Fluorophobic Effect Promoting Lamellar Self‐Assembly of Donor Acceptor Dyes

Abstract

To combine liquid crystalline and linear optical properties in the same molecule, the fluorophobic effect was probed for the first time in donor acceptor dyes. Thus, a series of mono-, bi-, and tricyclic donor acceptor dyes with 1H,1H-perfluorinated alkyl chains of different lengths as donor units and nitrile, malononitrile or barbiturate as acceptor units was synthesized in 5 steps and 1.4-6.6 % overall yield. UV/Vis and fluorescence spectroscopy, cyclic voltammetry and DFT calculations revealed that absorption and emission maxima, Stokes shifts and LUMO energies were mainly governed by the chromophore size and acceptor strengths. The perfluorinated chain was electronically almost decoupled from the remaining chromophore and induced only slight changes of the absorption maxima as compared to the alkyl substituted counterparts. However, in contrast to the non-mesomorphic alkyl donor-substituted derivatives, the perfluorinated donors resulted in self-assembly into partially interdigitated SmA bilayers according to differential scanning calorimetry (DSC), polarizing optical microscopy (POM), X-ray diffraction (WAXS, SAXS) studies and electron density profile calculations.

Liquid Crystalline Benzoic Acid Ester MIDA Boronates: Synthesis and Mesomorphic Properties

“…However, the slightly bent ester led to the appearance of a second crystalline phase (temperature range: 60-70 K) and an SmA phase (phase widths: 18-43 K) for Est12-Est16. However, the known tendency of fluorinated or partially fluorinated side chains to reduce the conformational mobility 29,47 significantly stabilized the SmA phase up to the thermal decomposition at 240-287°C.…”

Merging liquid crystalline self-assembly and linear optical properties of merocyanines via tailored donor units

“…This is consistent with previously performed measurements on fluorinated molecules. 32 Along the z-axis, the electron density subsequently decreases along the phenyl ring and reaches its minimum in the aliphatic chromophore. A molecule length of L M = 30.2 Å was determined for Mal-2-C( 8)F( 6) by using Chem3D software after geometry optimization (MM2 force field).…”

“…In order to improve nanosegregation and enable self-assembly, we relied on perfluorinated alkyl side chains, which were grafted to the donor subunit of the merocyanines instead of alkoxy side chains. 32 It is well known that the high polarity and low polarizability of the C–F bond leads to helical conformations of the perfluorinated chain and increases lipophilicity and rigidity, phenomena commonly known as fluorophobic effect. 33 Indeed stable lamellar mesophases were found for merocyanines 13 consisting of two or more rings and perfluorinated side chains.…”

“…Scheme 2 Preliminary work29,31,32 and our new strategy to induce strong absorption/emission properties and liquid crystalline self-assembly of merocyanines via donor tailoring.…”