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Excited-state properties, although extremely useful, are hardly accessible. One indirect way would be to derive them from relationships to ground-state properties which are usually more readily available. Herewith, we present quantitative correlations between triplet excited-state (T-1) properties (bond dissociation energy, D-0(T1), homolytic activation energy, E-a(T1), and rate constant, k(r)) and the ground-state bond dissociation energy (D-0), taking as an example the photodissociation of the C-Si bond of simple substituted allylsilanes CH2=CHC((RR2)-R-1)-SiH3 (R-1 and R-2 = H, Me, and Et). By applying the complete-active-space self-consistent field CASSCF(6,6) and CASPT2(6,6) quantum chemical methodologies, we have found that the consecutive introduction of Me/Et groups has little effect on the geometry and energy of the T-1 state; however, it reduces the magnitudes of D-0, D-0(T1) and E-a(T1). Moreover, these energetic parameters have been plotted giving good linear correlations: D-0(T1) = alpha(1) + beta(1) . D-0, E-a(T1) = alpha(2) + beta(2) . D-0(T1), and E-a(T1) = alpha(3) + beta(3) . D-0 (alpha and beta being constants), while k(r) correlates very well to E-a(T1). The key factor behind these useful correlations is the validity of the Evans-Polanyi-Semenov relation (second equation) and its extended form (third equation) applied for excited systems. Additionally, the unexpectedly high values obtained for E-a(T1) demonstrate a new application of the principle of nonperfect synchronization (PNS) in excited-state chemistry issues. Journal of Physical Chemistry A