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Abstract A series of four oligothiophenes end‐capped with −Pt(PBu3)2Cl moieties on both ends of the oligomers was synthesized, and their excited state properties were investigated. The observation of low fluorescence quantum yield (<2 %) for the oligomers indicates the strong effect of platinum on the intersystem crossing (ISC) efficiency. No phosphorescence was detected for any of the oligomers; however, strong triplet‐triplet absorption was observed by nanosecond transient spectroscopy for oligomers with more than one thiophene unit. The oligomers displayed short triplet lifetimes (∼1–2 μs) compared to the unmetallated oligomers, due to large spin‐orbit coupling induced by the platinum atom. The lower limits of the ISC yields were indirectly determined by measuring the singlet oxygen quantum yields. Femtosecond–picosecond transient absorption studies revealed that the ISC rate ranges from 1012–1010 s−1, decreasing with increasing oligomer length. Electrochemical studies showed that the oligomers exhibit relatively low oxidation potentials (ca. 0.1 V vs. Fc/Fc+). Quenching of the oligomers’ triplet state absorption, simultaneously with the rise of their corresponding cationic radical absorption band in nanosecond transient spectra in the presence of methyl viologen, as an electron acceptor, established that the electron transfer occurs from their triplet state.
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Photophysical Insights of Halogenated Dipyrrolonaphthyridine‐Diones as Potential Photodynamic Therapy Agents †
Abstract We report the synthesis and photophysical characterization of novel halogenated dipyrrolonaphthyridine‐diones (X2–DPNDs, X = Cl, Br, and I), as candidates for photodynamic therapy (PDT) application. Apart from the heavy atom‐induced spin‐orbit coupling (SOC) dynamics in the investigated X2–DPNDs, it was found that the position of the halogen atom (relative to the nitrogen of the pyrrole ring) also influenced the triplet excited state behavior. Interestingly, the faster/efficiency sensitization of3O2to1O2using X2–DPND correlates with the rate of triplet population,kISC >1.6 × 108s−1for I2–DPNDvs kISC >2.9 × 109s−1for Cl2–DPND and Br2–DPND (whereτISC = 343 ± 3 ps for I2–DPND andτISC = 5–6 ns for Cl2–DPND and Br2–DPND are the lowest time constants/values for ISC). Furthermore, the heavy atom‐induced SOC in Cl2–DPND and Br2–DPND did not lead to a reduction of the corresponding fluorescence (ca75%vs67% for the parent DPND). The attractive photophysical characteristics of Cl2/Br2–DPND put them on the landscape as not only promising PDT agents but also as fluorescence probes. The present study is a stepping stone in the development of novel organic photosystems for synergistic photomedicinal applications.
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- Award ID(s):
- 2211296
- PAR ID:
- 10420650
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Photochemistry and Photobiology
- Volume:
- 99
- Issue:
- 2
- ISSN:
- 0031-8655
- Page Range / eLocation ID:
- p. 761-768
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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