Playing with Pt^II and Zn^II Coordination to Obtain Luminescent Metallomesogens

Abstract

Blue–green luminescent terpyridine‐containing PtII and ZnII complexes are reported. Equipped with lipophilic gallate units, which act as monodentate ancillary coordinating ligands and/or as anions, they display low‐temperature mesomorphic properties (lamello‐columnar and hexagonal mesophases for PtII and ZnII complexes, respectively). The mesomorphic properties were investigated by polarised optical microscopy, differential scanning calorimetry, thermogravimetric analysis and X‐ray scattering of bulk materials and oriented thin films. The model of self‐assembly into the lamello‐columnar phase of the PtII complex has been described in detail. The optical properties of the complexes were investigated in the liquid and condensed liquid crystalline states, highlighting the delicate balance between the role of the metal in determining the type of excited state responsible for the emission, and the role of the ancillary ligand in driving intermolecular interactions for proper mesophase formation.

Role of the Environment Polarity on the Photophysical Properties of Mesogenic Hetero-Polymetallic Complexes

“…As for the analogues Zn(II) complexes previously reported [ 19 , 21 ], the pentacoordination around Zn is fulfilled by a tpy -chelating center and two monodentate units of gallate derivative. The successful coordination was firstly assessed using FT-IR spectroscopy, by the significant shift to higher frequencies of the ν C=C and ν C=N ligand characteristic bands ( Figure 2 and Figure S3—Supplementary Information ) and the monodentate coordination mode of the gallate units evidenced by the separation of the stretching vibrations of the COO − group: Δ ≈ 260 cm −1 [ 43 ]. The shift in the aromatic protons of the tpy ligand close to the coordination center and the singlet due to the gallate aromatic proton observed in the 1 H NMR spectra further confirmed the obtainment of the coordination complexes ( Figures S1 and S2—Supplementary Information ).…”

“…The absorption spectra are very similar: they all have three main bands each accompanied by shoulders. The first two bands, positioned at 260 and 283 nm, respectively, are attributed to ligand-centered (LC) transitions located on the terpyridine fragment (see Figures S4–S7—Supplementary Information ) [ 21 ], while the third band, positioned at 325 nm, is attributed to a ligand-to-ligand charge transfer (LLCT) transition from the gallate to the terpyridine ligand [ 43 ]. All complexes are fluorescent, showing a band maximum ranging from 405 to 428 nm, depending on the complex (405 nm for Zn 1 ; 414 nm for Zn 1 Fe 2 ; 428 nm for Zn 2 Fe 4 ), but all are due to the deactivation from LLCT state.…”

Thermochromic Meltable Materials with Reverse Spin Transition Controlled by Chemical Design

“…Furthermore,t he diffractograms of melted pm2-6 and pm2-8 manifest abroad peak centered at 2q = 11.58 8, d-spacing % 8 ,a pproximately corresponding to the stacking periodicity within the head-group layers.T he stacking is regularly observed for soft matter compounds with the structure favoring supramolecular aggregation. [13] Indeed, the single crystal data of pm2-6 demonstrate collinear alignment Fe•••Fe•••Fe( see above), which, apparently,i sr etained in melted phase,b ut due to partial amorphization the peak becomes broadened and shifted. To confirm the assignment, we conducted an additional XRD examination of analogous pm1-6 and pm4-6 with methyl and butyl ketone substituents, respectively,a lso demonstrating forward ST upon melting.…”

Role of the Environment Polarity on the Photophysical Properties of Mesogenic Hetero-Polymetallic Complex

“…As for the analogues Zn(II) complexes previously reported [19,21], the pentacoordination around Zn is fulfilled by a tpy chelating center and two monodentate units of gallate derivative. The successful coordination was firstly assessed by FT-IR spectroscopy, by the significant shift to higher frequencies of the νC=C and νC=N ligand characteristic bands (Figure 2a,b) and the monodentate coordination mode of the gallate units evidenced by the separation of the stretching vibrations of COOgroup: Δ ≈ 260 cm -1 [43]. The purity of the final complexes was assessed by elemental analysis and atomic absorption spectroscopy (AAS -Experimental Section).…”

“…The absorption spectra are very similar: they all have three main bands each accompanied by shoulders. The first two bands, positioned at 260 and 283 nm respectively, are attributed to ligandcentered (LC) transitions located on the terpyridine fragment (see Figures S5, S6, S7, S8 in SI) [21], while the third band, positioned at 325 nm, is attributed to a charge transfer transition from the gallate to the terpyridine ligand (LLCT) [43]. All complexes are fluorescent, showing a band ranging from 405 to 428 nm, depending on the complex, but due for all to deactivation from LLCT state.…”