6-Chloro-1-phenylindoline-2,3-dione: absolute structure, non-linear optical and charge-transport properties

A polycrystalline sample of the title compound exhibits a considerable second-order non-linear optical effect (frequency doubling of 1064 nm light to output 532 nm light). In the crystal, molecules are linked by C—H⋯O hydrogen bonds, generating chains along the [100] direction. Based on a DFT calculation, [100] proves to be the most favourable direction for charge transport and the title crystal could be used as a hole-transport material because of its high hole mobility.

In the title compound, C 14 H 8 ClNO 2 , the dihedral angle between the isatin moiety (r.m.s. deviation = 0.014 Å ) and the phenyl ring is 51.8 (1) . All molecules have the same 'frozen chiral' conformation in the non-centrosymmetric P2 1 2 1 2 1 space group. A polycrystalline sample of the title compound exhibits a considerable second-order non-linear optical effect (frequency doubling of 1064 nm light to output 532 nm light). In the crystal, molecules are linked by C-HÁ Á ÁO hydrogen bonds, generating chains along the [100] direction. Based on a DFT calculation, [100] proves to be the most favourable direction for charge transport and the title crystal could be used as a holetransport material because of its high hole mobility.

Chemical context
Derivatives of isatin, also called indoline-2,3-dione, have drawn great attention for their biological and pharmacological properties such as anticonvulsant (Prakash et al., 2010), anticancer (Abadi et al., 2006) and anti-HIV (Bal et al., 2005) activities. The isatin skeleton can be found in analytical reagents, pesticides and dye intermediates. Isatin derivatives are also versatile precursors in the synthesis of a variety of heterocyclic compounds. However, the opto-electronic properties of isatin derivatives are rarely investigated.
As a result of the P2 1 2 1 2 1 space group of the crystal, all molecules have the same 'frozen chiral' conformation (defined as conformation I). The single conformation of these molecules in this as-tested crystal is confirmed by a Flack parameter x = 0.03 (5) and R 1 factor of 0.0317. By comparison, an inversion operation to the present structure resulted in an incorrect structure of conformation II with x = 0.97 (5) and R 1 = 0.0336. 1-Phenylindoline-2,3-dione also crystallized in P2 1 2 1 2 1 (Shukla & Rajeswaran, 2011) and this space group may be well suited to accommodate this class of molecules.
As shown in Figs. 1 and 2, the isoenergic conformations I and II are mirror images and non-superposable one another. The calculated rotation barrier (rotating around the N1-C9 bond to transform from I to II) is 8.74 kcal mol À1 , which is much higher than the thermal energy k B T = 0.596 kcal mol À1 at 300 K. The main hindrance from free rotation may be the H7Á Á ÁH10 steric repulsion with a calculated distance of 1.759 Å at the transition state (see Fig. 2).

Supramolecular features
As shown in Fig. 3, the intermolecular interactions in the aaxis direction are characterized by a C10-H10Á Á ÁO1 hydrogen bond (Table 1) and an O1Á Á ÁH11(x À 1, y, z) [2.63 (2) Å ] short contact between two side-by-side molecules. The strength of the hydrogen bond can be scaled by the electronic transfer integral (t) between two molecules and it was calculated by equation (3). The t value between the above two adjacent molecules is maximal (t 1 = 0.196 eV), indicating that a kind of side-by-side one-dimensional chain has formed along the a-axis direction. We believe that this a-directional chain plays an important role in guiding the crystal growth, for the long axis of the bar-shaped crystal was indexed to be in the [100] direction.

Figure 1
The molecular structure of the title compound, with displacement ellipsoids shown at the 50% probability level.
between such two face-to-face molecules is somewhat smaller (t 2 = 0.116 eV) in this direction. Along the c-axis direction, there is a H5Á Á ÁO2( 1 2 + x, 3 2 À y, 1 À z) [2.69 (2) Å ] short intermolecular contact and the t value between the two molecules is a minimum (t 3 = 0.0794 eV, see

