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Synthesis and fluorescence study of sodium-2-(4′-dimethyl-aminocinnamicacyl)-3,3-(1′,3′-alkylenedithio) acrylate
ARTICLE IN PRESS
Journal of Luminescence 124 (2007) 365–369 www.elsevier.com/locate/jlumin
Synthesis and fluorescence study of sodium-2-(40 -dimethylaminocinnamicacyl)-3,3-(10,30-alkylenedithio) acrylate Zhenjun Si, Yun Shao, Chunxia Li, Qun Liu School of Chemistry, Northeast Normal University, Changchun 130024, PR China Received 9 January 2006; received in revised form 5 April 2006; accepted 14 April 2006 Available online 5 June 2006
Abstract We synthesized two new compounds: Sodium 2-(40 -dimethyl-aminocinnamicacyl)-3,3-(10 ,30 - ethyl- enedithio) acrylate (STAA-1) and Sodium 2-(40 -dimethyl-aminocinnamicacyl)-3, 3-(10 ,30 -propylenedithio) acrylate (STAA-2). The maximum absorption of these compounds ranges from 460 to 520 nm with different molecular structures in different solvents. Meanwhile, the emission peak of these compounds arranges from yellow (510 nm) to red (605 nm). The emission spectra show red shift according to the strength of the hydrogen bonding property of the solvent. But the absorption spectra do not show clearly relationship with the strength of the hydrogen bonding property of the solvent. The Stoke shift of the compounds ranges from 42 to 102 nm. It changes in the following order, EtOH4H2O4DMF, and STAA-14STAA-2 in the same solvent. The fluorescent quantum yield of STAA-1 was measured to be 7.12% with quinine sulphate as the standard compound in ethanol. Furthermore, the relationship of the fluorescence of STAA-1 with pH (ranges form 4 to 14) in water (c ¼ 104) was studied to make sure that these compounds could be used as proton sensors. r 2006 Elsevier B.V. All rights reserved. PACS: 07.07.Df; 78.55.m; 81.20.n Keywords: Proton sensor; Fluorescence quantum yield; Synthesis
1. Introduction p-Conjugated organic compounds have emerged in the past two decades as a promising class of materials for potential applications in photonics and optoelectronics. Lots of active materials used in these fields are the derivatives of aniline. These materials are used in nonlinear optics [1], photovoltaic cell [2], light emitting devices [3], and optically pumped lasers [4]. The photo-physical properties of the aromatic amino acids depend on the status of the amino and carboxyl groups although they are separated form chromophore by some methylene groups [5,6] or other groups [7,8], the quenching efficiency is controlled by the orientation of the quenching groups and the process is distance dependent. The rotamer model of fluorescence decays of aromatic amino acids has been
Corresponding author. Tel.: +86 0431 5099667.
E-mail address: [email protected] (Y. Shao). 0022-2313/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2006.04.005
supported by some investigations [9–11] that included studies of constrained tryptophan [12,13], tryptophan in protein crystals [14] and tryptophan in peptides with defined secondary structure [15]. For several decades, fluorescence spectroscopy has been widely used for the detection and analysis of different analytes [16,17]. Wavelength-ratiometric [18,19], fluorescence lifetime-based sensing [20,21] and polarization assays [22] are some techniques available for the detection and analysis of analytes by fluorescence spectroscopy. Fluorescence techniques for pH sensor have been used most of the time with enzymes and proteins [23]. Despite some promising results, enzymes and proteins show some stability problems against organic solvents and heat. In contrast, synthetic organic probes show high stability and flexibility due to the versatility of the organic synthesis. Modification of the affinity for the analyte, of the wavelength of emission of the probes and of the immobilization of the probes is in support for the building of a sensor.
ARTICLE IN PRESS Z. Si et al. / Journal of Luminescence 124 (2007) 365–369
366
2.2. Preparation of materials (Scheme 1)
In this essay, we introduce two compounds we synthesized, present photo-physical properties of STAA-1 and STAA-2 in different solvents in order to study the solvent polarity effects on the photo-physical property, furthermore we present the photo-physical property of STAA-1 in water at different pH value. Up to now, the latest report is about the fluorescent molecular, which contains dithioacetals as we know.
