Efficient fluorophores based on pyridyl-enolato and enamido difluoroboron complexes: Simple alternatives to boron-dipyrromethene (bodipy) dyes

Accepted Manuscript Efficient Fluorophores Based on Pyridyl-Enolato and Enamido Difluoroboron Complexes: Simple Alternatives to Boron-Dipyrromethene (BODIPY) Dyes Markus Graser, Holger Kopacka, Klaus Wurst, Markus Ruetz, Christoph R. Kreutz, Thomas Müller, Christa Hirtenlehner, Uwe Monkowius, Günther Knör, Benno Bildstein PII: DOI: Reference:

S0020-1693(13)00307-1 http://dx.doi.org/10.1016/j.ica.2013.05.034 ICA 15489

To appear in:

Inorganica Chimica Acta

Received Date: Accepted Date:

15 March 2013 24 May 2013

Please cite this article as: M. Graser, H. Kopacka, K. Wurst, M. Ruetz, C.R. Kreutz, T. Müller, C. Hirtenlehner, U. Monkowius, G. Knör, B. Bildstein, Efficient Fluorophores Based on Pyridyl-Enolato and Enamido Difluoroboron Complexes: Simple Alternatives to Boron-Dipyrromethene (BODIPY) Dyes, Inorganica Chimica Acta (2013), doi: http://dx.doi.org/10.1016/j.ica.2013.05.034

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Efficient Fluorophores Based on Pyridyl-Enolato and Enamido Difluoroboron Complexes: Simple Alternatives to Boron-Dipyrromethene (BODIPY) Dyes Markus Graser,a Holger Kopacka,a Klaus Wurst,a Markus Ruetz,b Christoph R. Kreutz,b Thomas Müller,b Christa Hirtenlehner,c Uwe Monkowius,c Günther Knör,c and Benno Bildsteina,* a

Institut für Allgemeine, Anorganische und Theoretische Chemie, Universität Innsbruck, Centrum

für Chemie und Biomedizin (CCB), Innrain 80-82, 6020 Innsbruck, Austria b

Institut für Organische Chemie, Universität Innsbruck, Centrum für Chemie und Biomedizin

(CCB), Innrain 80-82, 6020 Innsbruck, Austria c

Institut für Anorganische Chemie, Johannes Kepler Universität Linz, Altenbergerstraße 69, 4040

Linz, Austria * Corresponding author: Tel. +43-512-507-57007, fax: +43-512-507-57099, E-mail: [email protected]

Keywords: N,O ligand, N ligand, boron complex, X-ray structure, fluorescence

Abstract Simple [N,O] and [N,N] -pyridyl or quinolyl enolato/enamido difluoroboron complexes are easily accessible and highly luminescent with good photophysical properties, comparable to BODIPY benchmark dyes. Complete characterization by multinuclear NMR and by single crystal structure analysis as well as pertinent photophysical data are reported.

1. Introduction Fluorescent dyes are useful materials with many multidisciplinary applications in bioimaging and electroluminescence. Different classes of fluorescent organic dyes are known, but without doubt the family of BODIPY dyes [1–4] represents the most useful and versatile class of fluorophores, due to their convenient synthesis and functionalization, chemical robustness, and excellent photochemical properties with high fluorescence quantum yields and sharp emission bands. Many efforts have been undertaken to optimize BODIPY dyes, but most of these studies are based on the generic symmetrical boron-dipyrromethene core structure with only peripheral modifications [2–4]. Much less is known on unsymmetrical systems [4–12], due to their inherent difficult synthesis. In this contribution, we report easily accessible pyridyl/quinolyl enolato/enamido difluoroboron complexes with excellent photophysical and chemical properties. Structurally, these compounds are

inspired from boron-dipyrromethene and -(di)ketiminates [13] but importantly one of the two Ndonor atoms is part of an aromatic heterocycle (pyridine or quinoline), thereby extending the chromophore and increasing the rigidity of the ligand (Scheme 1). Such a desymmetrized structural motif offers various options for development of new, task-specific biolabels in the future.

Scheme 1. Structural comparison of BODIPY dyes with pyridyl/quinolyl-enolato/enamido-BF2 complexes.

