Spectroscopic Study of the E/Z Photoisomerization of a New Cyrhetrenyl Acylhydrazone: A Potential Photoswitch and Photosensitizer†. (28th July 2020)

• Record Type: Journal Article
• Authors: Toro, Patricia M.; Jara, Danilo H.; Klahn, A. Hugo; Villaman, David; Fuentealba, Mauricio; Vega, Andrés; Pizarro, Nancy
• Is Part Of: Photochemistry and photobiology. Volume 97:Number 1(2021)
• Page Start: 61
• Page End: 70
• Publication Date: 2020-07-28
• Subjects: Photochemistry -- Periodicals; Light -- Physiological effect -- Periodicals; 541.35
• DOI: 10.1111/php.13309
• Languages: English
• ISSNs: 0031-8655

Abstract

Abstract: The new cyrhetrenyl acylhydrazone [(CO)3 Re(η 5 ‐C5 H4 )‐C(O)‐NH‐N = C(CH3 )‐(2‐C4 H2 S‐5‐NO2 )] ( E ‐CyAH ) has been designed, synthesized and fully characterized to study the effect of having a cyrhetrenyl fragment (sensitizer) covalently bonded to an acylhydrazone moiety (switch), on its photophysical and photochemical properties. The crystal structure reveals that E ‐CyAH adopts an E ‐configuration around the iminic moiety [‐N = C(CH3 )]. The absorption spectrum of E ‐CyAH displays two bands at 270 and 380 nm, which are mainly ascribed to π → π* intraligand (IL) and dπ → π* metal‐to‐ligand charge transfer (MLCT) transitions, being consistent with DFT/TD‐DFT calculations. Upon 365 nm irradiation, E ‐CyAH photoisomerizes to Z ‐CyAH, as evidenced by UV‐Vis and 1 H‐NMR spectral changes, with a quantum yield value Φ E ‐CyAH → Z ‐CyAH of 0.30. Z ‐CyAH undergoes a first‐order thermal back‐isomerization process, with a relatively short half‐life τ1/2 of 277 min. Consequently, E‐ CyAH was quantitatively recovered after 24 h, making it a fully reversible T‐type molecular photoswitch. This remarkable behavior allows us to measure the individual photophysical properties for both isomers. In addition, E ‐CyAH and Z ‐CyAH efficiently photosensitize the generation of singlet oxygen (O2 ( 1 Δg )) with good yield (ΦΔ = 0.342). Abstract : Bonding a cyrhetrenyl core to a photoisomerizable acylhydrazone fragment yields a novel organometallic photoswitch and photosensitizer for singlet oxygen generation.