Accepted Manuscript Highly efficient halochromic behaviors in solution and film states with 9,19dichloro-5,15-dihydrocarbazolo[3′,4':5,6][1,4]oxazino[2,3-b]indolo[3,2-h]phenoxazine derivative Young Un Kim, Gi Eun Park, Suna Choi, Chang Geun Park, Min Ju Cho, Dong Hoon Choi PII: S0143-7208(18)30614-4 DOI: 10.1016/j.dyepig.2018.08.030 Reference: DYPI 6944 To appear in: Dyes and Pigments Received Date: 20 March 2018 Revised Date: 28 June 2018 Accepted Date: 19 August 2018 Please cite this article as: Kim YU, Park GE, Choi S, Park CG, Cho MJ, Choi DH, Highly efficient halochromic behaviors in solution and film states with 9,19-dichloro-5,15-dihydrocarbazolo[3′,4':5,6] [1,4]oxazino[2,3-b]indolo[3,2-h]phenoxazine derivative, Dyes and Pigments (2018), doi: 10.1016/ j.dyepig.2018.08.030. 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 AC C EP TE D M AN U SC RI PT Graphical abstract ACCEPTED MANUSCRIPT DOI: 10.1002/ ((please add manuscript number)) Article type: Full Paper Highly Efficient Halochromic Behaviors in Solution and Film States with b]indolo[3,2-h]phenoxazine Derivative RI PT 9,19-Dichloro-5,15-dihydrocarbazolo[3',4':5,6][1,4]oxazino[2,3- SC Young Un Kim, Gi Eun Park, Suna Choi, Chang Geun Park, Min Ju Cho* and Dong Hoon Choi* Department of Chemistry, Research Institute for Natural Sciences, Korea University, 145 Anam-ro, M AN U Sungbuk-Gu, 02841 Seoul, Republic of Korea. Corresponding authors: Min Ju Cho (E-mail: email@example.com); Dong Hoon Choi (E-mail: firstname.lastname@example.org) Abstract: We demonstrated 9,19-dichloro-5,15-bis(2-decyltetradecyl)-5,15- TE D dihydrocarbazolo[3',4':5,6][1,4]oxazino[2,3-b]indolo[3,2-h]phenoxazine (DTD-CzDxz) as a new halochromic compound with a prominent UV-vis absorption spectral response under acidic conditions. DTD-CzDxz was constructed with branched alkyl chains at the ends of a EP planar fused molecule to achieve good solubility in common organic solvents. When the nitrogen in the oxazine ring was diprotonated, the entire absorption spectrum shifted from the AC C visible region to the near-infrared (NIR) region for both solution and film states. Owing to a significant red shift of 256 nm in the solution state, the color of the sample quickly faded and the sample became colorless and transparent and could be easily recognized by the naked eye. In addition, the photoluminescence spectrum of DTD-CzDxz displayed significantly weakened emission intensity at 650 nm under acidic condition. When triethylamine was added into the acid-treated solution, the emission intensity at 650 nm was restored to its 1 ACCEPTED MANUSCRIPT initial value. The neat DTD-CzDxz film was transparent and colorless film when exposed to acid vapors. However, the absorption spectrum reverted to its original form as soon as the film was exposed to air at room temperature. The efficient cyclizability due to the RI PT halochromism of the DTD-CzDxz film showed that there was no significant degradation in the absorption intensity at 567 and 794 nm. Hence, it could be concluded that DTD-CzDxz is a good candidate for solid-state halochromic sensors that can operate under both acidic and SC basic conditions. M AN U Keywords: dye, dioxazine, halochromism, NIR absorption, pH sensor, acid vapor sensor 1. Introduction Organic dyes and pigments are major colorants containing specific chromophores and are TE D used