, 131.2, 130.0, 129.8, 129.6, 124.3, 123.2, 122.9, 29.9, 20.2, 19.9, 14.1. EPI-MS C16H14N2O4 ([M+H]+) calcd 299.3, found 299.1. Elem. Anal. for C16H14N2O4: calcd. C 64.42, H 4.73, N 9.39; found C 65.41, H 4.64, N 9.61. Synthesis of 3-amino-N-butyl-1,8-naphthalimide (3) 3

ACCEPTED MANUSCRIPT Compound 2 (0.3g, 1 mmol) was dissolved in ethanol (20 ml). Then, hydrazine hydrate (0.2 mL, 3.5 mmol) and 10% Pd/C were added slowly under magnetic stirring. The resulting solution was heated to reflux at 78 oC for 1h. The obtained solid was dried in vacuum to give a yellow solid of 175 mg, yield: 65%. M.p.150.2-152.1oC. 1H NMR (500 MHz, CDCl3): δ 8.32 (d, J = 3.5 Hz, 1H), 8.02 (d, J = 1.0 Hz, 1H), 7.93 (d, J = 4.0 Hz, 1H), 7.60 (t, J = 7.5 Hz, 1H), 7.30 (d, J = 1.0 Hz, 1H), 4.16 (t, J = 7.5 Hz, 2H), 1.73-1.67 (m, 2H), 1.48-1.40 (m, 2H), 0.97 (t, J =

RI PT

7.0 Hz, 3H). 13C NMR (125 MHz, DMSO-d6): δ 164.2, 164.0, 148.4, 134.0, 131.9, 127.4, 125.9, 123.0, 122.2, 122.2, 121.0, 112.2, 30.2, 20.3, 14.2. EPI-MS C16H16N2O2 ([M+H]+) calcd 269.3, found 269.2. Elem. Anal. for C16H16N2O2: calcd. C 71.62, H 6.01, N 10.44; found C 69.47, H 5.91, N 11.05. Synthesis of Nap-but 1

SC

Compound 3 (0.27g, 1 mmol) was dissolved in 1,4-dioxane (30 ml). Then, 2-Naphthoyl Chloride (1.2 mmol) was added slowly under magnetic stirring at 0 oC. The resulting solution was stirred at room temperature, and then

M AN U

heated to reflux at 105 oC for 10 min under microwave. The obtained solid was dried in vacuum to give a yellow solid. The residue was purified by column chromatography (silica gel, dichloromethane) to obtain a yellow powder of 317 mg, yield: 75%. M.p. 202.3-203.7 oC. 1H NMR (500 MHz, CDCl3): δ 9.08 (d, J = 1.0 Hz, 1H), 8.61 (s, 1H)，8.46 (d, J = 1.0 Hz, 1H), 8.46 (d, J = 1.0 Hz, 2H), 8.15 (d, J = 4.0 Hz, 1H), 8.00-7.98 (m, 1H), 7.93 (d, J = 4.0 Hz, 2H), 7.87 (d, J = 4.0 Hz, 1H), 7.70 (t, J = 7.5 Hz, 1H), 7.60-7.53 (m, 2H), 4.14 (t, J = 7.5 Hz, 2H),

TE D

1.72-1.66 (m, 2H), 1.44-1.37 (m, 2H), 0.95 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ 166.4, 163.8, 163.6, 138.5, 134.9, 134.2, 132.5, 132.4, 132.0, 129.5, 129.5, 128.8, 128.6, 128.5, 128.2, 127.9, 127.4, 125.3, 124.9, 124.6, 122.9, 122.4, 122.2, 100.0, 30.1, 20.3, 14.2. EPI-MS

C27H22N2O3 ([M+H]+) calcd 423.5, found

AC C

EP

423.3. Elem. Anal. for C27H22N2O3: calcd. C 76.76, H 5.25, N 11.36; found C 75.82, H 5.45, N 11.30.

4

ACCEPTED MANUSCRIPT

a

b

5 µm

RI PT

d

5 µm

M AN U

5 µm

SC

c

5 µm

Figure 1 SEM images of xerogels obtained from Nap-but 1-DMSO gel (a), Nap-but 1-methyl benzoate gel (b), Nap-but 1-toluene gel (c), Nap-but 1-bromobenzene gel (d) at their MGCs. 3. Results and discussion

TE D

3.1. Synthesis and gelation behaviour of target compound Nap-but 1

The synthesis of target compound Nap-but 1 involved three steps as shown in Scheme 1, which started with a condensation reaction of 3-nitro-1,8-naphthalic anhydride and n-butylamine. In order to shorten the reaction time,

EP

microwave irradiation was used for the first-step reaction to give intermediate 2 in 60% yield. Then, compound 2 was subjected to a reduction of nitro group on its 3 position to obtain amino derivative 3. Finally, the target compound was obtained by a microwave-assisted acylation reaction of precursor 3 with 2-naphthoyl chloride in a

AC C

satisfactory yield of 75%. All the synthetic compounds were characterized well by elemental analysis, 1H and 13C NMR, and mass spectroscopy.

