Multi‐Stimuli‐Responsive Properties of Aggregation‐Enhanced Emission‐Active Unsymmetrical Pt^II Metallomesogens through Self‐Assembly

Abstract

Herein, we report as eries of unsymmetrical bispyrazolate-typeP t II compounds that exhibit mesomorphism at low temperatures and photophysicalm ulti-stimuli-responsive properties.T hese Pt II compounds show a great ability to be self-assembled by intermolecular Pt···Pt interactions in the solid state,s og enerating ac olumnar stackingo fm olecules that is responsible for the formation of the mesophases. By controlling the nature of the molecular assembly through external stimuli such as the temperature, the pressure, or the presenceo fv apours or solvents, it is possible to modulate the luminescence behaviour of thesem aterials.T he Pt II monomers emit ag reenish light, whereas aggregation of molecules produces ar edshifted emission. These metallomesogens also show a high stability ands uccessive grinding/fuming cycles can be performedw ithoutd egradation of the sample. The applicationo ft hese materials is very attractive as rewritable luminescent platforms, and their use is already demonstrated.Metallomesogensa re consideredsoft materials in which the establishment of intermolecular interactions and short contacts is favoured. [1] Therefore, the self-assembly of molecules will determinet he energy levelso ft he HOMOa nd LUMO orbitals, this fact openingawide range of possibilities in relationw ith the photophysical behaviour of this kind of nanomaterials. [2] It is well known that the luminescence emission in such systems can be originated from ag reat variety of excited states, such as ligand centre charge transfer (LCT), intraligand charge transfer (ILCT), metal-to-ligand charge transfer (MLCT), and metalmetal-to-ligand charget ransfer (MMLCT). [3] Here the nature of the coordinated ligands, as well as that of the counter-ions (in the case of ionic species), play ak ey role. As mall modification in the molecular structure can induce the formation of new intermolecular interactions, and this can originaten otable changes in its properties ande ven give rise to stimuli-responsive behaviours. [4] Many authors have demonstratedt he versatility of the Pt II metallomesogens to emit light in aw ide spectral range of 400-800nm, simply by introduction of ab ulky substituent group, for example;o rb ym odification of the number of terminal alkyl chains. [5] Particularly,the study of species in which the platinum centre is coordinated to delocalised p-systems is arousing speciali nterest becauset he phosphorescent nature of the emission is boosted at room temperature. [6] Materials that exhibit both liquid crystal and stimuli-responsive properties have been reported in the literature, but are very scarce. [4b,c, 7] Herein, we describe as eries of unsymmetrically four-coordinated Pt II metallomesogens bearing one pyridylpyrazolate and one isoquinolinylpyrazolate ligands, both being additionally carriers of dicatenar alkyloxyphenyl substituents. The compounds are, thus, four-chained, decorated with alkyl chain lengthsf rom four to 18 carbona toms (compounds 1-8; Scheme 1). The introductiono fa symmetryi se xpected to fa...

Tuning the Molecular Packing of Self‐Assembled Amphiphilic PtII Complexes by Varying the Hydrophilic Side‐Chain Length

“…Additionally, for different luminescent Pt II mesogens, it has been demonstrated that the variation of alkyl chains can be used to modulate the mesophases with regards to their stability and photophysical behavior [6] . Interestingly, modification of the alkyl tail length for some of these compounds has led to the emergence of multistimuli‐responsive polymorphism in the solid state, [6a,b] thus demonstrating the key impact of small structural changes (e.g., C 14 vs. C 16 chain [6a] ) on the final properties of the systems.…”

Modulation of Solid‐State Aggregation of Square‐Planar Pt(II) Based Emitters: Enabling Highly Efficient Deep‐Red/Near Infrared Electroluminescence

“…[25] The metallophilic interactions can further manifest themselves as dimers, trimers, oligomers or even one-dimensional stacked structure with Pt•••Pt separation shorter than the sum of van der Waals radii. [26][27][28][29] Metallophilic Pt•••Pt interactions are known to be comparable to the bond strength of hydrogen bonding, but are much weaker than that of typical covalent and ionic bonding. [30] This means that these relatively weakened metallophilic bonding can be easily disturbed by both steric effect and other intra-or inter-molecular interactions, such as solvation, π-π stacking, both hydrogen and halogen bonding interactions, etc.…”

Molecular copper iodide clusters: a distinguishing family of mechanochromic luminescent compounds

“…The majority of the mechanochromic luminescent compounds are based on organic molecules, [12][13][14] in comparison with the metal-based compounds. 15 The latter demonstrated nonetheless a rich variety of mechanochromic properties, mainly based on Au [16][17][18][19][20][21][22][23][24][25][26][27][28][29] and Pt [30][31][32][33][34][35][36][37][38][39][40][41] complexes. Examples of Zn, [42][43][44][45][46][47][48][49] Al, 50,51 Ir [52][53][54][55][56][57][58][59][60][61]…”