to color other materials. [1-5] Apart from being used as colorants, they are used in optical components, semiconductors, and various sensors, owing to their conjugated structures. [6-10] EP The specific dyes and pigments used in sensor applications should have unique AC C characteristics that enable them to display varied functions when they selectively interact with target analytes through π-conjugation. It is known that long π-conjugation in planar molecules originate from polycyclic and acene- type compounds consisting of fused aromatic rings. Among the various acenes, heteroatoms including sulfur, nitrogen and oxygen have been used for forming heteroaromatic fused ring compounds. [11-13] In particular, nitrogen is highly effective for maintaining the aromatic structural stability under most conditions, including ambient conditions and its reactivity as an active site for possible reactions such as 2 ACCEPTED MANUSCRIPT alkylation and protonation. [14-16] As ionic or hydrogen bonds can be formed with nitrogen, the electron distribution of Ncontaining heteroaromatic compounds is expected to change on exposure to a hydrogen ion RI PT environment, i.e., acidic conditions. Therefore, heteroaromatic compounds with nitrogen atoms may exhibit halochromism, i.e., due to change in pH, because the incorporation of nitrogen for quaternization [17-18] can allow the manipulation of frontier molecular orbital SC energies and electrical conductivity. The quaternized nitrogen also facilitates intermolecular interactions through ionic interactions in solution and solid-states. Reynolds et. al. reported M AN U pronounced halochromism in N-containing heteroaromatic compounds that displayed a significant color change (from 450 to 750 nm) with a remarkably high absorption spectral AC C EP TE D shift of 300 nm.  Fig. 1. Molecular structures of DTD-CzDxz and DTD-CzDxz (2H+) and solution images in chloroform. 3 ACCEPTED MANUSCRIPT Garino et. al. and Ando et. al. also demonstrated a large Stokes shifts of 174 nm (from 304 to 478 nm) and of 120 nm (from 316 to 436 nm) for tetradentate polyazines based on imidazo[1,5-a]pyridine and N,N′-dicyclohexyl-3,6-dihydroxypyromellitimide, respectively, RI PT owing to the halochromic effect. [20-21] In this study, we synthesized an N-containing heteroaromatic acene compound DTDCzDxz, based on the bluish purple pigment carbazole dioxazine (CzDxz). The mother SC structure of DTD-CzDxz has long been used as a pigment-type colorant and therefore, its solubility should be improved for further application in film-based device fabrications. M AN U Through the modification of the molecular structure of DTD-CzDxz by attaching alkyl chains (e.g. decyltetradecyl) at two carbazole sides, its solubility is improved to convert it into a soluble dye molecule. CzDxz comprised five fused rings in a row with two oxazine rings. The oxazine rings and the position of the nitrogen atoms well resemble the structure of TE D N-heteroaromatic acene compounds exhibiting effective halochromism. The properties of CzDxz have been investigated in detail previously. [22-23] However, the optical characteristics of N-heteroaromatic acenes with nine fused rings and continuous π- EP conjugation has been scarcely reported, which makes the current study important. Although a spectral shift is recognized as a common feature in chromic sensors, most shifts lead to a AC C color change within the visible region. [24-26] However, only a few studies have reported color bleaching in known halochromic compounds.  