Solid-State Fluorescence-based Sensing of TATP via Hydrogen

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Article Cite This: ACS Sens. XXXX, XXX, XXX−XXX

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Solid-State Fluorescence-based Sensing of TATP via Hydrogen Peroxide Detection Shengqiang Fan, Jonathan Lai, Paul L. Burn,* and Paul E. Shaw* Centre for Organic Photonics & Electronics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia

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ABSTRACT: Fluorenylboronate ester chromophore-based thin films were investigated for the detection of triacetone triperoxide (TATP) vapors via the decomposition product, hydrogen peroxide. Sensing with a high level of sensitivity was achieved using a fluorescence “turn-on” mechanism based on the significant shifts in the absorption and photoluminescence spectra that occurs when the boronate esters were converted to phenoxides by hydrogen peroxide under basic conditions. The addition of an organic base was found to be critical for achieving fast conversion reactions and the formation of the phenoxide anions. Addition of a nitrile group to the fluorenyl boronate ester moiety improved the stability of the material to photooxidation, increased the photoluminescence quantum yields, and enhanced the absorption and emission shifts to longer wavelengths. In real-time sensing measurements, films comprising the cyanofluorenyl boronate ester moiety and tetra-n-butylammonium hydroxide had a response time to aciddecomposed TATP vapor of seconds and a limit of detection of 40 ppb in 60 s. KEYWORDS: triacetone triperoxide, hydrogen peroxide, fluorenylboronate ester, fluorescence, phenoxide, nitrile

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decomposition to hydrogen peroxide, which is a strong oxidant, and thus offers more options for detection.6−11 Most studies on the detection of hydrogen peroxide using fluorescence have been solution-based in the context of biological systems where hydrogen peroxide is a smallmolecule metabolite that exerts diverse physiological and pathological effects.12−14 A key feature of current materials that are used for fluorescence-based detection of hydrogen peroxide is that they are designed to be non- (or weakly) fluorescent in the absence of the hydrogen peroxide, with the fluorescence increased in its presence. This detection method is described as “turn-on” detection as the fluorescence increases during the detection process. In contrast to the biological studies, there have only been a small number of reports of materials developed for the detection of hydrogen peroxide in solution in the context of organic peroxide explosives,7,9 and even fewer describing sensing materials usable in thin film form that can detect hydrogen peroxide vapors.15,16 One of the more widely studied methods for hydrogen peroxide detection (and thereby organic peroxide sensing) has been to use the known reactivity of organic boronate esters with hydrogen peroxide.12,17 Hydrogen peroxide can be used to convert arylboronate esters to their corresponding phenols. Using this strategy, a small

he noncontact detection of explosive vapors of different classes is an ongoing challenge given the low concentrations of the analyte vapors in the air and the limited number of truly portable detection technologies. Fluorescence-based detection can be highly sensitive and significant effort has been made to develop fluorescent materials that detect nitro-based explosives and taggants.1−4 Detection of such explosives is typically achieved via fluorescence quenching, whereby the analyte has an electron affinity that is sufficiently high to oxidize the exciton that is formed on the sensing material, thereby leading to a reduction in the measured fluorescence. That is, in the absence of the analyte the sensing material is fluorescent, but in its presence the fluorescence is either fully or partially quenched and hence the process is classified as “turn-off” detection. However, not all explosives of interest have a sufficiently high electron affinity to be detected using fluorescence quenching. Falling into this category are the organic peroxide-based explosives, which are important to detect due to their relatively simple manufacture from readily available starting materials.5 While such homemade explosives can be detected using standard analytical instruments, there are much fewer studies on fluorescence-based detection of organic peroxide vapors. A key reason for this is that, while organic peroxides are highly explosive (being unstable to shock and/or friction), they are relatively chemically inert, particularly to redox reactions.6 As a consequence, an indirect strategy has been adopted to detect organic peroxides, which involves their © XXXX American Chemical Society

Received: September 13, 2018 Accepted: December 25, 2018

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DOI: 10.1021/acssensors.8b01029 ACS Sens. XXXX, XXX, XXX−XXX

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Figure 1. Structures of the sensing materials.

Scheme 1a

Reactions and conditions: (i) THF, Ar, −78 °C, then n-BuLi, −78 °C, 30 min, then 2-iso-propoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, −78 °C, 30 min, then rt 3 h; (ii) H2O2 (30%), DMF, rt, 3−16 h; (iii) CuCN, NMP, Ar, 175 °C, 6 h; (iv) Bis(pinacolato)diboron, KOAc, 1,1′bis(diphenylphosphino)ferrocenepalladium(II)-dichloride dichloromethane complex, 1,4-dioxane, Ar, 100 °C, 16 h; (v) Tetra-n-butylammonium bromide, PhCH3, Ar, then aq. NaOH, 65 °C, Ar, 15 min then 8, Ar/N2, 65 °C, 2 h. R = 2-ethylhexyl. a

molecule boronate ester based on naphthalimide was designed for solid-state detection of hydrogen peroxide vapor such that it was non- (or weakly) fluorescent in its initial state and fluorescent after interaction with hydrogen peroxide.16 However, for the detection to work it was reported that it was necessary to adsorb the weakly fluorescent sensing material onto a hydrophilic porous substrate before exposure to hydrogen peroxide vapor.16 That is, the typical thin film format used for the detection of nitro-based explosives and taggants, which consist of nonscattering thin films, was

considered not useful for the detection of hydrogen peroxide vapors. A further issue with the reported approach was the need to have a nonfluorescent sensing material to avoid the reduction in the sensitivity of the measurement caused by background fluorescence. Many desirable conjugated boronate esters are fluorescent, and hence, it would be advantageous to have a method that would enable a broader range of materials to be used for the detection of hydrogen peroxide vapor. In this Article, we describe a simple method of using fluorescent arylboronate esters for the “turn-on” detection of B

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ACS Sensors hydrogen peroxide vapor that significantly reduces the impact of background “fluorescence noise” from the sensing material. Three sensing materials have been developed and used, namely, 9,9-di-n-propyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-fluorene 1, 9,9-di-n-propyl-7-(4,4,5,5-tetramethyl1,3,2-dioxaborolan-2-yl)-9H-fluorene-2-carbonitrile 2, and the dendronized version of 2, 9,9-bis[(4,4″-bis{[2-ethylhexyl]oxy}{1,1′:3′,1″-terphenyl}-5′-yl)methyl]-7-bromo-9H-fluorene-2carbonitrile 3 (Figure 1). We show that the materials can be blended with a base and processed to form thin films, capable of the rapid detection of hydrogen peroxide vapors directly derived from triacetone triperoxide (TATP). 4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl was chosen as the boronate ester as it has been previously reported to be relatively inert to other oxidizing interferents such as ozone.18,19

