Long-Lived Charge-Transfer State Induced by Spin-Orbit Charge Transfer Intersystem Crossing (SOCT-ISC) in a Compact Spiro Electron Donor/Acceptor Dyad.

ABSTRACT: We prepared conceptually novel, fully rigid, spiro compact electron donor (Rhodamine?B, lactam form, RB)/acceptor (naphthalimide; NI) orthogonal dyad to attain the long-lived triplet charge-transfer (3 CT) state, based on the electron spin control using spin-orbit charge transfer intersystem crossing (SOCT-ISC). Transient absorption (TA) spectra indicate the first charge separation (CS) takes place within 2.5?ps, subsequent SOCT-ISC takes 8?ns to produce the 3 NI* state. Then the slow secondary CS (125?ns) gives the long-lived 3 CT state (0.94??s in deaerated n-hexane) with high energy level (ca. 2.12?eV). The cascade photophysical processes of the dyad upon photoexcitation are summarized as 1 NI*?1 CT?3 NI*?3 CT. With time-resolved electron paramagnetic resonance (TREPR) spectra, an EEEAAA electron-spin polarization pattern was observed for the naphthalimide-localized triplet state. Our spiro compact dyad structure and the electron spin-control approach is different to previous methods for which invoking transition-metal coordination or chromophores with intrinsic ISC ability is mandatory.

SUBMITTER: Liu D 

PROVIDER: S-EPMC7496792 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature