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 (3CT) 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 3NI* state. Then the slow secondary CS (125 ns) gives the long‐lived 3CT state (0.94 μs in deaerated n‐hexane) with high energy level (ca. 2.12 eV). The cascade photophysical processes of the dyad upon photoexcitation are summarized as 1NI*→1CT→3NI*→3CT. 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.

Detection of the Dark States in Thermally Activated Delayed Fluorescence (TADF) Process of Electron Donor‐Acceptor Dyads: Insights from Optical Transient Absorption Spectroscopy

“…The reason for the slow 1 CT→ 3 CT transition of molecule 1 is still unclear. It can be due to the slow kinetics of the hyperfine interaction‐enhanced 1 CT→ 3 CT ISC, or weak spin vibronic coupling for 1 CT→ 3 LE→ 3 CT process [50] . The 1 CT state (2.6 eV) energy is close to that of 3 AQ state (2.7 eV).…”

Charge Transfer, Intersystem Crossing, and Electron Spin Dynamics in a Compact Perylenemonoimide-Phenoxazine Electron Donor–Acceptor Dyad

“…Some compact orthogonal dyads showing efficient SOCT-ISC have been reported. ,,− However, there are still some challenges for the investigation of SOCT-ISC; for instance, the chromophores used for SOCT-ISC are limited. The majority of the reported studies are focused on chromophores such as naphthaleneimide, , Bodipy, ,− rhodamine, , and perylene bisimide. , Perylene-3,4-dicarboximide (PMI) has been widely used in various fields of photochemistry. − Recently, we reported N -(2,6-diisopropylphenyl)-perylene-3,4-dicarboximide - phenothiazine ( PMI–PTZ ) dyads; moderate ISC was observed, and the singlet oxygen quantum yield (Φ Δ ) was 57%. Phenoxazine ( PXZ ), an analogue of PTZ except only one-atom variation, is a typical electron donor (oxidation potentials are 0.20 and 0.18 eV for PXZ and PTZ, respectively, vs Fc/Fc + ).…”

“…38,47,50−52 However, there are still some challenges for the investigation of SOCT-ISC; for instance, the chromophores used for SOCT-ISC are limited. The majority of the reported studies are focused on chromophores such as naphthaleneimide, 53,54 Bodipy, 48,55−57 rhodamine, 51,58 and perylene bisimide. 59,60 Perylene-3,4dicarboximide (PMI) has been widely used in various fields of photochemistry.…”

Palladium(II)-Catalyzed Dehydrogenative Strategy for Direct and Regioselective Oligomerization of BODIPY Dyes

“…Enhancing the ISC efficiency through exciton coupling and correspondingly increased spin−orbit charge transfer coupling (SOCT) 14 has been reported in orthogonal BODIPY dimers, 7,15 making them promising heavy-atom-free photosensitizers through the formation of reactive oxygen species (ROS). Thus dimer 2a was first used to evaluate the ROS generation ability in five different solvents using 1,3diphenylisobenzofuran (DPBF) as an ROS scavenger (Figure 5a and Figure S12).…”