2.2.1. 3-(10 , 30 )-Dithiolan-2-ylidene-pentane-2, 4-dione Ia Anhydrous K2CO3 (13.8 g) and 6.25 mL acetic acid ethyl ester were added to 100 mL DMF in 250 mL flask, the mixture was stirred 0.5 h and cooled to 0–5 1C, 3.5 mL CS2 was added, the stirring was continued for another 0.5 h, then 4.75 mL 1,2-Dibromo-ethane was added to the mixture. The mixture was poured into a 400 mL flask with 200 g ice after it was stirred overnight. The deposition was filtrated, the yield of Ia was 98%. (The data of characterization is in Refs. [25,26].)
2. Experiment 2.1. Materials
2.2.2. Sodium-2-(40 -dimethyl aminocinnamicacyl)-3,3-(10 ,30 propylenedithio) acrylate STAA-1 2.2 mmol 4-Dimethylamino-benzaldehyde and 2.0 mmol compound Ia were added into 10 mL EtOH in a 25 mL flask, then 2.0 mmol EtONa was dropped into the flask, then stirred at 70 1C, detected with TLC until the completion of the reaction. Then the yellow solid was filtrated and collected after the mixture was cooled to room temperature. The yield was 70%. The synthesis of Ib and STAA-2 is similar to that of Ia and STAA-1, respectively.
Ethanol (EtOH), N,N-dimethylformamide (DMF), carbon bisulphide (CS2), acetic acid ethyl ester, potassium carbonate (K2CO3), 1,2-dibromoethane, 1,3-dibromopropane were used as supplied, but only after checking the purity fluorometrically in the wavelength region of interest. The solvent, water, was distilled twice in vacuum and tested for the absence of any emission in the wavelength regions studied. Absorption and emission spectra were recorded on Shimadzu Model 3100 spectrometer and Hitachi Spectrophotometer model F-4500, respectively. Spectrum correction has been performed in order to measure a true spectrum by eliminating instrumental response such as wavelength characteristics of the monochromators or detectors. For all measurements, the sample concentration was restricted at 105 mol/L in order to avoid the aggregation problems such as self-quenching. The cut-off filter was used to prevent scattering of excitation beam. The relative fluorescent quantum yield of STAA-1 was measured with quinine sulphate as the standard compound in sulphuric acid according to the following equation [24]: ffx ¼ n2x F x ffstd =n2std F std .
2.3. Characterization of compounds STAA-1 and STAA-2 STAA-1: Yellow solid, yield: 85%, m.p. 210–211 1C HNMR: 7.370 (2 H, d, J ¼ 21 ArH), 7.234 (2H, d, H), 6.670(2H, d, J ¼ 3.8, H), 6.549 (1H, d, J ¼ 3.8, J ¼ 21, ArH), 3.36 (4H, tri, J ¼ 6, –SCH2–), 2.945 (6H, s, –NC2H6); IR n (cm1) 1579, 1524, 1348, 1182, 3425. STAA-2: Green-yellow solid, yield: 83%, m.p. 207–208.5 1C 1HNMR 7.407(2H, d, J ¼ 22 ArH), H), 6.797(1H, d, J ¼ 4, H), 7.301(1H, d, J ¼ 4, 6.718 (2H, d, J ¼ 22, ArH), 2.965 (6H, s, –NC2H6), 1
(1)
O
O
O ONa
+ CS2 Br + Br ( )n
O
K2CO3 DMF
S
OC2H 5 S
ONa
O O
S (
I O
OC2H 5 S
O 1
2
)n
O
N
S
N
S ( )n
I
II
S
O
R
n = 1,2
(a)
ONa
O
ONa
+
S (
II a
O
O
S
R
)n
(b)
S
II b
Scheme 1. (a) Synthesis of compounds STAA-1 and STAA-2 and (b) the configurations of compounds STAA-1 and STAA-2.
