Ligand-to-metal charge-transfer states in emissive d0 metallocenes: Design strategies for titanocene based photocatalysts

ACS Citation

Wagenknecht, P. S. Ligand-to-metal charge-transfer states in emissive d0 metallocenes: Design strategies for titanocene based photocatalysts. In Photochemistry and Photophysics of Earth Abundant Metal Compounds; Ford, P. C., van Eldik, R., Eds.; Advances in Inorganic Chemistry 83; Elsevier; Amsterdam, 2024.


Complexes of d0 transition metals with photoactive ligand-to-metal charge-transfer (LMCT) excited states have recently shown significant promise as photocatalysts involving earth-abundant metals. Over the past four decades, a handful of examples of metallocenes with d0 metals (ScIII, ZrIV, HfIV, NbV, and TaV) have demonstrated emission from LMCT states in room-temperature (RT) fluid solution. Recently, Cp2TiCl2 has also been shown to act as a photocatalyst, despite a lack of emission in RT solution. In fact, emission from LMCT states for TiIV complexes in RT fluid solution has been elusive. This review summarizes the findings of earlier investigations into emissive ScIII, ZrIV, HfIV, NbV, and TaV metallocenes to extract clues regarding design principles for emissive metallocenes. Complexes of the type Cp2TiX2 (where X = halide or pseudohalide) are emissive only at 77 K, and are discussed as the first examples of emissive titanocenes. Complexes of the type Cp2Ti(C2R)2 (where R = ferrocenyl or an aryl substituent) have recently been investigated for their C2R-to-TiIV LMCT states. The first example of a TiIV complex with an emissive ligand-to-TiIV LMCT state in RT fluid solution is Cp2Ti(C2Ph)2. However, this complex undergoes efficient photodecomposition. Coordination of CuX (X = Cl, Br) between the alkyne ligands results in complexes that are significantly more photostable but not emissive in RT fluid solution. Mechanistic investigations suggested that the main path for nonradiative decay for such complexes involves excited-state structural reorganization. A titanocene with greater steric bulk, Cp2Ti(C2Ph)2CuBr, is emissive in RT THF solution (λmax = 693 nm, Φem = 1.3 ×10–3, τ = 0.18 μs). The possible role of the Cp ligand in facilitating emission in titanocenes is discussed.

Source Name

Advances in Inorganic Chemistry

Publication Date




Document Type


Citation Type

Book Chapter