Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101008009/sk1476sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270101008009/sk1476Isup2.hkl |
CCDC reference: 169953
trans-4-[(4-Dimethylaminophenyl)iminomethyl]-N-methylpyridinium iodide was synthesized as described previously (Matsui et al., 1992) and metathesized to (I) by precipitation from water/aqueous sodium para-toluenesulfonate (Acros). Found: C 62.23, H 6.44, N 10.01%; calculated for C22H25N3O3S·0.7H2O: C 62.30, H 6.27, N 9.91%. 1H NMR data (300 MHz, CD3CN): δ 8.82 (1H, s, CH), 8.63 (2H, d, J = 6.6 Hz, C5H4N), 8.32 (2H, d, J = 6.5 Hz, C5H4N), 7.65 (2H, d, J = 8.1 Hz, C6H4), 7.55 (2H, d, J = 9.2 Hz, C6H4SO3),7.20 (2H, d, J = 7.8 Hz, C6H4), 6.87 (2H, d, J = 9.2 Hz, C6H4SO3), 4.31 (3H, s, N—Me), 3.10 (6H, s, NMe2), 2.38 (3H, s, Me). λmax/nm (ε/M-1 dm3) 506 (22700), 274 (12900). Crystals suitable for single-crystal X-ray diffraction measurements were obtained by slow diffusion of diethyl ether (BDH) vapour into a methanol (BDH) solution of (I) at room temperature; note that the same method is used to produce SHG-active crystals of DAST (Marder et al., 1994). The crystals of (I) were hygroscopic and were therefore protected from air prior to and during the crystallographic analysis.
H atoms were included in idealized positions with their displacement parameters tied to those of their parent atoms.
Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1990).
Fig. 1. A representation of the molecular structure of (I), with 50% probability displacement ellipsoids. |
C15H18N3+·C7H7O3S− | F(000) = 872 |
Mr = 411.51 | Dx = 1.345 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 7.0956 (14) Å | Cell parameters from 18258 reflections |
b = 19.035 (4) Å | θ = 2.9–27.5° |
c = 15.312 (3) Å | µ = 0.19 mm−1 |
β = 100.61 (3)° | T = 150 K |
V = 2032.8 (7) Å3 | Block, black |
Z = 4 | 0.14 × 0.08 × 0.04 mm |
Nonius KappaCCD area-detector diffractometer | 2549 reflections with I > 2σ(I) |
ϕ and ω scans to fill Ewald sphere | Rint = 0.076 |
Absorption correction: multi-scans (SORTAV; Blessing, 1995) | θmax = 27.5°, θmin = 3.1° |
Tmin = 0.974, Tmax = 0.993 | h = −9→9 |
16234 measured reflections | k = −24→24 |
4634 independent reflections | l = −19→19 |
Refinement on F2 | H-atom parameters constrained |
Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.0506P)2] where P = (Fo2 + 2Fc2)/3 |
R[F2 > 2σ(F2)] = 0.049 | (Δ/σ)max = 0.014 |
