Titanocene as a New Acceptor (A) for Arylamine Donors (D) in D−π–A Chromophores

Charge transfer (CT)
transitions are relevant in the fields of
solar energy conversion and nonlinear optical materials. Herein, a
series of complexes with an alkynyl linkage between an aryl amine
donor and a TiIV (titanocene) acceptor is reported. Each
complex displays a strong (15000 < ε < 24,000 M–1cm–1), low-energy (520 < λ < 560 nm)
absorption ascribed to an amine to TiIV ligand-to-metal
CT. This characterization is supported by UV–vis spectroscopy,
cyclic voltammetry, and TD-DFT calculations. These complexes are not
photostable; therefore, an alternate architecture, wherein the amine
donor is appended to the titanocene cyclopentadienyl ligand, has been
designed. The molar absorptivity of the amine to TiIV CT
in this latter architecture is lower (2100 M–1 cm–1), indicating weaker donor–acceptor coupling.
This architecture is indeed much more photostable.