Systematic Investigations on 1,2,3-Triazole-Based Compounds

Jan 31, 2014 - 1,2,3-Triazole-functionalized ene–yne compounds, synthesized by ...... we postulate that the introduction of electron-donating motive...
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Systematic Investigations on 1,2,3-Triazole-Based Compounds Capable of Second Harmonic Generation Daniel Lumpi,*,† Florian Glöcklhofer,† Brigitte Holzer,† Berthold Stöger,‡ Christian Hametner,† Georg A. Reider,§ and Johannes Fröhlich† †

Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163, A-1060 Vienna, Austria Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/164, A-1060 Vienna, Austria § Photonics Institute, Vienna University of Technology, Gußhausstraße 27-29, A-1040 Vienna, Austria ‡

S Supporting Information *

ABSTRACT: 1,2,3-Triazole-functionalized ene−yne compounds, synthesized by thiophene (selenophene) ring fragmentation followed by azide−alkyne cycloaddition, were investigated as a basis for nonlinear optical (NLO) materials capable of second harmonic generation (SHG). The structure−property relationship was mapped by systematic variation of the molecular scaffold, viz., elongation of the alkyl groups, isomerizations of both the double bond as well as the triazole moiety, sulfur oxidations, and a sulfur−selenium exchange. Nine novel molecular compounds were synthesized, of which eight are solids at room temperature. The latter were characterized by single-crystal X-ray diffraction (XRD). Five crystal structures lacked of inversion symmetry, a prerequisite for NLO activity. The corresponding materials were examined regarding SHG, UV−vis absorption, and powder XRD. By substituting S for Se, we were able to increase the SH intensity by a factor of 20. On the basis of the results, we propose a strategy to further improve the SHG efficiency of this class of materials.

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INTRODUCTION

applications generally rely on a donor−(π-linker)−acceptor design to impart the electronic bias.8 Just recently, we reported on a novel class of NLO materials capable of second harmonic generation yielding an estimated SH efficiency of more than twice the value of potassium dihydrogen phosphate (KDP).9,10 The introduced NLO chromophore 4ba (Figure 1) relies on the application of a 1,2,3-triazole as the electron acceptor subunit, which was demonstrated to be conveniently accessible within the concept of “click” chemistry.11−13 As an electron donor part of the molecule the Z-(methylthio)propenyl group derived from thiophene ring-opening14−16 reactions is applied. The donor− acceptor interactions on the one hand lead to promising SHG efficiencies but on the other hand also feature desirable optical properties (wide transparency window). In addition, the particular configuration of the molecule, namely, a phenyl/triazole pair extended by a Z-(methylthio)propenyl subunit, was revealed to promote enantiomorphic crystallization as a consequence of alkyl−alkyl group interactions (supported by torsion angle dependent potential calculations (DFT)).10 The chiral crystallization, although the molecule is nonchiral and flexible, is a relatively rare

Quadric nonlinear optical (NLO) materials are of critical importance for applications in quantum electronics and telecommunication technology.1 There are several manifestations of this nonlinearity such as the electro-optic effect, optical three wave mixing, second harmonic generation (SHG), parametric amplification, and downconversion. The common material property responsible for this phenomenologically disparate effect is the second-order susceptibility, which, on a microscopic level, relates to the first-order hyperpolarizability. It should be noted that for symmetry reasons quadric nonlinear optical materials are also potentially piezoelectric, rendering them useful for integrated sensor applications as well. A necessary (but not sufficient) condition for SHG to appear in a crystal is that it belongs to one of the noncentrosymmetric crystal classes, with the exception of 432.2 Organic NLO crystals are particularly attractive for these applications.3−7 Their NLO figures of merit can be orders of magnitude higher compared to inorganics, and their long-term stability is orders of magnitude better than that of electrooptic polymers. The reason for the fast response of nonlinear organic compounds is that their hyperpolarizability is due to (delocalized) electrons in contrast to inorganic materials where polar optical lattice vibrations may play a large role. Thus, organic molecules capable of second-order NLO © 2014 American Chemical Society

Received: October 4, 2013 Revised: January 24, 2014 Published: January 31, 2014 1018

dx.doi.org/10.1021/cg4014762 | Cryst. Growth Des. 2014, 14, 1018−1031

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phenomenon17 and combines the advantages of a convenient and straightforward synthesis (of nonchiral compounds) with the capability of characteristics such as, e.g., SHG. Hence, the molecular structure of this class of compounds is of great interest as it comprises both an attractive donor− acceptor scaffold and a subunit facilitating noncentrosymmetric crystallization. This paper presents a systematic study on the structure−function relationship of these promising materials. The investigations focus on the effects induced by variations of both steric as well as electronic constitution on quadric NLO properties. As a result of the aforementioned applications of noncentrosymmetric (chiral) materials, clearly outlining the broad scope of potential applications of these structural building blocks, the findings are of relevance for diverse fields of material chemistry.

