jp9b06170_si_001.pdf (22.36 MB)
Spin–Orbit Charge-Transfer Intersystem Crossing (SOCT-ISC) in Bodipy-Phenoxazine Dyads: Effect of Chromophore Orientation and Conformation Restriction on the Photophysical Properties
journal contribution
posted on 2019-09-10, 18:48 authored by Yu Dong, Andrey A. Sukhanov, Jianzhang Zhao, Ayhan Elmali, Xiaolian Li, Bernhard Dick, Ahmet Karatay, Violeta K. VoronkovaThe spin–orbit
charge-transfer-induced intersystem crossing (SOCT-ISC) in Bodipy-phenoxazine
(BDP-PXZ) compact electron-donor/-acceptor dyads was studied. PXZ
is the electron donor, and BDP is the electron acceptor. The molecular
geometry is varied by applying different steric hindrance on the rotation
about the linker between the two subunits. Charge-transfer (CT) absorption
bands were observed for the dyads with more coplanar geometry (electronic
coupling matrix elements is up to 2580 cm–1). Ultrafast
charge separation (0.4 ps) and slow charge recombination (3.8 ns,
i.e., SOCT-ISC process) were observed. Efficient ISC (ΦT = 54%) and long triplet-state lifetime (τT = 539 μs) were observed for the dyads. Notably, the triplet-state
lifetime is 2-fold of that accessed with heavy-atom effect, indicating
the advantage of using a heavy-atom-free photosensitizer. The low-lying
CT state in the dyads in polar solvents was confirmed with intermolecular
triplet photosensitizing method. Time-resolved electron paramagnetic
resonance spectroscopy show that the electron spin polarization of
the triplet state formed by the SOCT-ISC is the same as that of spin–orbit-ISC
(SO-ISC). 3CT and localized excited triplet states (3LE) were simultaneously observed for one of the dyads, which
is rare. Normally, the CT state was observed as spin-correlated radical
pair. The dyads were used as triplet photosensitizers for triplet–triplet
annihilation upconversion, the quantum yield is up to 12.3%. A large
anti-Stokes shift (5905 cm–1) was achieved by excitation
into the CT absorption band, not the conventional LE absorption band.