Bulk organisation and alignment in Langmuir and Langmuir–Blodgett films of tetrachloroperylene tetracarboxylic acid esters

• Tetrachloroperylene tetracarboxylic acid esters can crystallize into polycrystalline powder.
• In Langmuir and LB films tilted head-on orientation of molecules is postulated.
• Different molecular aggregates are formed depending on molecular structure.
• Strong impact of twisted core of molecules on their arrangement is showed.

Perylene derivatives with chlorine atoms attached at the bay position to the dye core are expected to affect organisation and tendency to aggregation in Langmuir and Langmuir–Blodgett (LB) films. Therefore, newly synthesized core–twisted homologous series of tetrachloroperylene tetracarboxylic acid esters with n = 1,4,5,6,9 carbon atoms in terminal alkyl chains were studied. Phase transitions and crystalline structures were specified by differential scanning calorimetry (DSC) and single crystal X–ray diffraction (XRD), respectively. Intermolecular interactions and organisation of the dyes in monomolecular films were investigated by means of Brewster angle microscope (BAM), UV–Vis absorption and emission spectroscopy, fluorescence microscopy and atomic force microscopy (AFM).The dyes investigated do not form thermotropic mesogenic phases in bulk. The crystalline triclinic elementary cell with P–1 symmetry is revealed from X–ray experiments. In Langmuir and Langmuir–Blodgett films molecular tilted head–on alignment is postulated. Spectroscopic research confirmed by AFM texture images of the LB films show that in the Langmuir and LB films the dyes, depending on length of terminal chains, have a tendency to create H or I molecular aggregates. The impact of the twisted core on the molecular behavior in a bulk and thin films is discussed.

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