5

11.0

10.5

10.0

9.5

9.0

8.5

8.0

7.67

7.68

7.84

8.05

8.40

9.05 8.92

a

8.72

11.00

8.12

7.83

8.05

SC

7.81

8.03

RI PT

7.66

8.10

8.36 8.34 8.33 8.13 8.11 8.07 8.02 8.00 7.79 7.77 7.65 7.63 8.40

M AN U

b

8.72

9.03 8.92

10.96

8.11

c

8.70

9.00 8.91

10.90

8.37

d

8.69

8.96 8.90

10.82

ACCEPTED MANUSCRIPT

7.5

TE D

Figure 2. Temperature-dependent partial 1H NMR (500 MHz) spectra of gelator Nap-but 1 (3.5 wt%, gel state at 293 K) in DMSO-d6 (0.5 mL): (a) 293 K, (b) 308 K, (c) 323 K, (d) 338 K. The gelation behaviour of Nap-but 1 was examined by the heating-and-cooling method in various organic

EP

solvents. In general, 30 mg of the gelator and 0.3 mL solvent were added into a sealed glass vial prior to obtaining a clear solution by heating. Then the resulting solution was cooled to room temperature unless otherwise stated

AC C

and left for 30 min, and gel formation was determined by the fact that the sealed vial was turned upside down without any solvent flow observed inside, which is so-called “inversion-vial” method. The minimum gelation concentration (MGC) values of Nap-but 1 in various solvents were determined by a dilution strategy. Generally, 30 mg of the gelator was added to an organic solvent of 0.3 mL in a septum-capped vial. The resultant gel was diluted gradually by the solvent, and the heating-and-cooling process was repeated until the gelator never formed a stable gel any more. The smallest concentration keeping the gel state was referred to as the MGC (wt% as the unit). The temperature for gel-to-sol transition (Tg) was measured by using a “dropping ball” method. In the experiment, a small steel ball (100 mg) was put carefully on the top of the gel in a test vial. The gel was slowly heated (1 oC/min) in a thermostatted oil bath, and the temperature at which the ball fell to the vial bottom was recorded as the Tg. It was found that toluene, chlorobenzene, bromobenzene, nitrobenzene, methyl benzoate, and 6

ACCEPTED MANUSCRIPT DMSO could be gelated by Nap-but 1 out of the 21 tested solvents as summarized in Table S1. Moreover, the resultant orangogels could keep stable for several months at room temperature without appreciable loss in integrity and endure the heating-and-cooling cycles more than 50 times, indicating their themoreversible stability. 9.0

a b c

1.5

400

425

450

475

M AN U

0.0 375

SC

3.0

RI PT

×

4.5

-3

10 M -3 10 M -4 10 M

×

c 6.0 b 3.0 a 6.0

6.0

Absorbance

×

7.5

Wavelength(nm)

Figure 3. UV-vis spectra of Nap-but 1 in DMSO: 6.0 × 10-4 M (a); 3.0 × 10-3 M (b); 6.0 × 10-3 M (c). In order to give insight into the self-assembly patterns of Nap-but 1 in gel phase, the morphologies of the xerogels which were prepared in some organic solvents were examined by scanning electron microscopy (SEM).

TE D

As shown in Figure 1, the SEM images show well-defined three-dimensional (3D) networks which were self-assembled by the gelator in organic solvents. It is noteworthy that Nap-but 1 can display different aggregation morphologies in different kinds of organic solvents. For instance, the xerogel obtained from DMSO exhibits strip-like self-assembly structure. Whereas the gelator prefers to form a sarcoid-like aggregation structure

EP

in methyl benzoate. And the SEM images of the gelator in toluene and bromobenzene reveal the similar branch-like network structure. Based on these results, it is concluded that the aggregation mode of the gelator in

AC C

organic solvents depends on the nature of the gelation solvents.

7

ACCEPTED MANUSCRIPT

25.0 (0.36 nm) 21.46 (0.41 nm)

21.44 (0.41 nm)

b

25.22 (0.35 nm)

21.08 (0.42 nm)

c

21.52 (0.41 nm)

d

25.0 (0.36 nm)

RI PT

Intensity (a. u.)

a

24.75 (0.36 nm)

10

15

20

25

SC

5

30

M AN U

Degree (2θ)

Figure 4. X-ray diffraction patterns (r. t.) of xerogels obtained from Nap-but 1-DMSO gel (a); Nap-but 1-bromobenzene gel (b); Nap-but 1-toluene gel (c); Nap-but 1-methyl benzoate gel (d) at their MGCs. In our previous researches, hydrogen bondings played the major role in the gel formation due to the intermolecular interactions of the carbamate ester groups [8a, 8c]. In this work, the temperature-dependent 1H

TE D

NMR experiment of Nap-but 1 was carried out to investigate the driving forces that induce the self-assembly of the gelator into gel in an organic solvent. It is shown in Figure 2 that the amide NH resonance signals shift gradually upfield from 11.00 to 10.82 ppm along with the increase in the temperature from 293 to 338 K, indicating the presence of the intermolecular hydrogen bondings between gelator molecules in gel phase.

