Synthesis, Photophysics, and Optical Limiting of Platinum(II) 4‘-Tolylterpyridyl Arylacetylide Complexes

Abstract

A series of 4'-tolylterpyridyl platinum(II) complexes with different arylacetylide ligands, namely, phenylacetylide, 4-bromophenylacetylide, 4-nitrophenylacetylide, 4-methoxyphenylacetylide, 4-dimethylaminophenylacetylide, 1-naphthylacetylide, and 3-quinolinylacetylide, were synthesized. Their photophysical properties, such as electronic absorption spectra, emission characteristics at room temperature and 77 K, and transient difference absorption spectra, have been investigated. All of these complexes exhibit a metal-to-ligand charge-transfer (1MLCT) transition at ca. 420-430 nm in their electronic absorption spectra. For ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, an additional solvatochromic charge-transfer band appears at ca. 460-540 nm. This band is sensitive to the para substituents on the phenylacetylide ligand and is tentatively assigned to a metal- or/and acetylide-to-terpyridyl charge-transfer transition (i.e., a 1MLCT or/and 1LLCT transition). All of the complexes exhibit room-temperature phosphorescence. The emission can be attributed to a 3MLCT state except for ttpy-C6H4NO2-4, for which the emission likely originates from an intraligand 3pi,pi* state involving the nitrophenylacetylide ligand. For ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, there probably is more than one low-energy state in close energy proximity, resulting in multiple exponential decays. In addition, the triplet transient absorption difference spectra of ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4NO2-4, and ttpy-Quin exhibit moderately intense, broad absorption bands in the visible region and extending into the near-IR region, which likely originate from the same excited state that emits or from a state that is in equilibrium with the emitting state. It appears that the electron-rich arylacetylide ligands, especially 4-methoxyphenylacetylide and 4-dimethylaminophenylacetylide, cause a decrease of the emission efficiency and disappearance of the transient absorption. In contrast, the complexes that exhibit positive absorption bands in the visible spectral region of the triplet transient difference absorption spectra show substantial optical limiting for nanosecond laser pulses at 532 nm.

Optical Properties of Hybrid Organic‐Inorganic Materials and their Applications

“…For instance the platinum(II) square-planar complex trans-[P(n-Bu) 3 ] 2 Pt[(C C-p-C 6 H 4 -C C-p-C 6 H 5 ] 2 [326,346,347] was reported for efficient nonlinear absorption in solution, [326,[346][347][348] and series of derivatives were prepared with improved properties. [294,[349][350][351][352][353][354][355][356][357][358] The use of PMMA monoliths hosting platinum derivatives was an efficient route towards OPL materials. [278,359] The measured linear transmissions were nearly 90% in the visible and NLO properties were maintained in the solid.…”

Switching between Ligand‐to‐Ligand Charge‐Transfer, Intraligand Charge‐Transfer, and Metal‐to‐Ligand Charge‐Transfer Excited States in Platinum(II) Terpyridyl Acetylide Complexes Induced by pH Change and Metal Ions

“…As reported by Sun and co-workers, the transient absorption from 3 was too weak to be observed. [21] Each spectrum in Figure 6 features an absorption band in the near-UV, a bleaching in the 430-540 nm region, and a broad absorption throughout the visible region. In all cases, the decay of the absorption transients throughout the absorption region and the recovery of the bleach occur on the same time scale, indicating that a single type of excited state is responsible for the experimental observations.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Indeed, these complexes have demonstrated promise for various applications, including optical power limiting, [20][21][22] electroluminescence, [13,[23][24][25][26] as photosensitizers for the generation of singlet oxygen [27] or hydrogen, [28] as molecular probes for biological macromolecules, [12,29] and as optical sensors. [17,18,[30][31][32][33][34] In particular, platinum(II) complexes bearing terpyridyl and acetylide ligands have been extensively investigated in view of their rich photophysical properties.…”

“…[17,18,[30][31][32][33][34] In particular, platinum(II) complexes bearing terpyridyl and acetylide ligands have been extensively investigated in view of their rich photophysical properties. [12,17,20,21,28,31,35,36] The spectroscopic properties and low-energy absorptions of these complexes may arise from metal-to-ligand charge transfer (MLCT), intraligand charge transfer (ILCT), ligand-to-ligand charge transfer (LLCT), or intraligand (IL) transitions, depending very much on the substitution on their terpyridyl and/or acetylide ligands. In most instances, these complexes exhibit long-lived excited states with photophysical properties consistent with a dp(Pt)!p*(terpyridyl) MLCT transition.…”

“…Sun and co-workers have studied the optical limiting of such complexes. [21] It has also been established that introduction of an amino group (NR 2 ) at the 4-position of the phenyl in 4'-phenyl-substituted 2,2':6',2''-terpyridine, to give 4'-(4-NR 2 -C 6 H 4 )-2,2':6',2''-terpyridine, results in the intramolecular charge-transfer (ICT) transition from the p orbital of the amino-substituted phenyl to the p* orbital of the terpyridyl moiety becoming the lowest-energy absorption. [38] This substituted terpyridine has served as a ligand in the assembly of Pt II complexes that display a low-lying ILCT excited state in which the aminosubstituted phenyl acts as the electron donor and the metalbound terpyridyl as the acceptor.…”