Mesomorphism and Photophysics of Some Metallomesogens Based on Hexasubstituted 2,2′:6′, 2′′‐Terpyridines

Abstract

The luminescent and mesomorphic properties of a series of metal complexes based on hexacatenar 2,2′:6′,2′′‐terpyridines are investigated using experimental methods and density functional theory (DFT). Two types of ligand are examined, namely 5,5′′‐di(3,4,5‐trialkoxyphenyl)terpyridine with or without a fused cyclopentene ring on each pyridine and their complexes were prepared with the following transition metals: ZnII, CoIII, RhIII, IrIII, EuIII and DyIII. The exact geometry of some of these complexes was determined by single X‐ray diffraction. All complexes with long alkyl chains were found to be liquid crystalline, which property was induced on complexation. The liquid‐crystalline behaviour of the complexes was studied by polarising optical microscopy and small‐angle X‐ray diffraction. Some of the transition metal complexes (for example, those with ZnII and IrIII) are luminescent in solution, the solid state and the mesophase; their photophysical properties were studied both experimentally and using DFT methods (M06‐2X and B3LYP).

Playing with PtII and ZnII Coordination to Obtain Luminescent Metallomesogens

“…In fact, only a few studies on the mesophases of luminescent liquid‐crystalline transition metal complexes have been carried out, with, just to cite non‐exhaustively, the contributions of Bruce et al. on Ir III , Espinet et al . and Tsutsumi et al .…”

“…Luminescent d-block metallomesogens are promising functional materials for practicala pplications.T hey have mainly been investigated in terms of obtaining polarised emission to be used as backlighting in displays, [1][2][3][4] but also some studies concerning their use as stimuli responsive materials for sensing [5,6] or security inks, [7] or high-hole mobility materials for electroluminescent devices [8] have been reported.D espite recentp rogress with square-planar Pt II and octahedral Ir III complexes, which are considered among the best emitters, there is still considerable work to be done to control the phase type and transition temperatures or to improvet he luminescence in the mesophase. [9] In fact, only af ew studies on the mesophases of luminescent liquid-crystalline transition metal complexes have been carried out, with, just to cite non-exhaustively,t he contributions of Bruce et al on Ir III , [8,[10][11][12] Espinet et al [13] and Tsutsumi et al [14,15] on Au I ,G imenØnez et al on Ag I [16] and Zn II , [17] Cârcu et al on Pd II , [18][19][20] Cano et al on Ag I [21][22] and Pucci, Crispini and Ghedini et al on Ru II , [23] Ag I , [24][25][26] Ir III [27] and Zn II [28,29] complexes. For practical applications,t echnological and economic issueshave to be taken into account,such as thermaland optical stabilities, availability and cost of the precursors and straightforward syntheses.…”

Multi‐Stimuli‐Responsive Properties of Aggregation‐Enhanced Emission‐Active Unsymmetrical PtII Metallomesogens through Self‐Assembly

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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. [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). These metallomesogens also show a high stability ands uccessive grinding/fuming cycles can be performedw ithoutd egradation of the sample.

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“…[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. The introductiono fa symmetryi se xpected to favourt he consecution of mesophases at low temperatures, [8] whereast he presence of the pyridinea nd isoquinolinem oiet-Scheme1.Synthesis of the unsymmetrical Pt II compounds [Pt(pz R(n,n)py )(pz R(n,n)iq )] (1)(2)(3)(4)(5)(6)(7)(8). [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.…”

“…[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.…”