wR(F2) = 0.115 | Δρmax = 0.23 e Å−3 |
S = 0.94 | Δρmin = −0.26 e Å−3 |
4634 reflections | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
267 parameters | Extinction coefficient: 0.0044 (8) |
0 restraints |
C15H18N3+·C7H7O3S− | V = 2032.8 (7) Å3 |
Mr = 411.51 | Z = 4 |
Monoclinic, P21/n | Mo Kα radiation |
a = 7.0956 (14) Å | µ = 0.19 mm−1 |
b = 19.035 (4) Å | T = 150 K |
c = 15.312 (3) Å | 0.14 × 0.08 × 0.04 mm |
β = 100.61 (3)° |
Nonius KappaCCD area-detector diffractometer | 4634 independent reflections |
Absorption correction: multi-scans (SORTAV; Blessing, 1995) | 2549 reflections with I > 2σ(I) |
Tmin = 0.974, Tmax = 0.993 | Rint = 0.076 |
16234 measured reflections |
R[F2 > 2σ(F2)] = 0.049 | 0 restraints |
wR(F2) = 0.115 | H-atom parameters constrained |
S = 0.94 | Δρmax = 0.23 e Å−3 |
4634 reflections | Δρmin = −0.26 e Å−3 |
267 parameters |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
S1 | 0.58936 (9) | 0.05248 (3) | 0.22670 (3) | 0.0338 (2) | |
O1 | 0.7337 (2) | −0.00106 (7) | 0.25458 (9) | 0.0454 (6) | |
O2 | 0.6718 (2) | 0.12176 (7) | 0.22175 (9) | 0.0435 (5) | |
O3 | 0.4545 (2) | 0.03347 (8) | 0.14679 (9) | 0.0450 (6) | |
C1 | 0.1350 (4) | 0.08629 (11) | 0.52509 (15) | 0.0474 (9) | |
C2 | 0.2460 (4) | 0.07579 (10) | 0.45069 (14) | 0.0372 (8) | |
C3 | 0.4455 (3) | 0.08089 (10) | 0.46684 (14) | 0.0376 (8) | |
C4 | 0.5478 (3) | 0.07210 (10) | 0.39885 (14) | 0.0364 (8) | |
C5 | 0.4533 (3) | 0.05852 (10) | 0.31257 (13) | 0.0333 (7) | |
C6 | 0.2547 (3) | 0.05307 (10) | 0.29607 (14) | 0.0370 (8) | |
C7 | 0.1526 (4) | 0.06125 (10) | 0.36448 (14) | 0.0404 (8) | |
N1 | 0.3424 (3) | 0.34610 (8) | 0.49094 (11) | 0.0407 (7) | |
N2 | 0.3086 (2) | 0.28248 (8) | 0.13063 (11) | 0.0354 (6) | |
N3 | 0.3149 (2) | 0.18238 (8) | −0.16927 (11) | 0.0332 (6) | |
C8 | 0.3325 (3) | 0.29147 (11) | 0.55625 (14) | 0.0410 (8) | |
C9 | 0.3709 (4) | 0.41815 (10) | 0.52189 (15) | 0.0476 (9) | |
C10 | 0.3292 (3) | 0.33012 (10) | 0.40311 (14) | 0.0334 (7) | |
C11 | 0.3493 (3) | 0.38152 (10) | 0.33955 (14) | 0.0398 (8) | |
C12 | 0.3386 (3) | 0.36412 (10) | 0.25164 (14) | 0.0381 (8) | |
C13 | 0.3118 (3) | 0.29498 (10) | 0.22187 (14) | 0.0331 (7) | |
C14 | 0.2849 (3) | 0.24409 (10) | 0.28396 (14) | 0.0343 (7) | |
C15 | 0.2928 (3) | 0.26083 (10) | 0.37197 (14) | 0.0348 (7) | |
C16 | 0.3326 (3) | 0.22008 (11) | 0.10291 (14) | 0.0344 (7) | |
C17 | 0.3243 (3) | 0.20726 (10) | 0.00822 (13) | 0.0312 (7) | |