EP

Meanwhile, the increase of the temperature can lead to a slight upfield shift for all the aromatic protons in naphthalene rings. This observation suggests the existence of π-π stacking interactions in gel which can be

AC C

weakened upon heating. Besides, the red shift of the UV-vis absorption spectra of Nap-but 1 in DMSO with a high concentration in contrast to those of low concentrations can also testify the participation of π-π stacking interactions (J-aggregation) in the gel formation (Figure 3). In addition, the π-π interactions between the adjacent naphthalene moieties can be also proven further by means of powder X-ray diffraction (PXRD) as shown in Figure 4. A d-spacing of 3.5nm or 3.6 nm which is assigned to the typical π-π interaction distance was generally observed in the XRD patterns of the xerogels obtained from four solvents [9]. On the basis of these experimental results, the intermolecular hydrogen bondings between the amide groups as well as the π-π interactions between aromatic moieties should drive the gel formation in organic solvents.

8

1200

Nap-but 1:F 1:0 1:2 1:5 1:7 1:10 1:12 1:15 1:20 1:25 1:30 1:35

a

1000 800 600 400 200

2.0

450

500

550

600

Nap-but 1:F 1:0 1:2 1:5 1:7 1:10 1:12 1:15 1:17 1:20 1:25 1:30 1:35

b

1.5 1.0 0.5

0 400

-

-

Absorbance

Fluorescent Intensity (a. u.)

ACCEPTED MANUSCRIPT 2.5

650

Wavelength (nm)

0.0 400

450

500

550

600

RI PT

Wavelength(nm)

Figure 5. Fluorescent (a, excitation at 360 nm) and UV/Vis (b) changes of compound Nap-but 1 (6.0 × 10-4 M in

M AN U

SC

2 mL of DMSO) in the presence of different quantities of TBAF (0-35 equiv.) at 25oC.

Figure 6. Photographs showing the changes of compound Nap-but 1 (0.1 M in 1 mL of DMSO) in the presence of 5 equiv. of various anions (as their tetrabutylammonium salts) at 25oC. (a) Free 1; (b) 1 + F-; (c) 1 + Cl-; (d) 1 + Br-; (e) 1 + I-; (f) 1 + CH3COO-; (g) 1 + HCO3-. Left: under the light; Right: under the UV irradiation. 3.2. Anion responsiveness

TE D

The response of Nap-but 1 towards various anions with their tetrabutylammonium salts as the sources was investigated in solution and in the gel state. First, we carried out anion-fluorescence titration experiments in the diluted DMSO solution (6.0×10-4 M) of Nap-but 1. As shown in Figure S1a, the maximum extent decrease of the

EP

fluorescence intensity of Nap-but 1 at 430 nm was observed with fluoride ions (as tetrabutylammonium fluoride, TABF) over the other anions of Cl-, Br-, I-, CH3COO-, and HCO3-. Moreover, the addition of fluoride ions to the

AC C

DMSO solution of Nap-but 1 could induce the appearance of a new UV absorption band at 475 nm (Figure S1b). The specific titration of fluoride ions indicated that the fluorescence of Nap-but 1 could be almost thoroughly quenched upon the addition of 35 equiv. of fluoride ions in solution as shown in Figure 5. On the other hand, the addition of fluoride ions to the organogel of Nap-but 1 in DMSO could lead to a distinct transition from the gel to a transparent solution. In the meantime, the gel-to-solution transformation was accompanied with a color change from yellow to red, and the fluorescence of Nap-but 1 was quenched as depicted in Figure 6. However, the gel state of Nap-but 1 was able to be remained upon the addition of the other anions, indicating a good selectivity of the gelation system towards fluoride ions in the present case. Particularly, only 5 equiv. of fluoride ions could result in the complete gel-to-solution phase transition within 10 min (Figures S2 and S3). The phase transition was considered to be induced by the destruction of the intermolecular hydrogen bondings which support the gel 9

ACCEPTED MANUSCRIPT state of the gelator in DMSO upon the reaction with fluoride ions [8a]. Vco2 (mL) Free Nap-but 1 Nap-but 1 +35 equiv.F 0.1 0.2 0.3 0.4 0.5 0.7 1.0 1.5 2.0

1000 800 600 400 200

2.5

Vco2 (mL)

b

Free Nap-but 1 Nap-but 1 + 35 equiv.F 0.1 0.2 0.3 0.4 0.5 0.7 1.0 1.5 2.0

2.0 1.5 1.0 0.5 0.0

0 400

450

500

550

600

450

650

RI PT

a

Absorbance

Fluorescent Intensity (a. u.)

3.0 1200

500

550

600

Wavelength (nm)

Wavelength(nm)

Figure 7. Fluorescent (a, excitation at 360 nm) and UV/Vis (b) spectral changes of compound Nap-but 1 (6.0 × 10-4 M in 2 mL of DMSO) in the presence of TBAF (35 equiv.) and CO2 at 25oC.

SC

3.3. Responsiveness of CO2

The response of Nap-but 1 towards CO2 was investigated by the anion-induced strategy in DMSO. As a result,

M AN U

the bubbling of CO2 to a low-concentration solution of Nap-but 1 (6.0 × 10-4 M in DMSO) in the presence of 35 equiv. of TBAF gave increase of the fluorescence emission at 430 nm, as well as decrease of the UV absorption centered at 475 as shown in Figure 7. Furthermore, the fluorescence and UV absorption spectral features of Nap-but 1 could be nearly restored to those of the original solution in the absence of TBAF upon the bubbling of 2.0 mL of CO2 with the flow velocity of 3.0 mL/min. The sensing mechanism should be due to the recovery of the

TE D

neutral structure of Nap-but 1 related to the complimentary of protons to the fluoride ion-deprotonated amides via the reaction of CO2 with the trace water in DMSO following the generation of HCO3- ions as our previous reports

500

EP

1500

400

I/I0

300

1000

200 100

AC C

Fluorescent Intensity (a. u.)