ARTICLE IN PRESS Z. Si et al. / Journal of Luminescence 124 (2007) 365–369
2.787(4H, m, J ¼ 17, –SCH2–), 2.019(2H, m, J ¼ 17,–CH2–); IR n (cm1) 1574, 1523, 1365, 3442, 1183. 3. Results and discussion 3.1. Absorption spectra These compounds show two strong main peaks between 256 and 446 nm (Fig. 1). The higher energy but weaker absorption band lies at 256 nm does not show obvious shift according to the change of solvents or the ring size of dithioacetals. It is assigned to be the absorption of the derivatives of benzene. The structureless broad absorption spectra whose peak lies in the range of 309–446 nm (Fig. 1) can be affected by both the size of the ring of dithioacetals and the property of the solvent. Comparing the position with benzene derivatives, we can assign the lower energy bands as 1La [26]. It shows red-shift according to the strength of the hydrogen bonding property of the solvent (Table 1). The two peaks show the largest span when those compounds are in water, and smallest in DMF unlike other benzene derivatives [7]. And the lower energy band of the compound STAA-2 shows somewhat red-shift compared with that of the compound STAA-1 in Water or EtOH, but
367
it only shows a little difference in the extent of the halfwave without any other difference. It is evidenced that the absorption property of these compounds is associated with the property of solvent and the ring size of the dithioacetals in the molecular. As for the property that these two compounds are strongly soluble in polar solvents and weakly soluble in non-polar solvents, we can assume them being polar in ground state. So from the aprotic solvent effect, the lower energy band can be attributed to intramolecular charge transfer electronic states. 3.2. Emission spectra at room temperature Both of the compounds exhibit only one anomalous emission band in different polar solvents. The structureless emission band of the two compounds shows a large redshift from non-polar to polar solvents at about 510–605 nm wavelength region (Figs. 2b and 3). The maximum emission point of compound STAA-2 is located at a lower energy region than that of compound STAA-1. So the fluorescence of these type of compounds is affected by not only the property of solvents but also the size of the ring of dithioacetals. As a result, the lowest energy emission is at
Fig. 1. The absorption spectra of compounds (a) STAA-1 and (b) STAA-2 in different solvents; rectangle—DMF, circle—EtOH, triangle—water.
Fig. 2. The fluorescent spectra of compounds (a) STAA-1 and (b) STAA-2 in different solvents; rectangle—DMF, circle—EtOH, triangle—water.
ARTICLE IN PRESS Z. Si et al. / Journal of Luminescence 124 (2007) 365–369
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605 nm for compound STAA-2 when in water, and the highest energy emission is at 510 nm for compound STAA1 when in DMF (Table 1). Because the emission of compound STAA-1 in EtOH is the strongest for these compounds, the fluorescent quantum efficiency of STAA-1 was measured to be 7.12% with quinine sulphate as the standard compound in ethanol at room temperature. It is interesting to note that the Stoke shift of these compounds 1.0
100% EtOH 20% DMF+80% EtOH 40% DMF+60% EtOH 60% DMF+40% EtOH 80% DMF+20% EtOH 100% DMF
Absorption (a.u.)
0.8
0.6
0.4
0.2
0.0 500
550
600
650
Wavelength (nm)
Fig. 3. The fluorescent spectrum of compound DTAA-1 in the mixed solvent of DMF and EtOH with different ratio; filled rectangle—EtOH, opened rectangle—20% DMF+80% EtOH, filled circle—40% DMF+60% EtOH, opened circle—60% DMF+40% EtOH, filled triangle—80% DMF+20% EtOH, opened triangle—DMF.