2. Results and discussion 2.1. Synthesis and characterization Synthetically, the ligand systems of complexes 1–5 are conveniently available by a recently developed protocol [14] comprising (i) lithiation of the corresponding methylated heterocycles, (ii) nucleophilic addition to benzonitrile, (iii) acidic hydrolysis, and finally, in the case of enamido ligands of complexes 3–5, (iv) condensation with anilines under azeotropic removal of water. The difluoroboron complexes 1–5 were synthesized from these ligands in 60–89% isolated yields as yellow, air-stable materials by (i) deprotonation in tetrahydrofuran (THF), (ii) metathesis with borontrifluoride, and (iii) crystallization from a mixture of dichloromethane/n-hexane. Similarly as BODIPY complexes, compounds 1–5 are also chemically exceptionally stable; they are unaffected by diluted hydrochloric acid and have melting points ranging from 102° to 238° C, dependent on their molar mass and substitution pattern. For all complexes X-ray single crystal structure analyses are available (Supporting Information), Figures 1 and 2 show the molecular structures of 2 and 4 as representative examples.

2

Figure 1. Molecular structure of 2. Selected bond lengths (Å) and angles (deg): B(1)–O(1), 1.445(1); B(1)–N(1), 1.590(2); B(1)–F(1), 1.383(1); B(1)–F(2), 1.383(1); O(1)–C(1), 1.325(1); C(1)–C(2), 1.352(2); C(2)–C(3), 1.422(2); C(3)–N(1), 1.351(1); N(1)–B(1)–O(1), 111.4(1).

Figure 2. Molecular structure of 4. Selected bond lengths (Å) and angles (deg): B(1)–N(1), 1.5469(16); B(1)–N(2), 1.5769(16); B(1)–F(1), 1.3922(16); B(1)–F(2), 1.3850(16); N(1)–C(1), 1.3513(14); C(1)–C(2), 1.3708(17); C(2)–C(3), 1.4112(17); C(3)–N(2), 1.3563(15); N(1)–B(1)–N(2), 110.32(9).

Overall, compounds 1–5 all have slightly distorted tetrahedral structures with geometrical parameters in line with expectations. Clearly evident is the increased steric shielding of enamido complexes 3–5 by the peripheral N-aryl ring that is tilted out of the plane of conjugation due to its 2,6substituents. Note that these substituents prevent free rotation of the N-aryl ring, thereby avoiding undesired nonradiative energy-loss in these dye structures. The steric bulk of this N-substituent also forces the C-phenyl group out of the conjugation plane of the ligand backbone, in contrast to enolato complexes 1 and 2 where such an effect is absent. In solution, compounds 1–5 were fully characterized by standard 1H and 13C NMR spectroscopy as well as by heteronuclear 11B and 19F NMR spectroscopy. The difluoroboron moiety is clearly observed by the corresponding multiplets (11B: t, 1:2:1, 1JB–F = 15.5–33.3 Hz, = 0.93–2.64 ppm; 19F: quadruplet, 1:1:1:1, = -143 to -126 ppm) with chemical shifts comparable to those in symmetrical -diketiminato-BF2 complexes [15]. In addition to their structural characterization in solution, com3

pounds 1–5 all display molecular ions in their HR-FAB-mass spectra, thereby giving further proof of their stability and molecular structure.

2.2. Fluorescence properties Complexes 1–5 all show strong fluorescence in the solid state and in solution, suggesting that simple pyridyl/quinoylyl enolato/enamido BF2 complexes represent indeed new structural motifs in fluorophore chemistry. To evaluate these new fluorophores in detail, electronic absorption and emission spectroscopy was performed (Table 1, Figure 3). Generally speaking, the performance of 1–5 is comparable to standard BODIPY systems [2–4]. Fluorescence quantum yields (

F)

ranging from

33–62% are quite high, with lower values for pyridyl derivatives 1 and 3 in comparison to quinolyl derivatives 2, 4, 5. Pyridyl derivatives 1 and 3 feature only one emission band with significantly higher Stokes shifts (

SS)

compared to those of quinolyl derivatives 2, 4 and 5. In addition, quinolyl

compounds 2, 4 and 5 display a mirrored vibrational structure in the lowest energy absorption and in the emission bands typical for the fluorescence of rigid p-systems. The vibrational spacings (e.g. 1200 cm-1 for 2) are typical for vibrational stretching modes of aromatic ligands [16]. All compounds feature additional high energy absorption bands at around 300 nm (quinolyl) and 323 nm (pyridyl). The absorption and excitation spectra are almost superimposable. Both the absorption and emission bands are hypsochromically shifted compared to BODIPY dyes, which usually show absorptions above ~500 nm and emissions above ~510 nm [4]. Comparison of 4 and 5, differing only by their 2,6-substituents of the N-aryl group, shows similar fluorescent behavior, indicating no beneficial effect of the larger isopropyl substituents in preventing radiationless deactivation of the excited state.

