i.e., n=6 acene and n=12 cumulene, <S 2 > BS ∼ 0.17 indicates the preferential existence of molecule in CSS ground state. Thereafter, <S 2 > BS starts approaching towards 1.0 indicating diradical ground state for n ≥ 7 for acenes and n ≥ 14 for cumulenes. However, for the higher members, the spin contamination in OSS becomes large with <S 2 > = 1.69 for n=12 acene and 1.26 for n=24 cumulene pointing towards the mixing of low-lying triplets.