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RESULTS AND DISCUSSION 9,9-Di-n-propyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2yl)-9H-fluorene 1, 9,9-di-n-propyl-7-(4,4,5,5-tetramethyl-1,3,2dioxaborolan-2-yl)-9H-fluorene-2-carbonitrile 2, and dendronized 3 were synthesized using the procedures shown in Scheme 1. Fluorenylboronate ester 1 was synthesized via halogenlithium exchange on 4 followed by reaction with 2-iso-propoxy4,4,5,5-tetramethyl-1,3,2-dioxaborolane. The synthesis of 2 was achieved in two simple steps from 2,7-dibromo-9,9-di-npropylfluorene 5. In the first step, 5 was reacted with cuprous cyanide to form the cyano-substituted 6 in a 53% yield. The desired 2 was then formed under palladium-catalyzed conditions by reaction with bis(pinacolato)diboron and isolated in a yield of 66%. The synthesis of 3 started from two previously reported compounds, 720 and the benzylbromide focused first generation biphenyl dendron with 2ethylhexyloxy surface groups, 8.21 The dialkylation of 7 with 8 was achieved in a yield of 91%. It should be noted that care needs to be taken to avoid oxidation of 7 to the corresponding fluorenone. Dendrimer 3 was then simply formed by borylation under palladium-catalyzed conditions in a 63% yield. The phenol derivatives, 1-OH, 2-OH, and 3-OH, corresponding to each of the boronate esters were synthesized by oxidation using aqueous hydrogen peroxide. The first step in the analysis of the materials was to determine their photophysical properties. The solution absorption and photoluminescence (PL) spectra of the three boronate esters (1, 2, and 3) are shown in Figure 2, and for comparative purposes in the same solvent, Figure S1. In Figure S1 it can be seen that the addition of the nitrile group causes a red shift of around 10−15 nm in both the absorption onset and the PL emission. Dendrimer 3, which has the same chromophore as 2, has a similar onset to the absorption as 2 but a much higher molar extinction coefficient at shorter wavelengths due to the biphenyl moieties in the dendrons. However, it was also found that the introduction of the dendrons led to a significant red shift in the PL peak and loss of vibronic structure. The [0,0] transition for 2 was at 326 nm, and the peak of the broad emission for 3 was at 422 nm. Such an unusual shift of the emission (relative to the Stokes shift) has been previously reported for fluorenyl-containing compounds that have restricted rotation of sp3−sp3 carbon−carbon bonds.22−24 For dendrimer 3 the large dendrons could lead to restricted rotation and potentially π−π interactions between the dendrons and the fluorenyl unit, leading to the red-shifted emission. The solution (dichloromethane) PL quantum yields

Figure 2. Solution UV−vis absorption and photoluminescence spectra of arylboronate esters (1, 2, and 3), phenols (1-OH, 2-OH, and 3-OH) and phenoxides (1-O− and 2-O−). 1-O− and 2-O− were obtained by mixing 1-OH (2.0 × 10−5 M) or 2-OH (5.8 × 10−6 M) with (n-Bu)4NOH (7.3 × 10−4 M) in ethanol. 3-O− was not investigated due to the poor solubility of 3-OH in ethanol.

(PLQY) of 1, 2, and 3 were 0.46, 0.67, and 0.13, respectively (Table S1). The relatively low PLQY of dendrimer 3 is consistent with the broad red-shifted PL spectrum arising from an intramolecular exciplex (between the dendrons and chromophore) emission. Rapid detection of hydrogen peroxide requires fast oxidation of the boronate ester group. The addition of organic bases to solutions25 or sensing films16 have been found to significantly speed up the oxidation reaction, and this is the key for rapid detection. However, what has not been appreciated in previous reports is that, under basic conditions, the corresponding phenoxides (ArO−) and not the neutral phenols (ArOH) are formed. The absorption and PL spectra of the starting arylboronate esters, phenols, and phenoxides (for 1 and 2) C

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phenoxides are the true reporter compounds that contribute to the fluorescence “turn-on”. Given that the organic base is important for increasing the reaction rate in solution and ensuring that the phenoxide was formed, we blended tetra-nbutylammonium hydroxide with the sensing boronate esters during the film forming process. We found that when tetra-nbutylammonium hydroxide was blended with 1 or 2, optical quality films could be formed by drop-casting from ethanol solution. However, in the case of dendrimer 3, the ethanolic solution required heating, and after processing, the films were optically scattering (Figure 3). Figure 3 also shows the absorption spectra (black solid lines) for the sensing film blends before and after exposure to {TATP} (derived from 8 ppm TATP) for 150 s. In all cases there was an increase in

are shown in Figure 2, and the photophysical properties are summarized in Table S1. Dendrimer 3 was not sufficiently soluble in ethanol to undertake the equivalent measurements, and so it and its corresponding phenol are reported as a dichloromethane solution. It can be seen that the onset to absorption and the PL spectra of the phenols are red-shifted compared with their boronate ester derivatives. However, there is significant overlap of both the absorption and PL spectra of the phenols and boronate esters, leading to difficulties in discriminating between the PL of the two species and thus detecting peroxides. Importantly, it was found that the absorption and PL spectra of the phenoxides were shifted significantly compared with their boronate ester derivatives. Furthermore, the introduction of nitrile group onto the fluorenyl ring (2) led to a much greater difference in the onset and peak of absorption relative to 1. The introduction of the nitrile group onto the fluorenyl ring also increased the molar extinction coefficient and PLQY of both the boronate ester and the corresponding phenoxide relative to those of compound 1. The molar extinction coefficient (ε) (dm3 mol−1 cm−1) of 2-O− was ∼33,000 at 370 nm in ethanol, which is three times that (∼11,000) of 1-O− at its peak at 332 nm. The PLQY of 2-O− was 0.81, while that of 1-O− was 0.26 in ethanol, which illustrates that the presence of the nitrile not only increases the shift in the emission to longer wavelengths but also enhances the emission intensity. With a clear understanding of the photophysical properties of the materials, in the first step of determining their sensing capability we examined whether the addition of the base accelerated the sensing rate. Compounds 1 and 2 were dissolved in ethanol with differing equivalents of tetra-nbutylammonium hydroxide before the addition of an excess of hydrogen peroxide. Figure S2 shows the change in absorption over time at wavelengths that only the phenoxides of 1 or 2 absorb. As can be seen, addition of 20 equiv of tetra-nbutylammonium hydroxide to the solution of 1 or 10 equiv to a solution of 2 significantly increased the rate of the phenoxide formation in solution. Finally, before moving onto the real time film measurements, it was important to determine that phenoxides were formed after exposure of the boronate esters to the TATP decomposition products. The TATP vapor used for generating the hydrogen peroxide was decomposed using a solid acid (Amberlyst-15)6 with the concentration modulated using two mass flow controllers (details in the Experimental Section). A 1 H NMR measurement of the collected vapor arising from the decomposition of TATP showed that acetone was formed and the vapor contained less than 0.2% of TATP (Figure S3). In the following discussion, the decomposed gas mixture containing acetone and hydrogen peroxide is defined as {TATP}. After basic ethanolic solutions of 1 and 2 were exposed to {TATP}, the absorption and PL spectra were compared to those measured for 1-OH and 2-OH in the presence of tetra-n-butylammonium hydroxide. It can be seen in Figure S4 that the absorption and PL spectra were identical under both conditions, meaning that after exposure to {TATP} the phenoxides were formed. The fact that the phenoxides absorb at wavelengths that the corresponding boronate esters do not provides a method for detecting peroxide with high sensitivity (maximum signal-tonoise ratio). Selective excitation of the phenoxide products avoids the generation of PL from the boronate esters, which would otherwise mask the detection signal. Thus, the