[7, 8a, 8c]. And it could be confirmed by the NMR titration experiments as shown in Figure S7

0 -

Nap-but 1 + F + CO2

500

0

1

2

3

4

5

VCO2 (mL) -

Nap-but 1 + F

0

400

500

600

700

800

Wavelength(nm)

Figure 8. Left: fluorescence spectral changes of compound Nap-but 1 (3.5 wt% in 1 mL of DMSO) in the presence of 5 equiv. of TBAF upon the bubbling of 5 mL of CO2 with the flow velocity under 4 mL/min, inset shows the linear correlation between CO2 volumes and relative intensities recorded at 468 nm with the excitation at 360 nm. Right: photograph of the reversible solution-and-gel transition in response to CO2 bubbling (solution to 10

ACCEPTED MANUSCRIPT gel) or N2 bubbling at > Tg (gel to solution). Then, the response of the solution with a high concentration of Nap-but 1 at above its MGC towards CO2 was also observed based on the reported sensing mechanism. For instance, upon the bubbling of CO2 (4 mL/min) to a solution of Nap-but 1 (3.5 wt% in 1 mL of DMSO) in the presence of 5 equiv. of TABF, the red transparent solution gradually turned turbid, and finally regeneration of a yellow opaque gel was observed when CO2 volume

RI PT

reached approximate 5 mL, which was accompanied with the gelator fluorescence recovery as shown in Figure 8 left. Particularly, the testing results obtained above afforded a near-linear correlation between the intensity ratios of the enhanced fluorescence value (I) to the initial one (I0) at 468 nm and the CO2 volumes [V(CO2)] that ranged from 0 to 4.7 mL [I/I0 = 117V(CO2) – 43, R = 0.9899] as shown in the inset to Figure 8 left. In addition, it was

SC

found that CO2 release out of the resulting gel was observed by the N2 bubbling at above Tg within several seconds which could be reflected by the recovery of the red solution state and the fluorescence quenching. And

M AN U

the reversible gel-and-solution transition cycle could be repeated at least seven times (Figure S4). 300 250

300

200

I/I0

150 100

200 -

50

Nap-but 1 + F + CO2

0

100

0

50

100

150

in air

200

TE D

Fluorescent Intensity (a. u.)

400

Time (min)

-

Nap-but 1 + F

0 400

500

600

700

800

in a

ir

Wavelength (nm)

EP

Figure 9. Changes of compound Nap-but 1 (3.5 wt% in 1 mL of DMSO in the presence of 5 equiv. of TBAF) upon exposed to the air. Left: Fluorescent spectra with the excitation at 360 nm (inset: relative fluorescence

AC C

intensities at 468 nm versus the exposure time); Right: Photographs. Very interestingly, gel regeneration could be also observed by naked eyes upon the direct exposure of the solution of Nap-but 1 (3.5 wt% in 1 mL of DMSO) containing 5 equiv. of TBAF to the air for 3 h. And the recovery of the gel gave rise to a significant fluorescence enhancement as shown in Figure 9. The control test further illustrated in Figure S5 that no changes of the solutions were distinguished by naked eyes upon exposed to nitrogenic or oxygenic atmosphere, which suggested CO2 in the air should be responsible for the gel recovery. Moreover, it was found that less than 10 min exposure could give rise to the re-gelation when the solution was exposed to the CO2 atmosphere (Figure S6). Subsequently, study on the response of the fluoride-stimulus induced solution towards CO2 in a sealed container was performed to mimick the cases in confined spaces. As depicted in 11

ACCEPTED MANUSCRIPT Figure 10 left, gel regeneration could be observed upon the exposure of the DMSO solution (1 mL) of Nap-but 1 (3.5 wt%) in the presence of 5 equiv. of TBAF to CO2 of 6% volume concentration in a rubber-plug-sealed wide-mouth bottle (2500 mL) at room temperature for more than 3 h. Further tests indicated that in such space ≥ 1% could recover the gel state of Nap-but 1 in DMSO with 5 equiv. of TBAF which was rested for 3 h. Meanwhile, the correspondingly increased fluorescence intensities of Nap-but 1 at 468 nm could be recorded at

RI PT

different CO2 volume concentrations as shown in Figure 10 right. In addition, if the exposure time was set as 1 h, at least 15% of CO2 could result in the gel recovery. The reformed gels were stable and not easy to collapse even with a moderate shaking. The experimental results obtained above suggest that the developed sensing system has the applicable potential not only in the visual sensing of CO2 via solution-to-gel transition but also in the

300

M AN U

250

SC

quantitative analysis of CO2 by fluorescence changes in confined spaces.

