Excited State Absorption Properties of Pt(II) Terpyridyl Complexes Bearing π-Conjugated Arylacetylides

Abstract

The synthesis, photophysics, and excited state absorption properties of three platinum(II) terpyridyl acetylide charge transfer (CT) complexes possessing a lone ancillary ligand systematically varied in phenylacetylide (PA) π-conjugation length, [Pt((t)Bu(3)tpy)([C≡C-C(6)H(4)](n)-H)]ClO(4) (n = 1, 2, 3), are described. Density functional theory (DFT) calculations performed on the ground states of complexes 1, 2, and 3 reveal that their HOMOs reside mainly on the ancillary π-conjugated PA moiety, ranging from 86 to 97%, with LUMOs predominantly centered on the terpyridyl acceptor ligand (91-92%). This electronic structure leads to the production of a triplet ligand-to-ligand CT ((3)LLCT) excited state upon visible light excitation with minor contributions from the corresponding triplet metal-to-ligand CT ((3)MLCT) excited state. Unusually strong red-to-near-IR transient absorptions are produced in the excited states of these molecules following selective long wavelength visible excitation of the low energy CT bands that do not emanate from the terpyridyl radical anion produced in the CT excited state or from an arylacetylide-based triplet intraligand ((3)IL) excited state. The extinction coefficients of these low energy absorption transients were determined using the energy transfer method with anthracene serving as the triplet acceptor. A detailed theoretical investigation using DFT and TDDFT methods reveals that these intense near-IR transient absorptions involve transitions resulting from transient oxidation of the PA subunit. In essence, the production of the (3)LLCT excited state transiently oxidizes the PA moiety by one electron, producing the corresponding highly absorbing radical cation-like species, analogous to that experienced in related intramolecular photoinduced electron transfer reactions. The computational work successfully predicts the oscillator strength and peak wavelength of the measured excited state absorption transients across this series of molecules. In the present effort, there is a convergence of theory and experiment given that the excited state absorption properties of these Pt(II) chromophores are determined by localized transitions that resemble open shell radical cation species.

Ligand-Localized Triplet-State Photophysics in a Platinum(II) Terpyridyl Perylenediimideacetylide

“…101 The metal−organic chromophores 1 and 2 were synthesized using established literature protocols, namely, Cu(I)-catalyzed cross-coupling reactions between the Pt(II) halide precursor and 4 in the presence of diisopropylamine in dichloromethane at room temperature under an inert atmosphere. 57,58,94 We note that this particular coupling reaction also readily proceeds without addition of Cu(I), as has been previously noted. 57 This latter approach affords the opportunity to completely avoid possible π-complex formation with Cu(I) to the resulting metal−carbon acetylide bond in the final isolated Pt(II) complex.…”

“…57,58,94 We note that this particular coupling reaction also readily proceeds without addition of Cu(I), as has been previously noted. 57 This latter approach affords the opportunity to completely avoid possible π-complex formation with Cu(I) to the resulting metal−carbon acetylide bond in the final isolated Pt(II) complex. As a result, complications associated with purification and subsequent characterization by MALDI-TOF MS and FT-IR spectroscopy are completely circumvented.…”

Femtosecond spectroscopy of the dithiolate Cu(ii) and Ni(ii) complexes

“…In the literature, work on the photophysics of metal complexes mainly with nitrogen-containing ligands [42][43][44][45] is present. Among them, studies devoted to the complexes with a sulfur containing ligand can be mentioned 46 46 The intermediate absorption is independent of the solvent (CH 3 CN or CHCl 3 ) and almost vanishes in 100 ps.…”

Ultrafast intersystem-crossing in platinum containing π-conjugated polymers with tunable spin-orbit coupling

“…Importantly, the dynamics of the internal conversion and ISC processes have not been elucidated, and a complete description of the essential electronic excited states involved is still lacking. For example, the metal-to-ligand charge-transfer ( MLCT ) state, which has been studied extensively in metal-organic complexes1011, has not been properly addressed in Pt-containing polymers. In the present work we use a broad arsenal of linear and nonlinear optical (NLO) spectroscopies, complemented with electronic structure calculations, for studying the photoexcitations dynamics in two Pt-containing π-conjugated polymers with different π-conjugated spacer unit length between the nearest Pt atoms on the chain, which controls the spin dynamics of excited states, namely the timescales of the ISC process in this class of materials.…”