Fluorescent organic molecules are an important class of compounds in modern science and technology, and are widely used in biological imaging probes, sensors, lasers, and light-emitting devices.1–3) Thus, the development of useful fluorescent organic molecules is crucial for the advancement of many industries, and has been a subject of intensive research.4–15) In particular, fluorescent organic molecules have received a great deal of attention in a pharmacology field, because the visualization of biologically active small compounds by introducing fluorophores is one of the most useful methods in mechanistic studies.16–22) However, the introductions of fluorescent organic molecules sometimes induces a loss of biological activities because the physical properties of fluorescent molecules affect the biological activities of the original compound. Furthermore, highly fluorescent organic molecules are usually larger than small biologically active compounds, and the fluorescent labeling reagent disturbs the original interactions of the parent compounds with target proteins such as receptors. To overcome these problems, there is strong demand for the development of small fluorophores. We recently discovered that 1,3a,6a-triazapentalene 1 is a compact and highly fluorescent chromophore23) (Fig. 1). Since the disclosure of the fluorescence properties of 1,3a,6a-triazapentalenes, the 1,3a,6a-triazapentalene system has attracted a great deal of interest as a novel fluorophores, and another group has also reported the alternative synthesis of 1,3a,6a-triazapentalenes.24) 1,3a,6a-Triazapentalenes exhibit various useful fluorescence properties such as intense fluorescence, a large Stokes shift, and a positive fluorescence solvatochromism. More interestingly, the fluorescence wavelengths of 1,3a,6a-triazapentalenes vary widely with 2-substituents. For example, the fluorescence maxima shifts to longer wavelengths as the inductive effect of the 2-substituents increases. On the basis of this effect, the fluorescence wavelength of 1,3a,6a-triazapentalenes has recently been extended to the red color region, and their molecules are smaller than the conventional yellow and red fluorescent molecules.25) The yellow derivatives were proven to be useful fluorescent labeling reagents. On the other hand, the introduction of an electron-donating substituent at the C5-position substantially increased the fluorescence intensity, whereas the fluorescence wavelength remained nearly unaffected.26) For example, the comparison of fluorescence quantum yield (ΦF) between the 5-methoxy derivative and an unsubstituted analog of 2-(4-cyanophenyl)-1,3a,6a-triazapentalene shows that the introduction of a methoxy group at the C5-position drastically increases the ΦF from 0.15 to 0.57 with no significant effect on the fluorescence wavelength. Recently, the development of wavelength-tunable and/or quantum yields-tunable fluorophores has been a subject of great concern for intelligent fluorescent probes.27–33) The 1,3a,6a-triazapentalene system also provides a novel fluorescent molecule that enables the same fluorescent chromophore to exhibit various fluorescence colors and quantum yields. That is, the fluorescence wavelength and quantum yield can be controlled by the 2- and 5-substituents, respectively.
Although we found that the 2- and 5-substitutents respectively change the fluorescence properties of 1,3a,6a-triazapentalenes in different ways, the effects of other positions, such as the 3-, 4-, and 6-positions, have not been elucidated. In particular, although a few 2,4-disubstituted-triazapentalenes have already been prepared in previous studies (vide infra),23,25) the effect of a 4-substituent on fluorescence properties has not been investigated in detail. Therefore, we herein report the changes in fluorescence properties of 1,3a,6a-triazapentalenes by the introduction of a 4-substituent (Fig. 2).
We first attempted to introduce a methyl group as the simplest substituent into 2-(4-cyanophenyl)-1,3a,6a-triazapentalene 1a, which is one of the stablest and highly fluorescent analog among synthetic triazapentalenes. According to our previous synthesis of 1,3a,6a-triazapentalenes,23) the azide 2a having two triflates was treated with alkyne 3a in the presence of 5 mol% of CuI and 5 equiv of triethylamine (TEA) to induce the following cascade reaction. The click reaction of 2a with 3a proceeded to afford triazole A, which underwent an intramolecular SN2 reaction to give triazolium ion B. Subsequent reactions of E2 elimination (B→C) and deprotonation (C→D) produced the desired 4-methyl-2-(4-cyanophenyl)-1,3a,6a-triazapentalene 4a in 86% yield (Chart 1).
Chart 1. Synthesis of 4-Methyl-2-(4-cyanophenyl)-1,3a,6a-triazapentalene 4a
After preparing a 4-methyl analog of 2-(4-cyanophenyl)-1,3a,6a-triazapentalenes, we compared its fluorescence properties with 5-methyl analog 5a and unsubstituted analog 1a in dichloromethane.34) As is the case with 5-methoxy analog depicted in Fig. 1, the ΦF of 5-methyl analog 5a (ΦF=0.46) was much higher than that of the unsubstituted analog 1a (ΦF=0.15), whereas the fluorescence wavelength showed only a slight shift. In clear contrast, the fluorescence maximum of 4-methyl analog 4a shifted to a longer-wavelength region (543 nm), and the ΦF value (0.17) was slightly increased. This suggested that the introduction of the methyl group at the C4-position induced an approximately 35 nm longer shift of the fluorescence maximum with only a small increase in fluorescence quantum yield (Fig. 3).
