In order to further search efficient 8circulene materials for OLED applications we have theoretically investigated the structure and electronic absorption spectra of functionalized tetrabenzo8circulenes with different substituents in the outer perimeter. These hydrocarbon materials complement the wide family of 8circulenes which earlier have been demonstrated to possess promising emissive and exciplex-forming properties suitable for organic light emitting diodes. The hydrocarbon tetrabenzo8circulenes show saddle shape of the molecular skeleton which can exist in two different conformations with different curvatures of the macrocycle. The aromaticity, electronic structure and orbital pattern are found to be principally different for these two isomers, where the global minimum isomer is weakly antiaromatic and electronically less stable comparing with the non-aromatic local minimum structure. The absorption spectra are also very different: the global minimum structure is more active in the long-wavelength region while the local minimum isomer shows absorption only at short wavelengths. Our computational findings suggest a new concept for optical tuning of curved 8circulenes through conformational isomerization and aromaticity control, thus through structural variations without changing the molecular composition. Based on this principle we have designed novel functionalized 8circulenes with promising fluorescence activity. Display omitted •Two conformational isomers of tetrabenzo8circulene have been theoretically studied.•Global minimum isomer is weakly antiaromatic and electronically less stable.•Local minimum isomer shows absorption only at short wavelengths.•Novel functionalized 8circulenes with promising fluorescence activity have been designed.•The concept of conformational-dependent fluorescence is proposed.