3,3-(Biphenyl-2,2′-diyl)-1-α,α,α-trifluoro-p-tolyl-allene, 9, sequentially forms head-to-tail, 12, cis-tail-to-tail, 13, and trans tail-to-tail, 14, 1,2-dialkylidene-cyclobutane dimers, each of which has been characterised by X-ray crystallography. Thermolysis at 180 °C yields the dispirotetracene, 15, and di-indenotetracene, 16; the latter compound forms an air-stable Diels–Alder adduct, 17, with N-methylmaleimide. In contrast, the dibenzo[a,d]cycloheptenylidene-allenes, (C14H10)C
C
C(Br)Ph, 20a, and (C14H10)C
C
C(H)Ph, 21a, do not dimerise under relatively mild conditions. However, protonation of the bromo-allene, 20a, and subsequent addition of hydride, provide a facile entry to the difficultly accessible bowl-shaped dibenz[cd,h]azulene framework, as in 30, that had not previously been structurally characterised. Among others, the X-ray crystal structures of 12, 13, 14, 17, 20a, 21a and 30 are reported.