1,4,5,8-Tetraisopropylanthracene

The molecules of the title compound, C26H34, possess crystallographically imposed inversion symmetry. The anthracene ring system is planar within 0.038 (1) Å. The two methyl groups in each independent isopropyl group are oriented on either side of the anthracene plane. In the crystal structure, the molecules adopt a herringbone-like arrangement without π–π stacking.

The molecules of the title compound, C 26 H 34 , possess crystallographically imposed inversion symmetry. The anthracene ring system is planar within 0.038 (1) Å . The two methyl groups in each independent isopropyl group are oriented on either side of the anthracene plane. In the crystal structure, the molecules adopt a herringbone-like arrangement withoutstacking.  that the introduction of linear alkyl side chains onto anthracene nucleus at the 1, 4, 5 and 8 positions brought about drastic changes in alkyl conformation, packing pattern, and solid-state fluorescence (Kitamura et al., 2007). To investigate the effects of branched alkyl side chains, we embarked on the investigation on 1,4,5,8-tetraisoalkylanthracenes. Herein we report the X-ray analysis of the title compound (I).

Related literature
The molecular structure of (I) is shown in Fig. 1. The molecule possesses a center of inversion, and half of the formula unit is crystallographically independent. The anthracene unit is essentially planar. The molecular structure is similar to that of 1,4,7,10-tetraisopropyltetracene (Kitamura et al., 2010). Two terminal methyl groups of the two isopropyl groups at the 1 and 4 positions point upward, and two methyl groups of the other two isopropyl groups at 5 and 8 positions point downward. Thus, the torsion angles C6-C1-C8-C9 and C3-C4-C11-C13 are 80.72 (18) and 107.76 (16)°, respectively.
Another two terminal methyl groups of the two isopropyl groups are nearly coplanar with the anthracene plane, and the C2-C1-C8-C10 and C3-C4-C11-C12 torsion angles are 25.6 (2) and -15.2 (2)°, respectively. In the crystal, the molecules adopt a herringbone-like (two-dimensional) arrangement as shown in Fig. 2. There are no π-π interatcions along the stacking direction.
To examine the influence of crystal packing on the solid-state fluorescence properties, the fluorescence spectrum and the absolute quantum yield of (I) were measured by a Hamamatsu Photonics PMA11 calibrated optical multichannel analyzer with a solid-state blue laser (λ ex = 377 nm) and a Labsphere IS-040-SF integrating sphere, respectively. Crystals of (I) exhibited a structured fluorescence spectrum with fluorescence maxima at 432 and 450 nm. The quantum yield of crystals of (I) was very high (Φ = 0.80). Among 1,4,5,8-tetraalkylanthracenes, the n-propyl derivative had the largest quantum yield of 0.85, indicating that the quantum yield of (I) is the second largest. Crystal packing without π-π stack and crystal rigidity in the presence of bulky isopropyl groups probably lead to the enhancement of the fluorescence quantum yield.

Refinement
All the H atoms were positioned geometrically and refined using a riding model with C-H = 0.94 Å and U iso (H) = 1.2U eq (C) for aromatic C-H, C-H = 0.99 Å and U iso (H) = 1.2U eq (C) for CH, and C-H = 0.97 Å and U iso (H) = 1.5U eq (C) for CH 3 group. Fig. 1. The molecular structure of (I), showing the atomic numbering numbering and 30% probability displacement ellipsoids for non-H atoms. Symmetry code: (i) 1 -x, -y, -z. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq