title: Increasing the triplet lifetime and extending the ground-state absorption of biscyclometalated Ir(iii) complexes for reverse saturable absorption and photodynamic therapy applications.
abstract: The synthesis, photophysics, reverse saturable absorption, and photodynamic therapeutic effect of six cationic biscyclometalated Ir(iii) complexes (1-6) with extended π-conjugation on the diimine ligand and/or the cyclometalating ligands are reported in this paper. All complexes possess ligand-localized1π,π* absorption bands below 400 nm and charge-transfer absorption bands above 400 nm. They are all emissive in the 500-800 nm range in deoxygenated solutions at room temperature. All complexes exhibit strong and broad triplet excited-state absorption at 430-800 nm, and thus strong reverse saturable absorption for ns laser pulses at 532 nm. Complexes 1-4 are strong reverse saturable absorbers at 532 nm, while complex 6 could be a good candidate as a broadband reverse saturable absorber at 500-850 nm. The degree of π-conjugation of the diimine ligand mainly influences the1π,π* transitions in their UV-vis absorption spectra, while the degree of π-conjugation of the cyclometalating ligand primarily affects the nature and energies of the lowest singlet and emitting triplet excited states. However, the lowest-energy triplet excited states for complexes 3-6 that contain the same benzo[i]dipyrido[3,2-a:2',3'-c]phenazine (dppn) diimine ligand but different cyclometalating ligands remain the same as the dppn ligand-localized3π,π* state, which gives rise to the long-lived, strong excited-state absorption in the visible to the near-IR region. All of the complexes exhibit a photodynamic therapeutic effect upon visible or red light activation, with complex 6 possessing the largest phototherapeutic index reported to date (>400) for an Ir(iii) complex. Interactions with biological targets such as DNA suggest that a novel mechanism of action may be at play for the photosensitizing effect. These Ir(iii) complexes also produce strong intracellular luminescence that highlights their potential as theranostic agents.
authors.affiliation: Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, USA. Wenfang.Sun@ndsu.edu.
authors.forename: Chengzhe
authors.initials: C
authors.lastname: Wang
authors.affiliation: Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, USA. Wenfang.Sun@ndsu.edu.
authors.forename: Levi
authors.initials: L
authors.lastname: Lystrom
authors.affiliation: Department of Chemistry, Acadia University, 6 University Avenue, Wolfville, NS B4P 2R6, Canada. sherri.mcfarland@acadiau.ca.
authors.forename: Huimin
authors.initials: H
authors.lastname: Yin
authors.affiliation: Department of Chemistry, Acadia University, 6 University Avenue, Wolfville, NS B4P 2R6, Canada. sherri.mcfarland@acadiau.ca.
authors.forename: Marc
authors.initials: M
authors.lastname: Hetu
authors.affiliation: Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, USA. Wenfang.Sun@ndsu.edu.
authors.forename: Svetlana
authors.initials: S
authors.lastname: Kilina
authors.affiliation: Department of Chemistry, Acadia University, 6 University Avenue, Wolfville, NS B4P 2R6, Canada. sherri.mcfarland@acadiau.ca and Department of Chemistry and Biochemistry, University of North Carolina at Greensboro, Greensboro, NC 27402-6170, USA. samcfarl@uncg.edu.
authors.forename: Sherri A
authors.initials: SA
authors.lastname: McFarland
authors.affiliation: Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, USA. Wenfang.Sun@ndsu.edu.
authors.forename: Wenfang
authors.initials: W
authors.lastname: Sun