Columnar self-assembly and alignment of planar carbenium ions in langmuir-blodgett films

TY - JOUR

T1 - Columnar self-assembly and alignment of planar carbenium ions in langmuir-blodgett films

AU - Simonsen, Jens Bæk

AU - Westerlund, Axel Rune Fredrik

AU - Breiby, Dag W.

AU - Harrit, Niels Holger

AU - Laursen, Bo Wegge

PY - 2011/1/18

Y1 - 2011/1/18

N2 - Structural and optical properties of multilayer Langmuir-Blodgett (LB) films of two amphiphilic carbenium salts 2-didecylamino-6,10-bis(dimethylamino)- 4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-1) and 2,6-bis(decylmethylamino)-10-dimethylamino-4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-2) are described. The LB films were prepared on lipophilic glass by standard vertical dipping. Grazing incidence X-ray diffraction (GIXD) measurements show that the planar organic cores, in spite of their positive charge, form closely packed columns with a repeating distance of ∼3.45 Å. Specular X-ray reflectivity (SXR) reveals the LB multilayers to consist of Y-type bilayers with thickness 31 Å for ATOTA-1 and 41 Å for ATOTA-2. This significant difference is ascribed to the different packing motifs of the alkyl chains in the two LB films. GIXD and polarized UV-vis absorption and emission spectroscopy show that the columnar aggregates in the LB films are oriented along the dipping direction. This alignment is attributed to shear effects during LB transfer. The main absorption band of the LB films is blue-shifted compared to that in solution, while the fluorescence is red-shifted by more than 100 nm. These findings suggest the presence of H-aggregates in agreement with the cofacial packing derived from the X-ray measurements. Polarized absorption spectroscopy with variable angle of incidence was used to resolve two perpendicular optical transitions in the visible range, one at 460 nm polarized perpendicular to the columnar direction, in the plane of the film, and one at 420 nm polarized along the film normal.

AB - Structural and optical properties of multilayer Langmuir-Blodgett (LB) films of two amphiphilic carbenium salts 2-didecylamino-6,10-bis(dimethylamino)- 4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-1) and 2,6-bis(decylmethylamino)-10-dimethylamino-4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-2) are described. The LB films were prepared on lipophilic glass by standard vertical dipping. Grazing incidence X-ray diffraction (GIXD) measurements show that the planar organic cores, in spite of their positive charge, form closely packed columns with a repeating distance of ∼3.45 Å. Specular X-ray reflectivity (SXR) reveals the LB multilayers to consist of Y-type bilayers with thickness 31 Å for ATOTA-1 and 41 Å for ATOTA-2. This significant difference is ascribed to the different packing motifs of the alkyl chains in the two LB films. GIXD and polarized UV-vis absorption and emission spectroscopy show that the columnar aggregates in the LB films are oriented along the dipping direction. This alignment is attributed to shear effects during LB transfer. The main absorption band of the LB films is blue-shifted compared to that in solution, while the fluorescence is red-shifted by more than 100 nm. These findings suggest the presence of H-aggregates in agreement with the cofacial packing derived from the X-ray measurements. Polarized absorption spectroscopy with variable angle of incidence was used to resolve two perpendicular optical transitions in the visible range, one at 460 nm polarized perpendicular to the columnar direction, in the plane of the film, and one at 420 nm polarized along the film normal.

U2 - 10.1021/la103785z

DO - 10.1021/la103785z

M3 - Journal article

C2 - 21155574

SN - 0743-7463

VL - 27

SP - 792

EP - 799

JO - Langmuir

JF - Langmuir

IS - 2

ER -