Final Report Summary - LH-NAN-LC (Luminescent Hybrid Nanomaterial showing liquid crystalline properties)
Hybrid organic-inorganic functional materials have become an intense field of research mixing chemistry and physics and giving rise to a wide range of materials with applications in optic, electronic, biology, photovoltaic or medicine. Controlling their structuration at the nanometric scale is a major challenge that requires the development of bottom-up approaches in their design. Thus, liquid crystalline (LC) hybrid materials are actually in a stage of rapid development. Indeed, LC materials are easy to process, are able to spontaneously self-assemble over large areas into highly ordered domains and show structural defects self-healing abilities. They have been employed in various applications ranging from the display market to optical switches or used as molecular sensors or in detectors, etc… The main objective of the LH-LAN-LC project is the design of new nanostructured hybrid organic inorganic materials containing transition metal clusters and showing liquid crystalline properties as well as bright luminescence in the red-NIR range. Indeed, introducing octahedral metallic cluster complexes in LC, can add unique valuable properties to the LC phase (such as magnetic, electronic or bright photoluminescence with high quantum yields up to 100%). However, beside advantageous self-organizing properties, combining inorganic bulky nanoobjects with an organic LC matrix is a challenging task as segregation phenomena that happen when inorganic and organic components are not in interaction should be avoided to get homogeneous and stable materials with high inorganic content.
The common approach to do so is the covalent grafting of mesogenic promoters on the surface of inorganic entities. The second way concerns anionic inorganic compounds and consists in the replacement of inorganic counter-cations by functional organic ones bearing LC promoters. A new and straightforward approach has been developed in the frame of the LH-NAN-LC project. This, as innovative as simple strategy, that can also be qualified as a double supramolecular approach, combines host-guest complexes formation and electrostatic interactions. It is based on the ability of functional azacrown ether macrocycle derivatives to complex the alkali cations contained in the nanometric A2Mo6X14 cluster-based ternary molecular solid state compound (in which A is an alkali cation and X a halogen atom). In that way, the careful design of the organic moieties involved in the hybrid complexes, associated to a judicious choice of the inorganic counterpart, allowed us to rationalize the structure/properties relationship of this new class of LC material. By using complementary techniques such as DSC, POM under white light or UV irradiation, and SAXS, we have been able to show that red NIR luminescent nematic or discotic hybrid LC could be obtained. Let us stress that the nematic LC phase is the most fluidic of all LC phases and thus the most used in LC based devices. Therefore, the hybrid materials developed in the frame of the LH-NAN-LC project show good promises for applications that need stable deep red or red-NIR emission.
The common approach to do so is the covalent grafting of mesogenic promoters on the surface of inorganic entities. The second way concerns anionic inorganic compounds and consists in the replacement of inorganic counter-cations by functional organic ones bearing LC promoters. A new and straightforward approach has been developed in the frame of the LH-NAN-LC project. This, as innovative as simple strategy, that can also be qualified as a double supramolecular approach, combines host-guest complexes formation and electrostatic interactions. It is based on the ability of functional azacrown ether macrocycle derivatives to complex the alkali cations contained in the nanometric A2Mo6X14 cluster-based ternary molecular solid state compound (in which A is an alkali cation and X a halogen atom). In that way, the careful design of the organic moieties involved in the hybrid complexes, associated to a judicious choice of the inorganic counterpart, allowed us to rationalize the structure/properties relationship of this new class of LC material. By using complementary techniques such as DSC, POM under white light or UV irradiation, and SAXS, we have been able to show that red NIR luminescent nematic or discotic hybrid LC could be obtained. Let us stress that the nematic LC phase is the most fluidic of all LC phases and thus the most used in LC based devices. Therefore, the hybrid materials developed in the frame of the LH-NAN-LC project show good promises for applications that need stable deep red or red-NIR emission.