Organometallic Pt(II) Compounds. A Complementary Study of a Triplet Emitter Based on Optical High-Resolution and Optically Detected Magnetic Resonance Spectroscopy

Abstract

The emitting triplet state of cyclometalated Pt(thpy)(CO)(Cl) monomers ((thpy)(-) = 2-(2'-thienylpyridinate), frequently also abbreviated as (2-thpy)(-)) is investigated at T = 1.2 K (typically) by use of the complementary methods of high-resolution optical spectroscopy and of optically detected magnetic resonance (ODMR) spectroscopy. Such a complimentary investigation is carried out for the first time for a Pt(II) compound. In solution, oligomer or short linear chain formation is also observed. However, the monomers can be investigated selectively, when they are dissolved in a relatively inert n-octane matrix (Shpol'skii matrix). This allows us to determine the energies of the T(1) triplet substates I, II, and III relative to the electronic ground state S(0)(0), the zero-field splittings (ZFSs) of T(1), and emission decay time constants (I/II <--> 0, 18012.5 cm(-1); III <--> 0, 18016.3 cm(-1); DeltaE(I,II) = 0.05437 cm(-1) (1.631 GHz), DeltaE(I,III) = 3.8 cm(-1) (114 GHz); tau(I) = 120 micros, tau(II) = 45 micros, tau(III) = 35 micros; spin-lattice relaxation time for the processes III --->I/II, tau(SLR) = 3.0 micros). The vibrational satellite structure observed in the emission of the T(1) state to the singlet ground state S(0) is also discussed. Moreover, it is possible to estimate the intersystem crossing time from the excited singlet state S(1) at 22952 cm(-1) to the triplet state T(1) to approximately 5 ps. The T(1) state is assigned as a thpy-ligand-centered (3)pipi* state with small metal-to-ligand charge-transfer (MLCT) admixtures. A comparison of Pt(thpy)(CO)(Cl) to a series of other organometallic Pt(II) compounds, such as heteroleptic Pt(ppy)(CO)(Cl) ((ppy)(-) = phenylpyridinate), Pt(dppy)(CO) ((dppy)(2-) = diphenylpyridinate), and Pt(i-biq)(CN)(2) (i-biq = 2,2'-bisisoquinoline) and homoleptic Pt(thpy)(2) and Pt(ppy)(2), is carried out. (The structures are shown in Figure 7.) Trends of photophysical properties are discussed. In particular, by chelation of two equal ligands the pattern of ZFS is strongly altered, resulting in a significant increase of the MLCT participation in the lowest triplet state of these organometallic compounds. This new observation represents an interesting further step concerning chemical tunability of photophysical properties.

Acid/base sensitive platinum terpyridyl complex: Switching between metal-to-ligand charge transfer (MLCT), ligand-to-ligand charge transfer (LLCT), and intraligand charge transfer (ILCT) states

“…Square-planar platinum(II) complexes have attracted a great interest in recent years due to their intriguing spectroscopic properties and potential applications in a variety of photonic devices, such as in organic light emitting diodes [1][2][3][4][5][6][7][8][9], photovoltaic cells [10][11][12][13], as nonlinear optical materials [14][15][16][17][18][19], photosensitizers [20][21][22][23], and chemical and biological sensors [24][25][26][27][28][29][30]. Platinum terpyridyl phenylacetylide complexes are particularly interesting because of their ease of synthesis and structural modifications.…”

“…To date, no platinum complexes that are sensitive to bases have been reported. To remedy this deficiency, we recently synthesized a new platinum terpyridyl complex (2) with dimethylamino substituent on the phenylacetylide ligand and a hydroxylphenyl substituent on the terpyridyl ligand (structure shown in Scheme 1). It is anticipated that upon addition of bases, the hydroxyl group would be deprotonated, which would influence the electron distribution of the complex and thus affect the nature of the lowest excited state.…”

Excited-State Distortions of Cyclometalated Ir(III) Complexes Determined from the Vibronic Structure in Luminescence Spectra

“…[34][35][36][37] In a recent study, sharp line vibronic structure from a planar organometallic compound in a Shpol'skii matrix was reported. 38 It is surprising that an octahedral organometallic ion can be incorporated in a Shpol'skii matrix.…”

Synthesis, characterization, photophysics and electrophosphorescent applications of phosphorescent platinum cyclometalated complexes with 9-arylcarbazole moieties

“…Among them, Pt(II) complexes incorporating pyridine ligands such as bipyridine [11][12][13][14][15][16][17][18][19][20][21][22][23] and terpyridine [24] derivatives have attracted a great deal of interest as luminescent dyes for OLED applications since they often exhibit high phosphorescence quantum yields. On the other hand, several cyclometalated homo-or heteroleptic Pt(II) complexes based on 2-phenylpyridine (ppy) and analogues have been reported in the literature [25][26][27].…”