Table 1. Selected Spectroscopic and Photophysical Dataa # Absorption

max

(lg ) [nm]

Excitation

max

Emission

max

SS

b

F

[nm]

[nm]

[cm-1]

[%]c

1 323 (3.81), 397 (4.17)

395

450

3000

33

2 294 (4,33), 300 (4.30), 385 (sh, 4.35), 404

295, 385 (sh), 404,

441, 466, 499

8000

57

(4.54), 426 (4.49)

425

3 323 (3.94), 397 (4.29)

325, 398

453

3100

36

4 303 (4.11), 326 (sh, 3.88), 403 (sh, 4.20),

305, 326 (sh), 403

468, 493, 529

1000

62

472, 499, 543

1200

48

425 (4.47), 447 (4.49) 5 304 (4.10), 328 (3.87), 428 (4.46), 447

(sh), 425, 448 305, 330 (sh), 430,

4

(4.45) a

450

Measured in dichloromethane or ethanol at room temperature. bDss = Stokes shift. cUsing coumarin

102/153 as references.

5

Figure 3. Normalized (nm) absorption (green), excitation (blue), emission (red) profiles of 1–5 (dichloromethane, c ≈ 1.5 × 10-6 molL-1.

3. Conclusions Difluoroboron complexes of unsymmetric [N,O] and [N,N] chelate ligands based on pyridyl or quinolyl enolates or enamides can be synthesized easily. They are efficient fluorophores with potential applications as biolabels, especially due to their convenient functionalization by simple condensation reactions with primary amines. From a materials design viewpoint, in particular pyridyl-enamido complexes like structure 3, synthesized easily by simple condensation of -pyridylketones with amine derivatives, represent new fluorophores with considerable scope in future biolabeling applications.

4. Experimental 4.1. General methods All reactions and manipulations of air-sensitive compounds were carried out under dry argon by using Schlenk techniques, glove-box techniques and/or vacuum line techniques. Solvents were dried prior to use by common methods in organometallic chemistry. Chemicals were commercially obtained and used as received. Starting materials (ligands for complexes 1–5) were prepared as recently published [14]. Melting points were measured with a Leica Galen III Kofler microscope. 1H, 11

B, 13C and 19F NMR spectra were recorded using Bruker Avance DPX 300 (300 MHz) or Bruker

Avance III (600 MHz) instruments. Chemical shifts are reported in ppm relative to Si(CH3)4 (1H, 13

C), BF3•Et2O (11B) or CFCl3 (19F), respectively, and coupling constants (J) are given in Hz. Mass

spectra were obtained on a Finnegan MAT 95 instrument. IR spectra were measured using a THERMO Nicolet 5700 ATR FT spectrometer. UV-Vis spectra were obtained using a Perkin Elmer XLS+ instrument. Fluorescence emission spectra were obtained using a Varian Cary Eclipse instrument or a Horiba Jobin Yvon Fluorolog-3. Fluorescence quantum yields (

F)

were measured using

coumarin 102 and coumarin 153 standards [17]. Single crystal X-ray measurements (Table 2) and structure determinations were performed with a Nonius Kappa CCD diffractometer, equipped with

6

graphite-monochromatized Mo-Ka-radiation ( = 0.71073 Å) and a nominal crystal to area detector distance of 36 mm. Intensities were integrated using DENZO and scaled with SCALEPACK [18]. Several scans in the - and -directions were made to increase the number of redundant reflections, which were averaged in the refinement cycles. This procedure replaces an empirical absorption correction. The structures were solved with direct methods (SHELXS-86) and refined against F2 (SHELX-97) [19]. Hydrogen atoms at carbon atoms were added geometrically and refined using a riding model. All non-hydrogen atoms were refined with anisotropic displacement parameters.

