Ligand control of donor-acceptor excited-state lifetimes.
Transient absorption and emission spectroscopic studies on a series of diimineplatinum(II) dichalcogenolenes, LPtL', reveal charge-separated dichalcogenolene → diimine charge-transfer (LL'CT) excited-state lifetimes that display a remarkable and nonperiodic dependence on the heteroatoms of the dichalcogenolene ligand. Namely, there is no linear relationship between the observed lifetimes and the principle quantum number of the E donors. The results are explained in terms of heteroatom-dependent singlet-triplet (S-T) energy gaps and anisotropic covalency contributions to the M-E (E = O, S, Se) bonding scheme that control rates of intersystem crossing. For the dioxolene complex, 1-O,O', E(T2) > E(S1) and rapid nonradiative decay occurs from S1 to S0. However, E(T2) ≤ E(S1) for the heavy-atom congeners, and this provides a mechanism for rapid intersystem crossing. Subsequent internal conversion to T1 in 3-S,S produces a long-lived, emissive triplet. The two LPtL' complexes with mixed chalcogen donors and 5-Se,Se show lifetimes intermediate between those of 1-O,O' and 3-S,S.
Department of Chemistry and Chemical Biology, The University of New Mexico , MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States.
Jing
J
Yang
Dominic K
DK
Kersi
Logan J
LJ
Giles
Benjamin W
BW
Stein
Changjian
C
Feng
Christopher R
CR
Tichnell
David A
DA
Shultz
Martin L
ML
Kirk
D007700:Kinetics; D008024:Ligands; D015394:Molecular Structure; D009944:Organoplatinum Compounds / Q000737:chemistry*
D008024:Ligands; D009944:Organoplatinum Compounds