Excited State Dynamics of a PtII Diimine Complex bearing a Naphthalene-Diimide Electron Acceptor

A combination of picosecond time-resolved infrared spectroscopy, picosecond transient absorption spectroscopy, and nanosecond flash photolysis was used to elucidate the nature and dynamics of a manifold of the lowest excited states in Pt(phen-NDI)Cl2 (1), where NDI = strongly electron accepting 1,4,5,8-naphthalene-diimide group. 1 is the first example of a PtII-diimine-diimide dyad. UV/vis/IR spectroelectrochemistry and EPR studies of electrochemically generated anions confirmed that the lowest unoccupied molecular orbital (LUMO) in this system is localized on the NDI acceptor group. The lowest allowed electronic transition in Pt(phen-NDI)Cl2 is charge-transfer-to-diimine of a largely Pt→phen metal-to-ligand charge-transfer (MLCT) character. Excitation of 1 in the 355−395 nm range initiates a series of processes which involve excited states with the lifetimes of 0.9 ps (1NDI*), 3 ps (3MLCT), 19 ps (vibrational cooling of “hot” 3NDI and of “hot” NDI ground state), and 520 μs (3NDI). Excitation of 1 with 39...