4.2. Synthesis and characterization of 1 A Schlenk vessel was charged with a magnetic stirring bar, dry toluene (15 mL) and 2pyridylacetophenone [14] (250 mg, 1.27 mmol). After the mixture was cooled to -70 °C, n-butyl lithium (1.27 mmol, 0.80 ml of a 1.6 molar solution in hexane) was added by syringe. The stirred mixture was allowed to warm to room temperature and boron trifluoride diethyl etherate (1.60 mmol, 0.20 ml of a 46% solution in diethyl ether) was added. After the resulting yellow suspension was refluxed for 1 hr, all volatiles were removed on a vacuum line. Work-up: The residue was dissolved in a mixture of dichloromethane and hexane (v/v = 3/1), precipitated lithium fluoride was filtered off, and the product was crystallized. Yield: 280 mg, 89%. M.p.: 102 °C. IR: 3097, 1630, 1545, 1490, 1453, 1375, 1261, 1169, 1125, 1082, 1026, 909, 802, 771, 686 cm-1. 1H NMR (300 MHz, CD2Cl2): 8.29 (m, 1H), 7.81 (m, 3H), 7.38 (m, 3H), 7.25 (d × d, J = 7.99 Hz, J = 6.0 Hz, 2H), 6.34 (s, 1H). 13C NMR (75 MHz, CD2Cl2): 162.7, 152.0, 142.1, 140.2, 134.7, 131.4, 129.1, 126.8, 123.2, 121.1, 93.8. 11B NMR (96 MHz, CD2Cl2): 0.93 (t, J = 15.5 Hz). 19F NMR (565 MHz, CD2Cl2): -142.5 (q, 1:1:1:1, J = 15.3 Hz). HRMS (FAB) calcd for C13H10BF2NO [M+] 245.0820; found 245.0877. UV-vis (CH2Cl2): (CH2Cl2):

exc

= 385 nm:

max

max

= 397 nm, = 14700 M-1cm-1. Fluorescence spectroscopy

= 450 nm;

F

= 33%. Single crystal structure analysis of 1: Table 2,

supporting information. 4.3. Synthesis and characterization of 2 A Schlenk vessel was charged with a magnetic stirring bar, dry toluene (15 mL) and 2quinolylacetophenone [14] (250 mg, 1.01 mmol). After the mixture was cooled to -70 °C, n-butyl lithium (1.01 mmol, 0.65 ml of a 1.6 molar solution in hexane) was added by syringe. The stirred mixture was allowed to warm to room temperature and boron trifluoride diethyl etherate (2.0 mmol, 0.25 ml of a 46% solution in diethyl ether) was added. After the resulting yellow suspension was refluxed for 1 hr, all volatiles were removed on a vacuum line. Work-up: The residue was dissolved 7

in a mixture of dichloromethane and hexane (v/v = 3/1), precipitated lithium fluoride was filtered off, and the product was crystallized as yellow crystals. Yield: 245 mg, 82%. M.p.: 233 °C. IR: 1599, 1541, 1483, 1219, 1109, 1080, 1055, 844, 748, 677 cm-1. 1H NMR (300 MHz, CD2Cl2): 8.67 (d, J = 9.16 Hz, 1H), 8.12 (d, J = 8.73 Hz, 1H), 7.90 (m, 2H), 7.72 (m, 2H), 7.43 (m, 3H), 7.23 (d, J = 8.72 Hz, 1H), 6.39 (s, 1H). 13C NMR (75 MHz, CD2Cl2): 165.0, 154.6, 142.1, 132.8, 132.1, 129.2, 127.2, 127.1, 123.1, 123.0, 121.9, 94.7. 11B NMR (96 MHz, CD2Cl2): 1.80 (t, J = 18.1 Hz). 19

F NMR (565 MHz, CD2Cl2): -130.9 (q, 1:1:1:1, J = 17.8 Hz). HRMS (FAB) calcd for

C17H12BF2NO [M+] 295.0978; found 295.0926. UV-vis (CH2Cl2): 1

. Fluorescence spectroscopy (CH2Cl2):

exc

= 385 nm:

max

max

= 404 nm, = 34900 M-1cm-

= 441, 466, 499 nm;

F

= 57%. Single

crystal structure analysis of 2: Figure 1, Table 2, supporting information.