200

I/I0

150 100

TE D

50 0

0

1

2

3

4

5

6

CO2 concentration (v/v%)

EP

Figure 10. Left: Photograph of gel regeneration of the DMSO solution (1 mL) of Nap-but 1 (3.5 wt%) in the presence of 5 equiv. of TBAF in a rubber-plug-sealed wide-mouth bottle of 2500 mL cubage containing 6 % of

AC C

CO2 with the exposure time as 3 h; Right: Relative fluorescence intensities of Nap-but 1 (3.5 wt% in 1 mL of DMSO solution in the presence of 5 equiv. of TBAF) at 468 nm (excitation at 360 nm) versus the volume concentration of CO2 in the 2500 mL sealed container with a standing time as 3 h. 4. Conclusion

In summary, we prepared a new 3-position modified naphthalimide organogelator bearing a naphthyl group at the 3-position, which could form stable gels in some aromatic solvents and DMSO. SEM images revealed the resulting gels possessed well-defined 3D network architectures. In combination with the characterization by using 1

H NMR spectra, UV-vis spectra, and PXRD, we concluded that hydrogen bondings were the major driving forces

for the gel formation, and π-π stacking interaction also participated in the self-assembly process. Furthermore, we found that the obtained organogel of the synthesized gelator in DMSO could recognize fluoride ion selectively by 12

ACCEPTED MANUSCRIPT the gel collapse into a transparent solution, accompanied with the fluorescence quenching. Moreover, the reslutant solution could permit a visual sensing of CO2 stream via the solution-to-gel transition and fluorescence spectra-based quantitative detection. More interestingly, the present gelation sensing system was found to be able to analyze CO2 directly in air via the phase transformation. These results indicated that based on the anion-induced strategy, the synthesized gelator possossed the applicable potential not only in the real-time

RI PT

detection of CO2 stream but also in the visual sensing of CO2 in closed spaces.

Acknowledgments

We thank to the support of the National Natural Science Foundation of China (No. 21502040 and 21272054), Nature Science Foundation of Hebei Province (No. B2016205211, B2016205249, and B2018205199), Youth

SC

Top-notch Talent Foundation of the Education Department of Hebei Province (No. BJ2014039 and BJ2018022),

Captions for Figures and Scheme

M AN U

Colleges and Universities in Hebei Province Science and Technology Research Project (ZD2015030).

Scheme 1. i) Butylamine, ethanol, microwave, reflux for 10 min, 60%; ii) hydrazine hydrate and 10% Pd/C, ethanol, reflux for 1h, 65%; iii) 2-naphthoyl chloride, 1, 4-dioxane, microwave, reflux for 15 min, 75%. Figure 1 SEM images of xerogels obtained from Nap-but 1-DMSO gel (a), Nap-but 1-methyl benzoate gel (b), Nap-but 1-toluene gel (c), Nap-but 1-bromobenzene gel (d) at their MGCs.

TE D

Figure 2. Temperature-dependent partial 1H NMR (500 MHz) spectra of gelator Nap-but 1 (3.5 wt%, gel state at 293 K) in DMSO-d6 (0.5 mL): (a) 293 K, (b) 308 K, (c) 323 K, (d) 338 K. Figure 3. UV-vis spectra of Nap-but 1 in DMSO: 6.0 × 10-4 M (a); 3.0 × 10-3 M (b); 6.0 × 10-3 M (c).

EP

Figure 4. X-ray diffraction patterns (r. t.) of xerogels obtained from Nap-but 1-DMSO gel (a); Nap-but 1-bromobenzene gel (b); Nap-but 1-toluene gel (c); Nap-but 1-methyl benzoate gel (d) at their MGCs.

AC C

Figure 5. Fluorescent (a, excitation at 360 nm) and UV/Vis (b) changes of compound Nap-but 1 (6.0 × 10-4 M in 2 mL of DMSO) in the presence of different quantities of TBAF (0-35 equiv.) at 25oC. Figure 6. Photographs showing the changes of compound Nap-but 1 (0.1 M in 1 mL of DMSO) in the presence of 5 equiv. of various anions (as their tetrabutylammonium salts) at 25oC. (a) Free 1; (b) 1 + F-; (c) 1 + Cl-; (d) 1 + Br-; (e) 1 + I-; (f) 1 + CH3COO-; (g) 1 + HCO3-. Left: under the light; Right: under the UV irradiation. Figure 7. Fluorescent (a, excitation at 360 nm) and UV/Vis (b) spectral changes of compound Nap-but 1 (6.0×10-4 M in 2 mL of DMSO) in the presence of TBAF (35 equiv.) and CO2 at 25oC. Figure 8. Left: fluorescence spectral changes of compound Nap-but 1 (3.5 wt% in 1 mL of DMSO) in the presence of 5 equiv. of TBAF upon the bubbling of 5 mL of CO2 with the flow velocity under 4 mL/min, inset shows the linear correlation between CO2 volumes and relative intensities recorded at 468 nm with the excitation 13

ACCEPTED MANUSCRIPT at 360 nm. Right: photograph of the reversible solution-and-gel transition in response to CO2 bubbling (solution to gel) or N2 bubbling at > Tg (gel to solution). Figure 9. Changes of compound Nap-but 1 (3.5 wt% in 1 mL of DMSO in the presence of 5 equiv. of TBAF) upon exposed to the air. Left: Fluorescent spectra with the excitation at 360 nm (inset: relative fluorescence intensities at 468 nm versus the exposure time); Right: Photographs.

RI PT

Figure 10. Left: Photograph of gel regeneration of the DMSO solution (1 mL) of Nap-but 1 (3.5 wt%) in the presence of 5 equiv. of TBAF in a rubber-plug-sealed wide-mouth bottle of 2500 mL cubage containing 6 % of CO2 with the exposure time as 3 h; Right: Relative fluorescence intensities of Nap-but 1 (3.5 wt% in 1 mL of DMSO solution in the presence of 5 equiv. of TBAF) at 468 nm (excitation at 360 nm) versus the volume

SC

concentration of CO2 in the 2500 mL sealed container with a standing time as 3 h.

References

M AN U

[1] (a) Sangeetha NM, Maitra U. Supramolecular gels: Functions and uses. Chem Soc Rev 2005; 34: 821-36. (b) Hirst AR, Escuder B, Miravet JF, Smith DK. High-tech applications of self-assembling supramolecular nanostructured gel-phase materials: From regenerative medicine to electronic devices. Angew Chem Int Ed 2008; 47: 8002-18.

[2] Abdallah DJ, Weiss RG. Organogels and low molecular mass organic gelators. Adv Mater 2000; 12: 1237-47

2012; 22: 38-50.

TE D

[3] (a) Yang X, Zhang G, Zhang D.Stimuli reponsive gels based on low molecular weight gelators. J Mater Chem

(b) Pal A, Basit H, Sen S, Aswal VK, Bhattacharya S. Structure and properties of two component hydrogels

EP

comprising lithocholic acid and organic amines. J Mater Chem 2009; 19: 4325-34. (c) Piepenbrock MOM, Lloyd GO, Clarke N, Steed JW. Metal- and anion binding supramolecular gels. Chem Rev

AC C

2010; 110: 1960-2004.

(d) Dou C, Li D, Gao H, Wang C, Zhang H, Wang Y. Sonication-induced molecular gels based on mono-cholesterol substituted quinacridone derivatives. Langmuir 2010; 26: 2113-8. (e) van Herpt JT, Stuart MCA, Browne WR, Feringa BL. Mechanically induced Gel Formation. Langmuir 2013; 29: 8763-7. [4] Tu T, Fang W, Sun Z. Visual-size molecular recognition based on gels. Adv Mater 2013; 25: 5304-13. [5] (a) Li L, Zhao N, Wei W, Sun YH. A review of research progress on CO2 capture, storage, and utilization in Chinese academy of sciences. Fuel 2013; 108: 112-30. (b) Dutcher B, Fan M, Russell AG. Amine-based CO2 capture technology development from the beginning of 2013-a review. ACS Appl Mater Interfaces 2015; 7: 2137-48. 14

ACCEPTED MANUSCRIPT (c) Lu XQ, Jin DL, Wei SX, Wang ZJ, An CH, Guo WY. Strategies to enhance CO2 capture and separation based on engineering absorbent materials. J Mater Chem A 2015; 3: 12118-32. [6] (a) Zhang G, Lui J, Yuan M. Novel carbon dioxide gas sensor based on infrared absorption. Opt Eng 2000; 39: 2235-40. (b) Mcguire MA, Teskey RO. Estimating stem respiration in trees by a mass balance approach that accounts for

RI PT

internal and external fluxes of CO2. Tree Physiol 2004; 24: 571-8. (c) Beyenal H, Davis CC, Lewandowski Z. An improved severinghaus-type carbon dioxide microelectrode for use in biofilms. Sens Actuators B 2004; 97: 202-10.

(d) Shimizu Y, Yamashita N. Solid electrolyte CO2 sensor using NASICON and perovskite-type oxide electrode.

SC

Sens Actuators B 2000; 64: 102-6.

(e) Star A, Han T, Joshi V, Gabriel JP, Grüner G. Nanoelectronic carbon dioxide sensors. Adv Mater 2004; 16:

M AN U

2049-52.

(f) Yanai N, Kitayama K, Hijikata Y, Sato H, Matsuda R, Kubota Y, et al. Gas detection by structural variations of fluorescent guest molecules in a flexible porous coordination polymer. Nat Mater 2011; 10: 787-93. (g) Guo Z, Song NR, Moon JH, Kim M, Jun EJ, Choi J, et al. Benzobisimidazoliumbased fluorescent and colorimetric chemosensor for CO2. J Am Chem Soc 2012; 134: 17846-9.

TE D

(h) Abraham S, Weiss RG. Control of pyrene fluorescence intensity by in situ addition of CO2 to an amidine/amine mixture or CO2 removal from an amidinium carbamate ionic liquid. Photochem Photobiol Sci 2012; 11: 1642-4. (i) Pandey S, Baker SN, Pandey S, Baker GA. Optically responsive switchable ionic for internally-referenced

EP

fluorescence monitoring and visual determination of carbon dioxide. Chem Commun 2012; 48: 7043-5. (j) Xu LQ, Zhang B, Sun M, Hong L, Neoh KG, Kang ET, et al. CO2-Triggered fluorescence “Turn-on” response

