unit cell contained one molecule in a general position and two half
molecules lying about their inversion centres. Final residuals were R1
= 0.0644 and wR2 = 0.1740 for 7547 reflections with I 4 2s(I).
Crystal structure data for [3ꢃ+ SbClꢁ6ꢁ, 2C7H8]. A suitable crystal (0.51
+
ꢀ 0.23 ꢀ 0.14 mm3) of 3ꢃ SbCl6 was obtained from a mixture of
dichloromethane–toluene solution at ꢁ30 1C. MW = 889.27, orthor-
hombic, space group Pnma, a = 13.8054(3), b = 12.5572(3), c =
23.6942(6) A, a = 901, b = 901, g = 901, Dc = 1.438 Mg mꢁ3, V =
4107.56(17) A3, Z = 4. The total number of reflections measured were
34 504, of which 3746 reflections were symmetrically non-equivalent.
Final residuals were R1 = 0.0268 and wR2 = 0.659 for 3746
reflections with I 4 2s(I). Note that all four components have
crystallographically imposed mirror symmetry. CCDC numbers of
Fig. 4 Left: lettering scheme for the pyrene skeleton. Right: showing
the localization of the HOMO of 3, obtained by DFT calculations at
the B3LYP-631G** level, on bonds labelled B and D.
+
complexes 3 and [3ꢃ SbCl6ꢁ, 2C7H8] are 674750 and 674751.
Table 1 Experimental and theoretical bond lengths of the neutral and
cation radical of 3 presented in picometres (pm)
y Note that a cofacial arrangement between the toluene and 3ꢃ+ at an
inter-planar separation of 3.5 A may stabilize the cationic tetraiso-
propylpyrene via an electron-donor acceptor interaction. Also note
that both the toluene molecules are rotationally disordered (within
their respective molecular planes) with the occupations of the minor
components being 23 and 37%.
B3LYP/6-31G**
X-Ray data
+
+
3
3ꢃ
D
3
3ꢃ
D
Bond type
A
B
C
D
E
F
139.6 139.5
141.7 144.0
143.5 142.4
135.9 138.0
143.4 143.0
144.0 143.1
ꢁ0.1 138.9 (3)
138.6 (2) ꢁ0.3
143.5 (3) +2.4
141.2 (3) ꢁ2.2
137.5 (3) +2.8
142.4 (3) ꢁ0.3
142.7 (4) ꢁ1.8
+2.3 141.1 (3)
ꢁ1.1 143.4 (3)
+2.1 134.7 (3)
ꢁ0.4 142.7 (3)
ꢁ0.9 144.5 (3)
1 (a) S. A. V. Arman and A. W. Czarnik, J. Am. Chem. Soc., 1990,
112, 5376; (b) M. Sassaroli, M. Ruonala, J. Virtanen, M. Vauhko-
nen and P. Somerharju, Biochemistry, 1995, 34, 8843; (c) A.
Okamoto, K. Kanatani and I. Saito, J. Am. Chem. Soc., 2004,
126, 4820; (d) K. Fujimoto, H. Shimizu and M. Inouye, J. Org.
Chem., 2004, 69, 3271; (e) I. V. Astakhova, A. D. Malakhov, I. A.
Stepanova, A. V. Ustinov, S. L. Bondarev, A. S. Paramonov and
V. A. Korshun, Bioconjugate Chem., 2007, 18, 1972.
2 (a) S. A. Benning, T. Hassheider, S. Keuker-Baumann, H. Bock, F.
D. Sala, T. Frauenheim and H.-S. Kitzerow, Liq. Cryst., 2001, 28,
1105; (b) T. Hassheider, S. A. Benning, H.-S. Kitzerow, M.-F.
Achard and H. Bock, Angew. Chem., Int. Ed., 2001, 40, 2060; (c) V.
de Halleux, J.-P. Calbert, P. Brocorens, J. Cornil, J.-P. Declercq,
J.-L. Bredas and Y. Geerts, Adv. Funct. Mater., 2004, 14, 649; (d)
A. Hayer, V. D. Halleux, A. Koehler, A. El-Garoughy, E. W.
Meijer, J. Barbera, J. Tant, J. Levin, M. Lehmann, J. Gierschner, J.
Cornil and Y. H. Geerts, J. Phys. Chem. B, 2006, 110, 7653.
3 (a) T. Oyamada, H. Uchiuzou, S. Akiyama, Y. Oku, N. Shimoji,
K. Matsushige, H. Sasabe and C. Adachi, J. Appl. Phys., 2005, 98,
074506; (b) M. Muccini, Nat. Mater., 2006, 5, 605; (c) C.-H. Yang,
T.-F. Guo and I.-W. Sun, J. Lumin., 2007, 124, 93.
marked A (dA 139 pm) and E (dB 142 pm). (ii) The increased
aromatization of the two internal rings of the pyrene molecule
on oxidation occurs by a simultaneous lengthening of the
short external bonds B and D by 2.2 and 2.9 pm, respectively,
and shortening of the adjacent long bonds C by 2.1 pm.
