Indexed by:Journal Papers

Date of Publication:2020-03-18

Journal:Chemistry (Weinheim an der Bergstrasse, Germany)

Included Journals:PubMed

Volume:26

Issue:16

Page Number:3591-3599

ISSN No.:1521-3765

Key Words:Tröger's bases,intersystem crossing,naphthalimides,photophysics,time-resolved spectroscopy

Abstract:Intersystem crossing (ISC) was observed for naphthalimide (NI)-derived Tröger's base, and the ISC was confirmed to occur by a spin-orbital charge-transfer (SOCT) mechanism. Conventional electron donor/acceptor dyads showing SOCT-ISC have semirigid linkers. In contrast, the linker between the two chromophores in Tröger's base is rigid and torsion is completely inhibited, which is beneficial for efficient SOCT-ISC. Femtosecond transient absorption (TA) spectra demonstrated charge-separation and charge-recombination-induced ISC processes. Nanosecond TA spectroscopy confirmed the ISC, and the triplet state is long-lived (46 μs, room temperature). The ISC quantum yield is dependent on solvent polarity (8-41 %). The triplet state was studied by pulsed-laser-excited time-resolved EPR spectroscopy, and both the NI-localized triplet state and triplet charge-transfer state were observed, which is in good agreement with the spin-density analysis. The Tröger's base was confirmed to be a potent photodynamic therapy reagent with HeLa cells (EC50 =5.0 nm).© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.