AC C

of perylene diimide-containing poly (N,N-dimethylaminoethyl methacrylate). J Mater Chem A 2013; 1: 1207-12. (k) Ishida M, Kim P, Choi J, Yoon J, Kim D, Sessler JL. Benzimidazole-embedded N-Fused aza-indacenes: Synthesis and deprotonation-assisted optical detection of carbon dioxide. Chem Commun 2013; 49: 6950-2. (l) Xu Q, Lee S, Cho Y, Kim MH, Bouffard J, Yoon J. Polydiacetylene-based colorimetric and fluorescent chemosensor for the detection of carbon dioxide. J Am Chem Soc 2013; 135: 17751-17754. (m) Lee M, Moon JH, Swamy KMK, Jeong Y, Kim G, Choi J, et al. A new bispyrene derivative as a selective colorimetric and fluorescent chemosensor for cyanide and fluoride and anion-activated CO2 sensing. Sens Actuators B 2014; 199: 369-76. (n) Lee M, Jo S, Lee D, Xu ZC, Yoon J. A new naphthalimide derivative as a selective fluorescent and colorimetric sensor for fluoride, cyanide and CO2. Dye Pigment 2015; 120: 288-92. 15

ACCEPTED MANUSCRIPT [7] Zhang X, Mu H, Li H, Zhang Y, An M, Zhang X, et al. Dual-channel sensing of CO2: Reversible solution-gel transition and gelation-induced fluorescence enhancement. Sens Actuators B 2018; 255: 2764-78 [8] (a) Zhang X, Lee S, Liu Y, Lee M, Yin J, Sessler JL, et al. Anion-activated, thermoreversible gelation system for the capture, release, and visual monitoring of CO2. Sci Rep 2014; 4: 4593/1-8. (b) Liu Y, Lee D, Zhang X, Yoon J. Fluoride ion activated CO2 sensing using sol-gel system. Dye Pigment 2017;

RI PT

139: 658-63. (c) Zhang X, Li H, Mu H, Liu Y, Guan Y, Yoon J, Yu H. Cholesteryl naphthalimide-based gelators: Their applications in the multiply visual sensing of CO2 based on an anion-induced strategy. Dye Pigment 2017; 147: 40-9.

SC

[9] Xu HX, Das AK, Horie M, Shaik MS, Smith AM, Luo Y, et al. An investigation of the conductivity of peptide

AC C

EP

TE D

M AN U

nanotube networks prepared by enzyme triggered self-assembly. Nanoscale 2010; 2: 960-6.

16

ACCEPTED MANUSCRIPT Supporting Information for: “Visual sensing of CO2 in air with a 3-position

modified naphthalimide-derived organogelator based on a fluoride ion-induced strategy”

RI PT

Xin Zhang, Yuanyuan Song, Meng Liu, Haimiao Li, Helue Sun, Mengmeng Sun, and Haitao Yu

National Demonstration Center for Experimental Chemistry Education, College of Chemistry and Materials Science, Hebei Normal University, Shijiazhuang, 050024, China

AC C

EP

TE D

M AN U

SC

[email protected] (H. Y.)

Table S1 Gelation ability of Nap-but 1 in various solvents in air at 25 oC. 17

ACCEPTED MANUSCRIPT Entry

Phasea

MGCb/wt%

Tgc/oC

aniline

S

-

-

2

N,N-dimethylaniline

P

-

-

3

cyclohexanone

S

-

-

4

acetylbenzene

S

-

-

5

ethanol

P

6

benzylalcohol

S

7

quinoline

S

8

morpholine

S

9

phenylhydrazine

S

10

cyclohexane

I

11

hexane

12

benzene

13

toluene

14

chlorobenzene

15

bromobenzene

16

nitrobenzene

17

RI PT

1

-

-

-

-

-

-

-

-

-

-

-

I

-

-

I

-

-

G

3.1

74

G

2.9

40

G

1.8

38

G

5.9

44

p-methoxybenzaldehyde

S

-

-

18

ethyl acetate

I

-

-

19

methyl benzoate

G

4.4

45

20

DMF

S

-

-

G

2.7

40

AC C

EP

TE D

M AN U

SC

-

21 a

Solvent

DMSO

The mixture containing 30 mg of gelator and 0.3 ml of solvent was heated until Nap-but 1 was dissolved in the

solvent and then cooled to 25 oC: G = Gel; S = Solution; I = Insoluble; P = Precipitation. b The minimum gelation concentration (MGC) values were represented by the mass percent. c Gel-to-sol transition temperature (Tg) was determined by a “dropping ball” method.

18

ACCEPTED MANUSCRIPT 3.0

1200

a

Anions F HCO3

1000

2.5

Absorbance

Fluorescent Intensity (a. u.)

1400

-

CH3COO

800

-

Cl I Br

600 400

b

Anions F HCO3

2.0

-

CH3COO

1.5

-

Cl I Br

1.0 0.5

200 0 400

450

500

550

600

Wavelength (nm)

0.0 400

450

500

550

600

RI PT

Wavelength(nm)

Figure S1 Fluorescent (a, excitation at 360nm) and UV/Vis (b) spectral changes of compound Nap-but 1 (6.0×10-4 M in 2 mL of DMSO) in the presence of 40 equiv. of various anions (as their tetrabutylammonium salts)

TE D

M AN U

SC

at 25oC.