4.4. Synthesis and characterization of 3 A Schlenk vessel was charged with a magnetic stirring bar, dry toluene (15 mL) and 1-phenyl-2-(2pyridyl)-vinyl)-2,6-dimethylphenylamine [14] (375 mg, 1.28 mmol). After the mixture was cooled to -70 °C, n-butyl lithium (1.28 mmol, 0.80 ml of a 1.6 molar solution in hexane) was added by syringe. The stirred mixture was allowed to warm to room temperature and boron trifluoride diethyl etherate (1.60 mmol, 0.20 ml of a 46% solution in diethyl ether) was added. During the addition, at first the solution turned red and changed later in color to a yellow suspension. After refluxing for 1 hr, all volatiles were removed on a vacuum line. Work-up: The residue was dissolved in a mixture of dichloromethane and hexane (v/v = 3/1), precipitated lithium fluoride was filtered off, and the product was crystallized. Yield: 270 mg, 60.5%. M.p.: 174–176 °C. IR: 3613, 3566, 2920, 2860, 1625, 1527, 1489, 1452, 1410, 1268, 1062, 1030, 1012, 970, 770, 698 cm-1. 1H NMR (300 MHz, CD2Cl2): 8.25 (d, J = 6.02 Hz, 1H), 7.72 (d × d, J = 7.18 Hz, J = 8.40 Hz, 1H), 7.32 (m, 1H), 7.30 (d, J = 1.66 Hz, 1H), 7.26 (m, 2H), 7.20 (d, J = 7.45 Hz, 2H), 7.06 (d × d, J = 6.90 Hz, J = 6.41 Hz, 1H), 6.91 (m, 3H), 5.72 (s, 1H), 2.18 (s, 6H). 13C NMR (75 MHz, CD2Cl2): 159.7, 151.6, 141.5, 139.2, 138.3, 137.8, 137.4, 129.5, 128.6, 128.5, 128.1, 126.7, 122.6, 117.6, 95.0, 19.4. 11B NMR (96 MHz, CD2Cl2): 1.35 (t, J = 30.2 Hz). 19F NMR (565 MHz, CD2Cl2): -139.2 (q, 1:1:1:1, J = 29.1 Hz). HRMS (FAB) calcd for C21H19BF2N2 [M+] 348.1604; found 348.1611. UV-vis (CH2Cl2): nm, = 19300 M-1cm-1. Fluorescence spectroscopy (CH2Cl2):

exc

= 385 nm):

max

max

= 453 nm;

= 397 F

=

36%. Single crystal structure analysis of 3: Table 2, supporting information.

4.5. Synthesis and characterization of 4 8

A Schlenk vessel was charged with a magnetic stirring bar, dry toluene (15 mL) and 1-phenyl-2-(2quinolyl)-vinyl)-2,6-dimethylphenylamine [14] (315 mg, 0.90 mmol). After the mixture was cooled to -70 °C, n-butyl lithium (0.90 mmol, 0.575 ml of a 1.6 molar solution in hexane) was added by syringe. The stirred mixture was allowed to warm to room temperature and boron trifluoride diethyl etherate (0.90 mmol, 0.13 ml of a 46% solution in diethyl ether) was added. During the addition, at first the solution turned red and changed later in color to a yellow suspension. After refluxing for 1 hr, all volatiles were removed on a vacuum line. Work-up: The residue was dissolved in a mixture of dichloromethane and hexane (v/v = 3/1), precipitated lithium fluoride was filtered off, and the product was crystallized. Yield: 230 mg, 64%. M.p.: 204 °C. IR: 2962, 1581, 1546, 1483, 1391, 1293, 1204, 1047, 869, 774, 733 cm-1. 1H NMR (300 MHz, CD2Cl2): 8.16 (d, J = 6.02 Hz, 1H), 7.57 (d, J = 8.80 Hz, 1H), 7.33 (d, J = 6.5 Hz, 1H), 7.25 (m, 1H), 7.07 (d, J = 7.02 Hz, 1H), 6.89 (m, 2H), 6.81 (m, 3H), 6.78 (m, 2H), 6.60 (d, J = 5.91 Hz, 2H), 5.40 (s, 1H), 1.85 (s, 6H). 13C NMR (75 MHz, CD2Cl2): 162.5, 153.2, 139.4, 137.3, 131.9, 129.9, 129.5, 129.2, 128.7, 128.6, 128.3, 128.3, 127.5, 126.3, 125.9, 125.8, 122.8, 122.4, 97.1, 19.5. 11B NMR (96 MHz, CD2Cl2): 2.64 (t, J = 33.3 Hz). 19

F NMR (565 MHz, CD2Cl2): -126.0 (q, 1:1:1:1, J = 33.5 Hz). HRMS (FAB) calcd for

C25H21BF2N2 [M+] 398.1760; found 398.1765. UV-vis (CH2Cl2): Fluorescence spectroscopy (CH2Cl2):

exc

= 385 nm,

max

max

= 447 nm, = 30800 M-1cm-1.

