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The role of crystal packing and weak intermolecular interactions in the solid state fluorescence of N-methylpyrazoline derivatives Bogumi#a Kupcewicz, and Magdalena Malecka Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b00512 • Publication Date (Web): 16 Jun 2015 Downloaded from http://pubs.acs.org on June 18, 2015

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Crystal Growth & Design

The role of crystal packing and weak intermolecular interactions in the solid state fluorescence of N-methylpyrazoline derivatives Bogumiła Kupcewicz1 , Magdalena Małecka2*

1

Department of Inorganic and Analytical Chemistry, Faculty of Pharmacy, Collegium Medicum

in Bydgoszcz, Nicolaus Copernicus University in Torun, Jurasza 2, Bydgoszcz, 85-089, Poland, 2

Department of Theoretical and Structural Chemistry, Faculty of Chemistry, University of Łódź,

Pomorska 153/165, Łódź, 90-236, Poland,

KEYWORDS crystal structure, fluorescence, Hirshfeld surface, intermolecular interactions

ABSTRACT Six compounds containing N-methylpyrazoline ring fused with flavanone derivatives have been synthesized and characterized by X-ray structural studies and fluorescence spectroscopy. The influence of molecular arrangement on the emission properties, including fluorescence lifetime and quantum yield, was discussed on the basis of structural data and detailed analysis of the Hirshfeld surfaces. The correlation of fluorescence and crystal packing reveals that 1 ACS Paragon Plus Environment


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solid state emission of this class of compounds strongly depends on intermolecular interactions present in different crystal lattice. It was observed that the inverse of fluorescence lifetime (1/τavg) is linearly dependent on a percentage contribution of H…O and H…N contacts in the Hirshfeld surface. In addition, the lipophilicity (log P) of these compounds is related to contribution of C…H interactions as well as non-covalent bonding involving a halogen atom.

INTRODUCTION The design of new solid luminescent materials with desirable optical and physical properties has drawn a great attention over recent years owing to their potential use in material science1,2 and biology.3,4,5 Several conditions, such as simple route of synthesis, photochemical stability, color purity and high quantum efficiency, are essential for the development of new luminescent compounds. Understanding the role of self-assembly and interactions of molecules in determining fluorescent properties is an important goal in material sciences.6,7 Fluorescence of organic compounds in the solid state depends not only on the structure of the fluorophore, but also on the architecture of the crystal packing and intermolecular interactions.8,9 Supramolecular aggregations may be achieved with various interactions, such as hydrogen bonds (O-H...O, N-H...O, C-H...O), π-π stacking and weak noncovalent forces.10,11 It has been revealed that strong intermolecular π-π interaction is a principal factor of fluorescence quenching in the solid state. Pyrazoline are five-membered nitrogen-containing heterocyclic compounds which show strong blue fluorescence and are excellent hole-transporters.12,13 In this study we have focused on the coupling of two moieties, 3-arylideneflavanone and pyrazoline to develop a new organic fluorescent material and to understand the role of crystal packing and different weak intermolecular interactions in obtaining efficient fluorescence in solid-state.

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To gain quantitative data of the contributions of various intermolecular contacts in crystals Hirshfeld surface has been calculated. Hirshfeld surface analysis also makes it possible to identify and highlight weaker and longer contacts other than hydrogen bonds. The 2D fingerprint plots give a quantitative analysis of the nature and type of interaction.

EXPERIMENTAL SECTION Materials and methods All reagents and solvents were obtained from commercial sources and used as received. The compounds I – VI (Table 1) were synthesized according to the procedure described in Supplementary data file. Melting points of the compounds were determined on Büchi540 apparatus and were uncorrected. The FTIR spectra (4000–400 cm-1) were recorded on a Shimadzu 8400S spectrometer as KBr pellets. The 1H NMR spectra were recorded using Varian Gemini 200 BB, CDCl3, 200 MHz.

Data collection, structure solution and refinement Data for compound I and III, were measured from single crystals using Oxford Diffraction Xcalibur CCD diffractometer at T=100(2) K with monochromatic MoKα radiation (λ=0.71073 Å) Data for V and VI were measured using CuKα radiation (λ=1.54178 Å) at T=100(2) K using SuperNova Dual diffractometer with Atlas S2 CCD detector. Data reduction in four cases were done using CrysAlis software14. Data were corrected for absorption correction, type of multi-scan (compounds I and III) and Gaussian (compounds V and VI). Diffraction data for compound II and IV were collected at the F1 beamline of storage ring DORIS III at HASYLAB/DESY in Hamburg. The beamline is equipped with Huber 4-circle diffractometer with MARCCD 165. The



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temperature was maintained at 150(1) K and the wavelength was λ= 0.6000 Å. The integration, data reduction and scaling of diffracted intensities were done using the XDS package version 2009.15 All structures were solved by direct methods with SHELXL-201316 and further refined on F2 using SHELXL-2013. A full matrix least-squares refinement procedure was used. Agreement 2

factors

(1 = ∑||�� − �� ||/ ∑|�� |, 2

2

2

1⁄ 2

2

2

2

1⁄ 2

and

2 = {∑[ (�� − �� ) ] / ∑ (�� )} are cited, where n is the number of reflections and p

