Ultrafast Energy Migration in Platinum(II) Diimine Complexes Bearing Pyrenylacetylide Chromophores

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)(C[triple bond]C-Ph)2 (dbbpy is 4,4'-di(tert-butyl)-2,2'-bipyridine and C[triple bond]C-Ph is ethynylbenzene) has a lowest metal-to-ligand charge transfer (3MLCT) excited state, while the multichromophoric Pt(dbbpy)(C[triple bond]C-pyrene)2 (CC-pyrene is 1-ethynylpyrene) contains the MLCT state, but possesses a lowest intraligand (3IL) excited state localized on one of the CC-pyrenyl units (Pomestchenko, I. E.; Luman, C. R.; Hissler, M.; Ziessel, R.; Castellano, F. N. Inorg. Chem. 2003, 42, 1394-96). trans-Pt(PBu3)2(C[triple bond]C-pyrene)2 serves as a model system that provides a good representation of the CC-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)(C[triple bond]C-Ph)2 is complete within 200 +/- 40 fs, and intersystem crossing to the 3IL excited state in trans-Pt(PBu3)2(C[triple bond]C-pyrene)2 occurs with a time constant of 5.4 +/- 0.2 ps. Selective excitation into the low-energy MLCT bands in Pt(dbbpy)(C[triple bond]C-pyrene)2 (lambda(ex) = 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)(C[triple bond]C-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(CC-pyrene)2 as well as vibrational relaxation in the MLCT excited state of Pt(dbbpy)(C[triple bond]C-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.

Synthesis, characterization, luminescence and nonlinear optical (NLO) properties of truxene-containing platinum(II) alkynyl complexes

“…This absorption is believed to arise from the 3 p,p * excited-state localized on the peripheral naphthalenecontaining ligands. Similar findings have been observed for a mononuclear platinum(II) bis(pyrenylethynyl) complex reported by Ziessel and Castellano [102,104].…”

Bi-molecular emissive excited states in platinum (II) complexes for high-performance organic light-emitting diodes

“…This indicates that the excimer formation rate constant s À1 r exceeds largely the mono-molecular decay rate constant, s À1 . The obtained value of s r is too long to reflect the rapid intersystem crossing from 1 M * to 3 M * (at a probable rate 10 12 s À1 ) [28], and suggests that only selected intermolecular arrangements can serve as the excimer forming sites at which the configuration of adjacent parallel molecules ensures a sufficient overlap; the molecular excitons need 10 ns to transfer the excitation energy to these sites. Otherwise, the excimer formation between 3 M * and 1 M for any configuration of the closelyspaced molecules in neat PtL 26 Cl films would be much faster falling in the time regime below 1 ns (cf.…”

Broad-Band N∧N Pt(II) Bisacetylide Visible Light Harvesting Complex with Heteroleptic Bodipy Acetylide Ligands

“…For example, an ISC of 5.4 ps was observed for N ∧ N Pt(II) bisacetylide complexes containing pyrenylacetylide ligands. 69 On the other hand, a trans bis(trialkyl)phosphine Pt(II) bisacetylide complex with diketopyrrolopyrrole ligand has an ISC of 135 ps. 40 We also studied the possibility of the backward energy transfer from the coordinated ligand EB-1 to the EB-2 in complexes Pt-1 and Pt-4 by performing another pump probe experiment with 590 nm excitation for Pt-1 and Pt-4, at which the energy acceptor, i.e., the coordinated EB-2 ligand, was selectively excited.…”