ranges form 42 to 102 nm in different solvents. And the Stoke shift of these compounds changes in the following order: EtOH4Water4DMF for both of the compounds, and STAA-14STAA-2 in the same solvent. Although we cannot offer a more thorough explanation for this phenomenon, we can assign that this might be the result of the special molecular structure. 3.3. Emission spectra of STAA-1 in water at room temperature In order to study the relationship between the fluorescence of the compounds STAAs and the pH value of water, we have detected the emission spectrum of STAA-1 (it’s fluorescence is stronger than the other one’s) in water with different pH value. We found that the emission spectrum of STAA-1 was affected by the pH value dramatically (Fig. 4). The emission intensity increases according to the increasing of pH value when the pH value is between 7.5 and 9.0. The maximum intensity appears when the pH value is 9.0. The intensity of fluorescence lowers slightly with further increase of the value of pH. We attribute the decrease to the effect of increased concentration of salt (Fig. 4b). If the value of pH is lower than 7.5, the fluorescence of STAA-1 disappears (Fig. 4a). So it is possible that the compounds STAAs could be used as the sensors of proton in the future. Though we do not know the exact principle of the quenching of the fluorescence of
Table 1 Absorption and fluorescence data of Sodium-2-(40 -dimethylaminocinnamicacyl)-3,3-(10 ,30 -alkylenedithio) acrylate (STAA-1, STAA-2) at room temperature Compounds
Absorption (lmax) DMF
STAA-1 STAA-2
407 396
EtOH
428 429
Fluorescence H2O
433 446
DMF
EtOH
H2O
lmax (em)
lmax (ex)
lmax (em)
lmax (ex)
lmax (em)
lmax (ex)
510 514
441 463
550 559
448 460
591 605
497 520
Fig. 4. (a) The fluorescent spectrum of compound DTAA-1 in water with different pH (c ¼ 104 mol/L) and (b) plot of maximum intensity fluorescence of compound DTAA-1 in water vs. pH.
ARTICLE IN PRESS Z. Si et al. / Journal of Luminescence 124 (2007) 365–369
this type of compounds, we attributed this phenomenon to the proton trapping of the dimethylaniline group in the molecules. When the pH is lower than 7.5, the donor groups (N(CH3)2) in the molecules trap the protons in the solvent and become another group, ammonium (+NH(CH3)2), then the donors in the molecules disappear. When the electron cannot be transported to the acceptor group in the molecular, the fluorescence of STAA-1 could not be detected any more. 4. Conclusion In summary, we synthesized two compounds by a twostep reaction in high yields (480%). The unique molecular structure awards these compounds special photo-physical property. The emission peak of these compounds shifts according to the hydrogen bonding property of the solvent. The Stoke shift changes as EtOH4Water4DMF for both of the compounds. But there is no obvious relationship between absorption spectrum and the property of the solvent. The fluorescent quantum efficiency of STAA-1 was measured to be 7.12% at room temperature. Furthermore, by studying the relationship between the fluorescent property of STAA-1 and the pH value of water, we found the compound STAA-1 could be the proton sensor in further studies. References [1] B.A. Reinhardt, et al., Chem. Mater. 10 (1998) 1863. [2] T. Horiuchi, H. Miura, K. Sumioka, S. Uchida, J. Am. Chem. Soc. 126 (2004) 12218.
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[3] C. Chen, Chem. Mater. 16 (2004) 4389. [4] Y. Huang, T. Cheng, F. Li, C. Huangect, J. Phys. Chem. B 106 (2002) 10041. [5] J.M. Beechem, L. Brand, Annu. Rev. Biochem. 