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band, which can be correlated with the HOMO → LUMO+2 55 Notes and references
transition (Figure 2a and b) and a substructured region between
a
Departamento de Quimica Orgánica, Facultad de Ciencias Químicas,
Universidad Complutense de Madrid, E-28040 Madrid, Spain, E-mail:
segura@quim.ucm.es.
4
10 and 520 nm, which corresponds to the absorption of always
present molecular aggregates, due to the reduced solubility of 2 in
all utilized solvents. The structured fluorescence band can
correspond to the reminiscent emission of the molecular
dissolved compound or to an aggregateꢀinduced emission. The
absorption band at 374 nm of derivative 3 corresponds to the
HOMO ꢀ 1→ LUMO transition (Figure 2a and b). No evidence of
b
5
Inst. for Organic Chemistry II and Advanced Materials, Uni.of Ulm,
60
Albert-Einstein-Allee 11, D-89081 Ulm, Germany. Fax: +49731-
5
022840; Tel: +497315022850; E-mail: elena.mena-osteritz@uni-ulm.de
Dept. de Física Aplicada I, Escuela Politécnica de Donostia, Univ. del
c
País Vasco UPV/EHU, Pl. Europa 1, E-20014 Donostia, Spain
† Electronic Supplementary Information (ESI) available: [chemicals,
1
1
2
0
5
0
charge transfer bands for derivatives 2 and 3 has been obtained 65 NMR, DPV, TGA, DSC]. See DOI: 10.1039/b000000x/
‡
Financial support from MICINN (CTQ2010ꢀ14982), Comunidad
from the calculations, in contrast to the results for 1. For all three
compounds the fluorescence quantum yield was below 1%.
All the compounds are shown to have high thermal stability
by thermogravimetric analysis (Figure S4 in ESI). 2 has the
highest thermal stability with an onset decomposition temperature
Autónoma de Madrid (S2009/MATꢀ1467), and the UCMꢀBSCH joint
project (GR35/10A, Gr. 910759) is gratefully acknowledged. JLS thanks
Fundación Caja Madrid for the funding of a research grant.
70
1
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(Td) of 500ºC. Differential scanning calorimetry (DSC) curves
show no phase transition from rt to T (Figure S5 in ESI).
d
The surface morphology of films of systems 1-3 spinꢀcoated
24
2
D. Gosztola, M. P. Niemczyk, W. Svec, A. S. Lukas and M. R.
on Si/SiO wafers has been analyzed using tapping mode AFM.
2
Wasielewski, J. Phys. Chem. A, 2000, 104, 6545.
For compound 1, elongated structures, whose height (1.43 ± 0.09
nm) correlates to the length of the molecule and small clusters are
observed to adsorb onto the substrate, with a low 32% surface
coverage (Fig. 3a).
3
H. Vollmann, H. Becker, M. Corell and H. Streeck, Liebigs Ann.,1937,
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31, 1.
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Figure 3: AFM height images of a) 1, b) 2 and c) 3 spinꢀcoated at 2000
ꢀ4
8
2
5
rpm during 300 s from 3ꢁ10 M solutions on Si/SiO
at 60ºC during 10 min. Scale bar: 400 nm
2
wafer and annealed
4
225.
9
1
M. F. Braña and A. Ramos, Curr. Med. Chem., 2001, 1, 237
a) P. A. Panchenko, Y. V. Fedorov, V. P. Perevalov, G. Jonusauskas, O.
0
For derivative 2 the images revealed a wide cluster
distribution on top of an almost clean substrate (Fig. 3b). Finally,
the deposition of 3 on the Si wafer produced interconnected
winding wormꢀlike structures formed by aggregation of small
A. Fedorova, J. Phys. Chem. A, 2010, 114, 4118; b) R. K. Jackson, Y.
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3
0
11
(~25ꢀ30 nm) wellꢀdefined clusters (Fig. 3c) with a 75% surface
1
1
2
3
coverage. The analysis of the structures shows a width of ~20 nm
with a persistent height of 1.0 ± 0.1nm. Because the size of the
molecules exceeds the last value, a tilted (30°ꢀ40°) adsorption
arrangement has to be postulated. As a consequence, hybrid 3
revealed the best, derivative 2 the worst filmꢀforming properties.
This can be related to the low solubility of 2, whose aggregation
tendency has been observed even in diluted solution (vide supra).
In summary, large linear and starꢀshaped naphthalimideꢀfused
pyrazinacenes were synthesized using the versatile diketone
building block 8. The novel systems were shown to have high
thermal stability and the extended large πꢀsurface in the symꢀ
metric derivatives 2 and 3 causes facile aggregation and selfꢀ
assembly due to πꢀπ interactions. Additionally, derivative 3
showed good film forming properties as indicated by the AFM
characterization. In conjunction with the interesting
morphological and photophysical behavior, the described novel
materials exhibit excellent electronꢀacceptor properties with
LUMO energies below ꢀ3.5 eV which are usually required for
efficient electron injection into semiconductors. Thus, the novel
molecular skeleton paves the way for the design and synthesis of
new nꢀtype semiconductors useful in organic field effect
transistors.
1
1
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3
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