To investigate the generality of the effect of the methyl group at the C4-position, various 4-methyl analogs of 1,3a,6a-triazapentalenes were next synthesized (Table 1). The similar click reaction of 2a with methyl propiolate 3b afforded 4b as an aliphatic derivative in 94% yield (entry 1). Although the reaction of ethynylbenzene analogs possessing electron-withdrawing groups (3c–e) and another phenyl ring (3f) also proceeded to give 4c–f in 50, 82, 19, and 28% yields, respectively (entries 2–5). The decline in yields of these analogs was due to the partial decomposition of 4-methyl analogs during silica gel column chromatography. The stability of 4-methyl analogs seems to be poorer than that of 4-unsubstituted analogs. Next, various alkynes that had never been applied to the synthesis of 1,3a,6a-triazapentalenes were attempted. Thus, 4-unsubstituted-1,3a,6a-triazapentalenes were also synthesized along with 4-methyl analogs. The naphthyl derivative 4g, expecting a longer-wavelength emission, was also obtained in acceptable yield (entry 6), and the corresponding 4-unsubstituted analog 1g was also obtained in acceptable yield (entry 6). In the case of 3h possessing two alkynes, the click reaction stopped at the formation of the first 1,3a,6a-triazapentalene, and the mono-triazapentalene intermediate readily decomposed during silica gel column chromatography. In contrast, a similar double click reaction leading to the corresponding 4-unsubstituted analog proceeded to give bis-1,3a,6a-triazapentalene 1h in 46% yield. Finally, the copper-free click reaction of strained alkyne 3i, reported by Igawa, Tomooka and colleagues,35) was applied to the 1,3a,6a-triazapentalene synthesis. Treatment of 2a with 3i in the presence of TEA without copper salt in tetrahydrofuran (THF) afforded the desired 4-methyl-1,3a,6a-triazapentalene 4i in 49% yield, and a similar click reaction leading to 4-unsubstiuted analog also proceeded to give 1i in 51% yield. This is the first successful example of the triazapentalene-forming reaction with internal alkyne.
Having prepared various 4-methyl analogs of 1,3a,6a-triazapentalenes, we compared their fluorescence with those of the corresponding 4-unsubstituted analogs were investigated in dichloromethane (Table 2). The 2-methoxycarbonyl analog 4b similarly showed a longer-wavelength fluorescence maximum and a higher ΦF in comparison with the 4-unsubstituted analog 1b, whereas the 25 nm longer shift of the fluorescence maximum in 4b was shorter than the 34 nm of the 2-phenyl analog 4a. On the other hand, all other 2-phenyl analogs 4c–f exhibited around 35 nm longer wavelengths of fluorescence maximum than the corresponding 4-unsubstituted analogs 1c–f. Therefore, the introduction of a methyl group at the C4-position to 2-phenyl derivatives of 1,3a,6a-triazapentalene was found to generally induce an approximately 35 nm long-wavelength shift of the fluorescence maximum. In contrast, a noteworthy regularity was not observed in the effect of 4-methyl group on the ΦF of 4c–f, although the ΦF tended to decrease in the case of highly electron-deficient phenyl group at the C2-position. Meanwhile, 2-naphthyl derivative 1g, and not 2-phenyl derivatives, showed the similar fluorescence properties as biphenyl derivatives 1f, and the 4-methyl group of 4g induced a 25 nm longer shift of the fluorescence maximum than 1g as with 2-methoxy carbonyl derivative 4b. Thus, the approximately 35 nm long-wavelength shift induced by the 4-methyl group was found to be a particular shift of 2-phenyl derivatives. Interestingly, the nine-membered analogs 1i and 4i did not exhibit fluorescence, and we found that the cyclic analogs at the C2- and C3-positions were non-luminescent compounds. Therefore, the substituent effect of the methyl group at the C4-position was found to generally induce the long-wavelength shift of around 35 nm or 25 nm in the cases of 2-phenyl derivatives or other than 2-phenyl derivatives, respectively, whereas the common rule on the ΦF was not found.