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not clarify whether phase matching was possible or not for a particular material. Nonetheless, a relative measurement of the nonlinear optical coefficients is possible since the SH efficiency scales quadratically with the nonlinear coefficient in this particle size regime.28 The quadric nonlinear properties of our samples were probed by second harmonic (SH) generation from powder samples. The output of an ultrafast (pulse duration 70 fs) Yb:KGW-Laser (Light Conversion) with 600 mW output power at a repetition rate of 75 MHz and a wavelength of 1034 nm was directed, with a 100 mm focusing lens, onto powder samples between thin sheets of glass. The diffusely reflected SH radiation was collected with a NA = 0.1 lens, separated from fundamental radiation with a color filter, and spectrally analyzed with a 0.25 m grating monochromator and a photomultiplier tube. The sample plane was positioned somewhat out of the focal plane (toward the lens) to prevent any damage to the sample. After each measurement, the samples were carefully checked for the absence of any damage or thermal modification. Halogen Dance (HD) Procedure toward 3-Bromo-5-ethyl-2(trimethylsilyl)thiophene 2c. To a solution of diisopropylamine (DIPA, 6.83 g, 67.5 mmol, 1.5 equiv) in dry THF (180 mL) under argon was added n-BuLi (21.6 mL, 54.0 mmol, 2.5 M in hexanes, 1.2 equiv) slowly at −30 °C. After 20 min 1c (8.55 g, 45.0 mmol, 1.0 equiv) was added in dry THF at −70 °C and the reaction stirred for 1.5 h at a temperature of −70 to −40 °C. Subsequently TMS−Cl (6.12 g, 56.3 mmol, 1.25 equiv) was added as a solution in dry THF and the mixture stirred at rt overnight. The reaction was poured on water (200 mL) and repeatedly extracted with Et2O, and the organic phases were dried over anhydrous Na2SO4 and concentrated under reduced pressure. Purification by vacuum distillation yielded 2c (9.50 g, 80%) as slightly yellow oil. BP: 108−110 °C (12 mbar). 1H NMR (200 MHz, CDCl3): δ = 6.82 (m, 1H), 2.83 (m, 2H), 1.31 (t, J = 7.5 Hz, 3H), 0.39 (s, 9H) ppm. 13C NMR (50 MHz, CDCl3): δ = 152.7 (s), 131.4 (s), 129.1 (d), 116.4 (s), 23.3 (t), 15.5 (q), −0.7 (q) ppm. Anal. Calcd for C9H15BrSSi: m/z 261.98 [M]+. Found: MS (EI) m/z 261.96 [M]+. General Procedure for the Thiophene Ring-Fragmentation (TRF) reaction. To a solution of 2b,c (1.0 equiv) in dry Et2O (∼0.2− 0.3 M)/dry THF (∼0.15 M) under an argon atmosphere at −60 to −80 °C was injected n-BuLi (1.1 equiv)/ethyllithium (1.1 equiv) dropwise. After the addition the reaction was immediately warmed to rt, stirred for 30 min, and again cooled to −40 °C. The appropriate alkyl iodide (1.5 equiv) was added and the temperature subsequently raised to rt. After a reaction time of 30 min the mixture was poured on water and extracted with Et2O, and the combined organic layers were dried over anhydrous Na2SO4 and concentrated in vacuo. Purification was performed by column chromatography (light petroleum). Trimethyl[(3Z)-4-(ethylthio)-3-penten-1-yn-1-yl]silane 3bb. Starting from 2b (498 mg, 2.0 mmol) in dry THF (13 mL), ethyllithium (4.4 mL, 2.2 mmol, 0.5 M in benzene:cyclohexane), and iodoethane (468 mg, 3.0 mmol), the pure Z-isomer 3bb (201 mg, 51%) was isolated as a colorless liquid. 1H NMR (200 MHz, CDCl3): δ = 5.43 (m, 1H), 2.89 (q, J = 7.4 Hz, 2H), 2.07 (m, 3H), 1.29 (t, J = 7.4 Hz, 3H), 0.19 (s, 9H) ppm. 13C NMR (50 MHz, CDCl3): δ = 148.6 (s), 103.7 (d), 101.8 (s), 100.9 (s), 24.8 (t), 22.8 (q), 15.0 (q), −0.0 (q) ppm. Anal. Calcd for C10H18SSi: m/z 199.0971 [M + H]+. Found: MS (APCI) m/z 199.0981 [M + H]+. Trimethyl[(3Z)-4-(propylthio)-3-penten-1-yn-1-yl]silane 3bc. Starting from 2b (2.49 g, 10.0 mmol) in dry Et2O (33 mL), n-BuLi (4.4 mL, 11.0 mmol, 2.5 M in hexanes), and 1-iodopropane (2.55 g, 15.0 mmol), 3bc (221 mg, 10%) was obtained as a mixture with 3bd (27.5 mol % 3bd content; determined by 1H NMR spectroscopy). The low yield can be explained by the fact that only the best product fraction (in terms of 3bd content) was considered for the yield calculation and subjected to further conversion. 1H NMR (200 MHz, CDCl3): 5.45−5.43 (m, 1H), 2.85 (t, J = 7.4 Hz, 2H), 2.07 (m, 3H), 1.65 (sext., J = 7.4 Hz, 2H), 1.02 (t, J = 7.3 Hz, 3H), 0.20 (s, 9H) ppm. 13 C NMR (50 MHz, CDCl3): δ = 148.7 (s), 103.9 (d), 102.0 (s), 100.9 (s), 32.7 (t), 23.4 (t), 23.0 (q), 13.4 (q), 0.0 (q) ppm. Anal. Calcd for C11H20SSi: m/z 213.1128 [M + H]+. Found: MS (APCI) m/ z 213.1125 [M + H]+. The NMR code is obtained from calculated

