热致变色

Communication

Fibers and Polymers 2007, Vol.8, No.2, 234-236

Effect of Alkyl Chain Length on Thermochromism of

Novel Nitro Compounds

Sang Cheol Lee*, Young Gyu Jeong, Suk Hyun Jang, and Won Ho Jo1

School of Advanced Materials and Systems Engineering, Kumoh National Institute of Technology, Kumi 730-701, Korea

1

Hyperstructured Organic Materials Research Center and School of Materials Science and Engineering,

Seoul National University, Seoul 151-742, Korea

(Received November 21, 2006; Revised February 16, 2007; Accepted March 19, 2007)

Abstract:2,4-dinitrobenzene (BDBx), are synthesized and their thermochromic behavior is investigated by using differential scanning A series of novel nitro compounds containing different alkyl chain length (x=2~5), 1,5-bis(hydroxyalkylamino)-calorimetry (x=2~4) samples display orange color even in the solid when heated above respective thermochromic transition temperature,and optical microscopy. All the BDBx crystals while the yellow color of BDB5 changes to orange with melting. The orange color of BDBx crystals returns to yellow whencooled down to room temperature, indicating that the thermochromic behavior of BDBx is reversible. The thermochromictransition temperatures of BDBx crystals are found to be decreased with increasing the alkyl chain length, exhibiting even-odd fluctuation.

Keywords: Thermochromism, Thermochromic transition temperature, Even-odd fluctuation

compounds The reversible or irreversible color thermochromism [1,2]. The thermochromic organic compoundsunder the stimulus of heat change is referred of organicto ashave received special attention in various applications such assmart dyes, temperature-indicating devices, temperature sensitivelight filters, optical switching, imaging systems, etc [1,3,4].Among thermochromic organic compounds, spiroheterocycliccompounds [5-7], Schiff base [8-11], and overcrowded ethyl-enes [12,13] have been extensively investigated. As a result,it equilibrium process between two isomeric molecular species.was revealed that their thermochromism occurs via anFor instance, the thermochromic behavior of spiroheterocycliccompounds such as spiropyrans and spirooxazines has beenidentified to be associated with a thermally sensitive equilibriumbetween open merocyanine-like structure formed by ring opening viathe spiroheterocyclic form and the quasi-planarthe C-O bond breaking [1,2].

compound, We have recently introduced a novel thermochromic nitro(BDB2), and investigated its thermochromic mechanism in1,5-bis(hydroxyethylamino)-2,4-dinitrobenzenethe solid state [14]. The yellow color of BDB2 at room tem-perature changed to orange in the solid state when heated.The yellow color is recovered when cooled again. From theresults of X-ray diffraction, thermal data, visible and infraredspectra, it was suggested that the reversible thermochromicbehavior of BDB2 stems from the crystal-to-crystal transitionaccompanying nitro-form transfer. In this communication, we report the synthesis andand the acid-form configurational via the intramolecular transformation hydrogenbetweenthermochromism benzene (BDBx, where x means the number of methyleneof 1,5-bis(hydroxyalkylamino)-2,4-dinitro-group) with a variety of alkyl chain lengths (x=2~5), whose

*Corresponding author: leesc@kumoh.ac.kr

show yellow color at room temperature. BDBxchain structure is investigated length is on shown thermochromic in Figure 1. by means of differential behavior The influence of scanningBDBxof BDBx with different alkyl chain length (x=m-dichlorobenzene (50g, 0.34 mol) was reactedl) at 3 (70130g, 0.693 mol) in a concentrated HoC for 1 hr. 2SO4 solution95% ethanol (1000mwas The l), and filtrated, reaction product recrystallized dissolved of at in 2,6-0g), 4-amino-1-butanol (33.5g), 3-g) were dissolved in ethanol (50g), andmml). Each mixed solution was stirred for 4 hrsg, 0.084mol) in ethanol Chemical structure of 1,5-bis(hydroxyalkylamino)-2,4-synthesized 234

chemical ofalkyl crystals calorimetry and optical microscopy.