54 (1981) 43. [6] J.B.A. Ross, W.R. Laws, K.W. Roussland, H.R. Wyssbrob, Topics of fluorescence spectroscopy, in: J.R. Lakowicz (Ed.), Biochemical Applications, vol. 3, Plenum Press, New York, 1992. [7] P.R. Bangal, S. Chakravorti, J. Photochem. Photobiol. A: Chem. 116 (1998) 191. [8] D.F. Hoelzl Wallach, T.L. Steck, Anal. Chem. 35 (1963) 1035. [9] B.S. Hudson, J.M. Hutson, J. Phys. Chem. 103 (1999) 2227. [10] M.C. Chang, J.W. Petrich, D.B. McDonald, G.R. Fleming, J. Am. Chem. Soc. 105 (1983) 3819. [11] R.J. Robbins, G.R. Fleming, G.S. Beddard, G.W. Robinson, P.J. Thistlethwait, G.J. Wolfe, J. Am. Chem. Soc. 102 (1980) 6271. [12] L. Tilstra, M.C. Sattler, W. Cherry, M.D. Barkley, J. Am. Chem. Soc. 112 (1990) 9176. [13] M.R. Eftink, Y. Jia, D. Hu, J. Phys. Chem. 99 (1995) 5713. [14] T.E.S. Dahms, J.K. Willis, A.G. Szabo, J. Am. Chem. Soc. 117 (1995) 3221. [15] A.H.A. Clayton, W.H. Sawyer, Biophys. J. 76 (1999) 3235. [16] D. Cui, X. Qian, F. Liu, R. Zhang, Org. Lett. 6 (2004) 2757. [17] T. Morii, K.I. Sugimoto, K. Makino, Ma. Otsuka, K. Imoto, Y. Mori, J. Am. Chem. Soc. 124 (2002) 1138. [18] K. Aslan, J.R. Lakowicz, C.D. Geddes, Anal. Chem. 77 (2005) 2007. [19] D. Roll, J. Malicka, I. Gryczynski, Z. Gryczynski, J.R. Lakowicz, Anal. Chem. 75 (2003) 3440. [20] E. Kuwana, E.M. Sevick-Muraca, Anal. Chem. 75 (2003) 4325. [21] C.M. Maragos, M.E. Jolley, R.D. Plattner, M.S. Nasir, J. Agric. Food Chem. 49 (2001) 596. [22] C.M. Maragos, R.D. Plattner, J. Agric. Food Chem. 50 (2002) 1827. [23] H. Frenkel-Mullerad, D. Avnir, J. Am. Chem. Soc. 127 (2005) 8077. [24] Y. Cui, et al., Chinese Journal of Analytical Chemistry 4 (1986) 616. [25] E.B. Choi, I.K. Youn, C.S. Pak, Synthesis 1984 (1984) 797. [26] Q. Liu, Z. Zhu, et al., J. Liaoning Normal Univ. 18 (1995) 304 (in Chinese).
Journal of Luminescence 124 (2007) 365–369 www.elsevier.com/locate/jlumin
Synthesis and fluorescence study of sodium-2-(40 -dimethylaminocinnamicacyl)-3,3-(10,30-alkylenedithio) acrylate Zhenjun Si, Yun Shao, Chunxia Li, Qun Liu School of Chemistry, Northeast Normal University, Changchun 130024, PR China Received 9 January 2006; received in revised form 5 April 2006; accepted 14 April 2006 Available online 5 June 2006
Abstract We synthesized two new compounds: Sodium 2-(40 -dimethyl-aminocinnamicacyl)-3,3-(10 ,30 - ethyl- enedithio) acrylate (STAA-1) and Sodium 2-(40 -dimethyl-aminocinnamicacyl)-3, 3-(10 ,30 -propylenedithio) acrylate (STAA-2). The maximum absorption of these compounds ranges from 460 to 520 nm with different molecular structures in different solvents. Meanwhile, the emission peak of these compounds arranges from yellow (510 nm) to red (605 nm). The emission spectra show red shift according to the strength of the hydrogen bonding property of the solvent. But the absorption spectra do not show clearly relationship with the strength of the hydrogen bonding property of the solvent. The Stoke shift of the compounds ranges from 42 to 102 nm. It changes in the following order, EtOH4H2O4DMF, and STAA-14STAA-2 in the same solvent. The fluorescent quantum yield of STAA-1 was measured to be 7.12% with quinine sulphate as the standard compound in ethanol. Furthermore, the relationship of the fluorescence of STAA-1 with pH (ranges form 4 to 14) in water (c ¼ 104) was studied to make sure that these compounds could be used as proton sensors. r 2006 Elsevier B.V. All rights reserved. PACS: 07.07.Df; 78.55.m; 81.20.n Keywords: Proton sensor; Fluorescence quantum yield; Synthesis
1. Introduction p-Conjugated organic compounds have emerged in the past two decades as a promising class of materials for potential applications in photonics and optoelectronics. Lots of active materials used in these fields are the derivatives of aniline. These materials are used in nonlinear optics [1], photovoltaic cell [2], light emitting devices [3], and optically pumped lasers [4]. The photo-physical properties of the aromatic amino acids depend on the status of the amino and carboxyl groups although they are separated form chromophore by some methylene groups [5,6] or other groups [7,8], the quenching efficiency is controlled by the orientation of the quenching groups and the process is distance dependent. The rotamer model of fluorescence decays of aromatic amino acids has been
Corresponding author. Tel.: +86 0431 5099667.