Both the solution and film states of DTD-CzDxz showed a bluish purple color in their absorption spectrum, which is close to the near infrared (NIR) wavelength range. When acid species was added to the solution or when the thin film was exposed to acid vapor, the absorption spectra remarkably shifted to the NIR wavelength range, leading to the 4 ACCEPTED MANUSCRIPT disappearance of the visible color in both solution and film states. Furthermore, when triethylamine (TEA) was added to an acid-containing solution of DTD-CzDxz, the absorption spectrum of the solution showing NIR absorption returned to its original form. In addition, RI PT the acid-treated thin film returned to its original color upon exposure to air, suggesting DTDCzDxz to be an excellent material for acid vapor sensors using solid-state films. SC 2. Experimental M AN U 2.1 Materials and synthesis All commercially available starting materials and solvents were purchased from Sigma Aldrich Chemical Co., Alfa Aesar Co., or Tokyo Chemical Industry Co., and were mostly used as-received. For specific reactions, the purchased chemicals were purified where TE D necessary. Carbazole was purchased from Alfa Aesar Co. Compounds 1, 2, and 3 were 2.2 Synthesis EP synthesized using previous methods with some modifications. [28-30] AC C 2.2.1. Synthesis of 2,5-dichloro-3,6-bis((9-(2-decyltetradecyl)-9H-carbazol-3yl)amino)cyclohexa-2,5-diene-1,4-dione, (4) Compound 3 (4 g, 9.84 mmol) was dissolved in ethanol (50 mL). The solution was poured dropwise into a three-necked round bottom flask after adding chloranil (1.14 g, 4.68 mmol) and potassium acetate (0. 97g, 9.84 mmol) under argon atmosphere. The reaction mixture was stirred for 4 h at 65 °C. After cooling to 25 °C, the mixture was extracted with 5 ACCEPTED MANUSCRIPT dichloromethane and additional water, and then evaporated in a vacuum evaporator to obtain 3.5 g (75.8%) of compound 4 as a solid violet product. 1H NMR (500 MHz, CDCl3, δ, ppm): 8.73 (s, 2H), 8.09 (d, J = 7.1 Hz, 2H), 7.91 (s, 2H), 7.52 (t, J = 7.4 Hz, 2H) , 7.39 (d, J = 8.5 RI PT Hz, 2H), 7.37 (d, J = 8.5 Hz, 2H), 7.25-7.32 (m, 4H), 4.20 (d, J = 7.1 Hz, 4H), 2.14 (s, 2H), 1.25 (m, 80H), 0.87 (d, J = 6.9 Hz, 12H). Elemental analysis: anal. calcd for C78H114Cl2N4O2 (%): C, 77.38; H, 9.49; Cl, 5.86; N, 4.63; O, 2.64. Found: C, 77.40; H, 9.46; N, 4.66. M AN U SC MALDI−TOF−MS (m/z): calcd for C78H114Cl2N4O2: 1210.67; found: 1211.83 [M]+ 2.2.2. Synthesis of 9,19-dichloro-5,15-bis(2- decyltetradecyl)-5,15-dihydrocarbazolo [3',4':5,6][1,4]oxazino[2,3-b]indolo[3,2-h]phenoxazine, (DTD-CzDxz) A methanol solution (60 mL) containing potassium acetate (1.05 g, 10.65 mmol) was added TE D to a mixture of compound 4 (3 g, 3.04 mmol) and dimethylhydrofuran (30 mL) under nitrogen. After adding (diacetoxy)iodobenzene (2.74 g, 8.52 mmol) dropwise, the mixture was stirred for 3 h at 25 °C. Then, the reaction mixture was poured into methanol. The EP resulting precipitate was collected by filtration and purified through silica gel column chromatography (n-hexane/dichloromethane = 1:1). DTD-CzDxz was obtained in a yield of 1 AC C 980 mg (30%) as a bluish purple solid. H NMR (500 MHz, CDCl3, δ, ppm): 8.43 (d, J = 7.6 Hz, 