Figure 3. UV−vis absorption and photoluminescence spectra of films on quartz substrates. The films were fabricated by drop-casting from a solution of boronate ester sensing material (a) 1, (b) 2, or (c) 3 with (n-Bu)4NOH (6 equiv). The high background absorbance of the films in (c) is due to scattering. D

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ACS Sensors absorption at longer wavelengths, in a similar manner to the solution measurements. On photoexcitation at a wavelength that the boronate ester did not absorb, a substantial increase in the PL was observed, indicating the detection of hydrogen peroxide. The largest change in the absorption spectrum was for films containing compound 2, with the smaller changes for 1 and 3 being due to the lack of the nitrile group and aggregation in the film, respectively. In most reported {TATP}/hydrogen peroxide detection protocols, measurements are done before and after exposure to the analyte and do not capture the response of the sensor material in real time. In the next part of the study we continuously illuminated the sensing film and monitored the PL change over time to mimic real world sensing. The PL kinetics for sensing films containing the different materials exposed to a range of TATP vapor concentrations are shown in Figure 4. Each compound shows a clear response to the {TATP} vapor within seconds. For compounds 1 and 2, the rate of the PL increase was directly related to the TATP vapor concentration. In particular for the 2-based sensing films, a good linear relationship between the PL signal and TATP concentration was observed (Figure S5) enabling a limit of detection (LOD) to be determined. By considering the PL intensity change in the first 60 s and comparing with three times the standard deviation (3σ)16 of the PL change in air, the LOD for films of compound 2 was calculated to be 40 ppb for TATP (see Experimental Section). For dendrimer 3 there was not the same rate of increase in PL with increasing TATP concentration, which we believe arises from aggregation in the film, the lipophilicity of the dendrimer, and a slow reaction rate. The impact of these effects can be observed in the results from a pulsed measurement in which {TATP} was applied to films of 2 or 3 for 180−250 s with the PL monitored during the initial period (Figure S6). After the pulse of analyte, the excitation was turned off for ∼10 min before the film was reilluminated. In the case of the film containing compound 2, there was little change in the PL signal, while the PL of dendrimer 3 was found to have significantly increased indicating that the oxidation reaction was continuing in the dark after the pulse had finished. A further feature of the PL kinetic measurements (Figure 4) was that the PL does not saturate to the same point over time, and in some cases, there was a decrease in the PL later during the measurements. The decrease in PL over time (at 5.3 ppm TATP vapor concentration in Figure 4a,b) was found to be at least in part due to photodegradation. As shown in Figure S7, the films made from 1-OH and 2-OH blended with tetra-n-butylammonium hydroxide showed slow degradation in air and faster degradation in the presence of hydrogen peroxide. It is important to note that compounds 2 and 3 both had slower photodegradation than 1, illustrating the improvement in stability arising from the presence of the nitrile group. Thus, in the sensing process there is a competition between the “turn-on” detection and subsequent decomposition of the emissive phenoxide. However, the photodegradation does not affect the ability of the materials to detect TATP. Finally, we consider how sensing materials 1, 2, and 3 might be incorporated into an actual detector. The response of a coating of 2 was tested in a prototype hand-held sensor to TATP vapors with and without the use of the Amberlyst catalyst (Figure S8). The increase in the fluorescence signal observed when the TATP vapors were decomposed by the Amberlyst catalyst shows that this approach is suitable for

Figure 4. PL kinetics for sensing films at various TATP vapor concentrations. ΔPL is the PL intensity change before and after exposure to {TATP}. The films were fabricated by drop-casting a solution of boronate ester sensing material (a) 1, (b) 2, or (c) 3 with (n-Bu)4NOH (6 equiv).

integration into a compact hand-held device. In addition, it indicates that a detector that could discriminate between TATP and hydrogen peroxide could be implemented by comparing the response of two identical coatings, only one of which features the Amberlyst catalyst upstream. TATP vapors would only illicit a response from the channel with the Amberlyst, while hydrogen peroxide would give a response from both channels, thus providing a simple and reliable approach to discriminate between the two analytes. E

