We report the synthesis and characterization of a series of di- [3]cumulene molecules containing the two [3]cumulene segments conjugated with a carbon-carbon single bond. Structural details are revealed by single crystal X-ray analyses and electronic properties of these new compounds are studied by optical spectroscopy. The di-[3]cumulenes display absorption profiles resembling those of [n]cumulenes previously reported and peaking between those from [5]-and [7]-cumulenes, suggesting [6]-cumulene like electronic behaviors and effective conjugation between the two [3]-cumulene segments. Our di-[n]cumulene design provides an alternative strategy to extend the lengths of [n]cumulenes beyond those obtainable by current synthetic methodologies while maintaining electronic features towards mimicking that of metallic carbyne. During the synthesis, we discovered an unexpected photo-switchable behavior from a di-[3]cumulene having central phenyl substituents. A [2+2] cycloaddition leads to a compound containing a highly strained cyclobutene ring as the more stable product, in equilibrium with the open di-[3]cumulene in the cis form as the minor component. The reverse [2+2] ring opening reaction can be accelerated by UV exposure, shifting the equilibrium towards the di-cumulene side, and kinetics of these processes are studied in detail with the aid of density functional theory calculations.