Quantitative analysis of hydrogen bonding and atomic thermal motion in the organic non-linear optical material DCNP using X-ray and neutron diffraction

Abstract

A single-crystal neutron diffraction study of the organic nonlinear optical material 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (hereafter DCNP), space group Cc, is presented. The study was conducted in order to relate the structural characteristics of the compound to its physical properties. DCNP exhibits a very large second harmonic generation (SHG) output, an extremely large linear electrooptical effect and photoconductive and pyroelectric properties. The nature of the hydrogen-bonding revealed by the study, in part, accounts for the ®rst two of these phenomena. The neutron study also shows that some rather atypical atomic thermal motion is present in part of the molecule. With the aid of a variable-temperature single-crystal X-ray diffraction study, in conjunction with the neutron study, this thermal motion is attributed to libration and is fully characterized. As a result, suitable corrections to the bond geometry and the anisotropic displacement parameters of DCNP are made. The libration is also shown to enhance the SHG effect. The cell parameters from the variable-temperature X-ray study are also used in order to evaluate the thermal expansivity coef®cients of DCNP.

On the origin of fluorescence emission in optically non-linear DCNP crystals

“…Next, a crude material was purified by sublimation under vacuum (''instabilities at the melt temperature preclude zone refining'', according to ref. 13).…”

“…Optical and NLO properties of a number of pyrazole derivatives were already reported in the literature. [5][6][7][8][9][10][11][12][13][14] The title compound 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole, abbreviated as DCNP (C 13 H 10 N 4 , M w = 222.25 g), is a good example of a low-molecular mass organic dye classified as a nonlinear optical chromophore due to its anisotropic ''push-pull'' character as described in ref. 12.…”

“…15 DCNP crystallizes in the monoclinic non-centrosymmetric space group Cc (point group m) with pseudo-orthogonal geometry where Z = 4 molecules of DCNP occupy a unit cell. The first crystallographic structure of DCNP crystals was reported by Allen et al 12 The more precise structural studies of this compound both by X-ray and neutron diffraction have been done by Cole et al 13 at 90, 100, 200 and 290 K. The cell parameters a = 11.8751 Å, b = 12.3735 Å, c = 7.8876 Å, b = 90.412, and Z = 4 at 290 K have been measured by XRD. 13 No phase transition was reported in this crystal down to 90 K. The densities at 290 K and 100 K as calculated from the unit cell parameters are 1.274 and 1.321 Mg m À3 , respectively.…”

Organic Nanocrystal Fabrication Using the Process of Resonant Second-Harmonic Generation of Light

“…The laser energy deposited at a crystallite cross section A = 7.85 10 9 nm 2 amounts to 1.57 10 –4 J. The volume of such a crystallite is V = 523 × 10 12 nm 3 , which gives the crystallite weight M ≈ 666 ng using the known DCNP density 44 ρ = 1.274 Mg m –3 . Then, assuming that the whole incident laser energy is transformed to heat, the temperature increase in the DCNP crystallite Δ T ≈ 160 K has been calculated using heat capacity C p = 1.5 J g –1 K –1 .…”

Chemical structure versus second-order nonlinear optical response of the push–pull type pyrazoline-based chromophores

“…The compounds differ in electron-acceptor moieties, which are mainly nitrile (-CN) and nitro (-NO 2 ) groups located in various positions and congurations giving pairs or triplets of derivatives and structural isomers. For instance, the compound (E)-2-(4-(2-(1-phenyl-4,5-dihydro-1Hpyrazol-3-yl)vinyl)benzylidene)malononitrile (abbreviation: PY-PhdiCN) is an extended version of the well-known DCNP (3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole) molecule, 10,[19][20][21] which in this study serves as the reference material among the newly introduced pyrazoline derivatives. PY-PhdiCN has two terminal nitrile groups in the acceptor region, whereas in comparison with DCNP, it also has an additional aromatic ring and ethenyl bond between the D-A parts.…”