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.