Photophysics of the Platinum(II) Terpyridyl Terpyridylacetylide Platform and the Influence of Fe^IIand Zn^IICoordination

Abstract

The synthesis, structural characterization, and photoluminescence (PL) properties of the square-planar terpyridylplatinum(II) complex [ ( t )Bu 3tpyPtCCtpy] (+) ( 1) and the octahedral trinuclear Fe (II) and Zn (II) analogues [Fe( ( t )Bu 3tpyPtCCtpy) 2] (4+) ( 2) and [Zn( ( t )Bu 3tpyPtCCtpy) 2] (4+) ( 3) are described. The photophysical properties of the mononuclear Pt (II) complex 1 are consistent with a charge-transfer excited-state parentage producing a large Stokes shift with a concomitant broad, structureless emission profile. The Fe-based ligand-field states in 2 provide an efficient nonradiative deactivation pathway for excited-state decay, resulting in a nonemissive compound at room temperature. Interestingly, upon chelation of 1 with Zn (II), a higher energy charge-transfer emission with a low-energy shoulder and a 215 ns excited-state lifetime is produced in 3. A spectroscopically identical species relative to 3 was produced in control experiments when 1 was reacted with excess protons (HClO 4) as ascertained by UV-vis and static PL spectra measured at room temperature and 77 K. Therefore, the chelation of Zn (II) to 1 is acid-base in nature, and its Lewis acidity renders the highest occupied molecular orbital level in 1 much less electron-rich, which induces a blue shift in both the absorption and emission spectra. At 77 K, complexes 1, 3, and protonated 1 display at least one prevalent vibronic component in the emission profile (1360 cm (-1)) resembling PL emanating from a ligand-localized excited-state, indicating that these emitting states are inverted relative to room temperature. These results are qualitatively confirmed by the application of time-dependent theory using only the 1360 cm (-1) mode to reproduce the low-temperature emission spectra.

Localized cell stimulation by nitric oxide using a photoactive porous coordination polymer platform

“…Both ligands present broad and intense absorption bands in the 260–430 nm range, assigned to the n − π * and π − π * transitions of the aromatic nitro functionalities. The similarity between the NOF-1 and 2nIm absorption spectra ( λ max =375 nm) indicates that the electronic environment of the ligand remains essentially unaffected on formation of the crystalline coordination framework; the Zn(II) ions do not become electronically involved in either the ground-state behaviour or the excited-state decay of their coordinating nitrogen-based ligands 39 . The situation is different for [Co(2nIm) 2 ] n , the cobalt analogue of NOF-1; a slightly broadened and bathochromically shifted ultraviolet absorption band and new absorption bands appear in the visible region from 450 to 650 nm ( λ max =550 nm), which can be assigned to the spin-allowed d – d transitions ( 4 A 2 (F)→ 4 T 2 (P)) of the Co(II) centres in a tetrahedral coordination environment 40 .…”

Light Harvesting and Directional Energy Transfer in Long‐Lived Homo‐ and Heterotrimetallic Complexes of FeII, RuII, and OsII

“…Low-spin complexes of first-row transition metal ions such as Fe II have not proved to be effective sensitizers, because low-energy ligand-field excited states on the metal center pro-vide nonradiative decay pathways that significantly decrease excited-state lifetimes and lead to facile decomposition of complexes. [32][33][34][35][36] In the present study, the photophysical behaviors of two trimetallic light-harvesting ensembles containing two Ru II and one Fe II or two Os II and one Fe II centers are of particular interest, because through synthetic control of the bridging ligand it was possible to produce Fe II -containing complexes with long-lived excited states. The selection of Fe II arose from the report by Schmehl et al that a trinuclear RuFeRu complex bridged by phenylenevinylene-substituted triimine ligands produces a long-lived intraligand triplet state ( 3 IL).…”

Photophysical properties of metal complexes

“…The related trinuclear analogues [M{Pt(4,4 0 ,4 0 0 -t Bu 3 -terpy)(CRC-terpy)} 2 ] 4+ show quenching of this emission from metal-based ligand-field states by efficient non-radiative decay pathways when M = Fe(II), but when M = Zn(II) a similar emission profile is observed. 136 The effect of a strongly electron-accepting diimine ligand on excited-state structure and dynamics were probed using compounds of general formula [Pt(MesBIAN)(CRC-R) 2 ] [MesBIAN = bis(mesitylimino)acenaphthene, R = functionalised aryl group]. The complexes show emission from a ''mixed metal-ligand to ligand charge transfer'' excited state (t = 8 to 36 ns) that is proposed to contain some contribution from a pseudocumulenic form of the Pt-acetylide moiety.…”