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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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Heavy‐Atom Tunneling Through Crossing Potential Energy Surfaces: Cyclization of a Triplet 2‐Formylarylnitrene to a Singlet 2,1‐Benzisoxazole
Abstract Not long ago, the occurrence of quantum mechanical tunneling (QMT) chemistry involving atoms heavier than hydrogen was considered unreasonable. Contributing to the shift of this paradigm, we present here the discovery of a new and distinct heavy‐atom QMT reaction. Triplet syn‐2‐formyl‐3‐fluorophenylnitrene, generated in argon matrices by UV‐irradiation of an azide precursor, was found to spontaneously cyclize to singlet 4‐fluoro‐2,1‐benzisoxazole. Monitoring the transformation by IR spectroscopy, temperature‐independent rate constants (k≈1.4×10−3 s−1; half‐life of ≈8 min) were measured from 10 to 20 K. Computational estimated rate constants are in fair agreement with experimental values, providing evidence for a mechanism involving heavy‐atom QMT through crossing triplet to singlet potential energy surfaces. Moreover, the heavy‐atom QMT takes place with considerable displacement of the oxygen atom, which establishes a new limit for the heavier atom involved in a QMT reaction in cryogenic matrices.
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- PAR ID:
- 10182882
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 59
- Issue:
- 40
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 17622-17627
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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