C18 | 0.2798 (3) | 0.26056 (10) | −0.05418 (14) | 0.0360 (8) | |
C19 | 0.2756 (3) | 0.24747 (10) | −0.14223 (15) | 0.0369 (8) | |
C20 | 0.3577 (3) | 0.12970 (10) | −0.11081 (14) | 0.0350 (7) | |
C21 | 0.3626 (3) | 0.14079 (10) | −0.02193 (13) | 0.0339 (7) | |
C22 | 0.3140 (3) | 0.16960 (11) | −0.26443 (13) | 0.0422 (8) | |
H1A | 0.20008 | 0.06170 | 0.57842 | 0.0711* | |
H1B | 0.00512 | 0.06740 | 0.50713 | 0.0711* | |
H1C | 0.12777 | 0.13655 | 0.53792 | 0.0711* | |
H3 | 0.51216 | 0.09053 | 0.52530 | 0.0451* | |
H4 | 0.68372 | 0.07536 | 0.41123 | 0.0437* | |
H6 | 0.18822 | 0.04366 | 0.23752 | 0.0444* | |
H7 | 0.01690 | 0.05686 | 0.35228 | 0.0485* | |
H8A | 0.43146 | 0.25610 | 0.55321 | 0.0615* | |
H8B | 0.35366 | 0.31225 | 0.61582 | 0.0615* | |
H8C | 0.20585 | 0.26924 | 0.54377 | 0.0615* | |
H9A | 0.27711 | 0.44869 | 0.48505 | 0.0715* | |
H9B | 0.35387 | 0.42098 | 0.58388 | 0.0715* | |
H9C | 0.50078 | 0.43337 | 0.51762 | 0.0715* | |
H11 | 0.37050 | 0.42905 | 0.35763 | 0.0478* | |
H12 | 0.34987 | 0.40020 | 0.21003 | 0.0458* | |
H14 | 0.26049 | 0.19688 | 0.26507 | 0.0411* | |
H15 | 0.27340 | 0.22498 | 0.41257 | 0.0418* | |
H16 | 0.35573 | 0.18224 | 0.14394 | 0.0412* | |
H18 | 0.25217 | 0.30640 | −0.03548 | 0.0432* | |
H19 | 0.24502 | 0.28416 | −0.18452 | 0.0443* | |
H20 | 0.38480 | 0.08432 | −0.13115 | 0.0421* | |
H21 | 0.39220 | 0.10312 | 0.01900 | 0.0407* | |
H22A | 0.28172 | 0.12032 | −0.27851 | 0.0633* | |
H22B | 0.21845 | 0.20005 | −0.30035 | 0.0633* | |
H22C | 0.44110 | 0.17993 | −0.27762 | 0.0633* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0626 (18) | 0.0410 (13) | 0.0405 (13) | 0.0030 (12) | 0.0145 (13) | −0.0019 (11) |
C2 | 0.0545 (17) | 0.0234 (11) | 0.0337 (13) | 0.0014 (10) | 0.0080 (12) | 0.0031 (10) |
C3 | 0.0523 (17) | 0.0299 (12) | 0.0283 (12) | −0.0007 (10) | 0.0013 (11) | −0.0014 (10) |
C4 | 0.0453 (15) | 0.0296 (12) | 0.0324 (12) | 0.0009 (10) | 0.0018 (11) | 0.0018 (10) |
C5 | 0.0515 (16) | 0.0214 (10) | 0.0268 (11) | −0.0038 (10) | 0.0063 (10) | 0.0005 (9) |
C6 | 0.0494 (16) | 0.0296 (11) | 0.0297 (12) | −0.0075 (11) | 0.0013 (11) | −0.0001 (10) |
C7 | 0.0459 (15) | 0.0358 (13) | 0.0395 (14) | −0.0055 (11) | 0.0080 (12) | 0.0007 (10) |
C8 | 0.0456 (15) | 0.0416 (13) | 0.0384 (13) | −0.0002 (11) | 0.0143 (11) | −0.0039 (11) |
C9 | 0.0667 (18) | 0.0382 (13) | 0.0425 (14) | 0.0063 (12) | 0.0219 (13) | 0.0082 (11) |
C10 | 0.0356 (13) | 0.0275 (11) | 0.0400 (13) | −0.0013 (10) | 0.0144 (10) | −0.0001 (10) |
