Pyridylpyrrolides as alternatives to cyclometalated phenylpyridine ligands: synthesis and characterization of luminescent zinc and boron pyridylpyrrolide complexes

Abstract

The synthesis, structure, and properties of six luminescent pyridylpyrrolide complexes and the first structural characterization of pyridylpyrrolide metal complexes are reported. A series of new zinc complexes, bis(pyridylpyrrolyl)zinc, (R2PyrPy)2Zn (R = Me, Et, iPr, tBu, and Ph), that vary in their substituents on the pyrrole ring (Me, Et, iPr, tBu, and Ph), were prepared. Pyrrole substitution produced small structural changes in the complexes and affected the fluorescence properties very little. The zinc complexes were found to be luminescent, emitting at 495 nm (Phi = 0.32, 0.32 0.31, 0.19 and 0.57, respectively). A boron analog, (Me2PyrPy)BF2, was prepared and was found to share the luminescent properties with the zinc complexes, emitting at 505 nm (Phi = 0.22), but not their water-sensitivity. A total of four crystal structures are reported, tBu2PyrPyH, (Me2PyrPy)2Zn, (tBu2PyrPy)2Zn, and (Me2PyrPy)BF2. tBu2PyrPyH crystallizes as a doubly hydrogen bonded dimer with non-coplanar pyridine and pyrrole rings. The solid-state structures of (Me2PyrPy)2Zn and (tBu2PyrPy)2Zn revealed that despite the large change in steric bulk, the two compounds have very similar structures. The structure of (Me2PyrPy)BF2 showed changes that are expected with the interaction between a smaller atom (B as compared to Zn). Molecular orbital calculations were performed on Me2PyrPyH, (Me2PyrPy)BF2, and (Me2PyrPy)2Zn using Gaussian 98 methods. It was found that the main transition (HOMO-LUMO) for all three molecules is a pi-->pi* transition and that in the inorganic complexes, the metal atom (zinc or boron) present has very little effect on transition, evidence that the optical properties are largely ligand based and that the B or Zn atom's main effect is lowering of the LUMO relative energy.

Synthesis, Structure, and Spectral Properties of Bis(pyrrol‐2‐yl)pyridines

“…Like pyridylpyrroles, [8][9][10] they may display not only high electrical conductivity, but also the capability to form complexes of various chemical natures with better electronic and optoelectronic characteristics than uncomplexed polymers. Luminescent complexes of pyridylpyrroles with boron and zinc compounds have thus been proposed as an alternative to cyclometallated phenylpyridine ligands for use in organic light-emitting diode (OLED) materials, [8] while complexes of pyridylpyrroles with alcohols have been thoroughly explored as model compounds (analogous to pyridylindoles) for investigation of the natures of hydrogen bonds in such biologically important objects as DNA and RNA and for study of the mechanism of photoinduced mutagenesis through intermolecular excited state double proton transfer. [9,10] Polypyridines are known to possess unique combinations of electroactive, coordinative, and optoelectronic properties and offer exceptional prospectives as materials for use in chemical power sources and OLEDs.…”

Syntheses, Characterization, and Luminescent Properties of Monoethylzinc Complexes with Anilido–Imine Ligands

“…[9] As Zn II with a closed shell is spectroscopically silent in essence, the luminescent properties of Zn II complexes can be easily tuned by the modification of the ligands. Meanwhile, Zn II complexes can have relatively flexible coordination numbers ranging from three-coordinate to six-coordinate depending on the structure of their ligands.…”

“…[1][2][3][4][5][6][7][8][9] Among these known luminescent Zn complexes, the ligands are mainly benzothiazolates, [1] quinolinolates, [2] salicylideneaminates, [3] dipyrrin,…”

Structure, photophysics, electrochemistry, DFT calculation, and in-vitro antioxidant activity of coumarin Schiff base complexes of Group 6 metal carbonyls

“…Heteroatom containing fluorophores develop partial charges due to internal charge transfer (ICT) and, interaction with charged groups can affect its energy. It has been reported that the metal ions can enhance or quench the fluorescence emission of pyridine containing compounds [57,58] depending on the strength interaction between ligand field potential and metal ion. In the absence of metal ions the fluorescence of ligand is probably quenched by the occurrence of PET process due to the presence of a lone pair on nitrogen atoms and vibrational relaxation of the molecule.…”