�� = {∑[ (�� − �� ) ]/(� − �)} is the total number of parameters refined. The positions of hydrogen atoms were calculated from known geometry and treated as riding, where the isotropic thermal parameters of these hydrogen atoms were fixed as the multiple of the equivalent isotropic thermal parameters of the parent atoms. Further experimental details and crystallographic data are presented in Table 2. Other calculations (geometry parameters) and graphics were done using PLATON,17 DIAMOND,18 Mercury.19

Hirshfeld surface analysis The Hirshfeld surfaces20 were generated using Crystal Explorer 3.1 20, 21,22 based on the results from X-ray studies. In Crystal Explorer, the internal consistency is important when comparing structures; therefore, bond lengths of hydrogen atoms were normalized to standard neutron values (C–H = 1.083 Å, O–H = 0.983 Å, N–H = 1.009 Å).23 The normalized contact distance(dnorm) based on both de (the distance from a point on the surface to the nearest atom outside the surface) and di (the distance from a point on the surface to the nearest atom inside the surface) and van der Waals radii of the atom, given by eq (1), enables the identification of the regions of particular importance to intermolecular interactions.24 The value of dnorm is negative (red color) or positive (blue color) when intermolecular contacts are shorter or longer than van der Waals separations, respectively. ACS Paragon Plus Environment

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� − ��

��

��

+=

�� − ��

�

(1)

�

= Fluorescence measurements Solid-state fluorescence spectra as excitation-emission matrix (EEM) were recorded on a Shimadzu spectrofluorophotometer RF-5301 equipped with the solid sample holder. Fluorescence lifetimes were determined using time-correlated single photon counting. The samples were excited with a PicoHarp PDL800-D pulsed diode with a centre wavelength of 375 nm. The emission was monitored at 440 nm. IRF was measured at excitation wavelength using a scattering Al slab. The intensity data were convoluted with the instrument response and evaluated with the software package FluoFitPro (PicoQuant). Photoluminescence quantum yield was measured using an FLS980 spectrofluorimeter (Edinburgh Instruments), equipped with an integrating sphere.



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Table 1. View of molecular structure with atom numbering scheme of compound I-VI. On the scheme of compound I all rings are labeled (similarly for all compounds).

2-ethyl-3,4-diphenyl-2,3,3a,4-tetrahydrochromeno[4,3-c]pyrazol-8-ol (compound I)

2-methyl-3,4-diphenyl-2,3,3a,4-tetrahydrochromeno[4,3-c]pyrazole (compound II)

3-(4-bromo-phenyl)-2-methyl-4-phenyl2,3,3a,4-tetrahydro-chromeno[4,3-c]pyrazole (compound III)

3-(4-chloro-phenyl)-2-methyl-4-phenyl2,3,3a,4-tetrahydro-chromeno[4,3c]pyrazole (compound IV)

3-(4-hydroxy)-2-methyl-4-phenyl-2,3,3a,4tetrahydro-chromeno[4,3-c]pyrazole (compound V)

3-(3-nitryl-phenyl)-2-methyl-4-phenyl2,3,3a,4-tetrahydro-chromeno[4,3c]pyrazole (compound VI)


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Table 2. Crystal data, data collection, spherical and multipole refinement of (I) - (VI). Compound

I

II

III

IV

V

VI

Chemical formula

C23H20N2O2

C23H20N2O

C23H19BrN2O

C23H19ClN2O

C23H22N2O3

C24H19N3O

Mr

356.41

340.41

419.31

374.85

374.42

365.42

Cell setting, space group

Monoclinic, P21/c 11.796(1), 6.181(1), 25.737(1)

Triclinic, P -1 8.947(6), 10.051(3), 11.786(3)

Triclinic, P -1 9.171(1), 10.0227(1), 12.071(1)

Triclinic, P -1 8.882(1), 10.347(1), 12.847(1)

Orthorhombic, Pbca 5.980(1), 21.585(1), 30.309(1)

Triclinic, P -1 8.947(1), 12.489(1), 16.866(1)

V (Å3)

90.0, 100.79(1), 90.0 1843.2(1)

103.9(1), 93.7(1), 117.4(1), 894.0(7)

92.4(1), 94.0(1), 116.7(1) 984.9(1)

112.9(1), 107.4(1), 68.4(1) 994.4(3)

3912.4(2)

100.52(1), 90.24(1), 91.52(1) 1852.2(1)

Z

4

2

2

2

8

4

Dx (Mg m-3)

1.284

1.430

1.414

1.252

1.271

1.310

Temperature (K)

100

150

100

150

100

100

Radiation type (Å)

0.71073

0.6000(2) (synchrotron)

0.71073

0.6000(2) (synchrotron)

1.54184

1.54178

µ (mm-1)

0.083

0.078

0.090

0.133

0.683

0.645

Crystal form, colour

plate, colorless

plate, colorless needle, colorless

block, colorless

needle, colorless

needle, colorless

Crystal data

a, b, c (Å)

α, β, γ (°)

-

7



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Crystal size (mm)

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0.36×0.11×0.044

0.4×0.2×0.2

0.42×0.1×0.08

0.45×0.4×0.4

0.26×0.03×0.02

0.87×0.06×0.03

Diffractometer

Xcalibur diffractometer

Huber diffractometer MAR165CCD detector *

Xcalibur diffractometer

Huber diffractometer MAR165CCD detector *

SuperNova Dual, AtlasS2

SuperNova Dual, AtlasS2

Data collection method

ω scans

ϕ scans

ω scans

ϕ scans

ω scans

ω scans

No. of measured unique reflections

24902, 3618

24851, 3135

10692, 3385

34674, 3488

7263, 3417

10490, 6470

2171

2805

3052

3199

2908

5732

Rint

0.0718

0.0306

0.0198

0.0246

0.0263

0.0281

θmax (°)

26.00

21.19

25.0

21.19

66.57

66.59

Overall completeness [%]

99.8

95.8

97.8

95.5

99.1

99.0

Refinement on

F2

F2

F2

F2

F2

F2

All data

3618

3135

3385

3488

3417

6470

R, wR [I>2σ(I)]

0.0392, 0.0747

0.0370, 0.0928 0.0257, 0.0712

0.0370/0.0956

0.0354/ 0.0976

0.0396/ 0.0992

R, wR (all data)

0.0811, 0.0817

0.0416, 0.0961 0.0288, 0.0716

0.0400/0.0979

0.0435/0.0909

0.0449/0.1042

Goodness of fit

0.841

1.045

1.173

1.023

0.945

1.041

No. of parameters

246

249

245

249

266

508

Data collection

Observed I>2σ(I)

data

and with

Refinement


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∆ρmax, ∆ρmin (eÅ-3)

0.200, -0.209

0.237, -0.158

0.552, -0.508

* diffractometer at Hasylab/DESY, beamline F1


0.205/-0.328

0.255, -0.184

0.229, -0.242


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Results and discussion Molecular structure of compounds I-VI. The main body of presented structures consists of three fused rings: pyrazole (ring 1), tetrahydropyran (ring 2) and benzene (ring 3). The pyrazole and tetrahydropyran rings adopt envelope conformation, with puckering parameters in the range: Q = 0.29 to 0.34 Å and Q = 0.41 to 0.52 Å, for five-membered and six-membered rings, respectively. It is similar to two published structures.25,26The tetrahydropyran ring is substituted in position 2 by the phenyl ring (ring 4) and is approximately perpendicular to the main fragment of the molecule with the dihedral angles of :75.78°, 83.99°, 87.15°, 80.78°, 84.68° and 85.45°/89.55° respectively for I, II, III, IV, V and VI (molecule A/B). The substituents in position 3 are also nearly perpendicular to the main body of molecule: dihedral angle between main 13-membered ring system and benzene ring are: 69.05°, 70.53°, 72.40°, 75.01°, 78.68°, 58.36°/60.96°, which gives nearly parallel rings substituted at atom C2 and C31 for all compounds except compound VI, where dihedral angle between benzene rings are: 44.41°/44.53°. Compounds I, III, IV, V, VI vary by different substituent at atom C31; it is benzene, chlorobenzene, bromobenzene, p-hydroxybenzene, m-cyanobenzene and compounds I and II differ by hydroxyl group in position 6 in the main fragment of the compounds investigated. Compound VI crystallizes in triclinic system with two molecules in the asymmetric unit. In the packing structure of crystal I molecules adopt dimers via a pair of C8-H8…O1i intermolecular hydrogen bonds (symmetry code (i): -x, -y, -z) resulting in R22(8) motif according to graph-set notation (Figure 1).27 Further dimers are linked by O2-H2…N2ii (symmetry code (ii): -x, -½+y, ½-z) intermolecular hydrogen bonds and form chain C(7) along c axis. The long centroid distance dC-C = 5.232 Å between parallel phenyl rings (ring 4) with the short interplanar separation dπ…π = 2.978 Å, and the lateral displacement (R = 4.302 Å) indicates that there is no π-π interaction


10

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in the crystal lattice. The lack of π…π interactions suggests that C-H…O, O-H…N and C-H…π (C7-H7…Cg4i and C31-H31…Cg3iii, Table 3) interactions act as the principal driving forces for the molecular packing. The crystal packing in the unit cell exhibits the lack of the layered structure (Fig 2).

Figure 1. Crystal structure of I with hydrogen bonding (cyan dotted lines) showing dimers and chains propagating in [001] direction. The red lines represent the interplanar separations (dπ...π) and centroid distance (dC-C). Green line represents lateral displacement.

Figure 2. Molecular packing of I in the unit cell in the bc, ac, ab plane, respectively. H-atoms are omitted for clarity.


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The crystal packing of molecules II (Figure 3) is dominated by C11-H11A…O1i intermolecular hydrogen bonds (symmetry code (i): -1+x, y, z) and C-H…π interaction (Table 3). The interaction C11-H11A…O1i links the molecules into chains that are parallel to a axis and have a graph-set motif C(7).27 Although, there is no evident π…π interaction between molecules (dC-C = 5.336 Å, dπ…π = 3.3178 Å, the lateral displacement equals R=4.391 Å) (Figure 3), the crystal packing along a axis shows favoured head to tail layered arrangement (Figure 4). Weak C-H…π interactions are also observed in the crystal lattice (C11-H11C…Cg4i, and C26-H26…Cg3ii, Table 3).

Figure 3. Molecular packing of II with hydrogen bonding (cyan dotted lines). Between phenyl rings the red lines represent the interplanar separations (dπ...π) and centroid distance (dC-C). Green line represents lateral displacement.


