Crystal Engineering for π-π Stacking
FIGURE 5. (a) A pair of on-top S · · ·C contacts (Å) can be found in the dimer of 2 (crystal structure). The nearby C · · ·C distances are also labeled.
(b) HOMO-1 of the dimer of 2 shows that the on-top contacts facilitate a good coupling between the HOMOs of the monomers.
1H NMR (δ, acetone-d6): 7.45 (td, 1 H, J ) 7.2, 1.2 Hz, C6H4),
7.51 (d, 1 H, J ) 5.2 Hz, thiophene), 7.55 (td, 1 H, J ) 7.2, 1.2
Hz, C6H4), 7.80 (d, 1 H, J ) 5.2 Hz, thiophene), 7.99 (d, 1 H, J )
8.0 Hz, C6H4), 8.07 (d, 1 H, J ) 8.0 Hz, C6H4), 8.14 (s, 1 H,
thiophene). 13C NMR (δ, acetone-d6): 163.7, 154.7, 145.0, 139.9,
136.4, 133.3, 132.0, 127.6, 127.0, 126.5, 123.7, 122.9, 122.6, 121.0.
FAB MS (m/z): 274.1 [M+ + H]. HRMS (m/z): calcd for C13H8NS3
273.9819, found 273.9818 [M+ + H]. Anal. Calcd for C13H7NS3:
C, 57.11; H, 2.58; N, 5.12. Found: C, 56.37; H, 2.13; N, 5.30.
2-Thieno[3,2-b]thiophene-2-yl-1H-benzoimidazole (6). To a
flask containing thieno[3,2-b]thiophene (1.4 g, 10 mmol) in 40 mL
of DMF immersed in a cold bath at 0 °C was added n-BuLi (7.0
mL, 1.6 M in hexane) dropwise. After addition was complete, the
solution was stirred for 1 h. Another 10 mL of DMF was added
and the solution was stirred for an additional 20 min at 0 °C. After
the solution was warmed to room temperature, the solution was
extracted with Et2O. The ether extracts were collected and dried
over MgSO4. The solvent was removed in vacuo to provide yellow
oily thieno[3,2-b]thiophene-2-carbaldehyde. To a flask containing
thieno[3,2-b]thiophene-2-carbaldehyde (1.51 g, 9.0 mmol) in 30
mL of EtOH immersed in a cold bath at 0 °C was added dropwise
30 mL of aqueous solution containing Na2S2O5 (10.8 mmol). The
solution was stirred at 0 °C for 6 h and filtered. The yellow
hydroxylthieno[3,2-b]thiophene-2-ylmethanesulfonate collected was
washed with H2O and EtOH and pumped dry. A flask was charged
with hydroxylthieno[3,2-b]thiophene-2-ylmethanesulfonate and 17
mL of DMF. After being stirred at 130 °C, the solution was cooled
to room temperature. The solid formed upon addition of H2O was
collected by filtration. It was then extracted with a mixture of
CH2Cl2 and saturated brine. The organic extracts were collected
and dried over MgSO4. After removal of the solvent, the residue
was recrystallized from CH2Cl2/hexane to afford off-white 6 in 15%
Computational Methods
All the structures were optimized at the DFT-B3LYP/6-31G(d,p)
level of theory and frequency calculations were performed to
confirm whether the optimized geometry was an energy minimum
on the potential energy surface with Gaussian 03.19 ( S2 for the
open-shell species is in the range of 0.7615-0.7702.) At high
temperature (including room temperature), the charge carriers in
thin-film OFET are believed to be localized at individual molecules,
and the charge-transport mechanism is a hopping mechanism
described by Marcus theory.16 The rate expression of self-exchange
process is:
4π2
h
1
λ
4kBT
ket )
t2 exp(-
)
(1)
4πλk T
√
B
in which the internal reorganization energy (λ) and intermolecular
electronic coupling (t) decide the value of the electron transfer rate (ket).
