Photophysics of Platinum−Acetylide Substituted Hexa-peri-hexabenzocoronenes

Abstract

This manuscript reports the synthesis and photophysical investigation of two hexa-peri-hexabenzocoronenes (HBCs) that are functionalized with platinum(II) acetylide units of the type trans-(Ar-CC-)2Pt(PBu3)2. In one complex, the platinum is directly linked to the HBC chromophore by an ethynyl spacer, whereas in the second, the platinum is separated from the HBC via a 1,4-phenylene ethynylene spacer. The Pt-acetylide units introduce strong spin-orbit coupling into the HBC chromophore, giving rise to high yields of the triplet excited state along with moderately intense phosphorescence at ambient temperature. On the basis of emission spectroscopy, the triplet state of the HBC chromophore is located at 2.14 eV and the S-T splitting is 0.6 eV. The triplet-triplet absorption and radical cation absorption spectra of the Pt-HBCs are determined by laser flash photolysis. Aggregation of the Pt-HBCs in a poor solvent such as hexane leads to quenching of the triplet state, but spectroscopy provides no evidence for the formation of a triplet excimer, even under conditions where the molecules are strongly aggregated.

Luminescent Bis‐Cyclometalated Gold(III) Complexes with Alkynyl Ligands of Hexaphenylbenzene and Hexabenzocoronene Derivatives and Their Supramolecular Assembly

“…The nanosecond lifetime, small Stokes shift (absorption onset at λ ≈460 nm), and insensitivity towards oxygen suggest a singlet excited‐state origin in the emission. With reference to reports in the literature, the high‐energy emission of 8 is tentatively assigned to originate from an excited state derived from a spin‐allowed 1 IL [π→π*(C≡C–HBC)] transition. In addition to the high‐energy emission, complex 8 shows a vibronic‐structured low‐energy emission with a characteristic narrow bandwidth emission maximum at λ =574 nm.…”

“…The additional absorption band at λ =414 nm in the complex, which is absent in the free ligand, probably involves a metal‐perturbed π–π* IL transition of the bis‐cyclometalating ligand, since an absorption band at λ =412 nm has also been observed in 6 , 7 , and 9 , which contain the same bis‐cyclometalating ligand as that in 8 . In related HBC–platinum(II) systems, the appearance of this additional band is attributed to the fact that the attachment of the metal complex moiety lowers the symmetry of the HBC–alkynyl ligand. A similar rationale may also be applied to the observation of the additional band in complex 8 .…”

“…Despite recent reports on related HBC‐ and HPB‐containing isoelectronic platinum(II) complexes, which focused on photophysical property studies of the platinum(II) systems, corresponding supramolecular assembly studies of the platinum(II) complexes have not been made . Therefore, supramolecular assembly studies on HBC‐ and HPB‐containing gold(III) complexes would be an interesting area to explore.…”

Recent Progress on the Photonic Properties of Conjugated Organometallic Polymers Built Upon the trans‐Bis(para‐ethynylbenzene)bis(phosphine)platinum(II) Chromophore and Related Derivatives

“…The photophysics of some yellow-coloured platinum(II)-phenylacetylide complexes functionalized with a hexaperi-hexabenzocoronene core 113-115 (Scheme 34) have been studied and reported during the same year by the groups of Müllen [109] and Schanze. [110] For 113, addition of organometallic Pt-phenylacetylene units to the large polycyclic aromatic hydrocarbon spacer primarily enhanced the spin-orbit coupling and decreased the phosphorescence lifetime of the triplet state by three orders of magnitude, which leads to the exclusive phosphorescence emission without any residues of fluorescence in the prompt and delayed emission spectra. Similarly, high yields of the triplet excited state together with intense phosphorescence at room temperature can be observed for 114 and 115 because of the heavy-atom effect of the Pt groups.…”

Terpyridine-fused polyaromatic hydrocarbons generated via cyclodehydrogenation and used as ligands in Ru(ii) complexes

“…6 In this way two essentially isoenergetic triplet excited states would be provided: a 3 MLCT ([Ru(terpy) 2 ] 2+ , λ ∼ 629 nm) 14,15 and a HBC-localised 3 ππ* excited state (HBC, λ ∼ 578 nm). 10,16,17 Excitation into one of these might then give rise to efficient energy equilibration between the two complementary energy levels and substantially prolong the excited state lifetimes. Terpy units have also been shown to be effective synthetic platforms on which to introduce dithiocarbamates as highly stable and robust anchoring units for attachment to Au surfaces.…”