The spectra of the [2+2+2] cycloadducts 12-14 show lowest energy absorptions in the range of 421 (for 14) to 448 (for 13) nm. With regard to the linearly fused derivatives, it is worth to note that while all the epoxyoligoacenes 23-25 exhibit almost identical lowest energy absorptions around 405-410 nm, associated to the benzo [b]biphenylene chromophore, the corresponding deoxygenated CBD-oligoacenes show larger lmax values (see Figure , for 25b/28b). The wavelength of these lowest absorptions increases with the size of the linear polycyclic system, from lmax ≈ 440 nm for 26, to 479 nm for 28b. In all cases, the absorption is also significantly red-shifted with respect to that of anthracene (lmax = 373 nm), the largest polycyclic benzenoid chromophore contained in each of the structures, demonstrating an important degree of electron delocalization along the polycyclic skeleton despite the presence of the antiaromatic cyclobutadiene moieties. Comparison of the spectra of the angularly shaped 13 with the linear analogue of similar size, 28, suggests that the electron delocalization is more significant in the latter. With regard to the fluorescence, it is remarkable the very small Stokes shifts observed in the linear CBDoligoacenes, ranging from 0 to 2 nm, which is indicative of the rigid structure of these compounds. As another interesting feature, the fluorescence spectra of solid 28a and 28b exhibit large bathochromic shifts with respect to measurements in solution (146 and 119 nm, respectively; see Figure for 28b), that are significantly larger than those observed for the same polycyclic systems provided with pendant phenyl and TIPS-ethynyl groups 8a and may constitute a