Enantiodifferentiating Z-to-E photoisomerizations of 1-methylcyclooct-1-ene (2) sensitized by (–)-menthyl benzene(poly)carboxylates were performed at varying temperatures and the steric effects of the methyl group introduced to the parent cyclooctene (1) upon both isomerization and enantiodifferentiation processes were studied. The photostationary state 2E:2Z ratio, (E/Z)_pss, was shown to decrease dramatically with decreasing irradiation temperature and increasing steric hindrance in the sensitizer. Kinetic analyses of the sensitzed photoisomerization demonstrated that the temperature- and sensitizer-dependent (E/Z)_pss ratios orginate solely from the quenching process. The steric effect on the (E/Z)_pss value of the introduced methyl group is much greater for the (Z)-isomer (2Z) than for the (E)-isomer (2E), as compared with the cyclooctene case reported previously. The optical purities(%op) of photoproduct 2E were found to be relatively low (< 10%) in general, and the increased steric hindrance induced by the methyl group does not appear to enhance the product's optical purity. However, the temperature dependence studies revealed that the differential activation enthalpy (ΔΔH^‡) and entropy (TΔΔS^‡) as functions of the number of chiral groups in benzene(poly)carboxylate sensitizer give a quite similar profile to those parameters obtained for parent 1, showing uniform increases for 2 of 0.4 and 0.15 kj mol^–1 in ΔΔH^‡ and TΔΔS^‡ respectively, for all chiral sensitizers.