Photophysical properties of trans-platinum acetylide complexes featuring N-heterocyclic carbene ligands†
A series of trans-N-heterocyclic carbene (NHC) platinum(II) acetylide complexes of the form (ICy)2Pt(R)2 (where ICy = 1,3-bis-(cyclohexyl)imidazol-2-ylidene and R = 1-Ethynyl-4-(phenylethynyl)benzene (PE2), 2-(9,9-Diethyl-9H-fluoren-7-yl)benzo[d]thiazole (BTF), and 9,9-Diethyl-7-ethynyl-N,N-diphenyl-9H-fluoren-2-amine (DPAF), 2a–c respectively), were synthesized via Hagihara reaction of the unprotected aryl-acetylide ligands with trans-(ICy)2PtCl2 (1) in 47–73% yield. Precursor 1 was generated in a one-pot synthesis via formation of a silver carbene precursor followed by transmetallation, and was obtained in high yield (95%). The single-crystal X-ray structures of 1, 2a–c were determined and analyzed. The photophysical properties of 2a–c were compared to their respective tributyl phosphine (PBu3) analogues. The optical properties of the series were studied by UV-Vis spectroscopy, photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, and open aperture nanosecond z-scan. Coupling of the organic chromophores to the platinum center affords efficient intersystem crossing as concluded by the complexes’ low fluorescence quantum yields, efficient phosphorescence and intense T1 − Tn absorption. Open aperture z-scan with 606 nm, 10 ns laser pulses showed comparable optical attenuation relative to a standard sample of (PBu3)2Pt(DPAF)2 (3c). Pulse limiting was achieved via a dual-mechanism of two-photon absorption (2PA) coupled with excited-state absorption (ESA). TD-DFT Computations were also employed for 2a–c to give greater insight into the nature of the singlet-singlet electronic transitions.
- This article is part of the themed collection: Spectroscopy of Inorganic Excited States