12

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Figure 4. Molecular packing of II in the unit cell in the bc, ac, ab plane, respectively. H-atoms are omitted for clarity. In the solid state of structure III molecules are self-assembled into dimers (Figure 5) through C36-H36…N2i hydrogen bond interaction (symmetry code (i): 1-x, 1-y, 1-z). This motif can be described using graph-set notation as R22 (14).27 Furthermore, the C-H…π interactions are also well evident in the crystal structure (C11-H11A…Cg4ii and C25-H25…Cg3iii, Table 3). The shortest centroid distance dC-C= 5.500 Å was found between parallel phenyl rings (ring 5), however the interplanar separation dπ…π = 2.926 Å and the large lateral displacement equal R=4.657 Å (Figure 5) does not indicate π…π interaction in the crystal lattice. Nevertheless, the molecules are organized into the layer structure along a axis (Figure 6a) as it was found for structure II. It is worth mentioning, that in the crystal lattice one can observe bifurcated C7-H7…Br1iii (symmetry code (iii): -x, 1-y, 1-z) interaction within the sum of van der Walls radii + 0.1Å. The connected molecules are forming chain propagating into [011] direction (Figure 7).


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Figure 5. Crystal structure of III with hydrogen bonding (cyan dotted lines) showing. The red lines represent the interplanar separations (dπ...π) and centroid distance (dC-C). Green line represents lateral displacement.

Figure 6. Molecular packing of III in the unit cell in the bc, ac, ab plane, respectively. H-atoms are omitted for clarity.


14

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Figure 7. The fragment of molecular structure of III with chain formed by C7-H7…Br1iii (symmetry code (iii): -x, 1-y, 1-z) interaction propagating along [011] direction.

In the case of structure IV again the molecules are organized into dimers (Figure 8) through the C34-H34…N2i hydrogen bond interaction (symmetry code (i): -x, 2-y, 2-z). Dimers can be described as R22(14) according to graph-set notation.27 Further stabilization of IV is produced via weak C-H…π (C23-H23…Cg3ii, (symmetry code (ii): 1-x, 2-y, 2-z) and Cl1…Cl1iii interactions (symmetry code (iii): -x, 3-y, 1-z); with Cl1…Cl1iii distance equal 3.232 Å (Figure 9). Although the supramolecular architecture of compound IV is also like a layered structure along the a axis (Figure 9), the distances between phenyl rings are much shorter than in structures I, II, III. None of the rings are parallel, but the shorter dC-C distances are: 4.621 Å, 4.538 Å, 4.621 Å for Cg4…Cg5 at 1+x, y, z, Cg4…Cg5 at x, y, z and Cg5…Cg4 at -1+x, y, z, respectively.


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Figure 8. Packing of molecules in the crystal IV with hydrogen bond (cyan dotted lines) which form dimers. The red lines represent the centroid distances (dC-C) of the adjacent phenyl rings.

Figure 9. Molecular packing of IV in the unit cell in the bc, ac, ab plane, respectively. H-atoms are omitted for clarity. On the left figure Cl1…Cl1iii interactions between two molecules are visible (green line). Compound V crystalizes in orthorhombic Pbca group together with one water molecule in the asymmetric unit. In the crystal packing of compound V, molecules are linked by different hydrogen bonds (Table 3) forming several aggregates. The O3-H3A…N2i (symmetry code (i): ½-x, ½+y, z) hydrogen bond connects molecules via water molecule in chain C(11) according to graph-set


16

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motifs.27 Further O3-H3B…O2ii (symmetry code (ii): -½-x, y, ½-z) and O2-H20…O3 hydrogen bonds interact between molecule and solvent. Moreover, weak C8-H8…O1iii (symmetry code (iii): -x, -y, -z) hydrogen bond forms two molecules into dimers, where hydrogen bond motif could be described as ring R22(8). In comparison with II, III and IV supramolecular structure of V is not layered. However, the molecules form ribbons along a axis (Figure 10b) and a zigzag chain, which is further extended along b axis (Figure 11c). In the crystal lattice C7-H7…π interaction is also evident (Table 3, and Figure 10b).

Figure 10. a) Crystal packing of structure V with hydrogen bonding (cyan dotted lines); b) the CH…π interaction between two molecules (Cg4 is a centroid of C21-C26 ring).


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Figure 11. Molecular packing of V in the unit cell in the bc, ac, ab plane, respectively. H-atoms are omitted for clarity. Compound VI crystalizes in triclinic P-1 group with two independent molecules in the asymmetric unit. The geometry parameters of two molecules do not differ significantly, however phenyl rings substituted at atom C2/C52 are not parallel and are twisted themselves about 8.87º. The crystal structure of VI includes a combination of C-H…N and C-H…π interactions similar as for structure III and IV. Molecules A and B are linked by two pairs of hydrogen atoms C2H2…N52i, C87-H87…N2ii, C52-H52…N2iii and C76-H76…N53iii into dimers (symmetry codes (i): 1-x, 1-y, 1-z; (ii): 2-x, 1-y, 1-z, (iii): 1+x, y, z) (Figure 12). Those interactions form two different rings: R22(11) and R22(12) according to the graph-set motif.27 Further, hydrogen bonds build (see Table 3) three-dimensional framework. Atoms C3, C7, C35 act as donors in C-H…π interactions, where the acceptor of π-electron are phenyl rings: C55-C60, C71-C76 and C82-C87, respectively. Cg3/Cg6 and Cg4/Cg7 is a centroid of ring 3 (the benzene ring fused in tetrahydrofuran ring) and the centroid of ring 4 (benzene ring substitued at C2 atom). Cg8 i the centroid of phenyl ring C82C87.


