The ultrafast excited-state dynamics of three structurally related platinum(II) complexes has been investigated using femtosecond transient absorption spectrometry in 2-methyltetrahydrofuran (MTHF). Previous work has shown that Pt(dbbpy)(CtC-Ph)2 (dbbpy is 4,4'-di(tert-butyl)-2,2'-bipyridine and CtC-Ph is ethynylbenzene) has a lowest metal-to-ligand charge transfer (3MLCT) excited state, while the multichromophoric Pt(dbbpy)- (CtC-pyrene)2 (CtC-pyrene is 1-ethynylpyrene) contains the MLCT state, but possesses a lowest intraligand (3IL) excited state localized on one of the CtC-pyrenyl units. trans-Pt(PBu3)2(CtC-pyrene)2 serves as a model system that provides a good representation of the CtC-pyrene-localized 3IL state in a Pt(II) complex lacking the MLCT excited state. Following 400 nm excitation, the formation of the 3MLCT excited state in Pt(dbbpy)(CtC-Ph)2 is complete within 200 (40 fs, and intersystem crossing to the 3IL excited state in trans-Pt(PBu3)2(CtC-pyrene)2 occurs with a time constant of 5.4 (0.2 ps. Selective excitation into the low-energy MLCT bands in Pt(dbbpy)(CtC-pyrene)2 (λex ) 480 nm) leads to the formation of the 3IL excited state in 240 (40 fs, suggesting ultrafast wire-like energy migration in this molecule. The kinetic data suggest that the presence of the MLCT states in Pt(dbbpy)(CtC-pyrene)2 markedly accelerates the formation of the triplet state of the pendant pyrenylacetylide ligand. In essence, the triplet sensitization process is kinetically faster than pure intersystem crossing in trans-Pt(PBu3)2(CtC-pyrene)2 as well as vibrational relaxation in the MLCT excited state of Pt(dbbpy)(CtC-Ph)2. These results are potentially important for the design of chromophores intended to reach their lowest excited state on subpicosecond time scales and advocate the likelihood of wire-like behavior in triplet-triplet energy transfer.
Ultrafast energy migration in Platinum(II) Diimine Complexes bearing Pyrenylacetylide Chromophores
GENTILI, Pier Luigi;
2005
Abstract
The ultrafast excited-state dynamics of three structurally related platinum(II) complexes has been investigated using femtosecond transient absorption spectrometry in 2-methyltetrahydrofuran (MTHF). Previous work has shown that Pt(dbbpy)(CtC-Ph)2 (dbbpy is 4,4'-di(tert-butyl)-2,2'-bipyridine and CtC-Ph is ethynylbenzene) has a lowest metal-to-ligand charge transfer (3MLCT) excited state, while the multichromophoric Pt(dbbpy)- (CtC-pyrene)2 (CtC-pyrene is 1-ethynylpyrene) contains the MLCT state, but possesses a lowest intraligand (3IL) excited state localized on one of the CtC-pyrenyl units. trans-Pt(PBu3)2(CtC-pyrene)2 serves as a model system that provides a good representation of the CtC-pyrene-localized 3IL state in a Pt(II) complex lacking the MLCT excited state. Following 400 nm excitation, the formation of the 3MLCT excited state in Pt(dbbpy)(CtC-Ph)2 is complete within 200 (40 fs, and intersystem crossing to the 3IL excited state in trans-Pt(PBu3)2(CtC-pyrene)2 occurs with a time constant of 5.4 (0.2 ps. Selective excitation into the low-energy MLCT bands in Pt(dbbpy)(CtC-pyrene)2 (λex ) 480 nm) leads to the formation of the 3IL excited state in 240 (40 fs, suggesting ultrafast wire-like energy migration in this molecule. The kinetic data suggest that the presence of the MLCT states in Pt(dbbpy)(CtC-pyrene)2 markedly accelerates the formation of the triplet state of the pendant pyrenylacetylide ligand. In essence, the triplet sensitization process is kinetically faster than pure intersystem crossing in trans-Pt(PBu3)2(CtC-pyrene)2 as well as vibrational relaxation in the MLCT excited state of Pt(dbbpy)(CtC-Ph)2. These results are potentially important for the design of chromophores intended to reach their lowest excited state on subpicosecond time scales and advocate the likelihood of wire-like behavior in triplet-triplet energy transfer.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
