Diindeno‐Fused Dibenzo[a,h]anthracene and Dibenzo[c,l]chrysene: Syntheses, Structural Analyses, and Properties

Diindeno‐fused dibenzo[a,h]anthracene 6 and diindeno‐fused dibenzo[c,l]chrysene 9 contain the key moieties 1,4‐quinodipropene (1,4‐QDP) and 2,6‐naphthoquinodipropene (2,6‐NQDP), respectively, and they both have an open‐shell singlet ground state. The latter compound exhibits a strong biradical character and interesting properties, including a low ΔET−S (2.44 kcal mol−1), a small HOMO–LUMO gap (1.06 eV), a wide photoabsorption range (250–1172 nm), and a large two‐photon absorption cross‐section (σ=1342±56 GM). This work verifies that 6 has a slightly larger HOMO–LUMO gap and ΔET−S than its helical isomer diindeno[2,1‐f:1′,2′‐j]picene (DIP), but is a much stronger two‐photon absorber, verifying the important effect of geometry on the photophysical properties. Radical chemistry! Diindeno‐fused dibenzo[a,h]anthracene and dibenzo[c,l]chrysene, which contain the key moieties of 1,4‐quinodipropene (1,4‐QDP) and 2,6‐naphthoquinodipropene (2,6‐NQDP), respectively, both have singlet biradical character and many interesting properties. Compound 6 with the quasi‐planar structure is suitable for verifying the through‐space interactions of the singlet biradical helicene DIP (see scheme).