Figure S2 Phorographs showing the process of the collapse of the gel (3.5 wt% of Nap-but 1 in 1 mL of DMSO)

AC C

EP

upon the addition of different equivalents of TBAF.

Figure S3 Phorographs showing the process of the collapse of the gel (3.5 wt% of Nap-but 1 in 1 mL of DMSO) upon the addition of 5 equiv. of TBAF with the time.

19

ACCEPTED MANUSCRIPT Gel

1250 1000 750 500

RI PT

Fluorescent Intensity(a.u.)

1500

250 0 Solution

SC

Cycles

Figure S4 Reversible fluorescence intensity of Nap-but 1 (3.5 wt% in 1 mL of DMSO) in the presence of 5 equiv.

(b)

(c)

TE D

(a)

M AN U

of TBAF at 468 nm with the excitation at 360 nm by the repeating processes of bubbling CO2 and N2 at > Tg.

Figure S5 Photographs of changes of TBAF-induced transparent solutions of gelator Nap-but 1 (3.5 wt% in DMSO) in oxygen (a), nitrogen (b), and carbon dioxide (c) atmospheres. 500

EP 400

400 300

I/I0

300

AC C

Fluorescent Intensity (a. u.)

500

200 100

200

0 -

Nap-but 1 + F + CO2

100 0

400

500

0

2

4

6

8

10

Time (min) -

Nap-but 1 + F

600

700

800

Wavelength (nm)

Figure S6 Changes of compound Nap-but 1 in DMSO (3.5 wt% with 5 equiv. of TBAF) upon exposed to the CO2 atmosphere. Left: Fluorescent spectra with the excitation at 360 nm (inet: relative fluorescence intensities at 468 nm versus the exposure time); Right: Photographs.

20

O

N

O

7.68 7.67 7.65 7.64

8.42 8.40 8.17 8.10 8.08 7.85

8.43

9.06 9.03

159.55

11.58

c)

8.82

ACCEPTED MANUSCRIPT

HCO3-

HF2HCO3NH O

N2, ∆

RI PT

15.8

9.06 8.94

a)

7.49 7.48 7.47

8.74 8.67 8.64 8.43 8.41 8.12 8.10 8.08 7.98 7.97 7.89 7.83 7.81 7.62 7.61

15.9

8.13

16.0

CO2 + H2O

O

N

O

8.07 8.05 7.87 7.86 7.84 7.70 7.68 7.67

16.1

8.46 8.44 8.41

16.2

8.73

16.3

Neutral Nap-but 1

11.01

16.4

HF215.90

16.39

b)

16.15

159.5

HF2-

N

O

11.0

10.5

10.0

9.5

9.0

8.5

8.0

7.5

SC

11.5

Deprotonated Nap-but 1

Figure S7 Partial 1H NMR (500 MHz) spectral changes of Nap-but 1 (6 mM) in DMSO-d6 (0.5 mL) triggered by

M AN U

fluoride ions and CO2 (a) free Nap-but 1; (b) addition of 10 equiv. of TBAF (inset: the peak of HF2- in 1H NMR); and (c) bubbling of excess CO2 (5 mL/min) in the presence of 10 equiv. of TBAF (inset shows the peak of HCO3in 13C NMR). The proposed sensing mechanism has been also given. 5eq F-

5eq F-

EP

1eq TEA

TE D

1eq TFA

In air for 12h

AC C

Figure S8 Photographs of responses of gel Nap-but 1 (3.5 wt%) in DMSO (0.5 mL) under the stimulations of trifluoroacetic acid (TFA, 1 equiv.) or triethylamine (TEA), fluoride anions (5 equiv.), and CO2 in air. Note: No significant changes were observed upon the addition of either TFA or TFA to the DMSO-gel of Nap-but 1 as shown in Figure S8. Further experiments indicated that fluoride ions could not make the gel turn into a transparent solution in the presence of TFA, just leading to the partial collapse of the gel. On the other hand, although a red solution could be formed by the stimuli of fluoride ions in the presence of TEA, too much time of about 2 h was taken to complete the phase transition, and the re-gelation also consumed a long time of 12 h. In conclusion, the presence of TFA or TEA is not conducive to the visual sensing of CO2 based on the fluoride ion-induced strategy. 21

ACCEPTED MANUSCRIPT H NMR spectrum of compound 2 (CDCl3, 298K, 500 MHz)

M AN U

SC

RI PT

1

13

AC C

EP

TE D

C NMR spectrum of compound 2 (DMSO-d6, 298K, 125 MHz)

22

ACCEPTED MANUSCRIPT

EP

TE D

H NMR spectrum of compound 3 (CDCl3, 298K, 500 MHz)

AC C

1

M AN U

SC

RI PT

EPI-MS of compound 2

23

ACCEPTED MANUSCRIPT

13

M AN U

SC

RI PT

C NMR spectrum of compound 3 (DMSO-d6, 298K, 125 MHz)

AC C

EP

TE D

EPI-MS of compound 3

24

ACCEPTED MANUSCRIPT H NMR spectrum of compound Nap-but 1 (CDCl3, 298K, 500 MHz)

M AN U

SC

RI PT

1

13

AC C

EP

TE D

C NMR spectrum of compound Nap-but 1 (DMSO-d6, 298K, 125 MHz)

25

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

EPI-MS of compound Nap-but 1

26