Regioisomeric Effects on the Electronic Features of Indenothiophene-Bridged D-π-A′-A DSSC Sensitizers

Two D–π‐A′–A regioisomers (A‐IDT‐D and D‐IDT‐A) featuring 4,4′‐di‐p‐tolyl‐4 H‐indeno[1,2‐b]‐thiophene as a π linker (π) between the diarylamino donor (D) and the pyrimidine–cyanoacrylic acid acceptor (A′–A) have been successfully synthesized and characterized as efficient sensitizers for the dye‐sensitized solar cells (DSSCs). The different arrangements of the D and A′–A blocks on the unsymmetrical indenothiophene (IDT) core render the dipole of IDT being along (A‐IDT‐D) or opposite (D‐IDT‐A) to the direction of intramolecular (donor‐to‐acceptor) charge transfer, and thus induce variations in the physical properties. The experimental observations correlated well with the theoretical analyses, clearly revealing the trade‐off between the molar extinction coefficient (ε) and the S0→S1 transition energy. As a result, a superior ε value was observed for D‐IDT‐A, whereas a bathochromic shift in the absorption occurred in A‐IDT‐D. The larger ε value of D‐IDT‐A together with its more favorable energy level relative to TiO2 led to a higher power conversion efficiency of 7.41 % for the D‐IDT‐A‐based DSSC, retaining approximately 95 % of the N719‐based DSSC efficiency. This work manifests the clear structure–property relationship for the case of donor and acceptor components being connected by an unsymmetrical π linker and provides insights for molecular engineering of organic sensitizers. Power of conversion: Two indenothiophene (IDT)‐based regioisomeric donor–π‐acceptor–acceptor (D‐π‐A′‐A) dyes are reported to reveal the trade‐off between the molar extinction coefficient (ε) and the S0→S1 transition energy (see figure; ICT=intramolecular charge transfer). The orientation mismatched D‐IDT‐A exhibits a superior ε and the matched‐type A‐IDT‐D exhibits a red‐shifted absorption. The larger ε value together with its more favorable energy level relative to TiO2 led to a higher power conversion efficiency of 7.41 % for the D‐IDT‐A‐based DSSC.