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sodium sulfate, and filtered. The filtrate was collected, and the solvent was removed. The residue was purified by column chromatography over silica using dichloromethane/petroleum ether (1:10−1:3) as eluent to give 1 as a white solid (1.28 g, 45%). mp 74−75 °C. Elemental analysis (%) calcd for C25H33BO2 C 79.8, H 8.8; Found: C 80.0, H 8.8. λmax(dichloromethane)/nm: 273 (log ε/dm3 mol−1 cm−1 4.46), 280 sh (4.48), 283 (4.51), 298 (4.30), 303 sh (4.23), 310 (4.43). λem(dichloromethane)/nm: 312, 326, 340 sh. 1H NMR (500 MHz, CDCl3) δ 7.81 (1 H, ddd, J = 1, J = 1, J = 7.5, Fl-H), 7.76 (1 H, d, J = 1, Fl-H), 7.71−7.73 (1H, m, Fl-H), 7.70 (1 H, ddd, J = 1, J = 1, J = 7.5, Fl-H), 7.34−7.37 (1 H, m, Fl-H), 7.30−7.33 (2 H, m, Fl-H), 1.92−2.04 (4 H, m, Pr-H), 0.57−0.65 (10 H, m, Pr-H). 13C NMR (125 MHz, CDCl3) 151.3, 149.8, 144.1, 140.9, 133.7, 128.8, 127.5, 126.7, 122.9, 120.1, 118.9, 83.7, 55.3, 42.6, 24.9, 17.1, 14.4. m/z [ESI+]: 377.1 ([M + H]+). 7-Bromo-9,9-di-n-propyl-9H-fluorene-2-carbonitrile 6. A mixture of 2,7-dibromo-9,9-di-n-propylfluorene 526 (4.08 g, 10.0 mmol), cuprous cyanide (896 mg, 10.0 mmol), and N-methyl pyrrolidone (30 mL) was heated under argon in an oil bath held at 175 °C for 6 h. The mixture was allowed to cool to 120 °C. Following a literature procedure,27 an acidified aqueous ferric chloride solution (6.00 g, 0.04 mol) in hydrochloric acid (1.4 M, 10.5 mL) was poured slowly into the hot reaction mixture. The mixture was heated at 90 °C for a further 20 min. The mixture was allowed to cool to room temperature and then water (50 mL) was added. The aqueous layer was then separated from the organic layer and was extracted with toluene (3 × 50 mL). The organic portions were combined, washed sequentially with hydrochloric acid (6 M, 2 × 50 mL), aqueous sodium hydroxide (10%, 2 × 50 mL), and distilled water (2 × 100 mL), and then dried over anhydrous sodium sulfate and filtered. The filtrate was collected and the solvent removed. The residue was purified by column chromatography over silica using ethyl acetate/petroleum ether (1:20−1:4) as eluent to give 6 as a white solid (1.88 g, 53%). mp 149−150 °C. Elemental analysis (%) calcd for C20H20BrN C 67.8, H 5.7, N 3.95; Found: C 68.2, H 5.8, N 4.0. IR νmax (solid)/cm−1 2221 (CN). λmax(dichloromethane)/nm: 282 sh (log ε/dm3 mol−1 cm−1 4.23), 293 (4.33), 306 (4.22), 318 (4.41). 1H NMR (400 MHz, CDCl3) δ 7.73 (1 H, dd, J = 1.0, J = 8.0, Fl-H), 7.63 (1 H, dd, J = 1.5, J = 8.0, Fl-H), 7.59−7.61 (2 H, m, Fl-H), 7.49−7.52 (2 H, m, Fl-H), 1.95 (4 H, t, J = 8.0, Pr-H), 0.51−0.71 (10 H, m, Pr-H). 13C NMR (100 MHz, CDCl3) δ 153.5, 151.0, 144.5, 138.1, 131.4, 130.6, 126.52, 126.47, 123.2, 122.1, 120.3, 119.6, 110.4, 56.0, 42.3, 17.1, 14.2. m/z [ESI+]: 375.9, 377.9 ([M + Na]+). 9,9-Di-n-propyl-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)9H-fluorene-2-carbonitrile 2. A mixture of 6 (886 mg, 2.5 mmol), bis(pinacolato)diboron (762 mg, 3.0 mmol), potassium acetate (736 mg, 7.5 mmol), 1,1′-bis(diphenylphosphino)ferrocenepalladium(II)dichloride dichloromethane complex (55 mg, 0.075 mmol), and 1,4dioxane (30 mL) was heated under argon in an oil bath held at 100 °C for 16 h. The mixture was allowed to cool to room temperature, and then the solvent was removed under reduced pressure. Water (50 mL) and dichloromethane (50 mL) were added to the reaction mixture, and the organic phase was separated. The aqueous layer was extracted with dichloromethane (3 × 30 mL). The dichloromethane extracts were combined, washed with brine (2 × 50 mL), dried over anhydrous sodium sulfate, and filtered. The filtrate was collected, and the solvent was removed. The residue was purified by column chromatography over silica using ethyl acetate/petroleum ether (1:20−1:6) as eluent to give 2 as a white solid (664 mg, 66%). mp 151−152 °C; mp(DSC) = 156 °C (first scan − DSC scan rate 50 °C/ min); Tg = 61 °C (second heating scan − DSC scan rate 100 °C/ min) T5% = 273 °C (sublimed). Elemental analysis (%) calcd for C26H32BNO2 C, 77.8; H, 8.0; N, 3.5. Found: C, 77.75; H, 8.1; N, 3.4. IR νmax/cm−1 2220 (CN). λmax(dichloromethane)/nm: 285 sh (log ε/ dm3 mol−1 cm−1 4.35), 294 (4.45), 308 (4.34), 315 sh (4.33), 321 (4.51). λem(dichloromethane)/nm: 326, 339, 355 sh. 1H NMR (500 MHz, CDCl3) δ 7.84 (1 H, dd, J = 1.0, J = 7.5, Fl-H), 7.77−7.79 (2 H, m, Fl-H), 7.73 (1 H, dd, J = 0.5, J = 7.5, Fl-H), 7.63 (1 H, dd, J = 1.5, J = 7.0, Fl-H), 7.62 (1 H, s, Fl-H), 1.92−2.06 (4 H, m, Pr-H), 1.39 (12 H, s, BE-H), 0.66 (6 H, t, J = 7.0, Pr-H), 0.51−0.63 (4 H, m,

CONCLUSIONS Fluorenylboronate esters are shown to be excellent candidates for the detection of organic peroxide vapors using films on flat fused silica substrates. The mechanism involves the conversion of the boronate esters to their corresponding phenoxides under basic conditions. Organic base added to the sensing films fulfilled two essential roles, accelerating the conversion reaction and leading to clearly defined changes in absorption and PL spectra before and after exposure to the TATP degradation products. The introduction of a nitrile group onto the fluorenyl ring was found to improve the PLQY and absorption of the corresponding phenoxides significantly and also improved their photostability. The limit of detection based on a nitrile-containing sensing material was around 40 ppb after 60 s exposure to the analyte. The PL kinetics were found to be controlled by two processes, formation of phenoxide and photodegradation, with the latter a slower process so not affecting the ability to detect peroxide.

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EXPERIMENTAL SECTION

Materials Synthesis. All reagents were purchased from commercial sources and were used as received unless otherwise stated. Tetrahydrofuran and toluene were dried on an LC Systems solvent purification system prior to use. Solvents for chromatography were distilled prior to use. Column chromatography was performed using Davisil LC60A 40−63 μm silica gel. Thin layer chromatography (TLC) was performed using aluminum backed silica gel 60 F254 plates. 1H and 13C NMR were performed using Bruker Avance 300, 400, or 500 MHz spectrometers in deuterated chloroform referenced to 7.26 ppm for 1H and 77.0 ppm for 13C, or deuterated dimethyl sulfoxide referenced to 2.50 ppm for 1H and 39.5 ppm for 13C; Fl-H = fluorenyl H; Bn-H = benzyl H; Pr-H = n-propyl H; G1-BP-H = first generation dendron branching phenyl H; G1-SPh-H = first generation dendron surface phenyl H; BE-H = boronate ester methyl H; EH-H = 2-ethylhexyl H. Coupling constants are given to the nearest 0.5 Hz. UV−visible spectrophotometry was performed using a Cary 5000 or Cary 60 UV−vis spectrophotometer on either thin films on quartz substrates or in dichloromethane or ethanol solution, with absorbance shoulders denoted as sh. FT-IR spectroscopy was performed on solid samples using a PerkinElmer Spectrum 100 FT-IR spectrometer with an ATR attachment. Melting points (MPs) were measured in a glass capillary on a Büchi B-545 melting point apparatus and are uncorrected. Microanalyses were performed using a Carlo Erba NA 1500 Elemental Analyzer. Low-resolution electrospray ionization (ESI) mass spectra were acquired on a Bruker Esquire HCT (High Capacity 3D ion trap) instrument with a Bruker ESI source. Highresolution electrospray ionization (HRMS) accurate mass measurements were recorded in positive mode on a Bruker MicroTOF-Q (quadrupole-time-of-flight) instrument with a Bruker ESI source. Thermal transitions were determined using a PerkinElmer Diamond Differential Scanning Calorimeter. Thermal gravimetric analysis was undertaken using a PerkinElmer STA 6000 Simultaneous Thermal Analyzer. Thermal decomposition temperatures [Td(5%)] are reported as the temperature corresponding to a 5% mass loss. 2-(9,9-Di-n-propyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane 1. 2-Bromo-9,9-di-n-propylfluorene (2.47 g, 7.5 mmol) was dissolved in anhydrous tetrahydrofuran (50 mL) under argon, and the resulting solution was cooled to −78 °C in a dry ice/acetone bath. A solution of n-butyl lithium in hexane (2.5 M, 3.6 mL, 9.0 mmol) was added dropwise over 10 min, and the mixture was stirred at −78 °C for another 30 min. 2-iso-Propoxy-4,4,5,5-tetramethyl1,3,2-dioxaborolane (2.6 mL, 11.3 mmol) was added, and the mixture was stirred at −78 °C for 30 min. Then the mixture was allowed to warm to room temperature and was stirred for 3 h at room temperature. The mixture was quenched with water (50 mL) and extracted with ethyl acetate (3 × 50 mL). The combined organic layers were washed with brine (100 mL), dried over anhydrous F

