Following up on our recent communication , we have expanded the scope of substituent groups to substitute the terpy ligand in the 4' position (Scheme 1). The selected Y substituents are listed in Table , along with the Hammett and Swain-Lupton parameters that describe their EW/ED properties. The Hammett parameter is a well-known substituent descriptor characterizing the ground-state electronic effect, which has been extensively applied in quantitative structure-property relationship studies. The Hammett parameter includes both inductive (σF ) and resonance (σR) effects (σ = σF +σR). Based on Hammet's substituent parameters Swain and Lupton derived separate R and F parameters for resonance and inductive effects. To evaluate R and F, Swain and Lupton used the σ= α F+R, equation, where σ is the Hammett constant and α=0.56 . In this paper we use the modified Swain-Lupton parameters( R, F and R + ) calculated by Hansch et al. to describe the field and resonance effects of the substituents. Halcrow and coworkers found that the ED/EW properties for γ-Py substituents are better characterised by the modified Hammett constants σ + p , developed for positive ions, than the simple σp, while Jakubikova et al. found that the Swain-Lupton parameter R correlated with the substitution effects on the iron(II) complex of 4,4'-di-Y-bipyridine even better than σ + p . We follow the latter example, and list the substituents as sorted by R in the table. As earlier, DFT calculations were performed to predict the energy difference between the ground state and the quintet excited state, and to estimate barrier height and the rate for the quintet to singlet relaxation. Subsequently these predictions were compared to experimental re-sults from time-resolved spectroscopy, and good agreement was found. Moreover, we also examine the substituent effects in these complexes on the ground state properties in a systematic way, using several stationary spectroscopic methods and DFT calculations.