TY - JOUR
T1 - Langmuir and Langmuir-Blodgett films of amphiphilic hexa-peri-hexabenzocoronene: New phase transitions and electronic properties controlled by pressure
AU - Reitzel, N.
AU - Hassenkam, T.
AU - Balashev, K.
AU - Jensen, T.R.
AU - Howes, P.B.
AU - Kjær, K.
AU - Fechtenkötter, A.
AU - Tchebotareva, N.
AU - Ito, S.
AU - Müllen, K.
AU - Bjørnholm, T.
PY - 2001
Y1 - 2001
N2 - We present the synthesis as well as the structural and electronic properties of an amphiphilic derivative of hexaalkylhexa-peri-hexabenzocoronene (HBC), which contains one alkyl substituent that is terminated with a carboxylic acid group. The molecules form well-defined Langmuir films when spread from a solution at the air-water interface. Grazing-incidence X-ray diffraction (GIXD) and X-ray reflectivity studies of the Langmuir monolayer reveal two crystallographic phases at room temperature which depend on the surface pressure applied to the film. Scattering from very well-ordered (xi = 200-400 Angstrom) pi -stacked lamellae of HBC molecules tilted approximate to 45 degrees relative to the surface normal is observed in the low-pressure phase. In this phase. the HBC molecules pack in a rectangular two-dimensional unit cell with a = 22.95 Angstrom and b = 4.94 Angstrom. In the high-pressure phase, coherence from the it stack is lost. This is a consequence of stress induced by the crystallization of the substituent alkyl chains into a hexagonal lattice, which has a trimerized superstructure in one direction: a = 3 x b = 15.78 Angstrom. b = 5.26 Angstrom, gamma = 120 degrees, A = 71.9 Angstrom (2) = 3 x 23.9 Angstrom (2). Thin monolayer films can be transferred to solid supports by the Langmuir-Blodgett (LB) technique. Atomic force microscopy (AFM) with atomic resolution reveals the crystalline packing of alkyl chains in the high-pressure phase. Kelvin force microscopy (KFM) shows a clear potential difference between the high- and low-pressure phases. This is discussed in terms of orbital delocalization (band formation) in the highly coherent low-pressure phase, which is in contrast to the localized molecular orbitals present in the high-pressure phase. The highly coherent pi stack is expected to sustain a very high charge-carrier mobility.
AB - We present the synthesis as well as the structural and electronic properties of an amphiphilic derivative of hexaalkylhexa-peri-hexabenzocoronene (HBC), which contains one alkyl substituent that is terminated with a carboxylic acid group. The molecules form well-defined Langmuir films when spread from a solution at the air-water interface. Grazing-incidence X-ray diffraction (GIXD) and X-ray reflectivity studies of the Langmuir monolayer reveal two crystallographic phases at room temperature which depend on the surface pressure applied to the film. Scattering from very well-ordered (xi = 200-400 Angstrom) pi -stacked lamellae of HBC molecules tilted approximate to 45 degrees relative to the surface normal is observed in the low-pressure phase. In this phase. the HBC molecules pack in a rectangular two-dimensional unit cell with a = 22.95 Angstrom and b = 4.94 Angstrom. In the high-pressure phase, coherence from the it stack is lost. This is a consequence of stress induced by the crystallization of the substituent alkyl chains into a hexagonal lattice, which has a trimerized superstructure in one direction: a = 3 x b = 15.78 Angstrom. b = 5.26 Angstrom, gamma = 120 degrees, A = 71.9 Angstrom (2) = 3 x 23.9 Angstrom (2). Thin monolayer films can be transferred to solid supports by the Langmuir-Blodgett (LB) technique. Atomic force microscopy (AFM) with atomic resolution reveals the crystalline packing of alkyl chains in the high-pressure phase. Kelvin force microscopy (KFM) shows a clear potential difference between the high- and low-pressure phases. This is discussed in terms of orbital delocalization (band formation) in the highly coherent low-pressure phase, which is in contrast to the localized molecular orbitals present in the high-pressure phase. The highly coherent pi stack is expected to sustain a very high charge-carrier mobility.
KW - Industrielle materialer
U2 - 10.1002/1521-3765(20011119)7:22<4894::AID-CHEM4894>3.0.CO;2-S
DO - 10.1002/1521-3765(20011119)7:22<4894::AID-CHEM4894>3.0.CO;2-S
M3 - Journal article
SN - 0947-6539
VL - 7
SP - 4894
EP - 4901
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 22
ER -