2H), 7.57 (d, J = 8.6 Hz, 2H), 7.32 (t, J = 6.4 Hz, 2H), 7.30 (d, J = 8.3 Hz, 2H), 7.17 (d, J = 8.4 Hz, 2H), 7.13 (d, J = 8.2 Hz, 2H), 4.04 (d, J = 6.6 Hz, 2H), 4.04 (d, J = 6.6 Hz, 2H), 2.04 (s, 2H), 1.22 (m, 80H), 0.88 (m, 12H). Elemental analysis: anal. calcd for C78H110Cl2N4O2 (%): C, 77.64; H, 9.19; Cl, 5.88; N, 4.64; O, 2.65. Found: C, 77.52; H, 9.16; N, 4.65. MALDI−TOF−MS (m/z): calcd for 6 ACCEPTED MANUSCRIPT C78H110Cl2N4O2: 1206.64; found: 1206.81 [M]+ 1 RI PT 2.3. Instrumentation H-nuclear magnetic resonance (NMR) spectra of all compounds were recorded on a Bruker 500 MHz spectrometer using deuterated chloroform (Cambridge Isotope Laboratories, Inc.). SC Differential scanning calorimetry (DSC) measurements were conducted in nitrogen using a TA Instruments Q2000 calorimeter. The samples were heated at a rate of 5 °C/min. The UV- M AN U Vis NIR absorption and photoluminescence (PL) spectra were obtained using an Agilent 8453 photodiode array UV-vis NIR absorption spectrometer and a Hitachi F-7000 fluorescence spectrophotometer, respectively. TE D 2.4 Fabrication and characterization of thin films for halochromic sensors The halochromic films were fabricated by coating DTD-CzDxz on a washed glass substrate. EP The glass substrate was cleaned by sonication for 10 min each in water, acetone, chloroform, and isopropanol sequentially. As a sensing layer, 1% v/v DTD-CzDxz in CHCl3 solution was AC C spin-coated at 2000 rpm for 40 s on the washed glass substrate. The bluish purple film exposed to acid vapor changed to a colorless film, which returned to its original color very quickly (<1.0 s) on exposure to air. Therefore, to observe the reversible acid sensing behavior of the film, the film sample was placed in a quartz cuvette for exposure to acid vapor. The lid was closed and the spectrum was recorded using UV-vis absorption spectroscopy. 7 ACCEPTED MANUSCRIPT 3. Result and discussion 3.1 Synthesis and physical properties Compound 4 was synthesized by the condensation of 2,3,5,6-tetrachlorocyclohexa-2,5-diene- RI PT 1,4-dione (chloranil) and 9-(2-decyltetradecyl)-9H-fluoren-3-amine through an electron transfer reaction. DTD-CzDxz was finally synthesized in a 30% yield through a simple ringclosure reaction using potassium acetate and (diacetoxyiodo)benzene as the catalysts at room M AN U SC temperature. 1 2 3 R=decyltetradecyl DTD-CzDxz TE D 4 EP Scheme 1. Synthetic route : (i) 2-decyltetradecyl bromide, NaH; (ii) HNO3, C2H4Cl2; (iii) N2H4-H2O, Pd/C, KOAc, EtOH; (iv) chloranil, KOAc, EtOH; (v) (diacetoxyiodo)benzene, KOAc, DMF/MeOH. 15 Heat Flow (W/g) AC C 10 Heating cycle Cooling cycle Cooling 5 0 -5 Heating -10 -15 150 200 250 300 o Temperature( C) Fig. 2. DSC curves of DTD-CzDxz during heating and cooling cycles. 8 ACCEPTED MANUSCRIPT The chemical structure of DTD-CzDxz was characterized and confirmed by 1H-NMR, Matrix assisted laser desorption ionization-time of flight, and elemental analysis. Because of the poor solubility of common CzDxz-based pigments in organic solvents including RI PT dichloromethane, chloroform, and tetrahydrofuran, the long and bulky branched alkyl chains were attached to the 9-position of each carbazole moiety to improve the solubility. The thermal properties of DTD-CzDxz were investigated by DSC (Fig. 2). The reversible melting SC transition behavior of DTD-CzDxz was observed at 291 and 277 °C in the heating and M AN U cooling cycles, respectively, indicating moderately high thermal stability. 3.2 Optical and electrochemical properties The absorption range of DTD-CzDxz in both solution and film states was measured by UVvis absorption spectroscopy. The DTD-CzDxz solution displayed highly intense absorption TE D in the 400–700 nm wavelength region. The absorption spectrum of DTD-CzDxz in chloroform showed λmaxabs at 615 nm (Fig. 3). The absorption spectra of DTD-CzDxz in EP different polar organic solvents were obtained and a small solvatochromic effect was observed in dichloromethane (1.60 D) and tetrahydrofuran (1.75 D) (∆λmaxabs = 4 nm and 13 AC C nm, respectively). The bandgap of a molecule changes according to the solvent polarity, thereby changing the absorption region. The PL spectrum of DTD-CzDxz was also measured and showed a λmaxem at 646 nm in chloroform solution. Moreover, a small solvatochromic effect was also observed in dichloromethane and tetrahydrofuran (∆λmaxem = 2 nm and 15 nm, respectively). When HCl [conc. = 1 × 10-2 M] was added to the DTD-CzDxz solution [conc. =1 × 10-5 M], the 9 ACCEPTED MANUSCRIPT SC RI PT absorption wavelength range immediately shifted to show a prominent color change (Fig. 1). M AN U Fig. 3. (a) Absorption and PL spectra of DTD-CzDxz in CHCl3 solution. (b) Solvatochromic behaviors; absorption and PL spectra of DTD-CzDxz in three different solvents. When three different acids were added [conc. = 1 × 10-2 M] to the DTD-CzDxz solution, the visible absorption bands in the range 450– 680 nm almost completely disappeared and new absorption bands appeared in the NIR wavelength range (λ = 650–1000 nm). As shown TE D in Fig. 4a, the absorption spectrum of the DTD-CzDxz in CHCl3 displayed red shift (∆λmaxabs. = 256 nm) from the visible to NIR wavelength region after adding each acid. EP To clarify such a color change and unique performance, the halochromism of DTD-CzDxz was investigated, as follows. The addition of acid to the DTD-CzDxz solution led to spectral AC C transformation, which could be attributed to the protonation of the two nitrogens of oxazine. Intramolecular charge transfer (ICT) absorption occurred because of the protonation of nitrogen in the N-heteroaromatic electron accepting unit. Therefore, π-conjugated structures with strong built-in donor–acceptor interactions tended to exhibit a more pronounced halochromic effect owing to the enhanced ability of these structures to redistribute charge density in the HOMO and LUMO levels and promote charge-transfer absorption in the NIR 10 ACCEPTED MANUSCRIPT wavelength range. NIR region 0.4 0.2 0.0 300 0.6 0.4 0.2 0.0 400 500 600 700 800 900 400 1000 0.4 0.2 0.0 (d) Absorbance (a.u.) -3 HCl (4.68 x 10 M) -3 HCl (5.85 x 10 M) -3 HCl (7.02 x 10 M) -3 HCl (8.19 x 10 M) -3 HCl (9.36 x 10 M) 0.6 800 1000 DTD-CzDxz -3 TFA (1.29 x 10 M) -3 TFA (2.58 x 10 M) -3 TFA (3.87 x 10 M) -3 TFA (5.16 x 10 M) M AN U Absorbance (a.u.) DTD-CzDxz -3 HCl (1.17 x 10 M) -3 HCl (2.34 x 10 M) -3 HCl (3.51 x 10 M) 0.8 600 Wavelength (nm) Wavelength (nm) (c) DTD-CzDxz -3 H2SO4 (1.84 x 10 M) -3 H2SO4 (3.68 x 10 M) -3 H2SO4 (5.52 x 10 M) -3 H2SO4 (7.32 x 10 M) -3 H2SO4 (9.20 x 10 M) -2 H2SO4 (1.10 x 10 M) 0.8 RI PT 0.6 (b) Dxz HCl H2SO4 TFA SC Absorbance (a.u.) 0.8 Absorbance (a.u.) (a) 0.8 -3 TFA (6.45 x 10 M) -3 TFA (7.74 x 10 M) -3 TFA (9.03 x 