Despite the numerous titanium-oxo clusters (TOCs) which have been reported, the nature of small clusters (nuclearity < 10) as model compounds showed large deviation from that of nanoscale TiO materials. Therefore, theoretical and experimental studies for large TOCs merit more attention. We recently prepared and crystallographically characterized a series of large TOCs: Ti11O15(OiPr)16(Cophen) (1), Ti11O15(OiPr)16(Mnphen) (2), Ti10O14(OEt)16(Mnphen)2 (3), and Ti10O14(OEt)16(Mnphphen)2 (4) (phen = 1,10-phenanthroline, phphen = 4,7-biphenyl-phen). These compounds are derivatives of a Ti12 parent cluster by replacing one or two of the five-coordinated titanium atoms of the Ti12 cluster with a transition metal M, Co(II) and Mn(II), that is chelated by a phen group. The effects of mono- and bis-substituted Mphen on the charge and structure of the clusters are discussed. Theoretical evaluation of the frontier orbitals of the clusters is carried out on the basis of the precisely defined crystal structures. Different from the dye molecule to TiO core charge transfer for the dye-modified TOCs, charge transfer in these clusters is from TiO/TiOM to phen/Mphen. The effects of different metal ions and the number of substituted Mphen moieties on the photocurrent properties are evaluated. The results will be of interest to research on cluster chemistry, especially on the TOC chemistry.