Intracellular Photophysics of an Osmium Complex bearing an Oligothiophene Extended Ligand

Abstract

This contribution describest he excited-state properties of an Osmium-complex when taken up into human cells. The complex 1 [Os(bpy) 2 (IP-4T)](PF 6) 2 with bpy = 2,2'-bipyridine and IP-4T = 2-{5'-[3',4'-diethyl-(2,2'-bithien-5-yl)]-3,4-diethyl-2,2'-bithiophene}imidazo[4,5-f] [1,10]phenanthroline) can be discussed as ac andidate for photodynamic therapy in the biological red/NIR window. The complex is takenu pb yMCF7 cells andl ocalizes rather homogeneously within in the cytoplasm. To detail the sub-ns photophysics of 1,c omparativet ransienta bsorptionm easurements were carried out in different solvents to derive am odel of the photoinduced processes. Key to rationalize the excited-state relaxationis al onglived 3 ILCT state associated with the oligothiophene chain. This model was then tested with the complex internalized into MCF7 cells, since the intracellular environment has long been suspected to take big influence on the excited state properties. In our study of 1 in cells, we were able to show that, though the overallm odel remained the same, the excited-state dynamics are affectedstrongly by the intracellular environment. Our study represents the first in depth correlation towards ex-vivo and in vivo ultrafast spectroscopy for apossible photodrug.

String-Attached Oligothiophene Substituents Determine the Fate of Excited States in Ruthenium Complexes for Photodynamic Therapy

“…This assertion is consistent with computational analysis suggesting planarization of the lowest-lying triplet state. 7,8,24,45 The 1.1 ns time constant (τ 3 ) reflects the formation of an ESA in the range of the ground-state absorption between about 420 and 520 nm. This increasing ESA on a 1.1 ns timescale causes the apparent GSB to diminish in this spectral region.…”

“…4−6 Combining different metals with various ligands controls the absorption characteristics of the complexes to shift light absorption to the relevant spectral region for a given application. 7,8 The choice of ligands also modulates cellular uptake and distribution of the complexes in the cells and tunes the nature of the lowest-energy excited states and their intrinsic lifetimes, which appear to be key to their action as PDT agents. 9,10 Certain metal complexes bearing π-expansive ligands appended to organic chromophores have prolonged triplet state lifetimes (tens of microseconds or longer).…”

“…Photoactive transition-metal complexes for PDT constitute an emerging class of PSs. − Combining different metals with various ligands controls the absorption characteristics of the complexes to shift light absorption to the relevant spectral region for a given application. , The choice of ligands also modulates cellular uptake and distribution of the complexes in the cells and tunes the nature of the lowest-energy excited states and their intrinsic lifetimes, which appear to be key to their action as PDT agents. , Certain metal complexes bearing π-expansive ligands appended to organic chromophores have prolonged triplet state lifetimes (tens of microseconds or longer). − Such long-lived triplet excited states are characteristic of organic chromophores, but their quantum yield for triplet state formation is generally quite limited in organic systems. − Tethering π-expanded organic chromophores to photoactive transition metal complexes has proven to be an effective strategy for capitalizing on the high spin orbit coupling afforded by the metal center for more efficient triplet state formation. , This is possible in metal–organic dyads that have low-energy ligand-localized excited states in close proximity to the lowest-lying triplet metal-to-ligand charge-transfer ( 3 MLCT) excited states that generally dominate the photophysics of Ru­(II) polypyridyl complexes . Population of these triplet intraligand ( 3 IL) excited states from the initially formed 1 MLCT or 1 IL states can yield 3 IL states with intrinsic lifetimes exceeding 50 μs .…”

Monitoring excited-state relaxation in a molecular marker in live cells–a case study on astaxanthin

“…The reference data of AXT in DMSO reveal an overall decay of the signal with a 5.3 ps time constant, in line with the literature reporting the S 1 lifetime of AXT to vary from 4.3 to 5.6 ps depending on the solvent. 7,25 To investigate the impact of the cellular environment on the dynamics of the S 1 state in AXT, when taken up by human cells, we utilized a recently reported setup, 26 which allows for studying pump-probe data from adherently growing cells. The setup (see Fig.…”

“…The setup (see Fig. 2a) has been introduced to study fixed cells; 26 however, live cell studies have not yet been performed. The sample is placed in a m-dish, while in principle an incubator can be inserted at the sample position.…”