Kinetic Analysis of Excited-State Dynamics of Emissive Oligomers of Pt(II) Complex in Solution.

[Pt(NCN)MeCN]+ (NCN = 1,3-di(2-pyridyl)benzene, MeCN = acetonitrile) forms oligomers, such as dimers and trimers, in solutions due to metallophilic interactions. The emission and absorption spectra in the visible region are considerably changed by the concentrations of the solutions because the excitation energy of the oligomers is dependent on the degree of oligomerization. In this study, excited-state dynamics of [Pt(NCN)MeCN]+ in acetonitrile were investigated by time-resolved emission spectroscopy in time regions from microseconds to nanoseconds at various concentrations. The time-resolved emission spectra recorded with 355 nm photoexcitation showed the decay of the blue-green emission and the rise of the red emission in the microsecond time region. Stern-Volmer analysis of the time-resolved data at various concentrations and wavelengths provides two bimolecular rate constants (4.1 × 109 and 8.2 × 108 M-1 s-1) for the formation processes of the excited-state T1 dimer and T1 trimer, respectively. Kinetic parameters, such as the intrinsic decay rate constants of the T1 monomer, T1 dimer, and T1 trimer, and the association and dissociation rate constants of the T1 dimer and T1 trimer were estimated by fitting the time-resolved emission data at various concentrations.