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ACS Sensors

9,9-Di-n-propyl-9H-fluoren-2-ol 1-OH. A mixture of 1 (140 mg, 0.37 mmol), aqueous hydrogen peroxide (30%, 3 mL), and N,Ndimethylformamide (10 mL) was stirred at room temperature for 3 h. Water (50 mL) and ethyl acetate (50 mL) were added to the reaction mixture, and the organic phase was separated. The organic phase was washed with water (8 × 50 mL), dried over anhydrous sodium sulfate, and filtered. The filtrate was collected, and the solvent was removed. The residue was purified by column chromatography over silica using dichloromethane as eluent to give 1-OH as a white solid (92 mg, 93%). mp 117−118 °C. Elemental analysis (%) calcd for C19H22O: C, 85.7; H, 8.3. Found: C, 85.7; H, 8.25. νmax(solid)/cm−1 3250 (OH). λmax(dichloromethane)/nm: 275 (log ε/dm3 mol−1 cm−1 4.25), 285 sh (4.13), 305 (3.83), 315 (3.89). λem(dichloromethane)/nm: 323. 1 H NMR (500 MHz, CDCl3) δ 7.59 (1 H, dd, J = 0.5, J = 7.5, Fl-H), 7.54 (1 H, dd, J = 0.5, J = 8, Fl-H), 7.27−7.31 (2 H, m, Fl-H), 7.23 (1 H, dddd, J = 0.5, J = 0.5, J = 7.5, J = 7.5, Fl-H), 6.83 (1 H, ddd, J = 0.5, J = 0.5, J = 2.5, Fl-H), 6.79 (1 H, dddd, J = 0.5, J = 0.5, J = 2.5, J = 7.5, Fl-H), 4.78 (1 H, brs, OH), 1.84−1.97 (4 H, m, Pr-H), 0.58− 0.72 (10 H, m, Pr-H). 13C NMR (125 MHz, CDCl3) δ 155.2, 153.0, 150.1, 140.9, 134.3, 126.7, 125.9, 122.7, 120.5, 118.8, 113.9, 110.1, 55.2, 42.9, 17.1, 14.4. m/z [ESI−]: 265.3 ([M − H]−). 7-Hydroxy-9,9-di-n-propyl-9H-fluorene-2-carbonitrile 2-OH. A mixture of 2 (61 mg, 0.12 mmol), aqueous hydrogen peroxide (30%, 3 mL), and N,N-dimethylformamide (10 mL) was stirred at room temperature for 3 h. Then ethyl acetate (30 mL) was added to the reaction mixture. The mixture was washed with hydrochloric acid (1 M, 2 × 50 mL), brine (3 × 30 mL), dried over anhydrous sodium sulfate, and filtered. The filtrate was collected and the solvent removed. The residue was purified by column chromatography over silica using dichloromethane as eluent to give 2-OH as a white solid (32 mg, 86%). mp 169−170 °C. Elemental analysis (%) calcd for C20H21NO: C, 82.4; H, 7.3; N, 4.8. Found: C, 82.5; H, 7.3; N, 4.7. IR νmax/cm−1 3350 (OH), 2230 (CN). λmax(dichloromethane)/nm: 285 sh (log ε/dm3 mol−1 cm−1 4.12), 300 (4.30), 315 sh (4.36), 324 (4.46). λem(dichloromethane)/nm: 352. 1H NMR (500 MHz, CDCl3) δ 7.63 (1 H, dd, J = 0.5, J = 8.0, Fl-H), 7.58−7.60 (2 H, m, Fl-H), 7.56 (1 H, brm, Fl-H), 6.83−6.85 (2 H, m, Fl-H), 5.03 (1 H, brs, OH), 1.87−1.97 (4 H, m, Pr-H), 0.57−0.69 (10 H, m, Pr-H). 13 C NMR (125 MHz, CDCl3) δ 156.8, 154.0, 150.8, 145.6, 132.3, 131.4, 126.2, 122.0, 120.0, 119.2, 114.7, 110.2, 108.6, 55.6, 42.5, 17.0, 14.3. m/z [ESI−]: 290.3 ([M − H]−). 9,9-Bis[(4,4″-bis{[2-ethylhexyl]oxy}-{1,1′:3′,1″-terphenyl}-5′-yl)methyl]-7-hydroxy-9H-fluorene-2-carbonitrile 3-OH. A mixture of 3 (60 mg, 0.046 mmol), aqueous hydrogen peroxide (30%, 3 mL), and N,N-dimethylformamide (50 mL) was stirred at room temperature for 16 h. Then ethyl acetate (50 mL) was added to the reaction mixture. The mixture was washed with water (7 × 30 mL), dried over anhydrous sodium sulfate, and filtered. The filtrate was collected, and the solvent was removed. The residue was purified by column chromatography over silica using dichloromethane/petroleum ether (1:10 to 1:1) as eluent to give 3-OH as a white solid (38 mg, 69%). mp 191−192 °C. Elemental analysis (%) calcd for C84H101NO5: C, 83.8; H, 8.5; N, 1.2. Found: C, 83.5; H, 8.5; N, 1.2. IR νmax/cm−1 3390 (OH), 2223 (CN). λmax(dichloromethane)/nm: 270 (log ε/dm3 mol−1 cm−1 4.93), 327 (4.27). λem(dichloromethane)/nm: 377. 1H NMR (500 MHz, DMSO-d6): δ 9.91 (1 H, s, OH), 8.49 (1 H, s, FlH), 7.60 (1 H, dd, J = 1.5, J = 8, Fl-H), 7.48 (1 H, d, J = 1.5, Fl-H), 7.45 (1 H, d, J = 8, Fl-H), 7.40 (1 H, d, J = 8.5, Fl-H), 7.28 (2 H, dd, J = 1.5, J = 1.5, G1-BP-H), 7.24 and 6.92 (16 H, AA’BB’, G1-SPh-H), 6.79 (1 H, dd, J = 2, J = 8.5, Fl-H), 6.78 (2 H, d, J = 1.5, G1-BP-H), 3.84−3.89 (8 H, m, EH-H), 3.68 and 3.60 (4 H, 2d, J = 13, Bn-H), 1.64−1.72 (4 H, m, EH-H), 1.23−1.50 (32 H, m, EH-H), 0.87−0.91 (24 H, m, EH-H). 13C NMR(125 MHz, CDCl3): δ 158.9, 156.5, 151.9, 148.8, 145.6, 140.4, 136.6, 133.2, 132.5, 131.7, 128.1, 128.0, 127.0, 123.3, 122.4, 119.7(1), 119.6(8), 115.2, 114.7, 112.1, 107.9, 70.6, 57.4, 45.3, 39.4, 30.5, 29.1, 23.9, 23.0, 14.1, 11.1. HRMS (ESI+): m/z found: 1226.759 (100.0%), 1227.762 (91%), 1228.763 (41%), 1229.767 (12%) ([M + Na]+). Expected 1226.757 (100.0%), 1227.761 (91%), 1228.764 (41%), 1229.767 (11%).