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Figure 12. Molecular packing of VI in the unit cell in the bc, ac, ab plane, respectively. H-atoms are omitted for clarity.


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Table 3. Hydrogen bond and other interactions geometry (Å, °). D-H…A

D-H

H…A

D…A

D-H…A

C8-H8…O1i

0.93

2.49

3.412(2)

171

O2-H2…N2ii

0.82

1.94

2.748(2)

164

C7-H7…Cg4i

0.93

2.78

3.600(2)

148

C31-H31…Cg3iii

0.98

2.92

3.876(2)

164

C11-H11A…O1i

0.98

2.605

3.460(2)

146

C11-H11C…Cg4i

0.98

2.70

3.530(3)

142

C26-H26…Cg3ii

0.93

2.84

3.660(3)

145

C36-H36…N2i

0.93

2.52

3.188(3)

129

C11-H11A…Cg4ii

0.98

2.98

3.687(3)

133

C25-H25…Cg3iii

0.93

2.76

3.605(2)

152

C7-H7…Br1iii

0.93

3.07

3.506(2)

139

C34-H34…N2i

0.95

2.59

3.426(2)

148

C23-H23…Cg3ii

0.95

2.92

3.806(2)

156

Cl1…Cl1iii

-

-

3.232(2)

-

O3-H3A…N2i

0.89(2)

1.93(2)

2.802(2)

169

O3-H3B…O2ii

0.90(2)

1.96(2)

2.836(2)

165

O2-H20…O3

1.00(2)

1.60(2)

2.588(2)

167

C8-H8…O1iii

0.93

2.50

3.406(2)

166

C7-H7…Cg4iii

0.93

2.83

3.625(2)

144

compound I

compound II

compound III

compound IV

compound V


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compound VI C2-H2…N52

0.98

2.47

3.434(2)

169

C87-H87…N2

0.93

2.60

3.469(2)

155

C52-H52…N2ii

0.98

2.51

3.455(2)

161

C76-H76…N53ii

0.93

2.60

3.460(2)

153

C3-H3…Cg6iii

0.98

2.91

3.766(2)

147

C7-H7…Cg7iv

0.93

2.86

3.701(2)

151

C35-H35…Cg8

0.93

2.98

3.541(2)

120

Symmetry codes : compound I (i): -x, -y, -z, (ii): -x, -1/2+y, ½-z, (iii): x, 1+y, z; compound II (i): -1+x, y, z, (ii): 2-x, 2-y, 1-z; compound III (i): 1-x, 1-y, 1-z, (ii): 1+x, y, z, (iii) –x, 1-y, 1-z; compund IV (i): -x, 2-y, 2-z, (ii): 1-x, 2-y, 2-z, (iii): -x, 3-y, 1-z; compound V (i): ½-x, ½+y, z, (ii): -½-x, y, ½-z, (iii): -x, -y, -z; compound VI (i): 1-x, 1-y, 1-z, (ii): 2-x, 1-y, 1-z, (iii): 1+x, y, z, (iv): -1+x, -1+y, 1+z.

Hirshfeld surface analysis Hirshfeld surface24 enables the visualization intermolecular interactions by different colors representing short or long contacts and color intensity indicating the relative strength of the interactions. Figure 13 shows the Hirshfeld surfaces of compounds I – VI mapped over dnorm, (0.65 to 1.53 Å) shape-index (-1.0 to 1.0 Å) and curvedness (-4.0 to 0.4 Å). The vivid red spots seen in Hirshfeld surfaces labeled a are due to short normalized O…H distance. Other visible contacts marked as b correspond to H…N interactions. The short C8H8…O1i interaction (distance H8….Oi equals 2.490 Å) observed in crystal structure of compound I is represented as two spikes in the 2D fingerprint plots (Figure 14) in the region 2.1 < (de + di) < 2.5 Å marked as 1a. Although, the similar C-H…O interaction is seen in the crystal structure of compound II, characteristic spikes are not visible on the 2D fingerprint plots, due to longer H11…Oi distance 2.605 Å. However, on the 2D fingerprint plot of structure V we can notice two spikes associated with H…O contact (on the Hirshfeld surface labeled 5a), for O3-H3B…O2ii and


