Discotic Twin and Triple Molecules with Charge-Transfer Interactions in Langmuir−Blodgett Films

Abstract

X-ray and atomic force microscopy observations reveal features of the surface morphology of Langmuir−Blodgett (LB) films from discotic donor−acceptor molecules with strong core-to-core interactions caused by a charge-transfer (CT) complexation. The compounds are designed to be twin and triple molecules composed of chemically connected donor (triphenylene) and acceptor (trinitrofluorenone) fragments which display liquid crystalline structure in the bulk state. The LB films from these compounds possess edge-on orientation of molecules within monolayers with a smooth surface on a submicron scale but with substantial macroscopic imperfections. These imperfections are represented by the micron size fractures and ruptures apparently caused by local deformations and tensions during transfer of the discotic monolayers from the air−water interface to a solid substrate. It is suggested that this is due to the excessive rigidity of the monolayers caused by the stiffness of the columns with positional intracolumnar ordering enhanced by the strong intracolumnar CT interactions.

Discotic liquid crystalline tris(hexahexyloxytriphenylene)triazines with separate columns of triphenylene and triazine cores

“…Normally, electron-deficient and electron-rich moieties tend to form mixed columns, as is found, for example, in trinitrofluorenone-triphenylene mixtures. [12,30,31] So, the current system indicates that it is possible to obtain well-ordered columnar phases with parallel hole and electron-conducting pathways. This ordering is of significant interest in, e.g., solar cell or other optoelectronic applications.…”

Transition in nanoscale electrical conductivity in the Langmuir-Blodgett film of a novel liquid crystalline oligomer

“…In this context, novel amphiphilic molecules containing discotic moieties are interesting, since the Π−Π stacking of the disk shaped cores in the LB film can result in the formation of two dimensional anisotropic structures [10,11]. The LB film of liquid crystalline molecules with different cores like anthraquinone [6], triphenylene [12][13][14][15] and phthalocyanine [16] have been studied.…”

“…In this regard, it is important to study the metal-film-metal junction with the well ordered molecules in the film having different molecular orbital structure is important. The presence of electron rich and deficient moieties in the molecules improves in charge transfer through the molecules in the film after tunnelling from the electrode [3,12]. In addition, the asymmetry in the structure of the molecules will result in asymmetric metal-film junctions and hence the resulting metal-film-metal junctions may have characteristics of a rectifier, which is interesting for many molecular device applications.…”

Monolayers of triaroylbenzene derivatives

“…A common core functional group in these molecules is triphenylene, the stacking of which in discotic arrangements results in films with Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 3227 -3238 www.elsevier.com/locate/tsf photoconductive and semiconductor properties [3][4][5][6][7][8]. Substituted triphenylenes have been studied as adsorbed monolayers on graphite [3][4][5], Langmuir-Blodgett films [6], and as selfassembled monolayers [7,8] of thiol-functionalized triphenylenes. In describing films of these molecules, the possibilities for a 'face-on' flat orientation and an 'edge-on' orientation either perpendicular or at an angle to the water surface becomes apparent along with possibilities for a transition between the face-on and edge-on orientations upon compression.…”