Table 2. Comparison of Fluorescence Properties of Synthetic 4-Methyl-1,3a,6a-triazapentalenes
4 with Corresponding 4-Unsubstituted Derivatives
1 in Dichloromethane
 | R1 |
|---|
| CO2Me | C6H4–SO3Me | C6H4–CO2Me | C6H3(CN) CO2Me | C6H4–Ph | Nap | — |
|---|
| R=Me | 4b | 4c | 4d | 4e | 4f | 4g | 4i |
| λabsmax (nm) | 354 | 393 | 380 | 436 | 360 | 356 | 0 |
| λemmax (nm) | 456 | 558 | 553 | 611 | 491 | 485 | 0 |
| ΦF | 0.24 | 0.40 | 0.56 | 0.11 | 0.40 | 0.082 | 0 |
| R=H | 1b | 1c | 1d | 1e | 1f | 1g | 1i |
| λabsmax (nm) | 342 | 379 | 376 | 420 | 345 | 358 | 0 |
| λemmax (nm) | 431 | 525 | 521 | 572 | 456 | 460 | 0 |
| ΦF | 0.18 | 0.43 | 0.44 | 0.34 | 0.20 | 0.35 | 0 |
Next, we attempted to investigate the effect of the π-extended system at the C4-position. Although two 4-phenyl-1,3a,6a-triazapentalene derivatives were previously reported,25) further 4-phenyl analogs were synthesized and investigated to ensure the generality and trend of the substituent effect of the 4-phenyl group on fluorescence properties (Table 3). The click reaction of 2b with 3a afforded 4-phenyl-2-(4-cyanophenyl)-1,3a,6a-triazapentalene 4j in 70% yield (entry 1). Unfortunately, although the 4-phenyl analog was expected to induce a noteworthy wavelength shift due to the expansion of π–conjugation, the fluorescence maximum of 4j (542 nm) was similar to that of the 4-methyl analogs 4a (543 nm), suggesting that the properties of functional groups have no appreciable effect on the shift value of the fluorescence wavelength. On the other hand, the ΦF increased to 0.46 from the 0.15 of 4-unsubstituted analog 1a and the 0.17 of 4-methyl analog 4a. Furthermore, the extinction coefficient (ε) value of 4j substantially increased to 6918 dm3 mol−1 cm−1 (387 nm) from 3020 dm3 mol−1 cm−1 (381 nm) for 1a and 1000 dm3 mol−1 cm−1 (389 nm) for 4-methyl analog 4a (Fig. 4). The expansion of π–conjugation system is probably responsible for increase in the ε value. In addition, a new absorption band appeared at 345 nm that had never been observed in various 1,3a,6a-triazapentalenes without a phenyl group at the C4-position, and its ε value became as high as 27542 dm3 mol−1 cm−1 (Fig. 4). Since the improvement of ε values has been a remaining goal of 1,3a,6a-triazapentalenes as a practical fluorophore, the 4-phenyl group was expected to have a general effect on the increase in the ε values of 1,3a,6a-triazapentalenes. Thus, various 4-phenyl analogs were synthesized and their fluorescence properties were investigated. To compare the ε values with the corresponding 4-unsubstituted analog, the ε values of synthetic 4-phenyl analogs were measured at the longer-wavelength absorption that was previously assigned as an intramolecular charge transfer (ICT) mechanism.25)
Table 3. Click Reaction of
2b with Various Alkynes
3 and Fluorescence Properties of Various 4-Phenyl-1,3a,6a-triazapentalenes in Dichloromethane
 |
|---|
| Entry | Alkyne (3) | Yielda) | λemmax (nm) | ΦF | ε dm3 mol−1 cm−1 |
|---|
| 1 | 3a: R=C6H4CN | 4j: 70% | 542 | 0.46 | 6918 (387 nm) |
| | | (509)b) | (0.15)c) | 3020 (381 nm)d) |
| 2 | 3b: R=CO2Me | 4k: 87% | 459 | 0.086 | 10648 (358 nm) |
| | | (431)b) | (0.18)c) | 2691 (342 nm)d) |
| 3 | 3c: R=C6H4SO3Me | 4l: 50% | 554 | 0.21 | 5497 (378 nm) |
| | | (525)b) | (0.43)c) | 2542 (358 nm)d) |
| Ref. 6 | 3d: R=C6H4CO2Me | 4m: 82% | 548 | 0.36 | 7500 (383 nm) |
| | | (521)b) | (0.44)c) | 1230 (376 nm)d) |
| Ref. 6 | 3e: R=C6H3(CN)CO2Me | 4n: 88% | 613 | 0.07 | 4560 (432 nm) |
| | | (572)b) | (0.34)c) | 631 (420 nm)d) |
| 4 | 3f: R=C6H4Ph | 4o: 72% | 482 | 0.10 | 19409 (369 nm) |
| | | (456)b) | (0.20)c) | 5011 (345 nm)d) |
| 5 | 3g: R=Naphthyl | 4p: 81% | 481 | 0.084 | 19822 (342 nm) |
| | | (460)b) | (0.35)c) | 4213 (358 nm)d) |
a) Isolated yield. b) Fluorescence maximum of corresponding 4-unsubstituted analog. c) Fluorescence quantum yield of corresponding 4-unsubstituted analog. d) The extinction coefficient value of corresponding 4-unsubstittuted analog.
