Strategy for Achieving Long-Wavelength Near-Infrared Luminescence of Diimineplatinum(II) Complexes

Abstract

Although many strategies have been used to help design effective near-infrared (NIR) luminescent materials, it is still a huge challenge to realize long-wavelength NIR luminescence of diimineplatinum(II) complexes in the solid state. Herein, we have successfully achieved long-wavelength NIR luminescence of a family of diimineplatinum(II) complexes based on a new strategy that combines a one-dimensional (1D) "Pt wire" structure with the electronic effect of the substituent. The structures of six solvated diimineplatinum(II) complexes based on 4,4-dichloro-2,2′-bipyridine or 4,4-dibromo-2,2′-bipyridine and 4-substituted phenylacetylene ligands have been determined, namely, and 6• 1 / 4 toluene. All of them crystallize in the monoclinic space group C2/c or C2/ m and stack in the 1D "Pt wire" structure. In the solid state, six complexes exhibited unusual long-wavelength metal−metal-to-ligand charge-transfer luminescence that peaked at 984, 1044, 972, 990, 1022, and 935 nm, respectively. Interestingly, 2• 1 / 2 THF has the shortest Pt•••Pt distance and the longest emission wavelength among the six complexes. As far as we know, the luminescence of 2• 1 / 2 THF at 1044 nm is the longest emission wavelength among known diimineplatinum(II) complexes. Systematic studies revealed that good molecular planarity, suitable substituent position, weak hydrogen-bond-forming ability of the substituents, appropriate molecular bending, and weakening of the interaction between solvated molecules and platinum molecules are conducive to the construction of a 1D "Pt wire" structure of the diimineplatinum(II) complex. Furthermore, the emission energy of the complex is mainly determined by the strength of the Pt−Pt interaction and electronic effect of the substituent.

Near-infrared metal agents assisting precision medicine: from strategic design to bioimaging and therapeutic applications

“…In 2021, Ni et al reported a series of diimine Pt(II) complexes by combining the one-dimensional (1D) ''Pt wire'' structure with the electronic effects of substituents. 121 The electron-withdrawing group in the pyridine ligand and the electron-donating group in the phenylacetylene ligand can greatly reduce the HOMO-LUMO energy gap. In the solid state, these complexes showed low-energy absorption bands between 600 and 783 nm due to the MMLCT transition.…”

Dual Emissive Mono- and Bis-alkynylpyridinium Pt(II) Complexes: Synthesis and Luminescent Properties

“…Electronic absorption spectra of the Pt(II) complexes in solution exhibit wide nonstructured bands in the 330–443 nm range (Table and Figure a,d). The spectra generally correspond to a superposition of the diimine-based ππ* transitions, acetylene-based intraligand charge transfer (ILCT), and metal-to-ligand charge transfer (MLCT) bands. ,,,− The intense nonstructured acetylene-based CT transition bands dominate in most spectra; however, the spectra of cyclometalated complexes 7 – 10 exhibit lower contributions of these transitions and relatively high energy absorption corresponding to the {Pt(C ∧ N ∧ N)} fragment.…”

Luminescence of Pyrazinyl Pyrazolate Pt(II) Complexes Fine-Tuned by the Solid-State Stacking Interaction

“…This observation suggests the existence of the weakest Pt···Pt stacking interaction for Pt­(II) complex 3 in a neat thin film, probably attributed to a combination of both electronic and steric effects among these fluoroalkyl substituents. It is also notable that, although there are a number of Pt­(II) complexes capable of showing efficient saturated red and even NIR emission in the solid state or as crystalline materials, − this class of azolate Pt­(II) complexes represent one rare example, where the well-stacked structure in a thin film was easily assembled by the chemical vapor deposition (or thermal vacuum deposition) technique.…”