Diindeno‐fused dibenzoa,hanthracene 6 and diindeno‐fused dibenzoc,lchrysene 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 diindeno2,1‐f:1′,2′‐jpicene (DIP), but is a much stronger two‐photon absorber, verifying the important effect of geometry on the photophysical properties. Radical chemistry! Diindeno‐fused dibenzoa,hanthracene and dibenzoc,lchrysene, 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).