10 M) -2 TFA (1.03 x 10 M) 0.6 0.4 0.2 0.0 600 800 1000 400 TE D 400 Wavelength (nm) 600 800 1000 Wavelength (nm) EP Fig. 4. (a) UV-Vis absorption spectra of DTD-CzDxz solutions (1 × 10-5 M in CHCl3) with 1 × 10-2 M acid. UV-Vis absorption spectra of DTD-CzDxz solutions (1 × 10-5 M in CHCl3) after adding (b) H2SO4, (c) HCl, and (d) TFA. (conc. of acid: 1 × 10-3 M – 1 × 10-2 M). AC C Experimental conditions with incremental addition of acid (conc. of acid in DTD-CzDxz solution= 1 × 10-3 M – 1 × 10-2 M) were applied, and the shifted absorption peak in the NIR region gradually increased in intensity (Fig. 4b–d). As the concentration of acid in the solution increased, the absorption intensity in the NIR wavelength range (λ = 650–1000 nm) also increased, whereas that in the visible region (λ = 450–680 nm) decreased. This phenomenon indicated the higher extent of quaternization and the occurrence of highly 11 ACCEPTED MANUSCRIPT effective ICT. The phenomenon of the DTD-CzDxz (2H+) solution becoming transparent at acidic conditions showed that protonation occurred only under diprotonation conditions (e.g., two-proton binding). As can be seen in Fig. 4, in comparison of the absorption spectra RI PT measured with varying the concentration of each acid, no spectral shift by mono-protonation was observed and only the decrease of the absorbance in the same wavelength region was displayed. Therefore, it can be conjectured that diprotonated DTD-CzDxz would be SC predominant in acidic conditions. Therefore, color change from bluish purple to colorless transparent could be explained by the occurrence of simultaneous protonation on both sides M AN U of the nitrogen atom of the oxazine rings or negligibly fast sequential protonation after monoprotonation. [19, 31, 32] The PL spectral change of DTD-CzDxz solutions with the acid concentration is displayed in Fig. S1 in the Supporting Information (SI). and basic conditions TE D 3.3 Reversible absorption and fluorescence spectral behaviors of DTD-CzDxz under acidic The reversible effect of protonation on the absorption and fluorescence of DTD-CzDxz is EP shown in Fig. 5. When TFA (conc. 5 × 10-3 M) was added to the DTD-CzDxz solution, the AC C absorption intensity in the range 450–680 nm significantly weakened, and new absorption bands appeared in the NIR region. As the concentration of the TFA solution increased, the visible absorption band almost disappeared and the NIR absorption band intensities strengthened remarkably. Subsequently, when TEA (conc. 6 × 10 -3 M) was added to the DTD-CzDxz (2H+) solution formed above, the absorption spectrum was restored to the original spectrum of initial DTD-CzDxz (Fig. 5a). 12 M AN U SC RI PT ACCEPTED MANUSCRIPT TE D Fig. 5. (a) UV/Vis absorption spectra and (b) PL spectra of DTD-CzDxz solutions (1 × 10-5 M in CHCl3) with addition of TFA and TEA. (c) Photographic images of DTD-CzDxz solutions (1 × 10-5 M in CHCl3) with the concentration of TFA [① no TFA, ② 2.58 × 10-3 M, -3 -3 -2 ③ 5.16 × 10 M, ④ 7.74 × 10 M, ⑤ 1.03 × 10 M], and with the concentration of TEA. [⑥ 2.16 × 10-3 M, ⑦ 3.60 × 10-3 M, ⑧ 5.04 × 10-3 M, ⑨ 6.48 × 10-3 M] EP Almost an identical reversible behavior could be observed in the PL spectra shown in Fig. 5b. AC C The addition of TFA to the DTD-CzDxz solution quenched the emission at 650 nm. After the addition of TEA to neutralize the above