Design and Integration in Electro‐Optic Devices of Highly Efficient and Robust Red‐NIR Phosphorescent Nematic Hybrid Liquid Crystals Containing [Mo₆I₈(OCOC_nF_2n+1)₆]²⁻ (n = 1, 2, 3) Nanoclusters

Abstract

wileyonlinelibrary.comare also very well known as smart materials to respond easily to external stimuli such as a change of temperature, application of a magnetic or electric fi eld. Thus, conferring new functionalities such as luminescence, redox states, and/or magnetism to LC is a challenge of particular interest to design new materials that would improve the efficiency of existing technologies or develop new ones. [ 3 ] In particular, photoluminescent materials play a key role in photonics, optoelectronics or lighting applications. [ 4 ] In this frame, inorganic luminophores appear as the most appropriate materials in terms of stability as compared to organic compounds which suffer from photo bleaching. Thus, luminescent transition metals, [ 3a,c , 5 ] lanthanide(III), [ 3d , 6 ] quantum dots or nanoparticles [ 7 ] have been introduced in LC giving birth to metallomesogens and liquid crystal nanosciences. [ 5,8 ] Recently, we discovered a new class of luminescent hybrid LC material called clustomesogen that contains transition metal clusters. [ 9 ] These inorganic entities were defi ned by Cotton as a fi nite group of metal atoms linked together by metal-metal bonds and are obtained, as ceramic-like powders, by high temperature solid state synthesis. [ 10 ] So far, three strategies were developed to design clustomesogens: i) a covalent approach in which organic LC promoters are covalently linked on an octahedral metallic cluster core, ii) a supramolecular one that combines electrostatic and host guest interactions to associate the LC organic promoters with an alkali Cs 2 Mo 6 Br 14 ternary salt, and, iii) an ionic approach that takes advantage of the cluster units anionic character to associate them with organic cations bearing the mesogenic promoters. Indeed, the octahedral [M 6 X i 8 X a 6 ] n − cluster units (M = Mo, W, or Re; X i = chalcogen/halogen; X a = halogen; i = inner, a = apical, 2 ≤ n ≤ 4) exhibit emission in the red-NIR area upon excitation in the UV-blue with high photoluminescence quantum yields and possess excited state lifetimes in the range of several tenths of microseconds, thanks to the full delocalization of their valence electrons on the all metallic octahedral scaffold. [ 11 ] These last decades, many efforts have been dedicated to their integration in supramolecular architectures, polymeric frameworks or nanomaterials that take advantage of their intrinsic properties. [ 12 ] Very recently, highly luminescent cluster compounds By combining [Mo 6 I 8 (C n F 2 n +1 COO) 6 ] 2− ( n = 1, 2, 3) nanocluster units with liquid crystalline ammonium cations, a new series of hybrid materials is developed that show a nematic liquid crystal phase, the most fl uid of all LC phase, on a large range of temperatures including room temperature. The photophysical studies performed in the LC state show that these selfassembled hybrid materials emit in the red-NIR with absolute quantum yields up to 0.7 and show a very good photostability under continuous irradiation. They are further integrated up t...

Amorphous Mn3O4 Nanocages with High‐Efficiency Charge Transfer for Enhancing Electro‐Optic Properties of Liquid Crystals

“…The electric double layer would diminish the effect of applied field and subjoin the driving voltages of liquid crystals, leading to the depletion of energy . To combat this problem, dispersion of nanoparticles (NPs) as active‐matrix component optimizing the electro‐optic (E‐O) properties of LCs is regarded as a quick and economical method . For incorporation of NPs in LC matrix, the proper selection of crystallographic phase, capping agent, shape, and size of the NPs is critical for the performance of the blend .…”

From supramolecular to solid state chemistry: crystal engineering of luminescent materials by trapping molecular clusters in an aluminium-based host matrix

“…Then, the self-assembling of building blocks to form the target material will be driven by a supramolecular organic linker, such as cyclodextrins as demonstrated earlier in CLUSPOM compounds. 9 the elaboration of hybrid nano-materials [30][31][32][33][34][35] and functional surfaces 36,37 . In particular, they i) absorb light continuously from UV to visible, ii) emit continuously from red to NIR region through several excited emissive states, iii) are able to photoinduce singlet oxygen generation, iv) exhibit interesting catalytic and photo-catalytic properties.…”

From Cs2Mo6Cl14 to Cs2Mo6Cl14·H2O and Vice Versa: Crystal Chemistry Investigations

“…Among these compounds, Cs 2 Mo 6 X i 8 X a 6 (X i and X a = Cl, Br and I) series is known for a long time and has been widely used as precursor for the preparation of hybrid nanomaterials due on one hand to their solubility in organic solvents like acetone, ethanol and acetonitrile [1,2,9,16], and on the other hand to their unique photochemical features such as redox properties [17], photocatalysis [8,18,19], and photoluminescence [16]. For instance, with iodine, the substitution via solution chemistry of apical I a by OCOC n F 2n?1 groups leads to Cs 2 Mo 6 I i 8 ðOCOC n F 2nþ1 Þ a 6 (n = 1, 2, 3) series [20,21]. From the viewpoint of optical properties, the Mo 6 [22,23].…”