Cyclometalated Ruthenium(II) Complexes Derived from α-Oligothiophenes as Highly Selective Cytotoxic or Photocytotoxic Agents

The photophysical and photobiological properties of a new class of cyclometalated ruthenium(II) compounds incorporating π-extended benzo[h]imidazo[4,5-f]quinoline (IBQ) cyclometalating ligands (C^N) bearing thienyl rings (n = 1–4, compounds 1–4) were investigated. Their octanol–water partition coefficients (log Po/w) were positive and increased with n. Their absorption and emission energies were red-shifted substantially compared to the analogous Ru(II) diimine (N^N) complexes. They displayed C^N-based intraligand (IL) fluorescence and triplet excited-state absorption that shifted to longer wavelengths with increasing n and N^N-based metal-to-ligand charge transfer (MLCT) phosphorescence that was independent of n. Their photoluminescence lifetimes (τem) ranged from 4–10 ns for 1IL states and 12–18 ns for 3MLCT states. Transient absorption lifetimes (τTA) were 5–8 μs with 355 nm excitation, ascribed to 3IL states that became inaccessible for 1–3 with 532 nm excitation (1–3, τTA = 16–17 ns); the 3IL of 4 on...