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O2-H20…O3 interactions in the region 1.85 < (de + di) < 2.35 Å and for C8-H8…O1iii interaction in the region 2.40 < (de + di) < 2.55 Å. For all presented crystal structures except compound II H…N interactions are observed in the crystal lattice visible in the Hirshfeld surfaces and labeled as b. For compound I and V it is associated with O2-H2…N2ii and O2-H3A…N2i hydrogen bonds with de + di in the region 1.8 to 1.9 Å, for compound I and V, respectively. The weaker C-H…N interactions for compound III, IV and VI are represented on 2D fingerprint plots in the region the region 2.5 to 2.65 Å. On all fingerprint plots we can distinguish characteristic spikes for C…H interactions in the region 2.9 to 3.1 Å related to particular C-H…π interactions found in all structures. Other principal interactions were identified on Figure 14a due to Br…H and Cl…Cl interactions, this time with greater di+de value equal 3.1 Å and 3.4 Å. The adjacent red and blue triangles on the shape index surface for compound II, III and IV indicate the occurrence of π···π interactions. However, we cannot observe short π…π stacking interactions in the crystal lattice. Nevertheless, the characteristic feature of layered packing with greater separation in the range 4.4 – 5.3 Å could be responsible for red/blue triangles on the shape index plot. The curvedness plots show flat surface patches in some regions. The relative contributions of various intermolecular interactions to the Hirshfeld surface area of compounds I – VI are illustrated in Figure 15. It can be seen that the molecular interactions in these compounds are predominantly of the H···H and C···H types, from 74.4% in compound III to 88.5% in II. The contribution of N···H and O···H interactions varies from 4.7% to 19.0% and from 3.4% to 11.4% respectively. The differences can be attributed to various placement of substituent (OH, Br, Cl or CN) on the base moiety, which lead to diverse crystal architecture.


22

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a)

b)

c)

compound I compound II compound III compound IV compound V compound VI

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 13. Hirshfeld surfaces mapped with (a) dnorm , (b) shape index and (c) curvedness of the compounds I – VI. Contacts labeled as a and b correspond to O…H and N…H interactions.


23


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Figure 14. 2D-fingerprint plots of compounds I – VI.


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Figure 15. 2D-fingerprint plots of particular interactions observed in the crystal structure of compounds III and IV .

Figure 16. Relative contributions in percentage of various intermolecular contacts to the Hirshfeld surface area of compounds I – VI.


25


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Page 26 of 38

In our previous study28 it was found that the contribution of C…H interactions to the Hirshfeld surface of coumarin derivatives corresponds with the log P value. Thus, in the present study we also compared the lipophilicity (expressed as log P) of compounds I – VI with respect to their relative contribution of different interactions to the Hirshfeld surfaces. As it can be seen in Figure 17, a similar relationship was found in present study. What is more, there is a clear division into two groups of compounds and for both groups the linear correlation between log P and % contribution of C…H interactions was confirmed.

Figure. 17 Relationship between log P and relative contribution of C…H contacts to the Hirshfeld surface of compounds I – VI


26

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Figure 18. Relationship between log P and sum of relative contribution of selected contacts to the Hirshfeld surface of compounds I – VI. In general, the presence of halogen substituents in molecule increases lipophilicity, hence the relatively high log P values of compounds III and IV are caused by the presence of Br and Cl atom, respectively. Therefore, an attempt was made to examine the effect of relative contributions of C…H close contacts and interactions with the participation of Br and Cl in molecule (15.1% for compound III and 12.2% for IV) on log P values. After taking into account interactions with the participation of Cl and Br, a good linear relationship for all six compounds was observed (Figure 18). Bromine atom in compound III takes part in Br…C and Br…H interactions, while chlorine substituent in compound IV involves Cl…Cl and Cl…H close contacts. The electronegative


27


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Page 28 of 38

chlorine connected to a carbon atom can withdraw electrons from other parts of the molecule strongly polarizing C-Cl bond which causing a dipole moment. On the other hand, the nonbonding electron pairs around the chlorine nucleus cause donating character of Cl atom and outer electrons are able to create nonbonding interactions with free electron pairs of other molecules. This leads to strong lipophilic properties of the Cl substituent locally and increase of lipophilicity of the whole molecule.29 Similar to chlorine substituent, a bromine atom can engage in interactions which cause further increase in lipophilicity.

Solid-state fluorescence To evaluate the fluorescent properties of compounds, their excitation-emission matrix (EEM), fluorescence quantum yield and lifetime in solid-state were investigated. All the compounds (with the exception of compound I) absorb light in the UV region (280-380 nm) and exhibit fluorescence in the blue region (400-460 nm) as shown Figure 19 and Figures S1-S5 of the Supporting Information. The first and second order Rayleigh scattering is also visible in the spectrum.


28

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Figure 19. Solid-state fluorescence 3-D contour map of compound II (contour interval =1000)

A key parameter for fluorescent compounds comparison is the photoluminescence quantum yield (ФPL), a direct measure of the efficiency of conversion of absorbed light into emitted light. The quantum yield can also be defined in terms of various rate constants: kr

ФPL = k

+ knr (1) where kr is the radiative and knr is nonradiative pathway. ФPL together with emission spectrum and r

the fluorescence lifetime (τ) characterizes a radiative transition. The fluorescence lifetime is the average time which a molecule spends in its excited singlet state before spontaneous emission occurs and can be calculated as: τ=

1

(2) kr + knr Radiative and non-radiative rate constants were calculated based on experimentally measured quantum yield and fluorescence lifetimes using the equations (1) and (2). The ФPL, fluorescence lifetime and radiative and non-radiative rate constants of compounds II – VI values are given in Table 4. The parent compound (II) is characterized by good photoluminescence quantum yield 0.24. The substitution on a phenyl by groups –OH, –CN, –Br decrease fluorescence quantum yield, although the highest ФPL (0.37) was obtained for the chlorinated derivative IV. The low ФPL of brominated derivative resulted from heavy atom effect30. In line with this this phenomenon, the heavy atoms incorporated into aromatic molecule cause decrease of photoluminescence efficiency due to substantial spin-orbit coupling in the molecule. The internal heavy atom effect is related to the increase intersystem crossing constants and the increase the phosphorescence quantum yield and


29


lifetime31. Similar heavy atom effect in solid state was observed for 2-phenyl-benzoxazole32 and biphenyl33 derivatives. Compounds II, III and IV have layered crystal structure and exhibit different quantum yield. The similar aggregation of molecules is responsible for the enhancement of fluorescence in the solid state of coumarin derivatives.34 To obtain further insight into the photophysical properties of compounds II - VI in solid state the fluorescence lifetime decay was measured (excitation at 375 nm and emission at 430 nm). The data of fluorescence lifetime are summarized in Table 4. The decay process for compound II can be described as monoexponential fit. Although for compounds III – VI, containing one additional substituent, the best fit gives biexponential function with two components. For compounds with halogen substituent (III and IV) the lifetime of the first component is approximately 5-6-times longer than of the second component. On the contrary, for compounds V and VI the second components have the longer lifetimes. Moreover, the presence of chlorine or bromine atom attached to phenyl ring causes increase of the average fluorescence lifetime as well as and the difference between lifetime of each component. This phenomenon should be attributed to different stacking mode in these crystals. Compounds II and III have layered architecture instead ribbonlike shape for V and three-dimensional framework for VI.

Table 4. Fluorescence lifetime (τ), quantum yield (ФPL) and rate constants of radiative (kr) and nonradiative decay (knr) of compounds II – VI in solid state

Lifetime [ns] ± 95% CI Comp.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 38

τ1

τ2

Average [ns] 2

χ

Intensity weighted1

lifetime

τavg Quantum yield (ФPL) Amplitude weighted2

knr

kr ·10

-9

[s-1]

-9

·10 [s-1]


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II

III

IV

V

VI

1

1.54±0.01

3.91±0.08

3.23±0.06

0.56±0.01

0.29±0.01

-

1.10

0.83±0.16

0.50±0.16

1.32±0.04

1.42±0.03

0.93

0.93

1.47

1.19

1.54

1.54

τ1(100%)

τ1(100%)

3.62

2.90

τ1(90.6%) τ2 (9.4%)

τ1(67.1%) τ2 (32.9%)

3.09

2.54

τ1(95.0%) τ2 (5.0%)

τ1(74.7%) τ2 (25.3%)

0.81

0.46

τ1(81.2%) τ2 (18.8%)

τ1(91.0%) τ2 (9.0%)

0.71

0.63

τ1(54.3%) τ2 (45.7%)

τ1(85.3%) τ2 (14.7%)

0.24

0.15

0.48

0.13

0.04

0.30

0.37

0.14

0.25

0.15

0.24

1.34

0.13

0.29

1.91

Fractional intensities of the positive decay components; 2Fractional amplitudes of the positive decay components

In order to find the potential relationships between intermolecular interactions in crystals, resulting from Hirshfeld surface analysis and fluorescence, the relative contributions of different close contacts were compared with their fluorescence characteristics such as lifetime, quantum yield and rate constants of fluorescence decay. It was found that 1/τavg perfectly correlates (R2=0.9997) with the sum of H…O and H…N contacts (%) (Fig. 20). 1 knr = (3) τ 1 − ФPL According to equation (3), similar relationship for non-radiative rate constant (knr) was expected (Fig. 20). This parabolic correlation means that the higher relative contribution of H…O and H…N contacts is responsible for increase of non-radiative decay and in consequence decrease of fluorescence lifetime.


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surface analysis revealed that significant role in fluorescence lifetime is played by H…O and H…N close contacts.

ASSOCIATED CONTENT Supporting information Detailed description of synthesis and characteristics of compounds. Solid-state fluorescence spectra of compounds I-VI. Relationship between log P and average fluorescence lifetime for compound I – VI. Fluorescence decay curves. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Tel: 48-42-635-5741. Fax: 48-42-635-5744. E-mail: [email protected]. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS The measurement of compound II and IV was carried out within the project I-20110099EC using the light source DORIS III at HASYLAB/DESY, Hamburg,Germany. The research leading to these


33


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Page 34 of 38

results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 226716 (MM). The project gets the support from Nicolaus Copernicus University, Grant 472 (BK). Authors thank Dr Carsten Paulmann and Dr Lilianna Chęcińska for assistance in synchrotron experiments (DESY/HASYLAB). Prof. Joachim Kusz from the University of Silesia is gratefully acknowledged for the X-ray measurements of compounds I, III, V and VI. We also acknowledge Prof. Elżbieta Budzisz from Medical University in Lodz for help in synthesis of arylideneflavanones and successful discussion.


