Every known form of animal vision relies on one specific chromophore: the Retinal Protonated Schiff-base (RPSB), suggesting that this specific molecule is ultimately suited for use as a photon detector. In order to understand what makes the RPSB so unique, we probe its intrinsic properties with gas phase measurements and compare them to RPSB derivatives. Using two stages of ion mobility spectroscopy, we examine how charge localization can affect the steric forces inside the molecule and its rigidity and how the length of the molecule affects the isomerization.