Pt(ii) diimine complexes bearing carbazolyl-capped acetylide ligands: synthesis, tunable photophysics and nonlinear absorption

Abstract

A series of new Pt(II) diimine complexes with different carbazolyl-capped acetylide ligands (Pt-1–Pt-5) were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. All complexes exhibit ligand-centered 1π,π* transitions in the UV region, and broad, structureless metal-to-ligand charge transfer (1MLCT)/ligand-to-ligand charge transfer (1LLCT) absorption bands in the visible spectral region. All complexes are emissive in solution at room temperature, with the emitting state being tentatively assigned to the 3MLCT/3LLCT states for Pt-1–Pt-4, and the emitting state of Pt-5 exhibiting a switch from the 3π,π* state in high-polarity solvents to the 3MLCT state in low-polarity solvents. Complexes Pt-1–Pt-5 all exhibit moderate triplet transient absorption (TA) from the visible to the NIR region, where reverse saturable absorption (RSA) could occur. The spectroscopic studies and theoretical calculations indicate that the photophysical properties of these Pt complexes can be tuned drastically by the carbazolyl-capped acetylide ligand, which would be useful for rational design of transition-metal complexes with high emission quantum yield, long excited-state lifetime, broadband excited-state absorption, and strong nonlinear transmittance for organic light-emitting and/or broadband nonlinear transmission applications.

Functional Platinum(II) Complexes with Four-Photon Absorption Activity, Lysosome Specificity, and Precise Cancer Therapy

“…The lifetimes of Pt2 obtained from the decay of TA are consistent with those measured from the decay of the emission (Table S4), which implies that Pt2 probably emanates from the same excited state or in equilibrium with the emitting state. Thus, the triplet excited state shown in TA for Pt2 is assigned to the 3 MLCT/ 3 LLCT excited states . Most importantly, the whole spectrum is broad and positive in the NIR region, and the excited-state absorption is stronger than that of the ground state, which is present in the MLCT state …”

“…Thus, the triplet excited state shown in TA for Pt2 is assigned to the 3 MLCT/ 3 LLCT excited states. 34 Most importantly, the whole spectrum is broad and positive in the NIR region, and the excited-state absorption is stronger than that of the ground state, which is present in the MLCT state. 35 Most of the platinum(II) complexes show weak emission in a solution at room temperature.…”

Photophysics and non-linear absorption of Au(i) and Pt(ii) acetylide complexes of a thienyl-carbazole chromophore

“…18,19 Porphyrin [20][21][22][23] and phthalocyanine [24][25][26] metal complexes have been widely investigated with respect to 2PA and long pulse NLA via the dual mode mechanism; however, metal complexes linked to π-conjugated segments that feature the carbazole moiety have not been well explored. 27 Even though the singlet excited state photophysics for carbazole containing oligomers and polymers are well established, the triplet excited state is relatively unexplored. Introduction of a heavy metal such as platinum or gold into the conjugated backbone of carbazole containing oligomers provides insight into the triplet excited state due to the "heavy atom effect" that is elusive in the strictly organic system.…”

“…[28][29][30][31] Most carbazole derivatives find application in OLEDs or bulk heterojunction solar cells as π electron donor materials; however, there are few reports on organometallic carbazole complexes that exhibit non-linear absorption. 27 Zhou et al reported a carbazole platinum acetylide polymer and a model platinum complex substituting 3,6 position of the aromatic ring, as an efficient optical power limiting material at 532 nm. 32 Tao et al reported a naphthalene platinum acetylide substituted carbazole as a two photon absorbing and two photon induced luminescence molecule with a 2PA cross section (σ 2 ) of 14 GM (λ ex = 740 nm).…”

1,3,5-Triazine-Based Pt(II) Metallogel Material: Synthesis, Photophysical Properties, and Optical Power-Limiting Performance

“…On the other hand, although a series of Pt­(II) acetylide complexes have been proved to exhibit strong reverse saturable absorption (RSA) for nanosecond laser pulses, − the investigation of a gelation device for these nonlinear optical materials is still limited. Schanze and group creatively linked Pt­(II) acetylide nonlinear absorption chromophores into poly­(methyl methacrylate) as a glassy host matrix, allowing fabrication of nonlinear absorbing materials that can be used as coatings or freestanding optical monoliths .…”