C—H⋯π packing interactions in 2-[5,5-bis(4-benzyloxyphenyl)-3-cyano-4-methyl-2,5-dihydrofuran-2-ylidene]malononitrile

The title molecule, C35H25N3O3, packs utilizing C—H⋯π attractive interactions causing the identical 4-benzyloxyphenyl groups to pack with different conformational angles. This difference is consistent with the variable interplanar dihedral angles found in closely related structures.

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009). materials (e.g. LiNbO3) as they have a much faster response times, are easer to prepare, have low drive voltages and low signal losses. However, issues of aggregation, photochemical & thermal stability are proving significant barriers to the successful uptake of organic NLO materials. A considerable effort has been made over the last two decades to develop organic chromophores with the largest possible NLO response. Due to their dipolar nature, strong electrostatic interactions are possible between individual NLO chromophore molecules which leads to a significant tendency to aggregate (Smith et al., 2006;Datta & Pati, 2003;Teshome et al., 2009). Therefore, much effort has been expended developing methods to minimize aggregation between NLO chromophores (Smith et al., 2010).
One of the most successful strategies to minimize aggregation has been to add bulky pendant groups onto the chromophores. If the pendant groups are aromatic in nature, stacking interactions between the aromatic rings may result, which can overcome the dipole-dipole interactions that cause aggregation (Smith et al., 2010). We have synthesized a new acceptor (the title compound) with bulky groups to reduce aggregation as well as reduce, or even eliminate rotation around the conjugated polyene bridge -acceptor bond.
The asymmetric unit contents of the title compound(I) are shown in Figure 1. The 5-membered ring plane of atoms O1,C4-C7 (hereafter "CDFP", [3-cyano-5,5-dimethyl-2,5-dihydrofuran-2-ylidene]propanedinitrile) can be regarded as planar with maximum out of plane deviation for O1 of 0.023 (1) Å. The dicyano group (N1,C1,C2,C3,N2,C6) is planar but twisted by 5.32 (10) ° with respect to the "CDFP" group; this is similar to the twist in related compound NOJKUT (Gainsford et al., 2008) of 5.69 (17) °. Atom C5 is essentially tetrahedral with the C23-C5-C10 angle widened to 115.83 (11) ° and the internal O1-C5-C4 102.11 (10) °. The phenyl rings are either close to or statistically planar (e.g. ring C17-C22, maximum deviation C19, 0.007 (2) Å). The mean planes of the phenyl groups bound directly to the CDFP atom C5 (C10-C15, The main difference observed in the structure is in the relative angular dispositions of the terminal phenyl groups. Here significant differences are seen with the different angles to their attached phenyl rings: 88.79 ° (C17-C22) and 37.81 (8) °( C30-C35) respectively. It is only after consideration of the molecular packing that this deviation for the pendant identical chemical groups can be rationalized. The crystal packing is dominated by C-H···π bonds (no other significant interactions are observed) with the strongest interaction involving the methylene hydrogen on C29 (H29A) and the phenyl hydrogen H33 (Table 1, Figure 2). The normal expectation for linked biphenyl rings is for their dihedral angles to be ~90 ° to alleviate supplementary materials sup-2 adjacent ring H···H interactions. Here the restricted twist (\sim 38 °) noted for just one of the ligand arms (involving C23-C28 & C30-C35 rings) ensures optimal C-H···π attractive overlap between glide plane related molecules.
The benzoyloxy-phenyl ring dihedral angles in the comparable structures, whilst variable, are reasonably consistent with the above analysis. For KIKKAR, the angle is 76.54 (9) ° with one C-H···π interaction involving the methylene hydrogen and for SUHNEP, 10.4 (2) & 8.6 (2) ° with six C-H···π interactions utilizing methylene & phenyl hydrogen atoms. Finally for GERLIY the angles are 78.9 (2), 7.7 (2) and 30.6 (2) ° with two C-H···π interactions involving one methylene and one phenyl hydrogen. Apparently, the orientation of the terminal benzoylozy groups with respect to the attached phenyl group is highly dependent on the C-H···π interactions, so no strict orientation rule can be defined.
There are other intermolecular interactions in (I) ( Table 1) but the two highlighted ( Figure 2 and above) are both closer (C g ···H < 2.8 Å) and have maximized C-H···C g angles (Desiraju & Steiner, 1999). In Table 1 & Figure 2, labels Cg1-3 represent the centroids of the phenyl rings C10-C15, C17-C22 & C23-C28 respectively. In conclusion, we note that C-H···π interactions add to the list of weak but important interactions in crystal formation, so that the preferred molecular alignment of the target molecules is not attained.