Because the reorganization energies (λ) calculated at the DFT-
B3LYP/6-31G(d,p) level agree well with experimental values,15b,17,20
λ is estimated at the same theory level. The total internal
(
(
reorganization energy (λ( ) is the sum of λ1 and λ2 (see
eqs 2-4):
λ( ) λ1( + λ2
(2)
(3)
(4)
(
λ1 ) E((QN) - E((Q()
λ2 ) EN(Q() - EN(QN)
where E ( (QN) is the total energy of the charged state in the neutral
geometry, E ( (Q ( ) is the total energy of the charged state in the
charged state geometry, EN(Q ( ) is the total energy of the neutral
state in the charged state geometry, and EN(QN) is the total energy
of the neutral state in the neutral geometry.
The t ( values were obtained via the direct coupling method (eq 5)
with the use of dimeric structures extracted from the X-ray structures.
The fragmental orbital approach implemented in the Amsterdam
density functional (ADF) program21 was used to derive the components
in eq 5. The details are described in two recent papers.22 The DZP
basis set in ADF was used and the local density functional VWN was
employed in conjunction with the PW91 gradient corrections.
1
yield. H NMR (δ, acetone-d6): 7.19-7.23 (m, 2 H, C6H4), 7.48
(d, 1 H, J ) 5.2 Hz, thiophene), 7.48-7.51 (m, 1 H, C6H4),
7.63-7.67 (m, 1 H, C6H4), 7.71 (d, 1 H, J ) 5.2 Hz, thiophene),
8.08 (s, 1 H, thiophene). 13C NMR (δ, acetone-d6): 148.3, 145.3,
141.8, 140.6, 136.9, 136.0, 130.5, 124.0, 123.0, 120.9, 120.0, 119.4,
111.9. FAB MS (m/z): 257.1 [M+ + H]. HRMS (m/z): calcd for
C13H9N2S2 257.0207, found 257.0202 [M+ + H]. Anal. Calcd for
C13H8N2S2: C, 60.91; H, 3.15; N, 10.93. Found: C, 61.26; H, 3.16;
N, 10.96.
HRP - SRP(HRR + HPP)/2
(19) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.;
Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian,
H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski,
J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg,
J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.
; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.;
Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.;
Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill,
P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian 03, Revision D.02; Gaussian, Inc.: Wallingford, CT, 2004.
(20) (a) Coropceanu, V.; Malagoli, M.; da Silva Filho, D. A.; Gruhn, N. E.;
Bill, T. G.; Bre´das, J. L. Phys. ReV. Lett. 2002, 89, 275503. (b) Kwon, O.;
Coropceanu, V.; Gruhn, N. E.; Durivage, J. C.; Laquindanum, J. G.; Katz, H. E.;
Cornil, J.; Bre´das, J. L. J. Chem. Phys. 2004, 120, 8186. (c) Chen, H. Y.; Chao,
I. ChemPhysChem 2006, 7, 2003.
t( )
(5)
1 - S2RP
where HRP is the charge transfer integrals, SRP is the spatial overlap,
and HRR and HPP are site energies.
Once λ( and t( are obtained, one can calculate the electron
transfer rate ket according to eq 1. The diffusion coefficient D of
charge carriers can then be given by eq 6, where L is the effective
(21) (a) te Velde, G.; Bickelhaupt, F. M.; van Gisbergen, S. J. A.; Guerra,
C. F.; Baerends, E. J.; Snijders, J. G.; Ziegler, T. J. Comput. Chem. 2001, 22,
931. (b) Fonseca Guerra, C.; Snijders, J. G.; te Velde, G.; Baerends, E. J. Theor.
Chem. Acc. 1998, 99, 391. (c) ADF 2005 01, SCM, Theoretical Chemistry, Vrije
(22) (a) Prins, P.; Senthilkumar, K.; Grozema, F. C.; Jonkheijm, P.;
Schenning, A. P. H. J.; Meijer, E. W.; Siebbeles, L. D. A. J. Phys. Chem. B
2005, 109, 18267. (b) Senthilkumar, K.; Grozema, F. C.; Buckelhaupt, F. M.;
Siebbeles, L. D. A. J. Chem. Phys. 2003, 119, 9809.
J. Org. Chem. Vol. 73, No. 12, 2008 4613