Outer-Sphere Electron-Transfer Process of Molecular Donor-Acceptor Organic Dye in the Dye-Sensitized Photocatalytic System for CO2Reduction

Sunghan Choi, Yun Jae Kim, Soohwan Kim, Hyun Seok Lee, Jae Yoon Shin, Chul Hoon Kim, Ho Jin Son, Sang Ook Kang

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


In dye-sensitized photocatalytic (DSPC) systems, the introduction and effective operation of the precious-metal free photosensitizing components are the critical issues which affect their practical applications. In this study, it was first found that the photosensitization process of a donor-π-acceptor (D-π-A)-type dye, which was designed to be immobilized onto a TiO2surface for efficient photoelectron collection, is also feasible at the outer-sphere of the TiO2surface despite the absence of chemical anchoring of the acceptor part (in the D-π-A dye) onto the TiO2surface. Two ethyl-protected D-π-A dyes, namely, (E)-2-cyano-3-(5-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)thiophen-2-yl)acrylate (1-Et) and ((E)-ethyl-3-(4-(7-(5′-(4-(bis(9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)-[2,2′-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazol-4-yl)phenyl)-2-cyanoacrylate) (2-Et), were prepared and investigated to elucidate the photoinduced electron transfer (PET) mechanism of the non-anchored D-π-A dye in solution. From serial fluorescence and anion absorption quenching experiments, we found that the reductively quenched [D-π-A dye]•-in solution efficiently can transfer the photoexcited electrons toward solid TiO2/Re(I) catalytic particles (dye•-→ |TiO2/Re(I) catalyst) through the outer-sphere electron transfer (OSET) process. The success of the collisional OSET process is attributed to the long lifetime of the solution-phase [D-π-A dye]•-species, which sufficiently can overcome the intrinsically inefficient heterogeneous electron transfer (ET) kinetics at the interface between the dye•-in solution and the dispersed TiO2particles and can decrease the dependency on the charge-transfer reorganization energy. The effectiveness of the OSET process was verified by the efficient photocatalytic CO2-to-CO conversion activities of binary [a turnover number (TON) of 330-470 for ∼8 h] by the photosensitization of the free [D-π-A dye]•-, which are comparable to those of the dye-anchored ternary analogues (D-π-A dye/TiO2/Re(I) catalyst, a TON of 194-391 for 8 h) based on the conventional inner-sphere ET (ISET) process at the early stage of the photoreaction. The two-way photosensitization processing (which considers both OSET and ISET) of organic dyes can be a major strategic advantage in conventional dye-sensitized solar cells and DSPC systems for H2production and CO2reduction.

Original languageEnglish
Pages (from-to)10526-10541
Number of pages16
JournalACS Applied Energy Materials
Issue number9
Publication statusPublished - 2022 Sept 26

Bibliographical note

Funding Information:
This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (NRF-2014R1A6A1030732 and NRF-2022R1A2C1012104). This work was supported in part by the Business Creation Support Program through the Ministry of Land, Infrastructure and Transport of Korean Government under grant 22TBIP-C162217-02.

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.


  • donor-acceptor organic photosensitizer
  • intramolecular charge transfer
  • outer-/inner-sphere electron transfer
  • photochemical COreduction
  • supported catalysis

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • Energy Engineering and Power Technology
  • Electrochemistry
  • Materials Chemistry
  • Electrical and Electronic Engineering


Dive into the research topics of 'Outer-Sphere Electron-Transfer Process of Molecular Donor-Acceptor Organic Dye in the Dye-Sensitized Photocatalytic System for CO2Reduction'. Together they form a unique fingerprint.

Cite this