Revealing the Photophysical Dynamics of Selected Rigid Donor-Acceptor Systems: From Ligands to Ruthenium(II) Complexes.

Newly designed push-pull ligands ( and ) with bithiophene () as a donor and phenazine () or quinoxalino[2,3-]quinoxaline () as acceptors were synthesized and also incorporated with a bipyridyl Ru(II) complex to give and , respectively. The ultrafast photophysical dynamics of the ligand and their respective Ru(II) complexes were well-characterized using time-resolved spectroscopies and quantum chemical calculations. Photoinduced charger transfer (CT) and intersystem crossing (ISC) processes were directly observed for and . In addition, the interplay of three different triplet excited states was directly observed in the related Ru(II) complexes. The lowest-lying triplet excited states of the ligands and their respective Ru(II) complexes were both attributed to the CT transitions from donor () to acceptor ( or ) and result in ICT (intramolecular charge transfer) and ILCT (intraligand charge transfer) excited states, respectively. The lifetimes of the lowest-lying triplet excited states of , , , and were measured to be 21.3, 50.4, 2.75, and 4.16 μs, respectively.