Luminescent Ionic Liquid Crystals from Self-Assembled BODIPY Disulfonate and Imidazolium Frameworks

• Published in: Chemistry : a European journal Vol. 16; no. 24; pp. 7134 - 7142
• Main Authors: Olivier, Jean-Hubert, Camerel, Franck, Ulrich, Gilles, Barberá, Joaquín, Ziessel, Raymond
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 25.06.2010; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc; Wiley-VCH Verlag
• Subjects: Acrylates; aggregation; Cationic polymerization; Cations; Chemical Sciences; Chemistry; Chemistry, Multidisciplinary; Differential scanning calorimetry; Fluorescence; liquid crystals; Mesophase; Organic chemistry; Physical Sciences; Polymerization; Science & Technology; self-assembly; Solid state; polymerization; DYES; COMPLEXES; aggregation; ORGANIZATION; self-assembly; ORGANOGELS; SENSITIZED SOLAR-CELLS; TRANSPORT; FACILE SYNTHESIS; fluorescence; CHEMISTRY; ENERGY-TRANSFER; liquid crystals
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201000339

A series of modular mesogenic salts based on the combination of anionic 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (F‐BODIPY) 2,6‐disulfonate dyes and trialkoxybenzyl‐functionalised imidazolium cations has been designed and synthesised. Each salt contains a rigid dianionic BODIPY core associated with two imidazolium cations functionalised by 1,2,3‐trialkoxybenzyl (alkyl=n‐C8, n‐C12 or n‐C16) units or, in one case, with imidazolium cations functionalised by a trialkylgallate (3,4,5‐trialkoxybenzoate) unit in which the 3,5‐dialkyl groups are terminated with a polymerisable acrylate entity. All these compounds were highly fluorescent in solution with quantum yields ranging from 54 to 62 %. In the solid state, the width of the emission band observed at around 650 nm is a clear signature of aggregation. With the trialkoxybenzylimidazolium cations, polarised optical microscopy (POM) and X‐ray scattering experiments showed that columnar mesophases were formed. Differential scanning calorimetry (DSC) studies confirmed the mesomorphic behaviour from room temperature to about 130 °C for salts with alkyl chains containing 8, 12 and 16 carbon atoms. The strong luminescence of the BODIPY unit was maintained in the mesophase and fluorescence measurements confirmed the presence of J aggregates in all cases. The salt containing the gallate‐functionalised imidazolium cations showed no mesomorphism but the acrylate terminal units could be used to engender photoinitiated polymerisation thereby allowing the material to be immobilised on glass plates. The polymerisation process was followed by FTIR spectroscopy and the fixed and patterned films were highly fluorescent with a solid‐state emission close to that of the complex in the solid state. Glow in the dark! Ionic self‐assembly involving functionalised imidazolium cations and 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene‐2,6‐disulfonates produces columnar luminescent ionic liquid crystals (ILCs; see figure) over a wide temperature range and luminescent patterned films when acrylates replace some of the terminal methyl groups.