solution, the emission peak at 650 nm re-appeared and the spectrum was found to be identical to that of original DTD-CzDxz. (Fig. S2) Therefore, a reversible on/off switching behavior could be expected in the solution state by adding acidic and basic species (Fig. 5c). The fluorescence images of DTD-CzDxz solution before and after adding acid are shown in Fig. S3 in the SI 13 RI PT ACCEPTED MANUSCRIPT M AN U SC Fig. 6. (a) UV-Vis absorption spectra of DTD-CzDxz thin film under exposure to HCl vapor. (b) Absorbance at λmax (567 nm and 794 nm) vs. number of sensing cycles (i) under acid vapor and (ii) in air. As shown in Fig. 6a, the absorption spectra of the thin film displayed a similar red shift (∆λmaxabs. = 227 nm) from the visible to NIR wavelength regions on exposure to acid vapors. The thin film of DTD-CzDxz exhibited a highly reversible absorption spectral behavior, TE D showing the color change from bluish purple to colorless in the presence of acid vapors. Under ambient conditions without acid vapor, the color of the thin film was recovered quickly from colorless to bluish purple. (Fig. S4) DTD-CzDxz, used as a thin film acid EP sensor, exhibited highly efficient cyclizability throughout the experiment. No significant permanent degradation in the intensities and wavelengths of the absorption region was AC C observed when the acid vapors were introduced into and removed from the sample more than 20 times under ambient conditions. The cyclizability measurements showed high efficiency and stability in the sensing behavior of DTD-CzDxz and demonstrated that DTD-CzDxz can be used as a solid-state devices showing very high sensitivity (Fig. 6b). 14 ACCEPTED MANUSCRIPT 4. Conclusion A new halochromic compound, DTD-CzDxz, based on a fused nine-ring heteroaromatic system was shown to exhibit unprecedentedly efficient halochromism with significant RI PT spectral shift of 256 nm (=∆λmaxabs) in the presence of acidic species. The shift in the absorption spectra induced a color change from purple to colorless when the solutions or films were exposed to acidic addition or acid vapors. Also, the optical properties of the DTD- SC CzDxz thin film were found to be useful for application as a pH sensor, showing fast response to acid vapors owing to fast diprotonation. 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EP  Tang S, Zhang Y, Thapaliya ER, Brown AS, Wilson JN, Raymo FM. Highlighting cancer cells with halochromic switches. ACS Sens 2017;2:92-101. AC C  Cai K, Yan Q, Zhao D. Large hydroazaacene diimides: synthesis, tautomerism, halochromism, and redox-switchable NIR optics. Chem Sci 2012;3:3175-3182.  Wang K, Huang S, Zhang Y, Zhao S, Zhang H, Wang Y. Multicolor fluorescence and electroluminescence of an ICT-type organic solid tuned by modulating the accepting nature of the central core. Chem Sci 2013;4:3288-3293. 18 ACCEPTED MANUSCRIPT  Genovese ME, Colusso E, Colombo M, Martucci A, Athanassiou A, Fragouli D. Acidochromic fibrous polymer composites for rapid gas detection. J Mater Chem A 2017;5:339-348. RI PT  Zavakhina MS, Yushina IV, Samsonenko DG, Dybtsev DN, Fedin VP, Argent SP, Blake AJ, Schröder M. Halochromic coordination polymers based on a triarylmethane dye for reversible detection of acids. Dalton Trans 2017;46:465-470. SC  Daws CA, Exstrom CL, Sowa JR, Mann KR. “Vapochromic” compounds as M AN U environmental sensors. 