Calculation and opto-electronic properties
It is well known that the necessary structural condition for second-order non-linear optical response is non-centrosymmetry, both for molecules and crystals. The P2 1 2 1 2 1 space group of the crystal prompted us to make a SHG (second harmonic generation) test. When the sample of crystalline powder was irradiated with infrared laser pulses (1064 nm), green light pulses (532 nm) could be observed.
Density functional theory (DFT) calculations for the electronic transfer integral t and the reorganization energy , were carried out using the GAUSSIAN03 program (Frisch et al., 2003) within the framework of b3lyp/6-311g(d).
The charge transport in organic semiconductors can be described by the hopping of an electron between a molecule and a neighbouring cation (hole) or anion shown below Based on the Marcus electron-transfer theory (Marcus, 1993), the mobility () in a one-dimensional uniform structure, can be expressed as (Sakanoue et al., 1999;Fang et al., 2015) where d is the distance between two neighbouring molecules and is reorganization energy. For the hole transport, can be expressed by (Berlin et al., 2003) Thus, 1 measures the energy difference between the stable molecule and the molecule with the cation geometry and 2 measures the energy difference between the stable cation and the cation with the molecule geometry. The t in equation (1) is the electronic transfer integral, which measures the intermolecular interactions between two neighbouring molecules and can be calculated by (Deng & Goddard, 2004) t where E HOMO and E HOMO-1 are the energy levels of the HOMO (highest occupied molecular orbital) and the HOMO-1 orbital of a two-molecule pair, respectively. The molecular geometry for the t calculation is based on this X-ray structure without optimization, while the geometries of The view along the a axis, showing the columnar structure and short contacts of C2Á Á ÁC12 ii and H10Á Á ÁC14 ii along the b-axis direction, also showing the short contact of H5Á Á ÁO2 iii along the c direction. [Symmetry codes: (ii) 2 À x, 1 2 + y, 3 2 À z; (iii) 1 2 + x, 3 2 À y, 1 À z.]

Figure 3
The view along the b axis, showing the chain linkage by the C10 i -H10 i Á Á ÁO1 hydrogen bond and the O1Á Á ÁH11 i short intermolecular contacts along the a-axis direction. [Symmetry code: (i) À1 + x, y, z.]

Figure 5
The view along the c axis, showing the cage-model for the DFT geometry optimization with one host molecule being surrounded by four guest molecules.
the molecule and the cation/anion have been optimized for the calculation. Since the molecule in the crystal is different from the free molecule, we adopted the cage model (Fang et al., 2015) in the course of geometry optimization, in which the host (molecule or cation or anion) being optimized is constrained by four guest molecules with fixed X-ray structures (see Fig. 5).
As shown in Table 2, (i) the hole mobility ( h ) is one order of magnitude larger than the electron mobility ( e ), indicating that the title crystal could be used as a hole-transport material rather than an electron-transport material and (ii) both the hole mobility ( h ) and the electron mobility ( e ) in the [100] direction (the side-by-side chain direction) are an order of magnitude larger than those in the [010] direction (the face-toface column direction).
In summary, the side-by-side hydrogen bonding in the onedimensional chain in the [100] direction is stronger than the face-to-faceinteractions in the [010] direction for this crystal, which relates to the non-linear optical and electronic transport properties of the crystal.

Database survey
A search in the Cambridge Structural Database (WebCSD, Version 1.1.2; last update November 2016), for indoline-2,3dione derivatives gave 137 hits. Among them, there are nine hits for halogen 6-substituted indoline-2,3-dione derivatives and two hits which contain the substructure of the 1-phenylindoline-2,3-dione skeleton. There are four non-centrosymmetric structures and seven centrosymmetric structures among these eleven crystal structures.

Synthesis and crystallization
We synthesized the title compound by the reaction of 6-chloroindoline-2-one and phenylboronic acid (see Fig. 6). 6-Chloroindoline-2-one (0.168 g, 1.00 mmol) was dissolved in DMF (18 ml). Then pyridine (0.05 mL), phenylboronic acid (0.244 g, 2.00 mmol) and Cu(OAc) 2 ÁH 2 O (0.197 g, 0.99 mmol) were sequentially added into the flask. The mixture was stirred for two h at room temperature in the presence of air. After filtration, the filtrate was poured into 100 ml water and Reaction scheme.

Figure 7
The 1 H NMR spectra of the title compound.  Flack (1983), 1583 Friedel pairs Absolute structure parameter 0.03 (5) Computer programs: APEX2 and SAINT (Bruker, 2005), SHELXS97, SHELXL97 and SHELXTL (Sheldrick, 2008). Table 2 Charge-transport properties (eV, cm 2 V À1 s À1 ) of the title crystal.  Fig. 7, the 1 H NMR signals of all protons of the compound are well separated and well characterized. Orange bar-shaped crystals were obtained by slow evaporation of a solution of the title compound in mixed solvents of dichloromethane and n-hexane.