TY - JOUR

T1 - Electron transfer and intersystem crossing in the coumarin-anthracene electron donor-acceptor dyads

AU - Zhao, Xiaoyu

AU - Kurganskii, Ivan

AU - Elmali, Ayhan

AU - Zhao, Jianzhang

AU - Karatay, Ahmet

AU - Mazzone, Gloria

AU - Fedin, Matvey

N1 - Acknowledgements: J. Z. thanks the NSFC (U2001222), the Research and Innovation Team Project of Dalian University of Technology (DUT2022TB10), the Fundamental Research Funds for the Central Universities (DUT22LAB610), the State Key Laboratory of Fine Chemicals and the Department of Education of the Xinjiang Uyghur Autonomous Region (TianShan Chair Professor) for financial support. M. F. and I. K. thank the Ministry of Science and Higher Education of the Russian Federation (Grant No. 075-15-2020-779) for financial support.

PY - 2023/10

Y1 - 2023/10

N2 - A series of compact coumarin (Cou)-anthracene (An) electron donor-acceptor dyads were prepared, in which the two units are directly connected at either 2- or 9- position of the An unit and the 3-position of the Cou unit to study the relationship between the molecular configuration, electronic coupling and the intersystem crossing (ISC) efficiency. Single crystal X-ray diffraction results indicate that the dihedral angles are 88.0° and 85.7°, respectively, in the dyads, in which the donor and acceptor are connected by 9- position of the An unit (Cou-9An and Cou-9AnCN). However, for Cou-2An the optimized ground state geometry indicates a more coplanar configuration with a dihedral angle of 38.6°. The solvent polarity-dependent singlet oxygen quantum yields (ΦΔ) of the orthogonal dyads (Cou-9An and Cou-9AnCN) are 39% (in acetonitrile) and 64% (in dichloromethane), respectively. whereas ΦΔ is negligible for the coplanar dyad (Cou-2An). These results indicated that orthogonal geometry is beneficial to spin−orbit charge transfer ISC (SOCT-ISC) mechanism. Nanosecond transient absorption spectra demonstrated that the lowest triplet state was mainly localized on An unit in Cou-9An and Cou-9AnCN, with the intrinsic triplet state lifetime of 234 and 207 μs, respectively. Triplet state delocalization was observed for Cou-2An, which prolongs the triplet state lifetime to 742 μs. Femtosecond transient absorption spectra results indicated fast charge separation (CS, 0.36−0.41 ps) and slow charge recombination (CR, 2.1−2.8 ns) in the orthogonal dyads. Time-resolved electron paramagnetic resonance (TREPR) spectra further confirmed the SOCT-ISC mechanism in the orthogonal dyads (Cou-9An and Cou-9AnCN), however, the SOCT-ISC and spin orbit ISC (SO-ISC) mechanism are both responsible for the triplet state formation in the coplanar dyad (Cou-2An). Electron spin polarization (ESP) pattern of the triplet state TREPR spectra of Cou-9An and Cou-9AnCN is (a,e,a,e,a,e), however, ESP phase pattern of (e,a,e,a,e,a) and (e,e,e,a,a,a) were observed for the two triplet states required for the simulation of the TREPR spectrum of Cou-2An, which indicated that ESP patterns of triplet state not only depend on the molecular geometry, but also on the structure of the electron donor and acceptor.

AB - A series of compact coumarin (Cou)-anthracene (An) electron donor-acceptor dyads were prepared, in which the two units are directly connected at either 2- or 9- position of the An unit and the 3-position of the Cou unit to study the relationship between the molecular configuration, electronic coupling and the intersystem crossing (ISC) efficiency. Single crystal X-ray diffraction results indicate that the dihedral angles are 88.0° and 85.7°, respectively, in the dyads, in which the donor and acceptor are connected by 9- position of the An unit (Cou-9An and Cou-9AnCN). However, for Cou-2An the optimized ground state geometry indicates a more coplanar configuration with a dihedral angle of 38.6°. The solvent polarity-dependent singlet oxygen quantum yields (ΦΔ) of the orthogonal dyads (Cou-9An and Cou-9AnCN) are 39% (in acetonitrile) and 64% (in dichloromethane), respectively. whereas ΦΔ is negligible for the coplanar dyad (Cou-2An). These results indicated that orthogonal geometry is beneficial to spin−orbit charge transfer ISC (SOCT-ISC) mechanism. Nanosecond transient absorption spectra demonstrated that the lowest triplet state was mainly localized on An unit in Cou-9An and Cou-9AnCN, with the intrinsic triplet state lifetime of 234 and 207 μs, respectively. Triplet state delocalization was observed for Cou-2An, which prolongs the triplet state lifetime to 742 μs. Femtosecond transient absorption spectra results indicated fast charge separation (CS, 0.36−0.41 ps) and slow charge recombination (CR, 2.1−2.8 ns) in the orthogonal dyads. Time-resolved electron paramagnetic resonance (TREPR) spectra further confirmed the SOCT-ISC mechanism in the orthogonal dyads (Cou-9An and Cou-9AnCN), however, the SOCT-ISC and spin orbit ISC (SO-ISC) mechanism are both responsible for the triplet state formation in the coplanar dyad (Cou-2An). Electron spin polarization (ESP) pattern of the triplet state TREPR spectra of Cou-9An and Cou-9AnCN is (a,e,a,e,a,e), however, ESP phase pattern of (e,a,e,a,e,a) and (e,e,e,a,a,a) were observed for the two triplet states required for the simulation of the TREPR spectrum of Cou-2An, which indicated that ESP patterns of triplet state not only depend on the molecular geometry, but also on the structure of the electron donor and acceptor.

KW - Anthracene

KW - Charge transfer

KW - Coumarin

KW - Spin−orbit charge transfer intersystem crossing

KW - Triplet state

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85163016499&origin=inward&txGid=2c860720f266d285802337494b6650ce

UR - https://www.mendeley.com/catalogue/567501a8-61a2-3212-ba4b-ba3d0bc9ba7d/

U2 - 10.1016/j.dyepig.2023.111480

DO - 10.1016/j.dyepig.2023.111480

M3 - Article

VL - 218

JO - Dyes and Pigments

JF - Dyes and Pigments

SN - 0143-7208

M1 - 111480

ER -