The similar click reaction of 2b with methyl propiolate 3b afforded the desired 4-phenyl-2-methoxycarbonyl-1,3a,6a-triazapentalene 4k in 87% yield (entry 2). The fluorescence maximum of 4k showed a long-wavelength shift as with 4j, and the ε value also substantially increased to 10648 dm3 mol−1 cm−1 (358 nm) from the 2691 dm3 mol−1 cm−1 (342 nm) of the 4-unsubstituted analog. The viewability of fluorophore in fluorescence observation is generally defined as the fluorescence brightness, and its intensity is proportional to those of both the ΦF and the ε value.36) Therefore, although the ΦF of 4k was slightly decreased, unlike the case with 4j, the fluorescence brightness of 4k was totally improved by the substantial increase in the ε value (entry 2). The reactions of ethynylbenzene derivatives 3c and f also afforded corresponding 4-phenyl analogs 4l and o in acceptable yields (entries 3, 4). In addition to previously reported 4m and n as a reference, the fluorescence properties of 2-phenyl derivatives 4l–o were similar to those of 4k such as the approximately 30 nm long-wavelength shift of the fluorescence maximum, the slight decrease in ΦF, and the substantial increase in the ε value, although the 41 nm shift of 4n was exceptionally longer than those of the other derivatives (entries 3–6). In the case of 2-naphthyl analog 4p, the long-wavelength shift of the fluorescence maximum was 21 nm, slightly shorter than the shift of the 2-phenyl analogs, and the ΦF and the ε value substantially decreased and increased, respectively. Throughout the various 4-phenyl analogs, the range of long-wavelength shifts induced by the phenyl group at the C4-position was similar to that of methyl group, and was insensitive to the properties of the substituent groups. In contrast, ε value was in general substantially higher in all 4-phenyl derivatives and proved to be a particular effect of the phenyl group, whereas the ΦF of most 4-phenyl analogs tended to decline slightly. Furthermore, the synthesized 4-phenyl-1,3a,6a-triazapentalenes exhibited strong positive fluorescence solvatochromism as is the case with 4-unsubstituted analogs, and the similar approximately 30 nm long-wavelength shifts were also observed in different solvent.37) The mechanistic details of long-wavelength shift induced by the 4-subustituents is currently investigated in our laboratory.
In conclusion, the substituent effect at the C4-position of 1,3a,6a-triazapentalenes was elucidated. Various 4-methyl- and 4-phenyl-1,3a,6a-triazapentalene derivatives were synthesized by the click-cyclization-aromatization cascade reaction of various alkynes with azidoditriflate possessing a methyl or phenyl group. The introduction of a methyl group at the C4-position induced a long-wavelength shift of the fluorescence maximum and an irregular change in the fluorescence quantum yield. Among the various 4-methyl-1,3a,6a-triazapentalenes, 2-phenyl derivatives showed an approximately 35 nm shift of the fluorescence maximum and other derivatives without a phenyl group at the C2-position exhibited a smaller (25 nm) shift. Additionally, the introduction of a phenyl group at the C4-position also showed a similar long-wavelength shift of the fluorescence maximum, and the range of shift was only slightly affected by the properties of the substituents. On the other hand, the ε value was substantially increased by the phenyl substituents at the C4-position, although the ΦF of the most 4-phenyl derivatives decreased. Therefore, the brightness of all 4-phenyl derivatives was totally enhanced due to the substantial increases in the ε values. Throughout the various 4-methyl and 4-phenyl derivatives of 1,3a,6a-triazapentalenes, we successfully elucidated the substituent effect on the fluorescence properties at the C4-position following the C2- and C5-positions. That is, in addition to the control of fluorescence wavelength and quantum yield by the 2- and 5-substituents, a further long-wavelength shift and enhancement of brightness can be induced by the 4-substituent. Since the 4-phenyl derivatives were relatively unstable compared with the corresponding 4-unsubstituted analogs, the improvement of their stability for the practical fluorophores is currently underway in our laboratory.
Experimental
Preparation of Ligand-Copper SolutionTo a solution of bis[2-(N,N-dimethylaminoethyl)]ether (19.0 µL, 0.10 mmol) in THF (10 mL) was added copper(I) iodide (19 mg, 0.10 mmol) at room temperature. The mixture was stirred until homogeneous. The clear solution of ligand–copper complex should be used before it became cloudy.
Synthesis of 4b as a Typical Procedure of the Click Reaction (Method A)To a solution of azidoditriflate 2a (36.5 mg, 0.092 mmol) in THF (9.0 mL) were added the ligand-copper solution (0.46 mL, 0.01 M solution in THF), Et3N (65 µL, 0.46 mmol), and alkyne 3b (12 µL, 0.14 mmol) at room temperature, successively. The mixture was stirred at room temperature for 2.5 h and concentrated under reduced pressure. The residue was purified by flash silica gel column chromatography (hexane/EtOAc=70/30 to 50/50, 1% Et3N contained) to give 4b (15.9 mg, 0.086 mmol, 94%) as green amorphous.
Synthesis of 4i as a Typical Procedure of the Click Reaction (Method B)To a solution of azidoditriflate 2a (27.0 mg, 0.069 mmol) in THF (4.6 mL) were added the ligand–copper solution (0.23 mL, 0.01 M solution in THF), Et3N (32 µL, 0.23 mmol), and alkyne 3i (20.0 mg, 0.046 mmol) at room temperature, successively. The mixture was stirred at room temperature for 16 h and concentrated under reduced pressure. The residue was purified by flash silica gel column chromatography (hexane/EtOAc=90/10 to 70/30, 1% Et3N contained) to give 4i (11.7 mg, 0.023 mmol, 49%) as clear amorphous.