Pr-H). 13C NMR (125 MHz, CDCl3) δ 152.0, 150.5, 145.5, 141.9, 134.0, 131.2, 129.0, 126.6, 120.6, 120.0, 119.8, 110.3, 84.0, 55.7, 42.3, 24.9, 17.1, 14.3. m/z [ESI+]: 440.0 ([M + K]+). 9,9-Bis[(4,4″-bis{[2-ethylhexyl]oxy}-{1,1′:3′,1″-terphenyl}-5′-yl)methyl]-7-bromo-9H-fluorene-2-carbonitrile 9. A mixture of 7bromo-9H-fluorene-2-carbonitrile 720 (42 mg, 0.15 mmol), tetra-nbutylammonium bromide (12 mg, 0.04 mmol), and toluene (4 mL) was placed under vacuum and then backfilled with argon three times. Then aqueous sodium hydroxide (50%, 4 mL) was purged with nitrogen for 10 min and added to the mixture. The resultant mixture was then placed under vacuum and backfilled with argon three times before being heated in an oil bath at 65 °C for 15 min. Then 5′[bromomethyl]-4,4″-bis[(2-ethylhexyl)oxy]-1,1′:3′,1″-terphenyl 821 (260 mg, 0.45 mmol) was quickly added under a stream of nitrogen, and the resultant mixture was stirred in the oil bath held at 65 °C for another 2 h. After cooling to room temperature, toluene (30 mL) was added. The organic layer was then washed with water (3 × 30 mL) and brine (2 × 50 mL), and then dried over anhydrous sodium sulfate and filtered. The filtrate was collected, and the solvent was removed. The crude product was purified by column chromatography over silica using dichloromethane/petroleum ether (2:3) as eluent to give 9 as a white solid (174 mg, 91%). mp 167−168 °C. Elemental analysis (%) calcd for C84H100BrNO4 C 79.6, H 8.0, N 1.1; Found: C 79.7, H 8.1, N 1.0. IR νmax/cm−1 2224 (CN). λmax(dichloromethane)/nm: 270 (log ε/dm3 mol−1 cm−1 4.98), 318 (4.14). 1H NMR (400 MHz, CDCl3): δ 7.98 (1 H, brd, J = 1, Fl-H), 7.92 (1 H, d, J = 1.5, Fl-H), 7.57 (1 H, dd, J = 1.5, J = 8.0, Fl-H), 7.50 (1 H, dd, J = 2.0, J = 8.0, FlH), 7.43 (1 H, d, J = 8.0, Fl-H), 7.35 (2 H, dd, J = 1.5, J = 1.5, G1-BPH), 7.31 (1 H, d, J = 8.0, Fl-H), 7.23 and 6.92 (16 H, AA’BB’, G1SPh-H), 6.79 (2 H, d, J = 1.5, G1-BP-H), 3.84−3.88 (8 H, m, EH-H), 3.51−3.58 (4 H, m, Bn-H), 1.71−1.78 (4 H, m, EH-H), 1.32−1.59 (32 H, m, EH-H), 0.91−0.97 (24 H, m, EH-H). 13C NMR(100 MHz, CDCl3): δ 159.0, 151.4, 149.2, 144.6, 140.5, 138.3, 136.2, 133.0, 131.7, 131.0, 128.6, 128.3, 128.0, 127.0, 123.3, 122.6, 122.5, 120.7, 119.3, 114.7, 109.7, 70.5, 58.1, 45.1, 39.4, 30.5, 29.1, 23.9, 23.1, 14.1, 11.1. MS (ESI): m/z found: 1288.3 (81%), 1289.3 (78%), 1290.3 (100%), 1291.3 (83%), 1292.3 (33%), 1293.3 (11%) ([M + Na]+);. Expected 1288.7 (72%), 1289.7 (67%), 1290.7 (100%), 1291.7 (73%), 1292.7 (30%), 1293.7 (12%). 9,9-Bis[(4,4″-bis{[2-ethylhexyl]oxy}-{1,1′:3′,1″-terphenyl}-5′-yl)methyl]-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-fluorene-2-carbonitrile 3. A mixture of 9 (39 mg, 0.03 mmol), bis(pinacolato)diboron (15 mg, 0.06 mmol), potassium acetate (10 mg, 0.10 mmol), and 1,1′-bis(diphenylphosphino)ferrocenepalladium(II)-dichloride dichloromethane complex (4 mg, 0.004 mmol) was placed in a vacuum for 1 h and then backfilled with argon. Anhydrous 1,4-dioxane (2 mL) was added, and the resulting mixture was heated at 105 °C for 16 h under argon. After cooling to room temperature, the 1,4-dioxane was removed, and the residue was purified by column chromatography over silica using dichloromethane/petroleum ether (1:1 to 1:0) as eluent to afford 3 as a white solid (25 mg, 63%). mp 102−103 °C. Tg = 76 °C (second heating scan − DSC scan rate 100 °C/min); T5%(decomp.) = 369 °C. Elemental analysis (%) calcd for C90H112BNO6 C 82.2, H 8.6, N 1.1; Found: C 82.2, H 8.6, N 1.0. IR νmax/cm−1 2223 (CN). λmax(dichloromethane)/nm: 270 (log ε/dm3 mol−1 cm−1 5.04), 320 sh (4.17). λem(dichloromethane)/nm: 422; (toluene)/nm: 391. 1H NMR (500 MHz, CDCl3): δ 8.29 (1 H, s, Fl-H), 7.94 (1 H, d, J = 1, Fl-H), 7.86 (1 H, dd, J = 1, J = 7.5, Fl-H), 7.55 (1 H, dd, J = 1, J = 8, Fl-H), 7.47−7.49 (2 H, m, Fl-H), 7.29 (2 H, dd, J = 1.5, J = 1.5, G1BP-H), 7.15 and 6.88 (16 H, AA’BB’, G1-SPh-H), 6.76 (2 H, d, J = 1.5, G1-BP-H), 3.82−3.85 (8 H, m, EH-H), 3.57−3.63 (4 H, m, BnH), 1.69−1.77 (4 H, m, EH-H), 1.30−1.55 (44 H, m, EH-H and BEH), 0.90−0.95 (24 H, m, EH-H). 13C NMR (100 MHz, CDCl3): δ 158.9, 149.6, 148.7, 145.6, 142.2, 140.3, 136.7, 134.4, 133.2, 131.5, 131.1, 128.5, 127.9, 127.1, 123.1, 121.1, 120.5, 119.5, 114.6, 109.5, 84.0, 70.5, 57.9, 45.1, 39.4, 30.5, 29.1, 24.9, 23.9, 23.1, 14.1, 11.1. MS (ESI): m/z found: 1335.4 (19%), 1336.4 (100%), 1337.4 (96%), 1338.4 (41%), 1339.4 (14%) ([M + Na]+). Expected 1335.9 (20%), 1336.8 (100%), 1337.9 (85%), 1338.9 (42%), 1339.9 (13%). G

