Uncovering the substituted-position effect on excited-state evolution of benzophenone-phenothiazine dyads

Jiayu Li; Sirui Yang; Ziqi Deng; Amjad Islam; Shiqi Wu; Jiaxing He; Shaofei Ni; Li Dang; Ming-De Li

doi:10.1063/5.0166630

Uncovering the substituted-position effect on excited-state evolution of benzophenone-phenothiazine dyads

J Chem Phys. 2023 Oct 14;159(14):144502. doi: 10.1063/5.0166630.

Authors

Jiayu Li¹, Sirui Yang², Ziqi Deng³, Amjad Islam¹, Shiqi Wu¹, Jiaxing He³, Shaofei Ni¹, Li Dang^{1

2}, Ming-De Li^{1

2}

Affiliations

¹ College of Chemistry and Chemical Engineering, Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Shantou, Guangdong 515063, People's Republic of China.
² Chemistry and Chemical Engineering Guangdong Laboratory, Shantou 515031, People's Republic of China.
³ Department of Chemistry, The University of Hong Kong, Hong Kong, People's Republic of China.

PMID: 37818997
DOI: 10.1063/5.0166630

Abstract

Photofunctional materials based on donor-acceptor molecules have drawn intense attention due to their unique optical properties. Importantly, Systematic investigation of substitution effects on excited-state charge transfer dynamics of donor-acceptor molecules is a powerful approach for identifying application-relevant design principles. Here, by coupling phenothiazine (PTZ) at the ortho-, meta-, and para-positions of the benzene ring of benzophenone (BP), three regioisomeric BP-PTZ dyads were designed to understand the relationship between substituted positions and excited-state evolution channels. Ultrafast transient absorption is used to detect and trace the transient species and related evolution channels of BP-PTZ dyads at excited state. In a non-polar solvent, BP-o-PTZ undergoes the through-space charge transfer process to produce a singlet charge-transfer (1CT) state, which subsequently proceeds the intersystem crossing process and transforms into a triplet charge-transfer (3CT) state; BP-m-PTZ experiences intramolecular charge transfer (ICT) process to generate the 1CT state, which subsequently transforms into the 3CT state by the intersystem crossing (ISC) and finally converts into the local-excited triplet (3LE) state; as for BP-p-PTZ, only 3LE states can be detected after the ISC process from the 1CT state. On the other hand, the twisted ICT states are generated via twisted motion between the donor and acceptor for all BP-PTZ dyads or planarization of the PTZ unit in high polar solvents. The excited-state theoretical calculations unveil that the features of ICT and intramolecular interaction between the three dyads play a decisive role in determining the through-bond charge transfer and through-space charge transfer processes. Also, these results demonstrate that the excited-state evolution channels of PTZ derivatives could be modified by tuning the substituted positions of the donor-acceptor dyads. This study provides a deep perspective for the substitute-position effect on donor-acceptor-type PTZ derivatives.