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-localized π,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 theπ,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-localized π,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.

Monocationic Iridium(III) Complexes with Far‐Red Charge‐Transfer Absorption and Near‐IR Emission: Synthesis, Photophysics, and Reverse Saturable Absorption

“…In order to facilitate RSA of nanosecond laser pulses, an absorber should have a weak ground‐state absorption to populate the excited states, but long–lived triplet excited states, large triplet‐triplet excited‐state absorption coefficients, and a high quantum yield for triplet excited‐state formation. In recent years, the RSA of heavy transition‐metal complexes, such as octahedral Ir(III) complexes, have been extensively explored by our group, , , , and other groups, because these complexes displayed the aforementioned characteristics that well match the requirements for RSA. In addition, by structural modifications, both the ground‐ and excited‐state properties can be readily tuned in these complexes for optimization of the RSA.…”

“…Among which the lack of considerable ground‐state absorption in the red to the near‐infrared (NIR) regions remains to be one of the obstacles. In seeking solutions to red‐shift the ground‐state absorption but meanwhile keep a long–lived and strongly absorbing triplet excited state, immense effects have been put by our group on exploring N ^ N or C ^ N ligands suitable for reverse saturable absorbers , , , , . We discovered that incorporation of quinoxaline or benzo[ g ]quinoxaline unit into either the N ^ N or C ^ N ligand red–shifted the spin‐forbidden 3 π ,π* / 3 CT (charge transfer) absorption bands into longer wavelengths , , .…”

Synthesis, crystal structure and electroluminescent properties of fac-bromotricarbonyl ([1,2,5]oxadiazolo[3',4':5,6]pyrazino- [2,3-f][1,10]phenanthroline) rhenium (I)

“…In the case of the latter O(1) atom has participated in the formation of rather rare symmetric  6 -mode for O… interaction with О…С distances varying in the range of 3.040-3.068(6)Å. 15 The luminescence of 9a in solid state at 300 K was negligible, while for degassed solutions in DMSO at the same temperature it can be seen by naked eye. The observed quenching of luminescence in the solid state can be the consequence of the above mentioned intermolecular contacts.…”

Dysprosium Single-Molecule Magnets Involving 1,10-Phenantroline-5,6-dione Ligand

“…The dysprosium complexes Dy(tta) 3 ·2H 2 O (tta -= 2-thenoyltrifluoroacetonate anion) [61] and Dy(hfac) 3 ·2H 2 O [62], as well as the 1,10-phenantroline-5,6-dione ligand [63] (L), were synthesized following previously reported methods. All other reagents were commercially available and used without further purification.…”