A series 2~5) were synthesized via two steps in the laboratory. In thefirst step, with KNO(250mdichloro-3,5-dinitrobenzene aboiling oCfor 24 hrs. In the second step, 2-amino-1-ethanol (23amino-1-protanol (28.35-amino-1-pentanol (34.7l),respectively, and then each solution was dropwisely addedinto 2,6-dichloro-3,5-dinitrobenzene (20solution (250to complete the reaction between 2,6-dichloro-3,5-dinitrobenzeneand aminoalcohol. The crude products of BDBx with differentalkyl chain length were filtrated and purified by recrystalli-zation in ethanol solution. Sample codes for BDBx (x=2~5)crystals prepared in this study are denoted as BDB2, BDB3,BDB4 and BDB5, respectively, depending on the alkyl chainlength. Here, it should be mentioned that each BDBx consistsof only one crystal structure, which is confirmed by X-raydiffraction method. Previously, we found that BDB2 exists

Figure 1.dinitrobenzene (BDBx).

Thermochromism of Novel Nitro Compounds

Figure assignments; (A) BDB2, (B) BDB3, (C) BDB4, and (D) BDB5.2. 1H NMR spectra of BDBx samples with peak

in two different crystal structures of on solvents (THF and ethanol) used for recrystallization [14].A- and B-forms, dependingBDB2 prepared in this study is composed of because it is recrystallized in ethanol solution.B-form crystals,identified using a The chemical structures of BDBx crystals synthesized were1

FTH NMR spectrometer (Bruker AMX500dissolved in DMSO--NMR, Germany). For NMR analysis, all the samples werestandard. The color changes of BDBx as a function of tem-d6 with tetramethylsilane (TMS) internalperature were recoded on a digital camera. Thermal propertiesof BDBx crystals were measured with a differential scanningcalorimeter nitrogen heating rate of 10atmosphere (DSC 200

oto minimize F3, NETZSCH, oxidative Germany) degradation. under Thea

1C/min is used.

are represented in Figure 2. The peaks at 3.33 and 2.50 ppmH NMR spectra of BDBx (x=2~5) with peak assignmentsresult respectively. It was confirmed from the quantitative analysisfrom H2O and DMSO contained in the solution,using 1

alkyl length were successfully synthesized.H NMR spectra that BDBx samples with differentcolor at room temperature, as shown in Figure 3. For BDB2,All the BDBx crystals synthesized exhibit optically yellowBDB3, and BDB4 crystals, the yellow color changes quicklyto thermochromic orange even in the solid state

remained unchanged when melted. On the other hand, BDBtransition temperature. when Their heated orange above coloreach5 does not display color change in the solid state, but exhibitorange color when melted, as can be seen in Figure 3. Theorange color of BDB2, BDB3, and BDB4 in the solid stateFibers and Polymers 2007, Vol.8, No.22353.

Optical images of BDBx samples; (A) at room4. DSC heating thermograms of BDBx samples; (A)mentioned above, it was identified for BDB2 that theconclude that the thermochromic behavior of BDB2,To identify the transition temperatures associated

withFigure temperature and (B) above thermochromic transition temperature.Figure BDB2, (B) BDB3, (C) BDB4, and (D) BDB5.returned to yellow when cooled to room temperature, indicatingthat the color changes of BDB2, BDB3, and BDB4 with thevariation of temperature are reversible even in the solid state.As color change in the solid state arises from the crystal-to-crystaltransition accompanying the configurational transformationbetween nitro-form and acid-form [14]. Therefore, it is validto BDB3, and BDB4 in the solid state undergoes via crystal-to-crystal transition, whereas that of BDB5 via crystal-to-melttransition together with configurational transformation.

