Spectroscopic properties of luminescent platinum(II) complexes containing 4,4′,4″-tri-tert-butyl-2,2′ : 6′,2″-terpyridine (tBu3tpy). Crystal structures of [Pt(tBu3tpy)Cl]ClO4 and [Pt(tBu3tpy){CH2C(O)Me}]ClO4

The 77 K emission spectrum of [Pt(^tBu₃tpy)Cl]ClO₄, 1(ClO₄) (^tBu₃tpy = 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine), in a 10^-3 mol dm^-3 MeOH/EtOH glassy solution exhibits a 625 nm band attributed to ^tBu₃tpy π-π interactions, whereas a dilute solution (10^-6 mol dm^-3) shows a vibronic intraligand emission at λ_max 467 nm. By comparing the UV-vis spectra of 1 with the ¹IL-dominated spectrum of [Au(^tBu₃tpy)Cl]²⁺ (4) in CH₃CN, the moderately intense absorption band at λ_max 373-386 nm for the former is ascribed to a ¹MLCT [(5d)Pt → π*(^tBu₃tpy)] transition. The absorption spectrum of 1 contains a weak shoulder at 465 nm (∈ = 57 dm³ mol^-1 cm^-1) which obeys Beer's law in the concentration range 5 × 10^-4 to 1 × 10^-2 mol dm^-3, and a ³MLCT assignment is proposed. Ketonyl platinum(II) complexes [Pt(^tBu₃tpy){CH₂C(O)R}]ClO₄ (R = Me, 2 and R = Ph, 3) have been prepared from 1(ClO₄) in the presence of aqueous NaOH and the corresponding methyl ketone. The molecular structures of 1(ClO₄) and 2(ClO₄)·C₂H₅OH reveal π-stacking orientations for the ^tBu₃tpy ligands with interplanar separations of ca. 3.8 and 3.6 Å, respectively. Complexes 2 and 3 are luminescent in solution at room temperature, and ³MLCT excited states are assigned, while 1 is nonemissive. The superior photophysical properties of 2 and 3 are ascribed to the stronger σ-donating ability of the ketonyl ligands. Like 1, complexes 2 and 3 also display low-energy emission at ca. 620 nm in 10^-3 mol dm^-3 MeOH/EtOH glass at 77 K. Complex 1(ClO₄) is emissive in crystalline form at 77 K only (λ_max 560 nm). Solid-state emissions of 2(ClO₄) and 3(ClO₄) at room temperature (λ_max 607 and 615 nm, respectively) are derived from weak stacking interactions between ^tBu₃tpy groups, while their emission maxima are red-shifted at 77 K. © 1999 American Chemical Society.