Mapping the primary photochemical dynamics and transient intermediates in functional chromophores is vital for crafting archetypal light-harvesting materials. Although the excited state dynamics in 9-acetylanthracene is well explored, the origin of near-quantitative triplet population and the atypical intersystem crossing (ISC) rate as compared with the regioisomeric analogs (1-/2-acetylanthracene) have rarely been scrutinized. We present a comprehensive account of the photoinduced dynamics in three regioisomeric monoacetylanthracenes using ultrafast transient absorption and quantum chemical calculations. The conjoint experimental and computational investigations suggest that (i) greater stabilization of the (1)n pi* relative to (1)pi pi* state, (ii) dissimilar (1)pi pi* -> (1)n pi* crossover barriers, and (iii) the strong spin-orbit coupling (nu(SO)) of the (1)n pi* state with the receiver (3)pi pi* state command the divergent triplet population in 1-/2-/9-acetylanthracenes. A tacit understanding of the subtle structural-alteration-facilitated contrasting ISC dynamics in carbonylated arenes can act as a stepping stone for the evolution of potent photofunctional materials.