The effect of one-atom substitution on the photophysical properties and electron spin polarization: Intersystem crossing of compact orthogonal perylene/phenoxazine electron donor/acceptor dyad

Abstract

A perylene (Pery)–phenoxazine (PXZ) compact orthogonal electron donor/acceptor dyad was prepared to study the relationship between the molecular structures and the spin–orbit charge transfer intersystem crossing (SOCT-ISC), as well as the electron spin selectivity of the ISC process. The geometry of Pery–PXZ (80.0°) is different from the previously reported perylene–phenothiazine dyad (Pery–PTZ, 91.5°), although there is only one atom variation for the two dyads. Pery–PXZ shows a high singlet oxygen quantum yield (84%). Femtosecond transient absorption spectra indicate that the charge separation (CS, faster than 120 fs) is faster than the Pery–PTZ analog (CS, 250 fs) and charge recombination (CR, i.e., SOCT-ISC, 5.98 ns) of Pery–PXZ is slower than the Pery–PTZ analog (CR, 0.9 ns). The intrinsic triplet state lifetime of Pery–PXZ is 242 µs vs the lifetime of 181 µs for the Pery–PTZ analog. Moreover, the triplet state lifetime of Pery–PXZ in the solid polymer matrix is extended to 4.45 ms, which indicates that the triplet state of Pery–PXZ in fluid solution is deactivated not only by the triplet–triplet annihilation effect but also by other factors such as vibration coupled relaxation. Interestingly, with pulsed laser excited time-resolved electron paramagnetic resonance spectroscopy, the electron spin polarization (ESP) pattern of the triplet state of the current dyad is opposite to that of Pery–PTZ. These results demonstrated the rich electron spin chemistry of the ISC of compact electron donor/acceptor dyads, e.g., the ESP is dependent on not only the molecular geometry but also the structure of the electron donor (or acceptor).

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

“…Moreover, we found that the electron spin selectivity of SOCT-ISC is not only dependent on the conformation of the dyads, as previously found, but also on the structure of the electron donor . The effect of one-atom substitution on the photophysical properties and electron spin polarization (ESP) was only reported in perylene-PXZ and perylene-phenothiazine (PTZ) compact dyads. , …”

“…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%.…”

Chromophore Orientation-Dependent Photophysical Properties of Pyrene–Naphthalimide Compact Electron Donor–Acceptor Dyads: Electron Transfer and Intersystem Crossing

“…However, to fully understand the SOCT-ISC efficiency as well as the electron spin selectivity of the ISC of these dyads, more examples are required. For instance, the spin dynamics of some systems are studied by time-resolved electron paramagnetic resonance (TREPR) spectroscopy. ,, It was proposed that the electron spin polarization (ESP) pattern of the TREPR spectra of the triplet state accessed by SOCT-ISC is always different than the conventional SO-ISC mechanism. ,, This is true but only for few cases: we found that the ESP pattern of the triplet TREPR spectra can be the same for both the mechanisms (SOCT-ISC and SO-ISC) and it is also dependent on the structures of electron donors/acceptors. ,,, Moreover, the effect of the mutual orientation of electron donor and acceptor chromophores on the SOCT-ISC efficiency and the electron spin selectivity was rarely studied.…”

“…27,31,35 This is true but only for few cases: we found that the ESP pattern of the triplet TREPR spectra can be the same for both the mechanisms (SOCT-ISC and SO-ISC) and it is also dependent on the structures of electron donors/acceptors. 30,36,38,39 Moreover, the effect of the mutual orientation of electron donor and acceptor chromophores on the SOCT-ISC efficiency and the electron spin selectivity was rarely studied.…”

Electron Spin Dynamics of the Intersystem Crossing of Triplet Photosensitizers That Show Strong Absorption of Visible Light and Long-Lived Triplet States

“…These results indicate that the triplet state of Rho-Pery-1 is localized on the perylene unit. We also prepared compact orthogonal electron donor–acceptor dyads with perylene unit as either electron donor or as electron acceptor. , The D and E parameters of the triplet state were determined as ca. 59.6 mT and 2.1 mT, respectively.…”