Photodecarbonylation of α-Diketones: A Mechanistic Study of Reactions Leading to Acenes
journal contributionposted on 2008-01-10, 00:00 authored by Rajib Mondal, Albert N. Okhrimenko, Bipin K. Shah, Douglas C. Neckers
Poly(acene)s are significant compounds for various electronic applications. A clean, one-step synthesis involves α-diketones (2−4), which undergo facile Strating−Zwanenburg photodecarbonylation producing the corresponding poly(acene)s (i.e., anthracene, hexacene, and heptacene, respectively). Compounds 2−4 show weak fluorescence (λF = ∼525−530 nm and ΦF = ∼0.1−0.4%) and phosphorescence (λPh = ∼565−570 nm) and have a small singlet−triplet energy gap (S1 − T1 gap, ∼4 kcal/mol) that facilitates rapid intersystem crossing from the singlet to the triplet state. Both the singlet states (τS = ∼20−218 ps) and the triplet states (τT = ∼370 ps to <7 ns) of 2−4 are short-lived, while the decarbonylation of 2−4 is a rapid process occurring within 7 ns from both the singlet and the triplet manifolds. The nanosecond laser flash photolysis of 4 also reveals the T−T absorption of heptacene (580 nm, τ = ∼11 μs).