Spectroscopic properties of luminescent platinum(II) complexes containing 4,4 ',4 ''-Tri-tert-butyl-2,2 ': 6 ',2 ''-terpyridine ((t)Bu(3)tpy). Crystal structures of [Pt((t)Bu(3)tpy)Cl]ClO4 and [Pt((t)Bu(3)tpy){CH2C(O)Me}]ClO4

The 77 K emission spectrum of [Pt((t)Bu(3)tpy)Cl]ClO4, 1(ClO4) ((t)Bu(3)tpy = 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine), in a 10(-3) mol dm(-3) M eOH/EtOH glassy solution exhibits a 625 nm band attributed to (t)Bu(3)tpy p i-pi interactions, whereas a dilute solution (10(-6) mol dm(-3)) shows a vi bronic intraligand emission at lambda(max) 467 nm. By comparing the UV-vis spectra of 1 with the (IL)-I-1-dominated spectrum of [Au((t)Bu(3)tpy)Cl](2) (4) in CH3CN, the moderately intense absorption band at lambda(max) 373-3 86 nm for the former is ascribed to a (MLCT)-M-1 [(5d)Pt --> pi*((t)Bu(3)tp y)] transition. The absorption spectrum of 1 contains a weak shoulder at 46 5 nm (epsilon = 57 dm(3) mol(-1) cm(-1)) which obeys Beer's law in the conc entration range 5 x 10(-4) to 1 x 10(-2) mol dm(-3), and a (MLCT)-M-3 assig nment is proposed. Ketonyl platinum(II) complexes [Pt((t)Bu(3)tpy){CH2C(O)R }]ClO4 (R = Me, 2 and R = Ph, 3) have been prepared from 1(ClO4) in the pre sence of aqueous NaOH and the corresponding methyl ketone. The molecular st ructures of 1(ClO4) and 2(ClO4). C2H5OH reveal pi-stacking orientations for the (t)Bu(3)tpy ligands with interplanar separations of ca. 3.8 and 3.6 An gstrom, 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 stro nger a-donating ability of the ketonyl ligands. Like 1, complexes 2 and 3 a lso display low-energy emission at ca. 620 nm in 10(-3) mol dm(-3) MeOH/EtO H glass at 77 K. Complex 1(ClO4) is emissive in crystalline form at 77 K on ly (lambda(max) 560 nm). Solid-state emissions of 2(ClO4) and 3(ClO4) at ro om temperature (lambda(max) 607 and 615 nm, respectively) are derived from weak stacking interactions between (t)Bu(3)tpy groups, while their emission maxims are red-shifted at 77 K.