The influence of the core extension of perylene tetracarboxdiimides on the thermotropic behavior has been investigated. A homologous series of alkyl substituted tetracarboxdiimides, namely, perylene diimide, terrylene diimide, quaterrylene diimide, and coronene diimide, was synthesized. These compounds display absorption maxima in the region of 430-760 nm with high extinction coefficients and show a high thermal stability up to 450 °C. Structural evaluation revealed an identical columnar self-organization for the derivatives below their isotropization temperature. An intracolumnar packing of the disks with a lateral rotation of 45°to each other resulted in a helical pitch containing four molecules. The phase transition to the isotropic phase is shifted to higher temperatures for larger aromatic cores within this series of compounds. On the other hand, differences in the self-assembly during crystallization from the isotropic phase were observed. While perylene tetracarboxdiimide and terrylene tetracarboxdiimide formed large and highly ordered domains with arranged edge-on molecules, the coronene tetracarboxdiimide disks self-organized face-on leading to a homeotropic phase. The different molecular orientation on surfaces was correlated with diversified substitution patterns of the aromatic cores. The manipulation of the molecular architecture opens thus the opportunity to control the spontaneous self-alignment. This improvement of the macroscopic organization ensures an undisturbed percolation pathway for charge carriers between electrodes in field-effect transistors or in photovoltaic cells.

Two synthetic routes for the benzannulation in the "bay"-region of rylenebis(dicarboximide)s leading to new pi-system-expanded chromophores are described. The first route follows a two-step approach: Suzuki coupling of bromo-substituted perylenebis(dicarboximide) with 2-bromophenylboronic acid, followed by palladium-catalysed dehydrobromination. The second route is best described as a palladium-assisted cycloaddition of benzyne, formed in situ, to the bay-region of the bromo-substituted rylene core. Two new types of core-expanded rylene dyes were synthesised: yellow dibenzocoronenebis(dicarboximide)s, absorbing at 490 nm, and a green dinaphthoquaterrylenebis(dicarboximide), which absorbs at 700 nm. These new chromophores are characterised by significant hypsochromic shifts of absorption, compared to their parent rylenebis(dicarboximide)s, excellent photostabilities and high fluorescence quantum yields.

Developing molecular systems with functions analogous to those of macroscopic machine components, such as rotors, gyroscopes and valves, is a long-standing goal of nanotechnology. However, macroscopic analogies go only so far in predicting function in nanoscale environments, where friction dominates over inertia. In some instances, ratchet mechanisms have been used to bias the ever-present random, thermally driven (Brownian) motion and drive molecular diffusion in desired directions. Here, we visualize the motions of surface-bound molecular rotors using defocused fluorescence imaging, and observe the transition from hindered to free Brownian rotation by tuning medium viscosity. We show that the otherwise random rotations can be biased by the polarization of the excitation light field, even though the associated optical torque is insufficient to overcome thermal fluctuations. The biased rotation is attributed instead to a fluctuating-friction mechanism in which photoexcitation of the rotor strongly inhibits its diffusion rate.

The straightforward synthesis of two new classes of core-extended perylene chromophores, dibenzocoronene tetracarboxdiimide and indenoperylene dicarboxmonoimide, proves that directional enlargement of the aromatic pi-system leads to tailored bathochromic and hypsochromic shifts.