E-mail address: [email protected] (Y. Shao). 0022-2313/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2006.04.005
supported by some investigations [9–11] that included studies of constrained tryptophan [12,13], tryptophan in protein crystals [14] and tryptophan in peptides with defined secondary structure [15]. For several decades, fluorescence spectroscopy has been widely used for the detection and analysis of different analytes [16,17]. Wavelength-ratiometric [18,19], fluorescence lifetime-based sensing [20,21] and polarization assays [22] are some techniques available for the detection and analysis of analytes by fluorescence spectroscopy. Fluorescence techniques for pH sensor have been used most of the time with enzymes and proteins [23]. Despite some promising results, enzymes and proteins show some stability problems against organic solvents and heat. In contrast, synthetic organic probes show high stability and flexibility due to the versatility of the organic synthesis. Modification of the affinity for the analyte, of the wavelength of emission of the probes and of the immobilization of the probes is in support for the building of a sensor.
ARTICLE IN PRESS Z. Si et al. / Journal of Luminescence 124 (2007) 365–369
366
2.2. Preparation of materials (Scheme 1)
In this essay, we introduce two compounds we synthesized, present photo-physical properties of STAA-1 and STAA-2 in different solvents in order to study the solvent polarity effects on the photo-physical property, furthermore we present the photo-physical property of STAA-1 in water at different pH value. Up to now, the latest report is about the fluorescent molecular, which contains dithioacetals as we know.
2.2.1. 3-(10 , 30 )-Dithiolan-2-ylidene-pentane-2, 4-dione Ia Anhydrous K2CO3 (13.8 g) and 6.25 mL acetic acid ethyl ester were added to 100 mL DMF in 250 mL flask, the mixture was stirred 0.5 h and cooled to 0–5 1C, 3.5 mL CS2 was added, the stirring was continued for another 0.5 h, then 4.75 mL 1,2-Dibromo-ethane was added to the mixture. The mixture was poured into a 400 mL flask with 200 g ice after it was stirred overnight. The deposition was filtrated, the yield of Ia was 98%. (The data of characterization is in Refs. [25,26].)
2. Experiment 2.1. Materials
2.2.2. Sodium-2-(40 -dimethyl aminocinnamicacyl)-3,3-(10 ,30 propylenedithio) acrylate STAA-1 2.2 mmol 4-Dimethylamino-benzaldehyde and 2.0 mmol compound Ia were added into 10 mL EtOH in a 25 mL flask, then 2.0 mmol EtONa was dropped into the flask, then stirred at 70 1C, detected with TLC until the completion of the reaction. Then the yellow solid was filtrated and collected after the mixture was cooled to room temperature. The yield was 70%. The synthesis of Ib and STAA-2 is similar to that of Ia and STAA-1, respectively.
Ethanol (EtOH), N,N-dimethylformamide (DMF), carbon bisulphide (CS2), acetic acid ethyl ester, potassium carbonate (K2CO3), 1,2-dibromoethane, 1,3-dibromopropane were used as supplied, but only after checking the purity fluorometrically in the wavelength region of interest. The solvent, water, was distilled twice in vacuum and tested for the absence of any emission in the wavelength regions studied. Absorption and emission spectra were recorded on Shimadzu Model 3100 spectrometer and Hitachi Spectrophotometer model F-4500, respectively. Spectrum correction has been performed in order to measure a true spectrum by eliminating instrumental response such as wavelength characteristics of the monochromators or detectors. For all measurements, the sample concentration was restricted at 105 mol/L in order to avoid the aggregation problems such as self-quenching. The cut-off filter was used to prevent scattering of excitation beam. The relative fluorescent quantum yield of STAA-1 was measured with quinine sulphate as the standard compound in sulphuric acid according to the following equation [24]: ffx ¼ n2x F x ffstd =n2std F std .
