Picosecond transient absorption studies of dipyridophenazine

Creely, Caitriona M.; Kelly, John M.; Selmi, Ania; McGovern, David A.; Blau, Werner J.; Matousek, Pavel; Towrie, Michael; Parker, Anthony W.

doi:10.1117/12.475457

Cited by 4 publications

(1 citation statement)

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“…It may be observed that 1 ps after excitation a new species is present which shows maximum absorption at 469 nm and several prominent shoulders. This transient spectrum is similar to that previously observed for dppz itself 53 and for [Re(CO) 3 py(dppz)] + 54 and assigned to a ππ* excited state. It is therefore consistent with this initially formed species from 1 being a ligand-centered (LC) excited state.…”

Section: Resultssupporting

confidence: 87%

Adenine Radical Cation Formation by a Ligand-Centered Excited State of an Intercalated Chromium Polypyridyl Complex Leads to Enhanced DNA Photo-oxidation

et al. 2021

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Assessment of the DNA photo-oxidation and synthetic photocatalytic activity of chromium polypyridyl complexes is dominated by consideration of their long-lived metal-centered excited states. Here we report the participation of the excited states of [Cr(TMP) 2 dppz] 3+ ( 1 ) (TMP = 3,4,7,8-tetramethyl-1,10-phenanthroline; dppz = dipyrido[3,2- a :2′,3′- c ]phenazine) in DNA photoreactions. The interactions of enantiomers of 1 with natural DNA or with oligodeoxynucleotides with varying AT content (0–100%) have been studied by steady state UV/visible absorption and luminescence spectroscopic methods, and the emission of 1 is found to be quenched in all systems. The time-resolved infrared (TRIR) and visible absorption spectra (TA) of 1 following excitation in the region between 350 to 400 nm reveal the presence of relatively long-lived dppz-centered states which eventually yield the emissive metal-centered state. The dppz-localized states are fully quenched when bound by GC base pairs and partially so in the presence of an AT base-pair system to generate purine radical cations. The sensitized formation of the adenine radical cation species ( A •+ T ) is identified by assigning the TRIR spectra with help of DFT calculations. In natural DNA and oligodeoxynucleotides containing a mixture of AT and GC of base pairs, the observed time-resolved spectra are consistent with eventual photo-oxidation occurring predominantly at guanine through hole migration between base pairs. The combined targeting of purines leads to enhanced photo-oxidation of guanine. These results show that DNA photo-oxidation by the intercalated 1 , which locates the dppz in contact with the target purines, is dominated by the LC centered excited state. This work has implications for future phototherapeutics and photocatalysis.

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Section: Resultssupporting

confidence: 87%