Photophysics of Platinum−Acetylide Substituted Hexa-peri-hexabenzocoronenes

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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−C⋮C−)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.