Spiroconjugated Donor-σ-Acceptor Charge-Transfer Dyes: Effect of the π-Subsystems on the Optoelectronic Properties

Charge-transfer-based materials with intramolecular donor-acceptor structures are attractive for technological applications. Herein, a series of donor-σ-acceptor dyes has been prepared in a modular approach. The design of these intramolecular charge-transfer dyes is based on the concept of spiroconjugation, which leads to unique materials with special optical properties. The optical transitions are based on intramolecular charge transfer, as shown by solvatochromic measurements and density functional theory (DFT) calculations. Crystallographic, computational, electrochemical, and optical studies were performed to clarify the effect of different perpendicular π-moieties on the optoelectronic properties. Our molecular tuning allowed for the synthesis of molecules exhibiting strong visible-range absorption. The compounds are not fluorescent due to structural changes in the excited state, as revealed by DFT calculations. Finally, our study describes enantiomerically pure spiroconjugated absorber molecules using 1,1'-binaphthyl-2,2'-diol (BINOL) units on the donor part.