EXPERIMENTAL SECTION

The syntheses of 2-bromo-5-methylthiophene (1b),18 2-bromo-5ethylthiophene (1c),19 3-bromo-2-(trimethylsilyl)thiophene (2a),20 3bromo-5-methyl-2-(trimethylsilyl)thiophene (2b),21 trimethyl[(3Z)-4(methylthio)-3-buten-1-yn-1-yl]-silane (3aa),22 trimethyl[(3Z)-4(methylthio)-3-penten-1-yn-1-yl]silane (3ba),10 trimethyl[(3Z)-4-(butylthio)-3-penten-1-yn-1-yl]silane (3bd),23 4-[(1Z)-2-(methylthio)ethenyl]-1-phenyl-1H-1,2,3-triazole (4aa),22 4-[(1Z)-2-(methylthio)1-propen-1-yl]-1-phenyl-1H-1,2,3-triazole (4ba),10 and azidobenzene24 were performed in analogy to published protocols; full characterization of the compounds is also given in the indicated references. Single crystals for compounds 4aa, 4ba, 4bb, 4ca, 5ba, 7ba, and 16 were obtained by slow evaporation of n-hexane at rt. 4bd was isolated as an oil which slowly crystallized upon standing at ∼5 °C. Crystals of the sulfone 9ba and 12ba were grown by slow evaporation of CD2Cl2 in NMR tubes at ∼5 °C. Similar to 4ba (see literature for details)10 noncentrosymmetric compounds 4bb, 4ca, and 7ba tend to crystallize in thin needles, which are still suitable for a general screening of NLO properties via the powder method; prior to technological application, however, further optimization of the crystallization process will be necessary. In contrast, oxidized species 12ba readily crystallize in blocks of >1 × 1 × 1 mm. The seleno derivative 16 crystallizes as rods with a significantly larger crystal size compared to 4ba, 4bb, etc., making the latter two particularly interesting for applications in optics. Crystals of the title compounds suitable for X-ray diffraction were selected under a polarizing microscope, embedded in perfluorinated oil and mounted on a Bruker APEX II diffractometer with κ-geometry equipped with a CCD detector. Intensity data were recorded at 100 K in a dry stream of nitrogen with Mo Kα radiation (λ = 0.71073 Å). Full reciprocal spheres were collected in ω- and φ-scan modes with 0.5° rotation width. Frames were integrated using SAINT PLUS,25 and an absorption correction was applied using a multiscan approach with SADABS.25 The crystal structures were solved using charge-flipping implemented in SUPERFLIP.26 All non-H atoms were directly located in the resulting electron density maps. The structures were refined with JANA2006.27 The protons were located in subsequent difference Fourier maps. In general, protons were freely refined. In 4bb and 4ca, the terminal H atoms of the thioalkyl group, and in 4bd all H atoms were placed at calculated positions and refined as riding on the parent C atoms. The H atoms in the heavy atom structure 16 were likewise constrained. In the final refinement cycles, all non-H atoms were refined anisotropically. Powder diffractograms were recorded on a Philips X’Pert Pro diffractometer system [Cu Kα1,2 radiation (λ = 1.54060, 1.54439 Å), X’Celerator multichannel detector, Bragg−Brentano geometry, silicon single-crystal sample holder, 5−70° 2θ, 2.546° scan length (2θ)]. The scans were converted into 0.02° step-size bins. For SHG measurements the powder samples were produced by grinding with a mortar; the maximum particle size was below 3σ(I)] reflections, 203 parameters, wR (all data) = 0.062, R [I > 3σ(I)] = 0.029; CCDC reference number 927487. (52) Kalman, A.; Parkanyi, L.; Argay, G. Acta Crystallogr., Sect. B: Struct. Sci 1993, B49, 1039. (53) (4bd): C15H19N3S, Mr = 273.4, monoclinic, P21/c, a = 7.9302(11) Å, b = 17.223(2) Å, c = 10.8814(14) Å, β = 94.771(7)°, V = 1481.1(3) Å3, Z = 4, μ = 0.209 mm−1, T = 100 K, 26 938 measured, 4157 independent and 2248 observed [I > 3σ(I)] reflections, 172 parameters, wR (all data) = 0.049, R [I > 3σ(I)] = 0.045; CCDC reference number 927488. (54) (4ca, polymorph 1): C13H15N3S, Mr = 245.3, monoclinic, Cc, a = 17.6465(9) Å, b = 5.0684(3) Å, c = 14.7768(8) Å, β = 112.225(2)°,

