Photochemistry of all-trans tert-butylamine retinal protonated Schiff-base (TB-RPSB) is investigated by femtosecond pump-hyperspectral probe spectroscopy. Unlike the n-butyl analogue (NB-RPSB) no shifting of the transient spectral bands is observed upon tuning the excitation pulses from 395 to 475 nm. The 15 nm shift observed for NB-RPSB in similar experiments was assigned to unspecified ground state structural inhomogeneity. Present results indicate that is most likely due to the coexistence of C-15=N double bond isomers in NB-RPSB. Elimination of this inhomogeneity in TB-RPSB makes it a more appropriate model for appreciating protein effects on RPSB photochemistry in retinal proteins. (c) 2009 Published by Elsevier B.V.