C11 | 0.0570 (16) | 0.0229 (11) | 0.0431 (14) | 0.0005 (11) | 0.0187 (12) | 0.0034 (10) |
C12 | 0.0505 (15) | 0.0244 (11) | 0.0428 (13) | −0.0014 (10) | 0.0172 (11) | −0.0022 (10) |
C13 | 0.0321 (13) | 0.0293 (11) | 0.0388 (13) | −0.0020 (10) | 0.0089 (10) | 0.0022 (10) |
C14 | 0.0351 (13) | 0.0240 (11) | 0.0448 (13) | −0.0005 (9) | 0.0103 (11) | 0.0015 (10) |
C15 | 0.0366 (14) | 0.0277 (11) | 0.0418 (13) | −0.0005 (10) | 0.0115 (10) | −0.0040 (10) |
C16 | 0.0349 (13) | 0.0316 (12) | 0.0354 (12) | −0.0027 (10) | 0.0034 (10) | −0.0017 (10) |
C17 | 0.0281 (12) | 0.0308 (11) | 0.0340 (12) | 0.0004 (9) | 0.0042 (10) | −0.0010 (10) |
C18 | 0.0368 (14) | 0.0276 (11) | 0.0425 (14) | −0.0018 (10) | 0.0045 (10) | 0.0006 (10) |
C19 | 0.0348 (14) | 0.0298 (12) | 0.0448 (14) | −0.0001 (10) | 0.0036 (11) | −0.0071 (11) |
C20 | 0.0418 (14) | 0.0257 (11) | 0.0379 (13) | 0.0018 (10) | 0.0078 (11) | −0.0010 (10) |
C21 | 0.0406 (14) | 0.0265 (11) | 0.0331 (12) | −0.0011 (10) | 0.0026 (10) | −0.0034 (10) |
C22 | 0.0504 (15) | 0.0445 (13) | 0.0323 (13) | 0.0043 (12) | 0.0091 (11) | −0.0035 (11) |
N1 | 0.0583 (13) | 0.0294 (10) | 0.0381 (11) | 0.0065 (9) | 0.0188 (10) | 0.0012 (8) |
N2 | 0.0357 (11) | 0.0317 (10) | 0.0399 (11) | −0.0010 (8) | 0.0099 (9) | 0.0037 (8) |
N3 | 0.0357 (11) | 0.0329 (10) | 0.0308 (10) | 0.0035 (8) | 0.0058 (8) | −0.0026 (8) |
O1 | 0.0590 (11) | 0.0353 (9) | 0.0417 (9) | 0.0097 (8) | 0.0088 (8) | 0.0010 (7) |
O2 | 0.0575 (11) | 0.0304 (8) | 0.0455 (9) | −0.0076 (7) | 0.0171 (8) | −0.0013 (7) |
O3 | 0.0616 (11) | 0.0465 (9) | 0.0258 (8) | −0.0083 (8) | 0.0049 (8) | −0.0002 (7) |
S1 | 0.0498 (4) | 0.0241 (3) | 0.0273 (3) | −0.0017 (3) | 0.0065 (3) | 0.0002 (2) |
C1—C2 | 1.513 (3) | C12—C13 | 1.394 (3) |
C1—H1A | 0.9800 | C12—H12 | 0.9500 |
C1—H1B | 0.9800 | C13—C14 | 1.395 (3) |
C1—H1C | 0.9800 | C13—N2 | 1.413 (3) |
C2—C7 | 1.392 (3) | C14—C15 | 1.376 (3) |
C2—C3 | 1.395 (3) | C14—H14 | 0.9500 |
C3—C4 | 1.384 (3) | C15—H15 | 0.9500 |
C3—H3 | 0.9500 | C16—N2 | 1.283 (2) |
C4—C5 | 1.391 (3) | C16—C17 | 1.461 (3) |
C4—H4 | 0.9500 | C16—H16 | 0.9500 |
C5—C6 | 1.389 (3) | C17—C18 | 1.390 (3) |
C5—S1 | 1.772 (2) | C17—C21 | 1.391 (3) |
C6—C7 | 1.388 (3) | C18—C19 | 1.366 (3) |
C6—H6 | 0.9500 | C18—H18 | 0.9500 |
C7—H7 | 0.9500 | C19—N3 | 1.351 (3) |
C8—N1 | 1.453 (2) | C19—H19 | 0.9500 |
C8—H8A | 0.9800 | C20—N3 | 1.341 (2) |
C8—H8B | 0.9800 | C20—C21 | 1.371 (3) |
C8—H8C | 0.9800 | C20—H20 | 0.9500 |