DOI: 10.1021/acssensors.8b01029 ACS Sens. XXXX, XXX, XXX−XXX

ACS Sensors

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Vapor Generation. TATP was synthesized from hydrogen peroxide (30%) and acetone in the presence of aqueous HCl as catalyst according to a reported procedure and purified by recrystallization from methanol.28 TATP vapor was generated using a setup similar to that previously reported.6 TATP powder (200 mg) was mixed with sand (10.5 g) and then placed into a glass tube (⌀ 0.5 cm × 20 cm). The glass tube was connected to a gas mass flow controller (MFC) at one end and to a Teflon tube (⌀ 2 mm × 20 mm) filled with Amberlyst-15 solid-state acid at the other end. The Amberlyst-15 was the catalyst used to decompose TATP into hydrogen peroxide and acetone {TATP}. A second gas MFC was employed for dilution. Nitrogen was used as both the carrier gas and dilution gas. The temperature at which the experiments were carried out was 20 ± 1 °C. The TATP vapor pressure was estimated from the Clausius−Clapeyron equation, log10 P = 19.791−5708/T, where P is vapor pressure (Pascal) and T is temperature (Kelvin).29 TATP vapor concentration was calculated from dilution factor. The PL response without hydrogen peroxide input was tested in air, rather than in nitrogen gas, in order to predict the LODs that would be expected under real world usage. Film Preparation. Films were prepared on planar fused silica substrates by drop-casting from solution. The typical solution comprises 2 mg of boronate ester sensing material, n-Bu4NOH (6 equiv), and 0.20 mL of ethanol. The solutions of 1 or 2 were stirred at room temperature in a 1 mL vial for 10 min before use. The solutions containing 3 were heated to reflux for dissolution and then cooled to room temperature before use. The coatings were fabricated by dropcasting the solution onto the substrate at a loading amount of 5 μL/ cm2 and then dried under a nitrogen stream followed by vacuum. Photophysical Measurements. Solution photoluminescence spectra and intensity were recorded on a Horiba Jobin-Yvon Fluoromax 4. Solution photoluminescence quantum yields (PLQYs) were measured by a relative method using quinine sulfate in 0.5 M sulfuric acid, which has a PLQY of 0.55, as a standard.30 Sensing Measurements. The sensing film samples on fused silica substrates were mounted in a sample cell in a fluorometer (JobinYvon Fluorolog 3). The sample cell possessed three optical windows to allow for excitation of the films and subsequent detection of the film PL at right angles to the excitation. The gas mixture containing diluted {TATP} was directed onto the sample at a flow rate (500− 1000 mL/min), controlled using two mass flow controllers. Film PL spectra before and after exposure to {TATP} were recorded. PL kinetics at the emissive peak were measured with an excitation wavelength at the absorption peak of the corresponding phenoxides. Prototype Detector Measurements. The prototype single channel explosives detector utilized a glass capillary (inner diameter ≈1 mm) coated on the inside with the sensing material. The films were coated inside the capillary by (i) immersing one end of the capillary into the solution containing the sensing material and base; (ii) wicking out the excess solution with a paper towel once the capillary was full; (iii) drying the residual film with a nitrogen stream. The solution contained 2 mg of sensing material 2 with (n-Bu)4NOH (6 equiv) in 200 μL of ethanol. The excitation source for the device was a 395 nm LED with a long-pass filter to isolate the fluorescence signal, which was detected with a photodiode. Air was drawn into the device and through the capillary with a pump at a rate of approximately 30 mL/min.

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AUTHOR INFORMATION

Corresponding Authors

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

Paul L. Burn: 0000-0003-3405-3517 Paul E. Shaw: 0000-0002-3326-3670 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS P.E.S. is supported by an Advance Queensland Research Fellowship. P.L.B. is an Australian Research Council Laureate Fellow (FL160100067). This research was supported by funding from the Australian Research Council under the Discovery Program (DP130102422).