Interestingly, the bonds which undergo most dramatic length-
ening in 3ꢃ+ (i.e. bonds B and D) are the bonds on which the
HOMO resides, i.e. Fig. 4 (right). (iii) The central bond F
undergoes a shortening of 1.8 pm in order to accommodate the
changes in the bond lengths of various annulenic bonds (i.e. B,
C, and D).
The experimental observations of the bond length changes
upon 1-electron oxidation of 3 were found to be in reasonable
agreement with the calculated values using DFT calculations
at the B3LYP-631G** level (see Table 1).13
4 G. Venkataramana and S. Sankararaman, Eur. J. Org. Chem.,
2005, 4162.
5 M. Minabe, S. Takeshige, Y. Soeda, T. Kimura and M. Tsubota,
Bull. Chem. Soc. Jpn., 1994, 67, 172.
6 (a) I. L. Zvarich, A. P. Zaraiskii and O. I. Kachurin, Ukr. Khim.
Zh. (Russ. Ed.), 1989, 55, 330; (b) A. Berg, J. Lam and P. E.
Hansen, Acta Chem. Scand., Ser. B, 1986, B40, 665; (c) K. K. Laali,
P. E. Hansen, E. Gelerinter and J. J. Houser, J. Org. Chem., 1993,
58, 4088 and references therein.
7 (a) M. Banerjee, S. V. Lindeman and R. Rathore, J. Am. Chem.
Soc., 2007, 129, 8070; (b) J. K. Kochi, R. Rathore and P. L.
Magueres, J. Org. Chem., 2000, 65, 6826; (c) R. Rathore, S. H.
Abdelwahed and I. A. Guzei, J. Am. Chem. Soc., 2004, 126, 13582;
(d) P. Debroy, R. Shukla, S. V. Lindeman and R. Rathore, J. Org.
Chem., 2007, 72, 1765 and references therein.
In summary, a simple and practical synthesis of 1,3,6,8-
tetraisopropylpyrene (3) has been accomplished from readily
available precursors. The emission and absorption spectro-
scopy of the neutral and cationic 3 clearly show that the p-
stacking is inhibited owing to the presence of bulky isopropyl
groups. The isolation and X-ray crystal structure determina-
+
ꢁ
tion of 3ꢃ SbCl6 as well as DFT calculations provide
unequivocal evidence that introduction of a cationic charge
(or polaron) in 3 largely affects the bonds on which the
HOMO resides. Studies are underway for a more comprehen-
sive investigation of the steric modulation of the p-stacking in
various polyaromatic hydrocarbons.
8 G. A. Molander and M. Ribagorda, J. Am. Chem. Soc., 2003, 125,
11148.
9 (a) F. M. Winnik, Chem. Rev., 1993, 93, 587; (b) C. G. Echeverrı
´
a,
J. Am. Chem. Soc., 1994, 116, 6031.
10 R. Rathore, S. V. Lindeman and J. K. Kochi, J. Am. Chem. Soc.,
1997, 119, 9393 and references therein.
11 R. Rathore, C. L. Burns, M. I. Deselnicu, S. E. Denmark and T.
Bui, Org. Synth., 2005, 82, 1.
Notes and references
12 (a) A. Tsuchida, Y. Tsujii, M. Oboka and M. Yamamoto, J. Phys.
Chem., 1991, 95, 5797; (b) Y. Mori, H. Shinoda, T. Nakano and T.
Kitagawa, J. Phys. Chem. A, 2002, 106, 11743; (c) E. H. Ellison, J.
Phys. Chem. B, 2004, 108, 4607; (d) M. Hara, S. Tojo, K. Kawai
and T. Majima, Phys. Chem. Chem. Phys., 2004, 6, 3215.
13 Compare: (a) A. Pathak and S. Rastogi, Chem. Phys., 2006, 326,
315; (b) S. F. Nelsen, M. N. Weaver, D. Yamazaki, K. Komatsu,
R. Rathore and T. Bally, J. Phys. Chem. A, 2007, 111, 1667.
z Crystal structure data for 3. A suitable crystal (0.20 ꢀ 0.18 ꢀ 0.06
mm3) of 3 was obtained from a mixture of dichloromethane–acetoni-
trile solution at 22 1C. MW = 370.55, triclinic, space group P1, a =
11.3272 (7), b = 12.6764(7), c = 16.9660(12) A, a = 94.595(4)1, b =
92.311(4)1, g = 115.064(3)1, Dc = 1.123 Mg mꢁ3, V = 2192.2(2) A3, Z
= 4. The total number of reflections measured were 25 845, of which
7547 reflections were symmetrically non-equivalent. Also note that
ꢀ
ꢂc
This journal is The Royal Society of Chemistry 2008
Chem. Commun., 2008, 1889–1891 | 1891