2.3. Characterization of compounds STAA-1 and STAA-2 STAA-1: Yellow solid, yield: 85%, m.p. 210–211 1C HNMR: 7.370 (2 H, d, J ¼ 21 ArH), 7.234 (2H, d, H), 6.670(2H, d, J ¼ 3.8, H), 6.549 (1H, d, J ¼ 3.8, J ¼ 21, ArH), 3.36 (4H, tri, J ¼ 6, –SCH2–), 2.945 (6H, s, –NC2H6); IR n (cm1) 1579, 1524, 1348, 1182, 3425. STAA-2: Green-yellow solid, yield: 83%, m.p. 207–208.5 1C 1HNMR 7.407(2H, d, J ¼ 22 ArH), H), 6.797(1H, d, J ¼ 4, H), 7.301(1H, d, J ¼ 4, 6.718 (2H, d, J ¼ 22, ArH), 2.965 (6H, s, –NC2H6), 1
(1)
O
O
O ONa
+ CS2 Br + Br ( )n
O
K2CO3 DMF
S
OC2H 5 S
ONa
O O
S (
I O
OC2H 5 S
O 1
2
)n
O
N
S
N
S ( )n
I
II
S
O
R
n = 1,2
(a)
ONa
O
ONa
+
S (
II a
O
O
S
R
)n
(b)
S
II b
Scheme 1. (a) Synthesis of compounds STAA-1 and STAA-2 and (b) the configurations of compounds STAA-1 and STAA-2.
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2.787(4H, m, J ¼ 17, –SCH2–), 2.019(2H, m, J ¼ 17,–CH2–); IR n (cm1) 1574, 1523, 1365, 3442, 1183. 3. Results and discussion 3.1. Absorption spectra These compounds show two strong main peaks between 256 and 446 nm (Fig. 1). The higher energy but weaker absorption band lies at 256 nm does not show obvious shift according to the change of solvents or the ring size of dithioacetals. It is assigned to be the absorption of the derivatives of benzene. The structureless broad absorption spectra whose peak lies in the range of 309–446 nm (Fig. 1) can be affected by both the size of the ring of dithioacetals and the property of the solvent. Comparing the position with benzene derivatives, we can assign the lower energy bands as 1La [26]. It shows red-shift according to the strength of the hydrogen bonding property of the solvent (Table 1). The two peaks show the largest span when those compounds are in water, and smallest in DMF unlike other benzene derivatives [7]. And the lower energy band of the compound STAA-2 shows somewhat red-shift compared with that of the compound STAA-1 in Water or EtOH, but
367
it only shows a little difference in the extent of the halfwave without any other difference. It is evidenced that the absorption property of these compounds is associated with the property of solvent and the ring size of the dithioacetals in the molecular. As for the property that these two compounds are strongly soluble in polar solvents and weakly soluble in non-polar solvents, we can assume them being polar in ground state. So from the aprotic solvent effect, the lower energy band can be attributed to intramolecular charge transfer electronic states. 3.2. Emission spectra at room temperature Both of the compounds exhibit only one anomalous emission band in different polar solvents. The structureless emission band of the two compounds shows a large redshift from non-polar to polar solvents at about 510–605 nm wavelength region (Figs. 2b and 3). The maximum emission point of compound STAA-2 is located at a lower energy region than that of compound STAA-1. So the fluorescence of these type of compounds is affected by not only the property of solvents but also the size of the ring of dithioacetals. As a result, the lowest energy emission is at
Fig. 1. The absorption spectra of compounds (a) STAA-1 and (b) STAA-2 in different solvents; rectangle—DMF, circle—EtOH, triangle—water.
Fig. 2. The fluorescent spectra of compounds (a) STAA-1 and (b) STAA-2 in different solvents; rectangle—DMF, circle—EtOH, triangle—water.
ARTICLE IN PRESS Z. Si et al. / Journal of Luminescence 124 (2007) 365–369
368
605 nm for compound STAA-2 when in water, and the highest energy emission is at 510 nm for compound STAA1 when in DMF (Table 1). Because the emission of compound STAA-1 in EtOH is the strongest for these compounds, the fluorescent quantum efficiency of STAA-1 was measured to be 7.12% with quinine sulphate as the standard compound in ethanol at room temperature. It is interesting to note that the Stoke shift of these compounds 1.0
100% EtOH 20% DMF+80% EtOH 40% DMF+60% EtOH 60% DMF+40% EtOH 80% DMF+20% EtOH 100% DMF
Absorption (a.u.)