2-(4-(Methoxysulfonyl)phenyl)pyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (1c) (Method B)1H-NMR (400 MHz, CDCl3) δ: 7.91 (1H, d, J=8.8 Hz), 7.78 (1H, d, J=8.5 Hz), 7.06 (1H, dd, J=1.5 Hz, 0.8 Hz), 6.53 (1H, d, J=1.2 Hz), 6.42 (1H, dd, J=3.0 Hz, 0.5 Hz), 6.13 (1H, t, J=2.8 Hz), 3.22 (3H, s). 13C-NMR (125 MHz, C6D6) δ: 146.0, 137.7, 135.5, 129.0, 126.6, 109.5, 102.3, 101.0, 94.5, 55.8. IR (KBr) cm−1: 3154, 2954, 1600, 1353, 1175. High resolution (HR)-MS electrospray ionization (ESI) m/z [M+H]+ Calcd for [C12H12N3O3S]+ 278.0599. Found 278.0606. UV/Vis (CH2Cl2): λmax (log ε)=379 (3.41), 283 (4.45) nm. FL (CH2Cl2): λmax=525 nm; ΦF=0.43 (reference to 9,10-diphenylanthracene (9,10-DPA); excited at 370 nm).
2-(Naphthalen-2-yl)pyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide) (1g) (Method B)1H-NMR (500 MHz, CDCl3) δ: 8.30 (1H, s), 7.87 (4H, dq, J=7.8 Hz, 1.5 Hz), 7.52–7.47 (4H, m), 7.15 (1H, d, J=3.0 Hz), 6.64 (1H, t, J=2.8 Hz). 13C-NMR (125 MHz, CDCl3) δ: 147.7, 133.5, 133.4, 128.8, 128.4, 127.8, 126.4, 126.2, 124.6, 123.9, 108.9, 102.4, 100.9, 93.7. IR (KBr) cm−1: 3141, 3047, 2921, 1380, 1141, 862, 747, 661. HR-MS (ESI) m/z [M+Na]+ Calcd for [C15H11N3Na]+ 256.0851. Found 256.0849. UV/Vis (CH2Cl2): λmax (log ε)=358 (3.62), 329 (3.56), 290 (4.47) nm. FL (CH2Cl2): λmax=460 nm; ΦF=0.35 (reference to 9,10-DPA; excited at 370 nm).
2,2′-(1,4-Phenylene)bis(pyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide) (1h) (Method A)1H-NMR (400 MHz, C6D6) δ: 8.02 (4H, s), 7.04 (2H, d, J=2.8 Hz), 6.66 (2H, d, J=1.2 Hz), 6.35 (2H, d, J=2.8 Hz), 6.06 (2H, t, J=2.8 Hz). 13C-NMR (125 MHz, C6D6) δ: 147.7, 132.3, 128.4, 126.5, 108.6, 101.6, 100.0, 93.4. IR (KBr) cm−1: 3153, 2926, 2107, 946, 848. HR-MS (ESI) m/z [M+Na]+ Calcd for [C16H12N6Na]+ 311.1021. Found 311.1031. UV/Vis (CH2Cl2): λmax (log ε)=356 (3.87), 292 (4.58) nm. FL (CH2Cl2): λmax=455 nm; ΦF=0.22 (reference to 9,10-DPA; excited at 370 nm).
2,6-Ditosyl-2,3,4,5,6,7-hexahydro-1H-pyrazolo[1′,2′:1,2][1,2,3]triazolo[4,5-g][1,5]diazonin-9-ium-8-ide (1i) (Method B)1H-NMR (500 MHz, CDCl3) δ: 7.73 (2H, d, J=8.0 Hz), 7.68 (2H, d, J=8.0 Hz), 7.54 (1H, d, J=3.0 Hz), 7.36–7.34 (5H, m), 6.62 (1H, t, J=3.0 Hz), 4.81 (2H, s), 4.34 (2H, s), 3.53–3.51 (2H, m), 3.03 (2H, t, J=6.0 Hz), 2.45 (6H, d, J=3.5 Hz), 1.92–1.88 (2H, m). 13C-NMR (125 MHz, CDCl3) δ: 143.7, 141.7, 130.0, 127.6, 127.0, 108.5, 103.9, 103.2, 102.6, 48.3, 48.06, 48.02, 43.4, 29.5, 21.5. IR (KBr) cm−1: 3155, 2925, 2857, 1449, 1335, 1160, 548. HR-MS (ESI) m/z [M+Na]+ Calcd for [C24H27N5O4S2Na]+ 536.1402. Found 536.1385.
