Photochromism describes the dye-based events of sensory photoreceptors initiating the signalling cascades in living organisms. Research on synthetic dye conjugates related to these primary processes are presented. Isoalloxazine(flavin)-borondipyrromethene la and its photoredox switching with 1,3-propanedithiol parallels in some aspects the flavin-based blue-light photoreceptors. Dihydroazulene/vinylheptafulvene (DHA/VHF) photochromism resembles the retinal-type photoreceptors. They both proceed by a photochemical "on" and a thermal "off" switching. Details on the electronically excited state properties of DHA/VHF photochromism. are reported.