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

Zhao X., Kurganskii I., ELMALI A., Zhao J., KARATAY A., Mazzone G., ...Daha Fazla

DYES AND PIGMENTS, cilt.218, 2023 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 218
  • Basım Tarihi: 2023
  • Doi Numarası: 10.1016/j.dyepig.2023.111480
  • Dergi Adı: DYES AND PIGMENTS
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, Aerospace Database, Chemical Abstracts Core, Chimica, Communication Abstracts, Compendex, INSPEC, Metadex, Civil Engineering Abstracts
  • Anahtar Kelimeler: Anthracene, Charge transfer, Coumarin, Spin−orbit charge transfer intersystem crossing, Triplet state
  • Ankara Üniversitesi Adresli: Evet

Özet

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 & DEG; and 85.7 & DEG;, 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 & DEG;. The solvent polarity-dependent singlet oxygen quantum yields (& phi;& UDelta;) of the orthogonal dyads (Cou-9An and Cou-9AnCN) are 39% (in acetonitrile) and 64% (in dichloromethane), respectively. whereas & phi;& UDelta; 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 Cou9AnCN, with the intrinsic triplet state lifetime of 234 and 207 & mu;s, respectively. Triplet state delocalization was observed for Cou-2An, which prolongs the triplet state lifetime to 742 & mu;s. 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 (Cou2An). 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.