2-(Methoxycarbonyl)-5-methylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4b) (Method A)1H-NMR (400 MHz, CDCl3) δ: 7.46 (1H, d, J=1.0 Hz), 7.41 (1H, dd, J=2.8 Hz, 1.0 Hz), 6.48 (1H, dd, J=2.6 Hz, 0.6 Hz), 3.95 (3H, s), 2.43 (3H, s). 13C-NMR (100 MHz, C6D6) δ: 162.4, 140.1, 109.8, 109.0, 102.0, 97.6, 51.5, 10.3. IR (KBr) cm−1: 3133, 2949, 1717, 1557, 1516, 1266, 1003. HR-MS (ESI) m/z [M+Na]+ Calcd for [C8H9N3O2Na]+ 202.0592. Found 202.0586. UV/Vis (CH2Cl2): λmax (log ε)=354 (3.44) nm. FL (CH2Cl2): λmax=456 nm; ΦF=0.24 (reference to 9,10-DPA; excited at 370 nm).
2-(4-(Methoxysulfonyl)phenyl)-5-methylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4c) (Method B)1H-NMR (500 MHz, CDCl3) δ: 7.96 (2H, d, J=8.8 Hz), 7.94 (2H, d, J=8.8 Hz), 7.42 (1H, d, J=2.2 Hz), 7.27 (1H, s), 6.40 (1H, d, J=2.2 Hz), 3.79 (3H, s), 2.44 (3H, s). 13C-NMR (125 MHz, CDCl3) δ: 145.4, 137.5, 134.0, 128.5, 126.3, 110.7, 108.0, 102.7, 91.5, 56.4, 11.2. HR-MS (ESI) m/z [M+H]+ Calcd for [C13H14N3O3S]+ 292.0756. Found 292.0757. UV/Vis (CH2Cl2): λmax (log ε)=393 (2.99), 284 (4.08) nm. FL (CH2Cl2): λmax=558 nm; ΦF=0.40 (reference to rhodamine B; excited at 370 nm).
2-(4-(Methoxycarbonyl)phenyl)-5-methylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4d) (Method B)1H-NMR (400 MHz, C6D6) δ: 8.25 (1H, d, J=8.5 Hz), 7.92 (1H, d, J=8.8 Hz), 7.05 (1H, d, J=2.5 Hz), 6.53 (1H, br s), 5.81 (1H, dd, J=2.8 Hz, 0.8 Hz), 3.52 (3H, s), 1.76 (3H, s). 13C-NMR (125 MHz, C6D6) δ: 166.4, 146.8, 136.9, 130.3, 128.4, 125.9, 109.2, 107.5, 101.7, 91.2, 51.5, 10.6. HR-MS (ESI) m/z [M+H]+ Calcd for [C14H14N3O2]+ 256.1086. Found 256.1095. UV/Vis (CH2Cl2): λmax (log ε)=380 (3.50), 288 (4.61) nm. FL (CH2Cl2): λmax=553 nm; ΦF=0.56 (reference to rhodamine B; excited at 420 nm).
2-(2-Cyano-4-(methoxycarbonyl)phenyl)-5-methylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4e) (Method B)1H-NMR (400 MHz, C6D6) δ: 8.29 (1H, d, J=8.3 Hz), 8.18 (1H, d, J=1.8 Hz), 8.00 (1H, dd, J=8.3 Hz, 1.8 Hz), 7.70 (1H, d, J=1.0 Hz), 6.99 (1H, dd, J=2.5 Hz, 1.0 Hz), 5.75 (1H, dd, J=2.5 Hz, 0.7 Hz), 3.41 (3H, s), 1.63 (3H, s). 13C-NMR (125 MHz, C6D6) δ: 164.8, 143.1, 139.0, 135.6, 133.8, 130.2, 128.9, 119.1, 110.8, 109.5, 108.5, 102.1, 94.1, 52.1, 10.5. HR-MS (ESI) m/z [M+Na]+ Calcd for [C15H12N4O2Na]+ 303.0858. Found 303.0854. UV/Vis (CH2Cl2): λmax (log ε)=436 (3.05), 287 (4.23) nm. FL (CH2Cl2): λmax=611 nm; ΦF=0.11 (reference to rhodamine B; excited at 420 nm).
2-([1,1′-Biphenyl]-4-yl)-5-methylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4f) (Method A)1H-NMR (500 MHz, CDCl3) δ: 7.86 (2H, d, J=8.5 Hz), 7.65 (4H, t, J=8.3 Hz), 7.46 (2H, br t, J=7.8 Hz), 7.42 (1H, br d, J=2.5 Hz), 7.36 (1H, br t, J=7.3 Hz), 6.36 (1H, br d, J=2.0 Hz), 2.44 (3H, s). 13C-NMR (125 MHz, CDCl3) δ: 147.4, 141.0, 140.7, 130.7, 128.8, 127.4, 127.0, 126.2, 109.9, 107.4, 102.3, 90.4, 11.3. IR (KBr) cm−1: 3151, 2923, 1471, 1445, 1412, 1393, 1236, 1112, 1034, 1006, 947, 843, 766, 728, 575. HR-MS (ESI) m/z [M+Na]+ Calcd for [C18H15N3Na]+ 296.1164. Found 296.1161. UV/Vis (CH2Cl2): λmax (log ε)=360 (3.71), 290 (4.69) nm. FL (CH2Cl2): λmax=491 nm; ΦF=0.40 (reference to 9,10-DPA; excited at 370 nm).
