Luminescent square-planar platinum(ii) complexes with tridentate 3-bis(2-pyridylimino)isoindoline and monodentate N-heterocyclic ligands

Abstract

A series of platinum(II) complexes with 1,3-bis(2-pyridylimino)isoindoline (BPI) derivatives were prepared by substitution of the coordinated Cl in the precursor complex Pt(BPI)Cl with a N-heterocyclic ligand such as pyridine, phthalazine or phenanthridine. These complexes display orange to red luminescence in fluid dichloromethane solutions and in the solid states at room temperature. The photophysical properties were tuned by introducing electron-withdrawing -NO(2) or electron-donating -NH(2) to the BPI ligand. The DFT computational studies suggest that the emission in the N-heterocyclic ligand substituted platinum(II) complexes originates mainly from the (3)[π→π*(BPI)] (3)IL triplet excited state, mixed with some (3)[dπ(Pt)→π*(BPI)] (3)MLCT character. Compared with the precursor Pt(BPI)Cl, both the low-energy absorption and the emission in the N-heterocyclic ligand substituted platinum(II) complexes exhibits a distinct blue-shift due to an obviously enhanced contribution from the (3)IL state and a reduced (3)MLCT character.

Isoindoline-derived ligands and applications

“…Its popularity can be attributed to the cyclopalladation phenomena. 41 After C-H and C-C bond activation takes place further Pd II can coordinate to exocyclic N atoms (87). 40 The flexibility of BIIs allows a flip on the axis of one C-N bond that is attributed to an intramolecular strain.…”

N-Assisted CPh–H Activation in 3,8-Dinitro-6-phenylphenanthridine. New C,N-Cyclometalated Compounds of Platinum(II): Synthesis, Structure, and Luminescence Studies

“…Numerous investigations in the field of Pt(II) coordination chemistry have been recently spurred on by their attractive photophysical properties [1][2][3][4][5][6][7][8][9][10][11] and potential applications of triplet-emitting platinum (II) complexes as phosphors in highly efficient organic light-emitting devices (OLEDs) [12][13][14][15] or as chemosensors for oxygen, 16,17 volatile organic compounds (VOCs) [18][19][20][21][22][23] or poisonous metal cations. 24,25 Room-temperature phosphorescence is attributed to the strong spin-orbit coupling constant of the platinum atom which allows an efficient singlet-triplet intersystem crossing (ISC).…”

Chromophores, Fluorophores and Robust Ancillary Ligands for Molecular Catalysts: 1,3‐Bis(2‐pyridylimino)isoindolines

“…The introduction of electron‐withdrawing as well as electron‐donating groups similarly influences the electronic structure and consequently the photophysical properties of the dyes. Hence Chen and co‐workers expanded their library of compounds to include Pt II complexes bearing N‐heterocyclic ligands and BPI derivatives with different electronic properties 52. As expected, electron‐withdrawing substituents lead to a redshift due to their higher π‐accepting abilities and thus lower LUMO energies 52.…”

“…Hence Chen and co‐workers expanded their library of compounds to include Pt II complexes bearing N‐heterocyclic ligands and BPI derivatives with different electronic properties 52. As expected, electron‐withdrawing substituents lead to a redshift due to their higher π‐accepting abilities and thus lower LUMO energies 52. On the other hand, electron‐donating substituents (such as the NH 2 group) induce a blueshift as a result of the higher HOMO–LUMO gap.…”

“…On the other hand, electron‐donating substituents (such as the NH 2 group) induce a blueshift as a result of the higher HOMO–LUMO gap. Replacing the coordinating chloride anion with a neutral N‐heterocyclic ligand had only a minimal effect on the absorption and emission energies and efficiencies 52…”