C9—N1 | 1.453 (2) | C21—H21 | 0.9500 |
C9—H9A | 0.9800 | C22—N3 | 1.476 (3) |
C9—H9B | 0.9800 | C22—H22A | 0.9800 |
C9—H9C | 0.9800 | C22—H22B | 0.9800 |
C10—N1 | 1.365 (3) | C22—H22C | 0.9800 |
C10—C11 | 1.406 (3) | O1—S1 | 1.4522 (15) |
C10—C15 | 1.410 (3) | O2—S1 | 1.4503 (15) |
C11—C12 | 1.375 (3) | O3—S1 | 1.4533 (15) |
C11—H11 | 0.9500 | ||
C2—C1—H1A | 109.5 | C12—C13—N2 | 117.29 (18) |
C2—C1—H1B | 109.5 | C14—C13—N2 | 125.27 (18) |
H1A—C1—H1B | 109.5 | C15—C14—C13 | 121.38 (19) |
C2—C1—H1C | 109.5 | C15—C14—H14 | 119.3 |
H1A—C1—H1C | 109.5 | C13—C14—H14 | 119.3 |
H1B—C1—H1C | 109.5 | C14—C15—C10 | 121.32 (19) |
C7—C2—C3 | 118.2 (2) | C14—C15—H15 | 119.3 |
C7—C2—C1 | 121.1 (2) | C10—C15—H15 | 119.3 |
C3—C2—C1 | 120.6 (2) | N2—C16—C17 | 119.97 (19) |
C4—C3—C2 | 120.9 (2) | N2—C16—H16 | 120.0 |
C4—C3—H3 | 119.5 | C17—C16—H16 | 120.0 |
C2—C3—H3 | 119.5 | C18—C17—C21 | 118.01 (19) |
C3—C4—C5 | 120.6 (2) | C18—C17—C16 | 121.53 (18) |
C3—C4—H4 | 119.7 | C21—C17—C16 | 120.46 (18) |
C5—C4—H4 | 119.7 | C19—C18—C17 | 120.42 (19) |
C6—C5—C4 | 118.8 (2) | C19—C18—H18 | 119.8 |
C6—C5—S1 | 122.22 (17) | C17—C18—H18 | 119.8 |
C4—C5—S1 | 118.91 (18) | N3—C19—C18 | 120.09 (19) |
C7—C6—C5 | 120.5 (2) | N3—C19—H19 | 120.0 |
C7—C6—H6 | 119.8 | C18—C19—H19 | 120.0 |
C5—C6—H6 | 119.8 | N3—C20—C21 | 120.57 (19) |
C6—C7—C2 | 121.0 (2) | N3—C20—H20 | 119.7 |
C6—C7—H7 | 119.5 | C21—C20—H20 | 119.7 |
C2—C7—H7 | 119.5 | C20—C21—C17 | 119.91 (19) |
N1—C8—H8A | 109.5 | C20—C21—H21 | 120.0 |
N1—C8—H8B | 109.5 | C17—C21—H21 | 120.0 |
H8A—C8—H8B | 109.5 | N3—C22—H22A | 109.5 |
N1—C8—H8C | 109.5 | N3—C22—H22B | 109.5 |
H8A—C8—H8C | 109.5 | H22A—C22—H22B | 109.5 |
H8B—C8—H8C | 109.5 | N3—C22—H22C | 109.5 |
N1—C9—H9A | 109.5 | H22A—C22—H22C | 109.5 |
N1—C9—H9B | 109.5 | H22B—C22—H22C | 109.5 |
H9A—C9—H9B | 109.5 | C10—N1—C9 | 120.79 (17) |
N1—C9—H9C | 109.5 | C10—N1—C8 | 121.01 (17) |
H9A—C9—H9C | 109.5 | C9—N1—C8 | 118.18 (17) |
H9B—C9—H9C | 109.5 | C16—N2—C13 | 120.27 (18) |
N1—C10—C11 | 121.98 (18) | C20—N3—C19 | 121.00 (18) |
N1—C10—C15 | 121.11 (18) | C20—N3—C22 | 119.66 (17) |
C11—C10—C15 | 116.90 (19) | C19—N3—C22 | 119.33 (17) |
C12—C11—C10 | 121.06 (19) | O2—S1—O1 | 112.59 (10) |
C12—C11—H11 | 119.5 | O2—S1—O3 | 113.06 (9) |
C10—C11—H11 | 119.5 | O1—S1—O3 | 113.08 (9) |
C11—C12—C13 | 121.8 (2) | O2—S1—C5 | 105.06 (9) |
C11—C12—H12 | 119.1 | O1—S1—C5 | 106.17 (9) |
C13—C12—H12 | 119.1 | O3—S1—C5 | 106.06 (10) |