2. Synthesis and near-infrared and infrared spectroscopy studies of [Pt(arylisocyanide)4][Pt(CN)4] upon exposure to volatile organic compound vapors. Chem Mater 1997;9:363-368.  Schweighauser L, Wegner HA. Cyclotetraazocarbazole – a multichromic molecule. TE D Chem Commun 2013;49:4397-4399.  Huo Z, Li Z, Wang T, Zeng H. Carbazole N-substituent effect upon DTMA: stabilizing EP and photochromic modulating. Tetrahedron 2013;69:8964-8973.  Tatsumi H, Wang Y, Aizawa Y, Tokita M, Mori T, Michinobu T. Halogen substitution AC C effects on the molecular packing and thin film transistor performances of carbazoledioxazine derivatives. J Phys Chem C 2016;120:26686-26694.  Mukhopadhyay A, Mishra AK, Jana K, Moorthy JN. A new MediaChrom (fluorosolvatochromic and acidochromic) based on bipolar donor-acceptor conjoined carbazolo-phenazine. J Photochem Photobiol A 2017;347:199-208. 19 ACCEPTED MANUSCRIPT  Aich K, Das S, Goswami S, Quah CK, Sarkar D, Mondal TK, Fun HK. Carbazole– benzimidazole based dyes for acid responsive ratiometric emissive switches. New J Chem AC C EP TE D M AN U SC RI PT 2016;40:6907-6915. 20 ACCEPTED MANUSCRIPT SUPPORTING INFORMATION Highly Efficient Halochromic Behaviors in Solution and Film States b]indolo[3,2-h]phenoxazine Derivative RI PT with 9,19-Dichloro-5,15-dihydrocarbazolo[3',4':5,6][1,4] oxazino[2,3- Young Un Kim, Gi Eun Park, Suna Choi, Chang Geun Park, Min Ju Cho* and Dong SC Hoon Choi* AC C EP TE D M AN U Department of Chemistry, Research Institute for Natural Sciences, Korea University, 145 Anam-ro, Sungbuk-Gu, 02841 Seoul, Republic of Korea. 21 M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D Fig. S1. PL spectra of DTD-CzDxz solutions (1 × 10-5 M in CHCl3) after adding (a) H2SO4, (b) HCl, and (c) TFA. (conc. of acid: 1 × 10-3 M–1 × 10-2 M). (d) PL spectra of DTD-CzDxz (1 × 10-5 M in CHCl3) after adding TEA (1 × 10-3 M – 6 × 10-3 M) sequentially to the solution bearing TFA. 22 M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D Fig. S2. UV-Vis absorption spectra of DTD-CzDxz solutions (1 × 10-5 M in CHCl3) after adding (a) TFA. (conc. of acid: 1 × 10-3 M – 1 × 10-2 M) and (b) TEA (1 × 10-3 M – 6 × 10-3 M). (c) Color change observed in DTD-CzDxz solutions (1 × 10-5 M in CHCl3) with the concentration of TFA, [① no TFA, ② 2.58 × 10-3 M, ③ 5.16 × 10-3 M, ④ 7.74 × 10-3 M, ⑤ 1.03 × 10-2 M] and with the concentration of TEA. [⑥ 2.16 × 10-3 M, ⑦ 3.60 × 10-3 M, ⑧ 5.04 × 10-3 M, ⑨ 5.76 × 10-3 M, and ⑩ 6.48 × 10-3 M] Fig. S3. Fluorescence images taken before (a) and after (b) the addition of acid to the DTDCzDxz solution while irradiating 254 nm and 365 nm UV light. 23 SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U Fig. S4. Photographs of DTD-CzDxz film taken after exposure to (a) HCl vapor (0-0.4 s) and (b) exposure to air. (c) Photographs obtained by repeatedly exposing the DTD-CzDxz film to acid vapor and then to air. The number of repeated experiments is in parentheses. 24 ACCEPTED MANUSCRIPT Highlight - A new halochromic compound DTD-CzDxz bearing oxazine and phenoxazine was RI PT synthesized. - The absorption spectrum shifted from the visible region to the near-infrared (NIR) region for both solution and film states in acidic conditions. SC - When triethylamine was added into the acid-treated solution, the absorption spectrum was AC C EP TE D M AN U recovered to its initial one.