5-Methyl-2-(naphthalen-2-yl)pyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4g) (Method A)1H-NMR (500 MHz, CDCl3) δ: 8.33 (1H, s), 7.97–7.88 (4H, m), 7.55–7.49 (3H, m), 7.47 (1H, br-s), 6.46 (1H, s), 2.43 (3H, d, J=3.5 Hz). 13C-NMR (125 MHz, CDCl3) δ: 147.4, 134.5, 134.2, 129.2, 128.6, 127.44, 127.37, 127.1, 125.04, 125.03124.8, 123.6, 110.0, 108.5, 11.2. IR (KBr) cm−1: 2925. HR-MS (ESI) m/z [M+H]+ Calcd for [C16H14N3]+ 248.1188. Found 248.1181. UV/Vis (CH2Cl2): λmax (log ε)=356 (3.88), 291 (4.53) nm. FL (CH2Cl2): λmax=485 nm; ΦF=0.082 (reference to 9,10-DPA; excited at 360 nm).
12-Methyl-2,6-ditosyl-2,3,4,5,6,7-hexahydro-1H-pyrazolo[1′,2′:1,2][1,2,3]triazolo[4,5-g][1,5]diazonin-9-ium-8-ide (4i) (Method B)1H-NMR (500 MHz, CDCl3) δ: 7.84 (2H, d, J=8.3 Hz), 7.69 (2H, d, J=8.3 Hz), 7.45 (2H, d, J=7.5 Hz), 7.37 (2H, d, J=8.3 Hz), 6.37 (1H, d, J=1.7 Hz), 5.09 (3H, s), 4.26 (2H, s), 3.30–3.26 (2H, m), 2.87–2.83 (2H, m), 2.72 (3H, s), 2.52 (3H, s), 2.48 (3H, s). 13C-NMR (125 MHz, C6D6) δ: 143.2, 138.2, 134.7, 130.2, 129.7, 113.6, 108.1, 102.6, 101.3, 49.6, 48.7, 44.7, 40.3, 30.0, 21.0, 11.2. IR (KBr) cm−1: 2924, 2865, 1335, 1159, 814, 547. HR-MS (ESI) m/z [M+Na]+ Calcd for [C25H30N5O4S2Na]+ 528.1739. Found 528.1742.
2-(Methoxycarbonyl)-5-phenylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4k) (Method A)1H-NMR (400 MHz, CDCl3) δ: 8.08(1H, s), 7.59–7.57 (3H, overlapped), 7.49 (2H, dd, J=8.3 Hz, 7.5 Hz), 7.30 (1H, t, J=7.5 Hz), 6.99 (1H, d, J=2.5 Hz), 3.99 (3H, s). 13C-NMR (100 MHz, C6D6) δ: 162.0, 140.4, 129.7, 129.3, 126.3, 123.6, 115.5, 108.1, 104.1, 101.1, 51.6. IR (KBr) cm−1: 3151, 2951, 1733, 1522, 1396, 1223, 1008. HR-MS (ESI) m/z [M+H]+ Calcd for [C13H12N3O2]+ 242.0930. Found 242.0937. UV/Vis (CH2Cl2): λmax (log ε)=358 (4.03) nm. FL (CH2Cl2): λmax=459 nm; ΦF=0.086 (reference to 9,10-DPA; excited at 370 nm).
2-(4-(Methoxysulfonyl)phenyl)-5-phenylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4l) (Method B)1H-NMR (500 MHz, CDCl3) δ: 8.03 (2H, d, J=8.5 Hz), 7.98 (2H, d, J=9.0 Hz), 7.90 (1H, d, J=1.0 Hz), 7.62 (1H, dd, J=11.5 Hz, 1.0 Hz), 7.61 (1H, d, J=0.5 Hz), 7.51 (2H, t, J=7.5 Hz), 7.31 (1H, d, J=7.5 Hz), 6.92 (1H, d, J=3.0 Hz), 3.81 (3H, s). 13C-NMR (125 MHz, CDCl3) δ: 146.0, 137.0, 134.5, 129.6, 129.3, 128.6, 126.6, 126.4, 123.7, 116.0, 107.1, 104.7, 94.7, 56.4. IR (KBr) cm−1: 2924, 2851, 1729, 1601, 1362, 1176, 988. HR-MS (ESI) m/z [M+H]+ Calcd for [C18H16N3O3S]+ 354.0912. Found 354.0912. UV/Vis (CH2Cl2): λmax (log ε)=378 (3.74) nm, 345 (4.29) nm, 277 (4.31) nm. FL (CH2Cl2): λmax=554 nm; ΦF=0.21 (reference to rhodamine B; excited at 400 nm).