C12—C13—C14 | 117.41 (19) |
Experimental details
Crystal data | |
Chemical formula | C15H18N3+·C7H7O3S− |
Mr | 411.51 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 150 |
a, b, c (Å) | 7.0956 (14), 19.035 (4), 15.312 (3) |
β (°) | 100.61 (3) |
V (Å3) | 2032.8 (7) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.19 |
Crystal size (mm) | 0.14 × 0.08 × 0.04 |
Data collection | |
Diffractometer | Nonius KappaCCD area-detector diffractometer |
Absorption correction | Multi-scans (SORTAV; Blessing, 1995) |
Tmin, Tmax | 0.974, 0.993 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 16234, 4634, 2549 |
Rint | 0.076 |
(sin θ/λ)max (Å−1) | 0.649 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.049, 0.115, 0.94 |
No. of reflections | 4634 |
No. of parameters | 267 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.23, −0.26 |
Computer programs: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998), DENZO and COLLECT, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 1990).
C10—N1 | 1.365 (3) | C19—N3 | 1.351 (3) |
C13—N2 | 1.413 (3) | C20—N3 | 1.341 (2) |
C16—N2 | 1.283 (2) | C22—N3 | 1.476 (3) |
C16—C17 | 1.461 (3) | ||
N1—C10—C11 | 121.98 (18) | C18—C17—C16 | 121.53 (18) |
N1—C10—C15 | 121.11 (18) | C21—C17—C16 | 120.46 (18) |
C12—C13—N2 | 117.29 (18) | C16—N2—C13 | 120.27 (18) |
C14—C13—N2 | 125.27 (18) | C20—N3—C22 | 119.66 (17) |
N2—C16—C17 | 119.97 (19) | C19—N3—C22 | 119.33 (17) |
Subscribe to Acta Crystallographica Section C: Structural Chemistry
The full text of this article is available to subscribers to the journal.
- Information on subscribing
- Sample issue
- Purchase subscription
- Reduced-price subscriptions
- If you have already subscribed, you may need to register
Much effort continues to be devoted to the discovery of new molecular compounds which exhibit non-linear optical (NLO) properties because such materials are expected to form the basis of emerging optoelectronic and photonic technologies (Bosshard et al., 1995; Chemla & Zyss, 1987; Nalwa & Miyata, 1997). The design of efficient quadratic (second order) NLO materials involves the optimization of both molecular and bulk-level properties. Most promising candidate compounds consist of dipolar donor–π-acceptor (D-π-A) molecules, which must be arranged in a non-centrosymmetric macroscopic structure in order to display bulk quadratic NLO effects, such as frequency doubling (second harmonic generation, SHG).
