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Interplay between Intra‐ and Interligand Charge Transfer with Variation of the Axial N‐Heterocyclic Ligand in Osmium( II ) Pyridylpyrazolate Complexes: Extensive Color Tuning by Phosphorescent Solvatochromism
Author(s) -
Li ShihWen,
Cheng YiMing,
Yeh YuShan,
Hsu ChengChih,
Chou PiTai,
Peng ShieMing,
Lee GeneHsiang,
Tung YungLiang,
Wu PeiChi,
Chi Yun,
Wu FangIy,
Shu ChingFong
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500434
Subject(s) - phosphorescence , chemistry , ligand (biochemistry) , crystallography , solvatochromism , osmium , pyridine , dihedral angle , photochemistry , solvent , ruthenium , molecule , fluorescence , hydrogen bond , medicinal chemistry , biochemistry , physics , receptor , catalysis , organic chemistry , quantum mechanics
The rational design and syntheses of a new series of Os II complexes with formula [Os(fppz) 2 (CO)(L)] ( 1 : L=4‐dimethylaminopyridine; 2 : L=pyridine; 3 : L=4,4′‐bipyridine; 4 : L=pyridazine; 5 : L=4‐cyanopyridine), bearing two (2‐pyridyl)pyrazolate ligands (fppz) together with one carbonyl and one N‐heterocyclic ligand at the axial positions are reported. Single‐crystal X‐ray diffraction studies of, for example, 2 reveal a distorted octahedral geometry in which both fppz ligands reside in the equatorial plane with a trans configuration and adopt a bent arrangement at the metal center with a dihedral angle of ∼23°, while the carbonyl and pyridine ligands are located at the axial positions. Variation of the axial N‐heterocyclic ligand leads to remarkable changes in the photophysical properties as the energy gap and hence the phosphorescence peak wavelength can be tuned. For complexes 1 and 2 the solvent‐polarity‐independent phosphorescence originates from a combination of intraligand 3 π–π* ( 3 ILCT) and metal‐to‐ligand charge transfer transitions ( 3 MLCT). In sharp contrast, as supported by cyclic voltammetry measurements and theoretical calculations, complexes 3 –‐ 5 exhibit mainly ligand‐to‐ligand charge transfer (LLCT) transitions, resulting in a large dipolar change. The phosphorescence of complexes 3 –‐ 5 thus exhibits a strong dependence on the polarity of the solvent, being shifted for example, from 560 (in C 6 H 12 ) to 665 nm (in CH 3 CN) and from 603 (in C 6 H 12 ) to 710 nm (in CH 3 CN) for complexes 3 and 5 , respectively. The results clearly demonstrate that a simple, straightforward derivatization of the axial N‐heterocyclic ligand drastically alters the excitation properties per se from intraligand charge transfer (ILCT) to LLCT transitions. The latter exhibit remarkable LLCT phosphorescence solvatochromism so that a broad range of color tunability can be achieved.