Crystal structure and optical properties of fused-ring chalcone (E)-3-(anthracen-9-yl)-1-(4-nitrophenyl)prop-2-en-1-one

The title chalcone derivative adopts an s-cis conformation with respect to the enone fragment and is non-planar with a dihedral angle of 48.63 (14)° between the anthracene ring system and the nitrobenzene ring. In the crystal, molecules are linked into inversion dimers with an (10) graph-set motif via pairs of intermolecular C—H⋯O hydrogen bonds.


Chemical context
Conjugated organic molecules with multiple fused aromatic rings have attracted a great deal of interest from researchers because of their excellent performance in organic semiconductor devices (Gu et al., 2015). These organic molecules with a delocalized -system represent attractive targets for applications in light-emitting diodes. In addition, the selection of the organic -system with an electron donor (D) and an electron acceptor (A) is important because it exhibits an essential role in charge transfer in the molecule, where the aromatic groups may lead to delocalization of electronic charge distribution, imparting higher polarization of the pushpull configuration and generation of a molecular dipole (Bureš, 2014). An organic chalcone derivative with aconjugated system provides a large transfer axis with appropriate substituent groups on both terminal aromatic rings. The chalcone -bridge consists of a ,-unsaturated carbonyl unit which is responsible for intramolecular charge transfer. From the previous studies by Xu et al. (2015), the introduction of fused aromatic rings into the push-pull system could lead to enhanced carrier mobility and a lower band gap. In a continuation of our previous work on the effect of a fused-ring substituent, i.e. naphthalene or pyrene, on anthracene chalcones (Zaini et al., 2018), we have synthesized the title compound and report herein on its molecular and crystal structure, and optical properties. ISSN 2056-9890

Figure 2
Packing diagrams of the title compound, showing C-HÁ Á ÁO interactions (dashed lines).    Fig. 3b, respectively. In the d norm surface, the bright-red spots indicate the intermolecular C-HÁ Á ÁO interactions. These contacts are also confirmed by the pale-orange region marked with arrows in the d e surface. The fingerprint plots (Ternavisk et al., 2014) of the intermolecular contacts with the corresponding d norm surfaces (Fig. 4) show that the percentage contributions to the total Hirshfeld surface are 23.8, 19.6 and 12.6%, respectively, for the OÁ Á ÁH/HÁ Á ÁO, CÁ Á ÁH/HÁ Á ÁC and CÁ Á ÁC contacts.

UV-vis analysis and frontier molecular orbitals
The measurement of the UV-vis absorption spectrum was carried out in an acetonitrile solution (10 À5 M) with cut-off wavelength of 190 nm. Two major peaks at 253 and 427 nm were observed (Fig. 5). The strong band of 253 nm was assigned to the n-* transition. This sharp absorption peak arises due to the presence of carbonyl (C O) and nitro substituent (NO 2 ) functional groups (Zaini et al., 2018). The energy band gap of 2.52 eV was evaluated from the UV-vis absorption edge ( a.e ) at 492.06 nm (Fig. 5). This small bandgap energy is suitable for optoelectronic applications as previously reported for the structure of chalcone (Prabhu et al., 2016), and therefore exhibits a semiconducting nature (Rosencher & Vinter, 2002). The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), known as frontier orbitals, obtained with the B3LYP/6-311G++(d,p) level calculation are illustrated in Fig. 6. The HOMO is mainly delocalized at the anthracene ring system. After excitation, the charge is localized at the enone and nitrobenzene moieties as depicted in the LUMO. The The fingerprint plots of the intermolecular contacts with the corresponding d norm surfaces, listing the percentage contributions to the total Hirshfeld surface. comparable with the UV-vis energy band gap obtained from the UV-vis absorption edge. Compounds EMULIT, JAHPUG and POPBAY are methoxy, chloro and bromo derivatives, respectively, substituted at the para position on the phenyl ring, while compounds KABHUS, UNUDUD (UNUDUD01) and WAFGOB are ortho-substituted ethoxy, hydroxy and bromo derivatives, respectively. Dihedral angles between the enone unit and the anthracene ring system and between the enone unit and the benzene ring are 81.6 (3) and 8.2 (4) , respectively, for EMULIJ, 47.  (11) between the enone unit and the anthracene ring system observed for KABHUS is due to the Z configuration of the molecule. Interestingly, EMULIJ with an E configuration also shows a large dihedral angle of 81.6 (3) between the enone unit and the anthracene ring system, whereas the dihedral angle between the enone unit and the benzene ring is extremely small [8.2 (4) ].

Synthesis and crystallization
A mixture of 4-nitroacetophenone (0.5 mmol) and 9-anthracencarboxaldehyde (0.5 mmol) was dissolved in methanol (20 ml) and the solution stirred continuously. A catalytic amount of NaOH (5 ml, 20%) was added to the solution dropwise until a precipitate formed and the reaction was stirred continuously for about 5 h at room temperature. After stirring, the solution was poured into 60 ml of ice-cold distilled water. The resultant crude product was filtered and washed several times with with distilled water until the filtrate turned colourless. The dried precipitate was further recrystallized to obtain the corresponding chalcone. Red plate-shaped single crystals suitable for X-ray diffraction were obtained by slow evaporation of an acetone solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were placed in calculated positions (C-H = 0.93 Å ) and were included in the refinement in the riding-model approximation, with U iso (H) = 1.2U eq (C). Four outliers (002) UV-vis spectrum of the title compound. Inset showed the experimental energy band gap obtained from absorption edge wavelength ( a.e ).

Figure 6
The spatial distributions of the HOMO and LUMO calculated for the title compound.

Special details
Experimental. The following wavelength and cell were deduced by SADABS from the direction cosines etc. They are given here for emergency use only: CELL 0.71075 3.957 11.583 40.623 82.797 90.074 69.980 Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refined as a 2-component twin.