Amongst known NLO compounds, stilbazolium salts are especially attractive for use in devices (Lee & Kim, 1999). Early studies showed that trans-4'-(dimethylamino)-N-methyl-4-stilbazolium para-toluenesulfonate (DAST) exhibits very pronounced bulk quadratic NLO activity, as evidenced by a powder SHG efficiency from a 1907 nm laser of ca 1000 times that of a urea reference (Marder et al., 1989, 1994). At the molecular level, quadratic NLO activity is governed by first hyperpolarizabilities β, and static (`off-resonance') first hyperpolarizabilities β0 are generally used when comparing active molecules. A hyper-Rayleigh scattering investigation of DAST using a 1064 nm laser afforded a large β0 value of 364 × 10 -30 e.s.u. (Duan et al., 1995). Hence, DAST has been intensively investigated in recent years (Meier et al., 2000), leading to the growth of large high-quality single crystals (Pan, Wong et al., 1996; Adachi et al., 1999; Sohma et al., 1999) and the fabrication of prototype NLO devices for parametric interactions and electro-optical modulation (Pan, Knöpfle et al., 1996; Meier et al., 1998; Bhowmik et al., 2000).
D-π-A molecules exhibit intense low-energy absorption bands due to π → π* intramolecular charge-transfer (ICT) excitations from the HOMO (highest occupied molecular orbital) primarily localized on the electron-rich D group to the LUMO (lowest unoccupied molecular orbital) localized on the electron-deficient A unit. According to the two-state model (Oudar & Chemla, 1977; Zyss & Oudar, 1982), β0 is proportional to the square of the ICT transition dipole moment but inversely proportional to the square of the ICT energy. Hence, β0 increases as the ICT absorption intensity increases and as the energy decreases. The ICT band in (I) is red-shifted by ca 0.16 eV, but roughly half as intense, when compared with the corresponding absorption in DAST (λmax = 476 nm, ε = 42,100 M-1 dm3 in methanol). Hence, the β0 value of (I) may be similar to that of DAST, potentially giving rise to pronounced bulk quadratic NLO effects. We have previously reported the synthesis and structure of the related compound trans-4-[(4-dimethylaminophenyl)iminomethyl]-N-phenylpyridinium hexafluorophosphate, (II) (Coe et al., 2000).
The molecular structure of the cation in (I) is as indicated by 1NMR spectroscopy, with the two aryl rings adopting the expected trans arrangement about the iminomethyl linkage. The dihedral angle of 23.49 (6)° defined by these ring planes (C10/C11/C12/C13/C14/C15 and N3/C17/C18/C19/C20/C21) is larger than that found in (II) [7.5 (2)°; Coe et al., 2000]. This difference in dihedral angles may arise from weaker π-electronic coupling through the D-π-A framework in (I), consistent with the larger molar extinction coefficient for the ICT band of (II) (λmax = 534 nm, ε = 32,900 M-1 dm3 in acetonitrile; Coe et al., 2000). The dipolar cation in (I) shows a small degree of ground-state polarization, with both the pyridyl and phenylene rings being partially quinoidal. For example, the average of the distances C11—C12 and C14—C15 is 0.025 Å less than the average of the other phenylene C—C distances. With the exception of the phenylene/pyridyl dihedral angle, the geometric parameters of the diaryl Schiff base unit in (I) are similar to those found in (II) (Coe et al., 2000).
The crystal packing structure of (I) is of interest with regard to quadratic N LO properties. The closely related compound DAST crystallizes in the non-centrosymmetric space group Cc (Marder et al., 1989), as does (II) (Coe et al., 2000). Unfortunately, (I) adopts the centrosymmetric space group P21/n and is hence not expected to display bulk NLO effects. Clearly, replacement of the ethylene unit in DAST with an iminomethyl group alters the crystallization behaviour. By contrast, (II) and the compound trans-4'-(dimethylamino)-N-phenyl-4-stilbazolium hexafluorophosphate are isostructural (Coe et al., 2001). Although the present structure is somewhat disappointing, it is quite possible that salts of the cation in (I) with other anions may adopt different crystal structures which are favourable for bulk NLO behaviour.