236Fibers and Polymers 2007, Vol.8, No.2 Sang Cheol Lee et al.thermochromism of BDBx (x=2~5), their thermal propertieswere characterized by using differential scanning calorimetry,as can be seen in Figure 4. DSC heating thermograms displaytwo dominant endothermic peaks for BDB2, BDB3 andBDB4, and one peak for BDB5. Here, the transition temperaturewas considered as the maximum of the endothermic peak. Itwas identified that the first endothermic peak of BDB2,BDB3, and BDB4 is the crystal-to-crystal transition temperature(Tcc) associated with the thermochromism in the solid stateand the second peak is the melting temperature (Tm). Theonly endothermic peak of BDB5 at 87oC corresponds to themelting temperature as well as thermochromic transitiontemperature at which its color changes from yellow to orange,as can be seen in Figure 3. It is interesting to note thatthermochromic transition temperatures (134 and 119oC) ofBDB2 and BDB4 are higher than those (116 and 87oC) ofBDB3 and BDB5. In other words, the thermochromic transitiontemperatures of BDBx decreased with increasing the alkylchain lengths, exhibiting an even-odd effect. It is believedthat the even-odd fluctuation in thermochromic transitiontemperatures of BDBx crystals is strongly related with themolecular packing in each crystal. Also, it should be mentionedthat the color recovery of BDB2 from orange to yellow inthe solid state takes a specific period of time when cooled [14].In contrast, the orange to yellow color changes of BDB3 andBDB4 in the solid state occurs immediately. It is alsobelieved that the kinetics of reversible thermochromism inthe solid state is related to the crystal structures before andafter thermochromic transition temperatures.In summary, we synthesized successfully a series ofthermochromic novel nitro compounds with various alkylchain lengths and found that the thermochromic behavior ofBDBx is varied, depending on the alkyl chain length. Thedetailed crystallographic data, spectral changes, reversiblethermochromic kinetics, and the possibility of photochromismof BDBx in the solid state are under investigation by meansof temperature- and time-dependent X-ray diffraction, infraredand UV/visible spectroscopy, which will be reported in thefuture.AcknowledgementsThis paper was supported by Research Fund of KumohNational Institute of Technology.References1.J. H. Day, Chem. Rev., 63, 65 (1963).2.A. Samat and V. Lokshin in “Organic Photochromic andThermochromic Compounds” (J. C. Crano and R. J.Guglielmetti Eds.), Kluwer Academic/Plenum Publishers,New York, 1999.3.L. Tansienhee, D. Lavabre, G. Levy, and J. C. Micheau,New J. Chem., 13, 227 (1989).4.M. A. White and M. LeBlanc, J. Chem. Edu., 76, 1201(1999).5.D. Ollis, K. L. Ormand, and I. O. Sutherland, J. Chem.Soc. Chem. Comm., 1697 (1968).6.P. N. Day, Z. Q. Wang, and R. Rachter, J. Phys. Chem., 99,9730 (1995).7.H.-J. Suh, W.-T. Lim, J.-Z. Cui, H.-S. Lee, G.-H. Kim, N.-H.Heo, and S.-H. Kim, Dyes Pigments, 57, 149 (2002).8.M. D. Cohen and G. M. J. Schmidt, J. Phys. Chem., 56,2442 (1962).9.A. Takase, S. Sakagami, K. Nonaka, and T. Koga, J.Raman Spectrosc., 24, 447 (1993).10.E. Hadjoudis, A. Rontoyianni, K. Ambroziak, T.Dziembowska, and I. M. Mavridis, J. Photochem.Photobiolo., A: Chem., 162, 521 (2004).11.T. Fujiwara, J. Harada, and K. Ogawa, J. Phys. Chem. B,108, 4035 (2004).12.I. Agranat and Y. Tapuhi, J. Org. Chem., 44, 1941 (1979).13.J. J. Stezowski, P. U. Biedermann, T. Hildenbrand, J. A.Dorsch, C. J. Eckhardt, and I. Agranat, J. Chem. Soc.Chem. Comm., 213 (1993).14.S. C. Lee, Y. G. Jeong, W. H. Jo, H.-J. Kim, J. Jang, K.-M.Park, and I. H. Chung, J. Mol. Struc., 825, 70 (2006).