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REFERENCES

(1) Mullen, K.; Scherf, U. Organic Light-Emitting Devices, Wiley-VCH, Weinheim, 2006. (2) Arbaciauskiene, E.; Kazlauskas, K.; Miasojedovas, A.; Jursenas, S.; Jankauskas, V.; Holzer, W.; Getautis, V.; Sackus, A. Dyes Pigm., 2010, 85, 79-85. (3) Hu, B.; Ping, L.; Wang, Y.; New J. Chem., 2013, 37, 1645-1653. (4) Yu,; Chen, L.; Zhang, J.; Li, J.; Liu, P.; Wang, W.; Yan, B. Talanta, 2011, 85, 1627-1633. (5) F-Ur-Rahman, Ali, A.; Guo, R.; Tian, J.; Wang, H.; Li, Z-T.; Zhang, D-W. Sens. Act. B:Chemical, 2015, 211, 544-550. (6) Allendorf, M. D., Bauer, C. A., Bhakta, R. K., Houk, R. J. T., Chem. Soc. Rev., 2009, 38, 1330-1352. (7) Cui, Y., Yue, Y., Qian, G., Chen, B., Chem. Rev., 2012, 112, 1126-1162. (8) Wagner, B. D., McManus, G. J., Moulton, B., Zaworotko, M. J., Chem. Commun., 2002, 2176-2177. (9) Lee, E. Y., Jang, S. Y., Suh, M. P., J. Am. Chem. Soc., 2005, 127, 6374-6381. (10) Kumar Seth, D.; Sakar, D.; Kar, T. CrystEngComm, 2011, 13, 4528-4535. (11) Ma, Y.; Lou, M.; Sun, Q.; Ge, S.; Sun, B. J. Mol. Struct., 2015, 1083, 111-120. (12) Zhang, X.H.; Lai, W,Y.; Gao, Z.Q.; Wong, T.C.; Lee, C.S.; Kwong, H.L. Chem. Phys. Lett. 2000, 320, 77-80.


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(13) Ji, S.J.; Shi, H.B. Dyes Pigm. 2008, 76, 348-352. (14) CrysAlis RED Oxford Diffraction, 2008, Oxford Diffraction Ltd, Yarnton, England (15) Kabsch,W. J. Appl. Cryst. 1993, 26, 795-800. (16) Sheldrick, G. M. (2013). SHELXL2013. University of Göttingen, Germany. (17) Spek, A. L. Acta Cryst.,2009, D65, 148-155. (18) Diamond 3.0 – Crystal and Molecular Structure Visualisation Crystal Impact- Putz, H. Brandenburg, K., Bonn, Germany. (19) Mercury CSD 3.5.1 New Features for the Visualization and Investigation of Crystal Structures,. Macrae, C. F, Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J., and Wood, P. A. J. Appl. Cryst., 41, 2008, 466470. (20) Spackman, M. A.; Jayatilaka, D. CrystEngComm, 2009, 11, 19-32. (21) Spackman M. A., McKinnon, J. J. CrystEngComm, 2002, 4, 378-392. (22) Spackman, M. A.; McKinnon, J. J.; Jayatilaka, D. CrystEngComm, 2008, 10, 377-388. (23) Allen, F. H.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. International Tables for X-ray Crystallography, Kluwer Academic Publishers, Amsterdam, 2006, ch. 9.5, vol. C, pp. 790-811. (24) McKinnon, J. J. ; Spackman, M. A.; Mitchell, A. S. Acta Crystallogr., Sect. B: Struct. Sci., 2004, 60, 627-668.


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(25) Gabbutt, C. D., Hargrove, T. F. L., Heron, B. M., Jones, D., Poyner, C., Yildiz, E., Horton, P. N., Hursthouse, M. B., Tetrahedron, 2006, 10945-10953. (26) Zhou, Z., Chen, Q., Yang, G., Chin.J.Org.Chem., 2009, 1774-1783. (27) Bernstein, J.; Davis, R.E.; Shimoni, L.; Chang, N.-L. Angew. Chem. Int. Ed. Engl. 1995, 34, 1555-1573. (28) ) Małecka, M.; Budzisz, E. CrystEngComm, 2014, 16, 6654-6663. (29) Naumann, K. How chlorine in molecules affects biological activity, Science Dossiers, 2003. (30) Lakowicz, J.R. Principles of fluorescence spectroscopy. 3rd edn. Springer, New York, 2009. (31) Kirillova, T.N.; Gerasimova, M.A.; Nemtseva, E.V.; Kudryasheva, N. S. Anal. Bioanal. Chem. 2011, 400, 343-351. (32) Ghodbane, A.; Saffon, N.; Blanc, S.; Fery-Forgues, S. Dyes Pigm, 2015, 113, 219-226. (33) Nijegorodov, N.; Luhanga, P. V. C.; Nkoma, J.S.; Winkoun, D.P. Spectrochim. Acta A, 2006, 64, 1-5.

(34) Park, S-Y.; Ebihara, M.; Kubota, Y.; Funabiki, K.; Matsui, M. Dyes Pigm., 2009, 82, 258267.


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Page 38 of 38

For Table of Contents Use Only

The role of crystal packing and weak intermolecular interactions in the solid state fluorescence of N-methylpyrazoline derivatives Bogumia Kupcewicz1 , Magdalena Małecka2* 1

Department of Inorganic and Analytical Chemistry, Faculty of Pharmacy, Collegium Medicum

in Bydgoszcz, Nicolaus Copernicus University in Torun, Jurasza 2, Bydgoszcz, 85-089, Poland, 2

Department of Theoretical and Structural Chemistry, Faculty of Chemistry, University of Łódź,

Pomorska 153/165, Łódź, 90-236, Poland,

Table of Contents Graphic

Synopsis The six compounds, derivatives of N-methylpyrazoline, was synthesized to develop new organic fluorescent material and to understand the role of crystal packing and different weak intermolecular interactions in crystals in quantum yield and lifetime of fluorescence in solid-state.


38

Role of Crystal Packing and Weak Intermolecular ... - ACS Publications

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