Liquid Crystalline Pt(Ⅱ) Complexes And Their Holographic Polymer Composites

Platinum（Ⅱ）complexes with unique square-planar geometries have drawn considerable attention in the frontier research fields including bioimaging,electroluminescence,photocatalysis and photodynamic therapy,which is due to the long excited state lifetime,high quantum yield（QY）,large stokes shift,good resistance to photobleaching and readily tunable emission characteristics.These attractive charateristics are not only attributed to the rich electronic structures of complexes in excited states,but also ascribed to the metal-metal-to-ligand charge transfer（MMLCT）during self-assembly via intermolecular Pt…Pt andπ-πinteractions.For developing new functional applications of platinum（Ⅱ）complexes,it is an effective way to enable their liquid crystallization and ordered compounding with holographic polymers.However,this way is significantly constrained due to the heterogeneity nature of platinum（Ⅱ）complexes.In this dissertation,several platinum（Ⅱ）complexes were designed and synthesized by using tridentate diphenyltriazolium as the primary ligand and pyridine derivatives as the ancillary ligand with a substitution at the position 4.Liquid crystallization of platinum（Ⅱ）complexes and ordered compounding with holographic polymer materials were realized.The effects of ancillary ligands’chemical structures on the liquid crystal（LC）behaviors and emission properties were systematically studied.A photo-triggered ligand exchange reaction was disclosed to dial the emission behaviors of the complexes.Orthogonal reconstruction and crosstalk-free display of holographic and emissive dual images were demonstrated in the holographic polymer/LC composites.Details are given as follows:（1）Several platinum（Ⅱ）complexes,whose skeleton consisted of a tridentate diphenyltriazolium ligand and an ancillary pyridine ligand with a substitution at the position4,were designed and synthesized.The pyridine ligand was modified by cholesterol（-Ch）,alkyl chains(-OC_nH_2n+1)and citronellol（-OCit）,producing Pt-Ch,Pt-3OC_nH_2n+1（n=6,12,16）and Pt-2OCit,respectively.The photophysical behaviors of these complexes in both solvents and bulk powder were studied.Results show that these complexes exhibit excellent emission performances and the absolute QY of Pt-Ch,Pt-2OCit and Pt-3OC_nH_2n+1（n=6,12,16）in bulk powder is 84%,84%and up to 88%,respectively.（2）The effects of ancillary ligands on the LC behaviors,emission properties and stimuli-responsive behaviors of platinum（Ⅱ）complexes were studied.Rresults show that no LC phase can be achieved in Pt-3OC₆H₁₃.Pt-Ch and Pt-3OC₁₂H₂₅show hexagonal columnar LC phase,while Pt-3OC₁₆H₃₃and Pt-2OCit exhibit rectangular columnar LC phase.These LCs show excellent emission performances and are still highly emissive in the isotropic phase.A left-handed structure can be obtained using Pt-Ch,which exhibits strong circularly polarized luminescence（CPL）at room temperature with a luminescent asymmetry factor（2）₀8)))of-5×10^-4.Pt-Ch shows reversible thermo/mechanochromism capabilities.Upon heating or grinding,the intermolecular interaction is weakened and emission wavelength is blueshifted up to 26 nm,which can be reversibly recovered upon CH₂Cl₂ fuming.Pt-3OC₁₂H₂₅,Pt-3OC₁₆H₃₃ and Pt-2OCit exhibit reversible vapochromism capabilities upon alternative CH₂Cl₂ and Et OH fuming.The emission wavelength can be reversibly shifted and the peak shift can be up to 30 nm.（3）Compatibility of the liquid crystalline platinum（Ⅱ）complexes with acrylate/acrylamide monomers and nematic LC were investigated.In addition,energy transfer from the nematic LC to the complexes was studied.Eventually,holographic polymer/LC composites containing the liquid crystalline platinum（Ⅱ）complexes were prepared.Results show that Pt-3OC₁₂H₂₅ and Pt-3OC₁₆H₃₃ are incompatible with the nematic LC.Pt-Ch is compatible with 5CB（up to 0.5 wt%）and chiral nematic LC can be achieved.Pt-2OCit shows good compatibility with acrylate/acrylamide monomers and the nematic LC.Holographic polymer/LC composites with a QY of 14%and diffraction efficiency of 90%are achieved by introducing Pt-2OCit into holographic polymer/LC materials.The blue color emission of P0616A can be completely converted into the orange-yellow emission of Pt-2OCit due to the energy transfer from P0616A to Pt-2OCit with a high efficiency up to 99%.It provides the possibility for further constructing holographic and emissive dual images within a single unit.（4）A photo-triggered ligand exchange reaction between platinum（Ⅱ）complex and photobase producer（PBG）was disclosed.Chemical structures and emission behaviors before and after ligand exchange reaction were studied.Results show that PBG can produce organic base TBD upon 365 nm irradiation,and TBD can act as a competitive ligand to replace the pyridine ancillary ligand of the complex.Consequently,a new platinum（Ⅱ）complex with the TBD ligand is generated,whose emission wavelength is significantly blue shifted.Based on the photo-triggered ligand exchange reaction,orthogonal storage and crosstalk-free display of holographic and emissive dual images can be realized in the holographic polymer/LC composites,which provides a new paradigm for multi-spectral anti-counterfeiting and identification.