2-(4-(Methoxycarbonyl)phenyl)-5-phenylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4m) (Method B)1H-NMR (400 MHz, CDCl3) δ: 8.11 (2H, d, J=8.3 Hz), 7.90 (2H, d, J=8.6 Hz), 7.86 (1H, s), 7.60 (2H, d, J=7.5 Hz), 7.58 (1H, d, J=2.5 Hz), 7.49 (2H, t, J=7.5 Hz), 7.31–7.24 (1H, m), 6.88 (1H, d, J=2.5 Hz), 3.94 (3H, s). 13C-NMR (125 MHz, CDCl3) δ: 166.7, 147.0, 135.6, 130.0, 129.8, 129.7, 129.2, 125.6, 123.4, 115.5, 106.7, 104.4, 94.5, 52.1. IR (neat) cm−1: 3155, 1950, 1715, 1277. HR-MS (ESI) m/z [M+Na]+ Calcd for [C19H15N3O2Na]+ 340.1062. Found 340.1064. UV/Vis (CH2Cl2): λmax (log ε)=345 (4.35), 279 (4.44) nm. FL (CH2Cl2): λmax=548 nm; ΦF=0.36 (reference to rhodamine B; excited at 400 nm).
2-(2-Cyano-4-(methoxycarbonyl)phenyl)-5-phenylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4n) (Method B)1H-NMR (400 MHz, CDCl3) δ: 8.44 (1H, s), 8.39 (1H, s), 8.31 (1H, d, J=8.0 Hz), 8.24 (1H, d, J=8.0 Hz), 7.66–7.59 (3H, m), 7.50 (2H, t, J=7.6 Hz), 7.30 (1H, t, J=7.6 Hz), 6.95 (1H, d, J=2.8 Hz), 3.98 (3H, s). 13C-NMR (125 MHz, CDCl3) δ: 164.9, 143.1, 138.0, 135.3, 133.8, 130.2, 129.4, 129.4, 128.7, 126.8, 123.7, 118.3, 116.3, 109.3, 107.6, 104.5, 96.9, 52.7. IR (neat) cm−1: 3155, 2960, 2228, 1733, 1300. HR-MS (ESI) m/z [M+H]+ Calcd for [C20H15N4O2]+ 343.1195. Found 343.1198. UV/Vis (CH2Cl2): λmax (log ε)=432 (3.66), 336 (4.58), 282 (4.48) nm. FL (CH2Cl2): λmax=613 nm; ΦF=0.070 (reference to rhodamine B; excited at 400 nm).
2-([1,1′-Biphenyl]-4-yl)-5-phenylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4o) (Method A)1H-NMR (500 MHz, CDCl3) δ: 7.92 (2H, d, J=8.3 Hz), 7.85 (1H, d, J=1.0 Hz), 7.71–7.62 (5H, m), 7.59 (1H, dd, J=2.9 Hz, 1.0 Hz), 7.52–7.44 (4H, m), 7.37 (1H, tt, J=7.3 Hz, 1.3 Hz), 7.29 (1H, tt, J=7.3 Hz, 1.2 Hz). 13C-NMR (100 MHz, C6D6) δ: 148.4, 141.7, 141.2, 131.2, 130.6, 129.3, 129.1, 128.0, 127.7, 127.0, 126.0, 123.7, 115.0, 106.6, 104.0, 94.2. IR (neat) cm−1: 3152, 3031, 2923, 2854, 2109, 1467, 1415, 1387, 766. HR-MS (ESI) m/z [M+H]+ Calcd for [C23H18N3]+ 336.1501. Found 336.1502. UV/Vis (CH2Cl2): λmax (log ε)=369 (4.29), 343 (4.35), 284 (4.57) nm. FL (CH2Cl2): λmax=482 nm; ΦF=0.10 (reference to 9,10-DPA; excited at 370 nm).
2-(Naphthalen-2-yl)-5-phenylpyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4p) (Method A)1H-NMR (400 MHz, CD3CN) δ: 8.46 (1H, s), 8.28 (1H, br d, J=0.8 Hz), 8.06–7.94 (4H, m), 7.78 (2H, d, J=7.2 Hz), 7.71 (1H, br dd, J=3.0 Hz, 1.0 Hz), 7.60–7.53 (4H, m), 7.32 (1H, t, J=7.4 Hz), 7.10 (1H, d, J=3.2 Hz). 13C-NMR (125 MHz, CDCl3) δ: 148.3, 133.54, 133.45, 130.0, 129.3, 128.6, 128.5, 128.3, 127.8, 126.5, 126.3, 126.2, 124.82, 123.9, 123.5, 115.4, 106.6, 104.4, 94.3. IR (neat) cm−1: 3152, 3055, 2924, 1205, 1599, 1522, 1389, 1239, 1029, 751. HR-MS (ESI) m/z [M+Na]+ Calcd for [C21H15N3Na]+ 332.1166. Found 332.1166. UV/Vis (CH2Cl2): λmax (log ε)=342 (4.30), 283 (4.24), 259 (4.67), 251 (4.69). FL (CH2Cl2): λmax=481 nm; ΦF=0.084 (reference to rhodamine B; excited at 360 nm).
