TY - JOUR

T1 - NIR emitting platinum pincer complexes based on the N^N^C ligand containing {benz[4,5]imidazo[1,2-a]pyrazin} aromatic system; synthesis, characterization and photophysical study

AU - Shakirova, Julia R.

AU - Hendi, Zohreh

AU - Zhukovsky, Daniil D.

AU - Sokolov, Victor V.

AU - Jamali, Sirous

AU - Pavlovskiy, Vladimir V.

AU - Porsev, Vitaly V.

AU - Evarestov, Robert A.

AU - Tunik, Sergey P.

N1 - Publisher Copyright: © 2020 Elsevier B.V.

PY - 2020/10/1

Y1 - 2020/10/1

N2 - In the present work we obtained a series of NIR luminescent platinum(II) complexes with a pincer N^N^C ligand based on the conjugated {benzoimidazo[1,2-a]pyrazine} system with the [Pt(N^N^C)L]n+ structural motif (L = phosphine, alkynyl or pyridine-type ligands). We have also synthesized two complexes with bidentate phosphines that demonstrate different types of coordination: 1) as chelating ligand (in case of 1,2-bis(diphenylphosphino)benzene), that led to de-coordination of pyridine ring of N^N^C ligand and formation of a [Pt(N^C)dppb]+ complex; 2) as a bridging ligand (in case of bis(diphenylphosphino)methane) between two {Pt(N^N^C)} fragments in a dimeric complex of type [{Pt(N^N^C)}2dppm]2+. The complexes obtained were fully characterized using spectroscopic methods, and their ground-state structures and photophysical properties were studied by DFT and TD DFT methods. According to the data obtained the aromatic {benzoimidazo[1,2-a]pyrazine} fragment plays a key role in the photophysics of this type of complexes and the triplet 3LC state located at the N^N^C ligand proved to be the only emissive state in all the complexes prepared. Unexpectedly variations in the nature of the ligands occupying the fourth coordination position in the square-planar structural motif, changes in the mode of the N^N^C ligand coordination and even the Pt-Pt bond formation did not result in significant variations of the emission profile. The photophysical behavior of these complexes has been analyzed using DFT calculations, which are in complete agreement with the experimental data and confirmed that the lowest relaxed triplet configuration responsible for the phosphorescence in the complexes studied is located at the N^N^C ligand.

AB - In the present work we obtained a series of NIR luminescent platinum(II) complexes with a pincer N^N^C ligand based on the conjugated {benzoimidazo[1,2-a]pyrazine} system with the [Pt(N^N^C)L]n+ structural motif (L = phosphine, alkynyl or pyridine-type ligands). We have also synthesized two complexes with bidentate phosphines that demonstrate different types of coordination: 1) as chelating ligand (in case of 1,2-bis(diphenylphosphino)benzene), that led to de-coordination of pyridine ring of N^N^C ligand and formation of a [Pt(N^C)dppb]+ complex; 2) as a bridging ligand (in case of bis(diphenylphosphino)methane) between two {Pt(N^N^C)} fragments in a dimeric complex of type [{Pt(N^N^C)}2dppm]2+. The complexes obtained were fully characterized using spectroscopic methods, and their ground-state structures and photophysical properties were studied by DFT and TD DFT methods. According to the data obtained the aromatic {benzoimidazo[1,2-a]pyrazine} fragment plays a key role in the photophysics of this type of complexes and the triplet 3LC state located at the N^N^C ligand proved to be the only emissive state in all the complexes prepared. Unexpectedly variations in the nature of the ligands occupying the fourth coordination position in the square-planar structural motif, changes in the mode of the N^N^C ligand coordination and even the Pt-Pt bond formation did not result in significant variations of the emission profile. The photophysical behavior of these complexes has been analyzed using DFT calculations, which are in complete agreement with the experimental data and confirmed that the lowest relaxed triplet configuration responsible for the phosphorescence in the complexes studied is located at the N^N^C ligand.

KW - Platinum complexes

KW - Pincer ligands

KW - NIR emission

UR - https://www.sciencedirect.com/science/article/abs/pii/S002016932030623X#!

UR - https://elibrary.ru/item.asp?id=43292058

UR - http://www.scopus.com/inward/record.url?scp=85086127022&partnerID=8YFLogxK

U2 - 10.1016/j.ica.2020.119776

DO - 10.1016/j.ica.2020.119776

M3 - Article

VL - 511

JO - Inorganica Chimica Acta

JF - Inorganica Chimica Acta

SN - 0020-1693

M1 - 119776

ER -