makes ene−yne compounds attractive molecular building blocks, e.g., for the design of further NLO chromophores. In fact, the demand of noncentrosymmetric materials in diverse fields of material science, as outlined in the Introduction, significantly broadens the scope of potential application.

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ASSOCIATED CONTENT

S Supporting Information *

General synthetic methods, spectroscopic (NMR) and crystallographic (X-ray) data, as well as information regarding the SHG experiments. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: 0043 650 5008277/0041 78 8799874. Fax: 0043 1 58801 16399. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge H. Schmidtbauer, A. Hammerl, and M. Möller for supporting the synthetic experiments, P. Kautny for performing the TGA analysis, as well as K. Föttinger for assisting the photophysical analysis. F. Kubel and E. Horkel are acknowledged for fruitful discussion, E. Rosenberg for performing the high resolution mass spectrometry, and N. Jankowski for conducting the ion chromatography. The authors also thank T. Balciunas and A. Pugzlys (Photonics Institute TU Wien) for their great support with the SHG measurements. The X-ray center of the Vienna University of Technology is acknowledged for providing access to the single-crystal diffractometer.

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REFERENCES

(1) Yariv, A.; Yeh, P. Photonics: Optical Electronics in Modern Communications; Oxford University Press: New York, 2007. (2) Klapper, H.; Hahn, T. In International Tables for Crystallography; Hahn, T., Ed.; Springer: Dordrecht, 2005; p 804. (3) Barlow, S.; Marder, S. R. In Functional Organic Materials Syntheses, Strategies and Applications; Mueller, T. J. J., Bunz, U. H. F., Eds.; WileyVCH Verlag: Weinheim, 2007; Vol. 1, p 393. (4) Zyss, J. Molecular Nonlinear Optics: Materials, Physics and Devices; Academic Press: New York, 1994. (5) Chemla, D. S.; Zyss, J. Nonlinear Optical Properties of Organic Molecules and Crystals; Academic Press: Orlando, 1987. (6) Cho, M. J.; Choi, D. H.; Sullivan, P. A.; Akelaitis, A. J. P.; Dalton, L. R. Prog. Polym. Sci. 2008, 33, 1013. (7) Dalton, L. In Polymers for Photonics Applications I; Lee, K. S., Ed.; Springer: Berlin: Heidelberg, 2002; Vol. 158, p 1. (8) Marder, S. R. Chem. Commun. 2006, 131. (9) Lumpi, D.; Horkel, E.; Stoeger, B.; Hametner, C.; Kubel, F.; Reider, G. A.; Froehlich, J. Proc. SPIE 2011, 8306, 830615/1. (10) Lumpi, D.; Stoeger, B.; Hametner, C.; Kubel, F.; Reider, G.; Hagemann, H.; Karpfen, A.; Froehlich, J. CrystEngComm 2011, 13, 7194. (11) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004. (12) Moses, J. E.; Moorhouse, A. D. Chem. Soc. Rev. 2007, 36, 1249. (13) Hein, J. E.; Fokin, V. V. Chem. Soc. Rev. 2010, 39, 1302. (14) Gronowitz, S.; Frejd, T. Chem. Heterocycl. Compd. 1978, 14, 353. (15) Iddon, B. Heterocycles 1983, 20, 1127. (16) Gilchrist, T. L. Adv. Heterocycl. Chem. 1987, 41, 41. (17) Pidcock, E. Chem. Commun. 2005, 3457. (18) Nakayama, J.; Konishi, T.; Murabayashi, S.; Hoshino, M. Heterocycles 1987, 26, 1793. 1030

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V = 1223.44(12) Å3, Z = 4, μ = 0.245 mm−1, T = 100 K, 13 776 measured, 6313 independent, and 6081 observed [I > 3σ(I)] reflections, 201 parameters, wR (all data) = 0.030, R [I > 3σ(I)] = 0.023; CCDC reference number 927489. (4ca, polymorph 2): C13H15N3S, Mr = 245.3, monoclinic, P21/c, a = 10.0699(6) Å, b = 10.4586(6) Å, c = 12.3674(7) Å, β = 98.777(2)°, V = 1287.25(13) Å3, Z = 4, μ = 0.233 mm−1, T = 100 K, 23 292 measured, 3783 independent and 3017 observed [I > 3σ(I)] reflections, 214 parameters, wR (all data) = 0.048, R [I > 3σ(I)] = 0.038; CCDC reference number 955415. (55) Hill, D. G. J. Am. Chem. Soc. 1932, 54, 32. (56) (5ba): C12H13N3S, Mr = 231.3, triclinic, P1̅, a = 5.9338(2) Å, b = 7.3798(2) Å, c = 13.2891(4) Å, α = 99.4247(11)°, β = 93.1907(12)°, γ = 92.2136(12)°, V = 572.51(3) Å3, Z = 2, μ = 0.257 mm−1, T = 100 K, 11 475 measured, 4115 independent and 3365 observed [I > 3σ(I)] reflections, 197 parameters, wR (all data) = 0.043, R [I > 3σ(I)] = 0.033; CCDC reference number 927490. (57) Kwok, S. W.; Fotsing, J. R.; Fraser, R. J.; Rodionov, V. O.; Fokin, V. V. Org. Lett. 2010, 12, 4217. (58) (7ba): C12H13N3S, Mr = 231.3, orthorhombic, P212121, a = 7.1809(3) Å, b = 10.2986(5) Å, c = 15.7680(8) Å, V = 1166.09(10) Å3, Z = 4, μ = 0.253 mm−1, T = 100 K, 27 604 measured, 3333 independent and 2884 observed [I > 3σ(I)] reflections, 198 parameters, wR (all data) = 0.035, R [I > 3σ(I)] = 0.027; CCDC reference number 927491. (59) (9ba): C12H13N3O2S, Mr = 263.3, monoclinic, P21/n, a = 5.7944(6) Å, b = 23.318(2) Å, c = 9.1374(9) Å, β = 97.601(4), V = 1223.7(2) Å3, Z = 4, μ = 0.262 mm−1, T = 100 K, 19 745 measured, 5297 independent and 4624 observed [I > 3σ(I)] reflections, 215 parameters, wR (all data) = 0.056, R [I > 3σ(I)] = 0.041; CCDC reference number 927492. (60) (12ba): C12H13N3O2S, Mr = 263.3, orthorhombic, Pna21, a = 12.7982(8) Å, b = 13.6159(8) Å, c = 7.1310(4) Å, V = 1242.64(13) Å3, Z = 4, μ = 0.258 mm−1, T = 100 K, 53 360 measured, 6545 independent and 5940 observed [I > 3σ(I)] reflections, 215 parameters, wR (all data) = 0.037, R [I > 3σ(I)] = 0.029; CCDC reference number 927493. (61) Shen, J. R. The Principles of Nonlinear Optics; Wiley-Interscience: New York, 2002. (62) Mehta, S.; Waldo, J. P.; Larock, R. C. J. Org. Chem. 2009, 74, 1141. (63) (16): C12H13 N3Se, Mr = 278.2, orthorhombic, P212121, a = 5.71930(10) Å, b = 9.5627(2) Å, c = 20.9579(5) Å, V = 1146.23(4) Å3, Z = 4, μ = 3.251 mm−1, T = 100 K, 25 987 measured, 3289 independent and 3081 observed [I > 3σ(I)] reflections, 146 parameters, wR (all data) = 0.031, R [I > 3σ(I)] = 0.024; CCDC reference number 927494. (64) Shannon, R. D. Acta Crystallogr., Sect. A 1976, A32, 751. (65) Boyd, R. W. Nonlinear Optics; 3rd ed.; Elsevier: New York, 2008; p 84. (66) Llinas, A.; Goodman, J. M. Drug Discovery Today 2008, 13, 198.

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