460355-60-6Relevant academic research and scientific papers
Light-emitting cyclopalladated complexes of 6-phenyl-2,2′-bipyridines with Hydrogen-bonding functionality
Neve, Francesco,Crispini, Alessandra,Di Pietro, Cinzia,Campagna, Sebastiane
, p. 3511 - 3518 (2002)
The tridentate ligand 4-carboxy-6-phenyl-2,2′-bipyridine (HL1) was used to prepare the cyclometalated Pd(II) complex [Pd(L1)Cl] (1). Similar ligands were effective in the formation of [Pd(L2)Cl] (2) and [Pd(L3)Cl] (3) (where HL2 = 4-carboxyphenyl-6-phenyl-2,2′-bipyridine and HL3 = 4-hydroxyphenyl-6-phenyl-2,2′-bipyridine). The crystal structure of [Pd(L1)DCl]· H2O has been determined by X-ray diffraction, revealing a variegated array of H-bonding motifs and π-stacking. The [Pd(L1)Cl] molecules are associated in dimers with an intradimer Pd?Pd distance of 3.27 A?, while dimers are separated by interdimer Pd?Pd contacts of 5.41 A?. All complexes 1-3 exhibited intense luminescence at 77 K, with lifetimes in the 10-200 μs range. The luminescence is assigned to metal-perturbed triplet ligand-centered (LC) excited states for 1 and 3 (partially mixed with an upper-lying metal-to-ligand charge transfer (MLCT) level) and to an excimeric excited state for 2. Room-temperature solid-state luminescence was also revealed by 1 (emission energy and lifetime of 650 nm and 1 μs, respectively), which has been assigned to oligomeric species. Differences in the photophysical properties of 1-3 are addressed with reference to the chemical structure and electronic properties of their polypyridine ligands.
