Self-Organizing Liquid Crystal Perylene Diimide Thin Films:  Spectroscopy, Crystallinity, and Molecular Orientation

Abstract

Three different liquid crystal (LC) perylene diimides were investigated with respect to the optical and physical characteristics of their thin films. Films were prepared by spin-coating, vacuum evaporation, and Langmuir−Blodgett (LB) techniques on substrates such as microscope glass, indium−tin oxide-coated glass and highly oriented pyrolytic graphite. Films were characterized by polarized optical microscopy, absorption and fluorescence emission spectroscopy, and X-ray diffraction. The self-organizing ability of the LC perylene diimides allows them to rapidly reach a stable, low-energy configuration, unlike many thin film materials, and reveals that they are driven to organize and orient in a highly specific fashion, independent of substrate or deposition method. The molecules tend to form a slipped stack arrangement that maximizes attractive π−π electronic interactions, with the π−π stacking axis oriented parallel to the substrate. Relative to the substrate plane, the LC 1 perylene cores are tilted ∼47° along the stacking axis and ∼58° perpendicular to this direction. The two other LCs have similar structures. An analysis of the intermolecular electronic and steric interactions, and of the interactions between the molecules and the substrates, is proposed to explain why this is such a strongly preferred orientation. The implications for the potential use of such molecules in electronic and photovoltaic applications is discussed.

Hierarchical Assembly of Organic/Inorganic Building Molecules with π–π Interactions

“…At the same time, the fluorescence intensity decreased, indicating the presence of strong fluorescence quenching effect with the formation of the aggregates. The large red shift and quenching in emission indicate strong intermolecular p-p stacking, which are associated with large exciton diffusion lengths [37][38][39][40][41][42] and high charge carrier mobility [43,44] Interestingly, the fluorescence spectra of hollow and solid micro-spheres show broader emission peak and larger red shift as compared to the spectrum of micro-tubes. Such an observation indicates that the fluorescence property is related to the assembly morphology, and a longer-range order resulted from a larger-length-scale assembly may provide more significant intermolecular interactions.…”

Ring‐Shaped J‐Type and Star‐Shaped H‐Type Nanostructures of an Unsymmetrical (Phthalocyaninato)zinc Complex

“…This value is about 10 % shorter than the total length of the molecule of 1 along the long axis, 3.10 nm, obtained from the energy-optimized conformation of the molecule by DFT calculation at the B3LYP/6-31G(d) level of theory (Scheme S1, Supporting Information). Based on this result and in combination with the electronic absorption spectrum of the nanostructures formed at the chloroform/water interface, this is probably due to the edge-on orientation [19] (which suggests that the long axes of the molecules are tilted to some extent away from the substrate plane, which is a common structural motif in organic semiconductor thin films) and face-to-face stacking occurring in the phthalocyanine molecules, in line with strong hydrophobic interactions between side-chains of neighboring (phthalocyaninato)zinc molecules, which results in effective side-chain interdigitation and leads to a shortened length along the longitudinal direction (Figwww.eurjic.orgure 3A). [6b,20] In addition, the XRD pattern displays one well-defined peak at the wide-angle range corresponding to a distance of 0.42 nm, which is related to the liquid-like order of the alkyl chains.…”

Supramolecular Organization of $$\pi $$-Conjugated Oligomers

“…Therefore, one can introduce electron-withdrawing groups like halogens, nitro or carboximide groups (22-26) [102][103][104][105][106]. Naphthalene and perylene bisimides derivatives (25,26) are probably the most prominent compounds of this class with similarly high electron charge-carrier mobilities [107][108][109][110]. Another, strategy to access n-type semiconducting compounds is to introduce nitrogen atoms in the core of the aromatic system to reduce its electron density as for instance in compounds 27-31 [111][112][113][114][115][116][117][118][119][120].…”