Synthesis of branched tetranuclear alkynylplatinum(II) terpyridine complexes and their photophysical properties

Herein we report the synthesis of two luminescent branched tetranuclear alkynylplatinum(II) complexes {[Pt(tBu3-tpy)]2[Ar(CC)4][Pt(tBu3-tpy)]}2(PF6)4 (I and II; tBu3-tpy = 4,4′,4″-tri-tertbutyl-2,2′:6′,2″-terpyridine; Ar = [(C6H4)2(CCCC)]). Two terminal alkyne ligands were synthesized by oxidative coupling in the air, and subsequently reacted with a chloroplatinum(II) terpyridine complex. Their photophysical properties have been studied by both steady-state spectroscopy and transient spectroscopy. The final two platinum(II) complexes were found to show long-lived excited states in solution at room temperature. The longest lifetime of ∼17 μs for the twisted branched molecule was observed in toluene at room temperature. Application of the two complexes as a light-harvesting chromophore in photocatalytic hydrogen production was further examined.