Substituent effects in several titanium(IV)-trichloride half-sandwich complexes with eta(5)-coordinated cyclopentadienyl or indenyl ligands including (eta(5)-C5H5)TiCl3 (1), (eta(5)-C9H7)TiCl3 (2), (eta(5)-1-SiMe3-C9H6)TiCl3 (3), (eta(5)-1-Me-C9H6)]TiCl3 (4), (eta(5)-4-MeC9H6)]TiCl3 (5), [eta(5)-5,6-(CH2)(3)-CqH(5)]TiCl3 (6), (eta(5)-2-SiMe3-CqH(6))TiCl3 (7), (eta(5)-1, 3-Me-2-C9H5)TiCl3 (8), (eta(5)-4, 7-Me2C9H6)TiCl3 (9), [eta(5)-3, 4-(CH2)(3)-CqH(5)]TiCl3 (10), (eta(5)-1-SiMe3-4, 7-Me-2-CqH(4))TiCl3 (11) and (eta(5)-1, 3, 4, 7-Me-4-C9H3)TiCl3 (12) were studied with cyclic voltammetry (CV) and UV-vis spectroscopy. Cyclic voltammograms of 1-12 showed current waves caused by the reversible redox process of the Ti(IV)/(III) redox couple at electrode potentials typical for do-titanium centers. In UV-vis spectra, two major absorption bands between 400-430 and 530-590 mn were observed. The latter is assigned to a ligand to metal charge transfer (LMCT). A comparison shows that the alkylation or Me3Si-substitution (complexes 3-12) induces a shift of the corresponding absorption to longer wavelengths indicating a smaller energy gap between the frontier orbitals. Based on the experimental data an additive increment system for Me3Si and alkyl-substituted eta(5)-indeny derivatives of titanium(IV)-trichloride species is proposed.