0.8
0.6
0.4
0.2
0.0 500
550
600
650
Wavelength (nm)
Fig. 3. The fluorescent spectrum of compound DTAA-1 in the mixed solvent of DMF and EtOH with different ratio; filled rectangle—EtOH, opened rectangle—20% DMF+80% EtOH, filled circle—40% DMF+60% EtOH, opened circle—60% DMF+40% EtOH, filled triangle—80% DMF+20% EtOH, opened triangle—DMF.
ranges form 42 to 102 nm in different solvents. And the Stoke shift of these compounds changes in the following order: EtOH4Water4DMF for both of the compounds, and STAA-14STAA-2 in the same solvent. Although we cannot offer a more thorough explanation for this phenomenon, we can assign that this might be the result of the special molecular structure. 3.3. Emission spectra of STAA-1 in water at room temperature In order to study the relationship between the fluorescence of the compounds STAAs and the pH value of water, we have detected the emission spectrum of STAA-1 (it’s fluorescence is stronger than the other one’s) in water with different pH value. We found that the emission spectrum of STAA-1 was affected by the pH value dramatically (Fig. 4). The emission intensity increases according to the increasing of pH value when the pH value is between 7.5 and 9.0. The maximum intensity appears when the pH value is 9.0. The intensity of fluorescence lowers slightly with further increase of the value of pH. We attribute the decrease to the effect of increased concentration of salt (Fig. 4b). If the value of pH is lower than 7.5, the fluorescence of STAA-1 disappears (Fig. 4a). So it is possible that the compounds STAAs could be used as the sensors of proton in the future. Though we do not know the exact principle of the quenching of the fluorescence of
Table 1 Absorption and fluorescence data of Sodium-2-(40 -dimethylaminocinnamicacyl)-3,3-(10 ,30 -alkylenedithio) acrylate (STAA-1, STAA-2) at room temperature Compounds
Absorption (lmax) DMF
STAA-1 STAA-2
407 396
EtOH
428 429
Fluorescence H2O
433 446
DMF
EtOH
H2O
lmax (em)
lmax (ex)
lmax (em)
lmax (ex)
lmax (em)
lmax (ex)
510 514
441 463
550 559
448 460
591 605
497 520
Fig. 4. (a) The fluorescent spectrum of compound DTAA-1 in water with different pH (c ¼ 104 mol/L) and (b) plot of maximum intensity fluorescence of compound DTAA-1 in water vs. pH.
ARTICLE IN PRESS Z. Si et al. / Journal of Luminescence 124 (2007) 365–369
this type of compounds, we attributed this phenomenon to the proton trapping of the dimethylaniline group in the molecules. When the pH is lower than 7.5, the donor groups (N(CH3)2) in the molecules trap the protons in the solvent and become another group, ammonium (+NH(CH3)2), then the donors in the molecules disappear. When the electron cannot be transported to the acceptor group in the molecular, the fluorescence of STAA-1 could not be detected any more. 4. Conclusion In summary, we synthesized two compounds by a twostep reaction in high yields (480%). The unique molecular structure awards these compounds special photo-physical property. The emission peak of these compounds shifts according to the hydrogen bonding property of the solvent. The Stoke shift changes as EtOH4Water4DMF for both of the compounds. But there is no obvious relationship between absorption spectrum and the property of the solvent. The fluorescent quantum efficiency of STAA-1 was measured to be 7.12% at room temperature. Furthermore, by studying the relationship between the fluorescent property of STAA-1 and the pH value of water, we found the compound STAA-1 could be the proton sensor in further studies. References [1] B.A. Reinhardt, et al., Chem. Mater. 10 (1998) 1863. [2] T. Horiuchi, H. Miura, K. Sumioka, S. Uchida, J. Am. Chem. Soc. 126 (2004) 12218.
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