TY - JOUR

T1 - Electronic coupling and spin-orbit charge transfer intersystem crossing (SOCT-ISC) in compact BDP-carbazole dyads with different mutual orientations of the electron donor and acceptor

AU - Hou, Yuqi

AU - Kurganskii, Ivan

AU - Elmali, Ayhan

AU - Zhang, Huimin

AU - Gao, Yuting

AU - Lv, Lingling

AU - Zhao, Jianzhang

AU - Karatay, Ahmet

AU - Luo, Liang

AU - Fedin, Matvey

PY - 2020/3/21

Y1 - 2020/3/21

N2 - In order to study the spin-orbit charge transfer induced intersystem crossing (SOCT-ISC), Bodipy (BDP)-carbazole (Cz) compact electron donor/acceptor dyads were prepared. Charge transfer (CT) emission bands were observed for dyads showing strong electronic coupling between the donor and the acceptor (coupling matrix elements VDA, 0.06 eV-0.18 eV). Depending on the coupling magnitude, the CT state of the dyads can be either dark or emissive. Equilibrium between the 1LE (locally excited) state and the 1CT state was confirmed by temperature-dependent fluorescence studies. Efficient ISC was observed for the dyads with Cz connected at the meso-position of the BDP. Interestingly, the dyad with non-orthogonal geometry shows the highest ISC efficiency (φΔ = 58%), which is different from the previous conclusion. The photo-induced charge separation (CS, time constant: 0.7 ps) and charge recombination (CR, ∼3.9 ns) were studied by femtosecond transient absorption spectroscopy. Nanosecond transient absorption spectroscopy indicated that the BDP-localized triplet state was exceptionally long-lived (602 μs). Using pulsed laser excited time-resolved electron paramagnetic resonance spectroscopy, the SOCT-ISC mechanism was confirmed, and we show that the electron spin polarization of the triplet state is highly dependent on the mutual orientation of the donor and acceptor. The dyads were used as triplet photosensitizers for triplet-triplet-annihilation (TTA) upconversion, and the quantum yield is up to 6.7%. TTA-based delayed fluorescence was observed for the dyads (τDF = 41.5 μs). The dyads were also used as potent photodynamic therapy reagents (light toxicity of IC50 = 0.1 μM and dark toxicity of IC50 = 70.8 μM).

AB - In order to study the spin-orbit charge transfer induced intersystem crossing (SOCT-ISC), Bodipy (BDP)-carbazole (Cz) compact electron donor/acceptor dyads were prepared. Charge transfer (CT) emission bands were observed for dyads showing strong electronic coupling between the donor and the acceptor (coupling matrix elements VDA, 0.06 eV-0.18 eV). Depending on the coupling magnitude, the CT state of the dyads can be either dark or emissive. Equilibrium between the 1LE (locally excited) state and the 1CT state was confirmed by temperature-dependent fluorescence studies. Efficient ISC was observed for the dyads with Cz connected at the meso-position of the BDP. Interestingly, the dyad with non-orthogonal geometry shows the highest ISC efficiency (φΔ = 58%), which is different from the previous conclusion. The photo-induced charge separation (CS, time constant: 0.7 ps) and charge recombination (CR, ∼3.9 ns) were studied by femtosecond transient absorption spectroscopy. Nanosecond transient absorption spectroscopy indicated that the BDP-localized triplet state was exceptionally long-lived (602 μs). Using pulsed laser excited time-resolved electron paramagnetic resonance spectroscopy, the SOCT-ISC mechanism was confirmed, and we show that the electron spin polarization of the triplet state is highly dependent on the mutual orientation of the donor and acceptor. The dyads were used as triplet photosensitizers for triplet-triplet-annihilation (TTA) upconversion, and the quantum yield is up to 6.7%. TTA-based delayed fluorescence was observed for the dyads (τDF = 41.5 μs). The dyads were also used as potent photodynamic therapy reagents (light toxicity of IC50 = 0.1 μM and dark toxicity of IC50 = 70.8 μM).

KW - TRIPLET-TRIPLET ANNIHILATION

KW - SINGLET OXYGEN GENERATION

KW - PHOTON UP-CONVERSION

KW - BODIPY-ANTHRACENE DYADS

KW - TIME-RESOLVED EPR

KW - STATE FORMATION

KW - PHOTODYNAMIC THERAPY

KW - EXCITED-STATES

KW - LOW-POWER

KW - HIGHLY EFFICIENT

UR - http://www.scopus.com/inward/record.url?scp=85082092428&partnerID=8YFLogxK

U2 - 10.1063/1.5145052

DO - 10.1063/1.5145052

M3 - Article

C2 - 32199436

AN - SCOPUS:85082092428

VL - 152

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 11

M1 - 114701

ER -