= 468, 493, 529 nm;

F

= 62%. Single

crystal structure analysis of 4: Figure 2, Table 2, supporting information.

4.6. Synthesis and characterization of 5 A Schlenk vessel was charged with a magnetic stirring bar, dry toluene (15 mL) and 1-phenyl-2-(2quinolyl)-vinyl)-2,6-diisopropylphenylamine [14] (323 mg, 0.79 mmol). After the mixture was cooled to -70 °C, n-butyl lithium (0.79 mmol, 0.50 ml of a 1.6 molar solution in hexane) was added by syringe. The stirred mixture was allowed to warm to room temperature and boron trifluoride diethyl etherate (0.85 mmol, 0.12 ml of a 46% solution in diethyl ether) was added. During the addition, at first the solution turned red and changed later in color to a yellow suspension. After refluxing for 1 hr, all volatiles were removed on a vacuum line. Work-up: The residue was dissolved in a mixture of dichloromethane and hexane (v/v = 3/1), precipitated lithium fluoride was filtered off, and the product was crystallized. Yield: 500 mg, 84%. M.p.: 238 °C. IR: 3617, 3563, 2962, 2867, 1625, 1597, 1542, 1482, 1427, 1320, 1049, 991, 871, 828, 763, 695, 642 cm-1. 1H NMR (300 MHz, CD2Cl2): 8.55 (d, J = 8.89 Hz, 1H), 7.91 (d, J = 8.91 Hz, 1H), 7.65 (d, J = 7.90 Hz, 1H), 7.56 (m, 1H), 7.38 (d, J = 7.31 Hz, 1H), 7.17 (m, 4H), 7.13 (m, 3H), 7.00 (d, J = 7.77 Hz, 2H), 5.91 (s, 1H), 2.96 (sept, J = 6.73 Hz, 2H), 1.06 (d, J = 6.67 Hz, 6H), 0.87 (d, J = 6.82 Hz, 6H). 13C NMR (75 9

MHz, CD2Cl2): 162.6, 153.2, 147.3, 146.6, 141.4, 130.7, 129.7, 129.6, 129.2, 128.8, 128.6, 128.3, 128.1, 125.8, 125.4, 124.5, 122.8, 122.2, 98.6, 29.1, 25.7, 23.7. 11B NMR (96 MHz, CD2Cl2): 2.29 (t, J = 32.7 Hz). 19F NMR (565 MHz, CD2Cl2): -128.6 (q, 1:1:1:1, J = 32.8 Hz). HRMS (FAB) calcd for C29H29BF2N2 [M+] 454.2386; found 454.2353. UV-vis (CH2Cl2): M-1cm-1. Fluorescence spectroscopy (CH2Cl2):

exc

= 385 nm,

max

max

= 428 nm, = 29000

= 472, 499, 543 nm;

F

= 48%.

Single crystal structure analysis of 5: Table 2, supporting information.

Table 2. Crystallographic data Compound

1

Formula

C13H10BF2NO C17H12BF2NO C21H19BF2N2 C25H21BF2N2 C29H29BF2N2

M

245.03

295.09

348.19

398.25

454.35

Crystal system

monoclinic

monoclinic

monoclinic

monoclinic

triclinic

Space group

P21/n

P21/n

P21/c

P21/c

P 1

a [Å]

7.2594(2)

7.7221(1)

15.7874(5)

14.2239(3)

8.5911(2)

b [Å]

12.6262(3)

12.0575(4)

15.5678(6)

18.0454(4)

9.7455(3)

c [Å]

12.6109(4)

14.4182(4)

7.4655(2)

7.8166(2)

16.0685(5)

[°]

90

90

90

90

76.634(2)

[°]

101.226(1)

95.069(2)

93.974(2)

101.076(1)