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REFERENCES

(1) Shaw, P. E.; Burn, P. L. Real-Time Fluorescence QuenchingBased Detection of Nitro-Containing Explosive Vapours: What Are the Key Processes? Phys. Chem. Chem. Phys. 2017, 19, 29714−29730. (2) Sun, X.; Wang, Y.; Lei, Y. Fluorescence Based Explosive Detection: from Mechanisms to Sensory Materials. Chem. Soc. Rev. 2015, 44, 8019−8061. (3) Salinas, Y.; Martinez-Manez, R.; Marcos, M. D.; Sancenon, F.; Costero, A. M.; Parra, M.; Gil, S. Optical Chemosensors and Reagents to Detect Explosives. Chem. Soc. Rev. 2012, 41, 1261−1296. (4) Thomas, S. W.; Joly, G. D.; Swager, T. M. Chemical Sensors Based on Amplifying Fluorescent Conjugated Polymers. Chem. Rev. 2007, 107, 1339−1386. (5) Sabatini, J. J.; Oyler, K. D. Recent Advances in the Synthesis of High Explosive Materials. Crystals 2016, 6 (1), 5. (6) Lin, H.; Suslick, K. S. A Colorimetric Sensor Array for Detection of Triacetone Triperoxide Vapor. J. Am. Chem. Soc. 2010, 132, 15519−15521. (7) Schulte-Ladbeck, R.; Kolla, P.; Karst, U. A Field Test for the Detection of Peroxide-Based Explosives. Analyst 2002, 127, 1152− 1154. (8) Schulte-Ladbeck, R.; Kolla, P.; Karst, U. Trace Analysis of Peroxide-Based Explosives. Anal. Chem. 2003, 75, 731−735. (9) Girotti, S.; Ferri, E.; Maiolini, E.; Bolelli, L.; D’Elia, M.; Coppe, D.; Romolo, F. S. A Quantitative Chemiluminescent Assay for Analysis of Peroxide-Based Explosives. Anal. Bioanal. Chem. 2011, 400, 313−320. (10) Chen, J.; Wu, W.; McNeil, A. J. Detecting a Peroxide-Based Explosive via Molecular Gelation. Chem. Commun. 2012, 48, 7310− 7312. (11) Malashikhin, S.; Finney, N. S. Fluorescent Signaling Based on Sulfoxide Profluorophores: Application to the Visual Detection of the Explosive TATP. J. Am. Chem. Soc. 2008, 130, 12846−12847. (12) Chan, J.; Dodani, S. C.; Chang, C. J. Reaction-Based SmallMolecule Fluorescent Probes for Chemoselective Bioimaging. Nat. Chem. 2012, 4, 973−984. (13) Chen, X.; Wang, F.; Hyun, J. Y.; Wei, T.; Qiang, J.; Ren, X.; Shin, I.; Yoon, J. Recent Progress in the Development of Fluorescent, Luminescent and Colorimetric Probes for Detection of Reactive Oxygen and Nitrogen Species. Chem. Soc. Rev. 2016, 45, 2976−3016. (14) Wu, D.; Sedgwick, A. C.; Gunnlaugsson, T.; Akkaya, E. U.; Yoon, J.; James, T. D. Fluorescent Chemosensors: the Past, Present and Future. Chem. Soc. Rev. 2017, 46, 7105−7123. (15) Sanchez, J. C.; Trogler, W. C. Polymerization of a BoronateFunctionalized Fluorophore by Double Transesterification: Applications to Fluorescence Detection of Hydrogen Peroxide Vapour. J. Mater. Chem. 2008, 18, 5134−5141.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssensors.8b01029. Photophysical properties and UV−vis/photoluminescence spectra of the arylboronate esters, phenols, and phenoxides in dichloromethane and ethanol. PL kinetics for sensing films in air and with TATP, decomposed TATP, and hydrogen peroxide vapors (PDF) H

DOI: 10.1021/acssensors.8b01029 ACS Sens. XXXX, XXX, XXX−XXX

Article

ACS Sensors (16) Xu, M.; Han, J.-M.; Zhang, Y.; Yang, X.; Zang, L. A Selective Fluorescence Turn-on Sensor for Trace Vapor Detection of Hydrogen Peroxide. Chem. Commun. 2013, 49, 11779−11781. (17) Liu, Y. A.; Liao, X. Fluorescent Probes for the Detection of Hydrogen Peroxide in Biological Systems. Curr. Org. Chem. 2013, 17, 654−669. (18) Miller, E. W.; Albers, A. E.; Pralle, A.; Isacoff, E. Y.; Chang, C. J. Boronate-Based Fluorescent Probes for Imaging Cellular Hydrogen Peroxide. J. Am. Chem. Soc. 2015, 127 (47), 16652−16659. (19) Miller, E. W.; Tulyathan, O.; Isacoff, E. Y.; Chang, C. J. Molecular Imaging of Hydrogen Peroxide Produced for Cell Signalling. Nat. Chem. Biol. 2007, 3 (5), 263−267. (20) Mani, T.; Grills, D. C.; Newton, M. D.; Miller, J. R. Electron Localization of Anions Probed by Nitrile Vibrations. J. Am. Chem. Soc. 2015, 137 (34), 10979−10991. (21) Lo, S.-C.; Bera, R. N.; Harding, R. E.; Burn, P. L.; Samuel, I. D. W. Solution-Processible Phosphorescent Blue Dendrimers Based on Biphenyl-Dendrons and Fac-tris(phenyltriazolyl)iridium(III) Cores. Adv. Funct. Mater. 2008, 18 (19), 3080−3090. (22) Zhu, L.; Zhong, C.; Liu, Z.; Yang, C.; Qin, J. New Intramolecular Through-Space Charge Transfer Emission: Tunable Dual Fluorescence of Terfluorenes. Chem. Commun. 2010, 46, 6666− 6668. (23) Minabe, M.; Suzuki, K. Fluorene Derivatives. XXXI. Stable Rotamers of 9,9’:9’,9’’-Terfluorenyls at Room Temperature. J. Org. Chem. 1975, 40 (9), 1298−1302. (24) Hou, Y.; Meyers, C. Y. The Surprising Formation of Structurally Distorted ap-9-(o-tert-Butylphenyl)-9-methylthiofluorene and Its Facile Homolysis into sp-9-(o-tert-Butylphenyl)-3-methylthiofluorene and sp-9-(o-tert-Butylphenyl)fluorene. Can. J. Chem. 1999, 77, 960−966. (25) Su, G.; Wei, Y.; Guo, M. Direct Colorimetric Detection of Hydrogen Peroxide Using 4-Nitrophenyl Boronic Acid or Its Pinacol Ester. Am. J. Anal. Chem. 2011, 2, 879−884. (26) Liu, Y.-Y.; Lin, J.-Y.; Bo, Y.-F.; Xie, L.-H.; Yi, M.-D.; Zhang, X.W.; Zhang, H.-M.; Loh, T.-P.; Huang, W. Synthesis and Crystal Structure of Highly Strained [4]Cyclofluorene: Green-Emitting Fluorophore. Org. Lett. 2016, 18 (2), 172−175. (27) Ding, J.; Day, M.; Robertson, G.; Roovers, J. Synthesis and Characterization of Alternating Copolymers of Fluorene and Oxadiazole. Macromolecules 2002, 35, 3474−3483. (28) Contini, A. E.; Bellamy, A. J.; Ahad, L. N. Taming the Beast: Measurement of the Enthalpies of Combustion and Formation of Triacetone Triperoxide (TATP) and Diacetone Diperoxide (DADP) by Oxygen Bomb Calorimetry. Propellants, Explos., Pyrotech. 2012, 37, 320−328. (29) Oxley, J. C.; Smith, J. L.; Shinde, K.; Moran, J. Determination of the Vapor Density of Triacetone Triperoxide (TATP) Using a Gas Chromatography Headspace Technique. Propellants, Explos., Pyrotech. 2005, 30, 127−130. (30) Demas, J. N.; Crosby, G. A. J. Measurement of Photoluminescence Quantum Yields. A Review. J. Phys. Chem. 1971, 75, 991−1024.

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DOI: 10.1021/acssensors.8b01029 ACS Sens. XXXX, XXX, XXX−XXX