89.907(2)

[°]

90

90

90

90

68.735(2)

Z

4

4

4

4

2

V [Å3]

1133.78(5)

1337.22(6)

1830.42(10)

1968.96(8)

1214.74(6)

T [K]

233(2)

233(2)

233(2)

233(2)

233(2)

3.01–24.99

2.21–26.00

1.84–24.98

2.26–26.00

2.62–25.00

Data

6284

8748

9521

12669

6860

Unique data

1980

2592

3222

3849

4235

Rint

0.0209

0.0171

0.0228

0.0211

0.0169

R1

0.0427

0.0398

0.0619

0.0427

0.0467

wR2

0.1019

0.0991

0.1292

0.0992

0.1002

Parameters

164

199

256

274

308

GooF

1.038

1.040

1.054

1.049

1.024

0.179/-0.157

0.198/-0.186

0.172/-0.158

0.168/-0.149

range [°]

peak/hole [e/Å3] 0.250/-0.216

2

3

4

5

10

Appendix A. Supplementary material CCDC-929334 (1), 929335 (2), 929336 (3), 929337 (4), 929338 (5) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

References [1] BODIPY is short for "boron-dipyrromethene", 4-bora-3a,4a-diaza-s-indacene (IUPAC nomenclature); the acronym is a trade name for "F-BODIPY", 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene: Haugland, R. P.; The Handbook. A Guide to Fluorescent Probes and Labeling Technologies, Molecular Probes, Invitrogen, Carlsbad, CA, 10th ed., 2005. [2] N. Boens, V. Leen, W. Dehaen, Chem. Soc. Rev. 41 (2012) 1130–1172. [3] G. Ulrich, R. Ziessel, A. Harriman, Angew. Chem. Int. Ed. 47 (2008) 1184–1201. [4] A. Loudet, K. Burgess, Chem. Rev. 107 (2007) 4891–4932. [5] J.F. Araneda, W.E. Piers, B. Heyne, M. Parvez, R. McDonald, Angew. Chem. Int. Ed. 50 (2011) 12214–12217. [6] Y. Yang, X. Su, C.N. Caroll, I. Aprahamian, Chem. Sci. 3 (2012) 610–613. [7] Y. Kubota, S. Tanaka, K. Funabiki, M. Matsui, Org. Lett. 14 (2012) 4682–4685. [8] R.-Z. Ma, Q.-C. Yao, X. Yang, M. Xia, J. Fluor. Chem. 137 (2012) 93–98. [9] F. Qiao, A. Liu, Y. Zhou, Y. Xiao, P.O. Yang, J. Mater. Sci. 44 (2009) 1283–1286. [10] J. Feng, B. Liang, D. Wang, L. Xue, X. Li, Org. Lett. 10 (2008) 4437–4440. [11] Y. Zhou, Y. Xiao, S. Chi, X. Qian, Org. Lett. 10 (2008) 633–636. [12] Y. Zhou, Y. Xiao, D. Li, M. Fu, X. Qian, J. Org. Chem. 73 (2008) 1571–1574. [13] L. Bourget-Merle, M.F. Lappert, J.R. Severn, Chem. Rev. 102 (2002) 3031–3065. [14] M. Graser, H. Kopacka, K. Wurst, T. Müller, B. Bildstein, Inorg. Chim. Acta (2013), in press. [15] B.X. Qian, S.W. Baek, M.R. Smith, Polyhedron 18 (1999) 2405–2414. [16] A.F. Rausch, U.V. Monkowius, M. Zabel, Y. Yersin, Inorg. Chem. 49 (2010) 7818–7825. [17] J.N. Dewas, G.A. Crosby, J. Phys. Chem. 75 (1971) 992–1024. [18] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1997) 307. [19] G.M. Sheldrick, SHELXTL V.5.1, Bruker Analytical X-ray Instruments Inc, Madison, USA, 1997.

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Synopsis for graphical table of contents: Difluoroboron complexes of unsymmetric [N,O] and [N,N] chelate ligands based on pyridyl or quinolyl enolates or enamides can be synthesized easily. They are efficient fluorophores with potential applications as biolabels, due to their convenient functionalization by simple condensation reactions with primary amines.

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Highlights for TOC:

Simple, desymmetrized fluorophores BODIPY-like photophysical properties potentially useful biolabel precursors

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