The uphill excitation energy transfer (EET) from the core antenna (LH1) to the reaction center (RC) of purple photosynthetic bacteria was investigated at room temperature by comparing the native LH1-RC from Thermochromatium (Tch.) tepidum with the hybrid LH1-RC from a mutant strain of Rhodobacter (Rba.) sphaeroides. The latter protein with chimeric Tch-LH1 and Rba-RC exhibits a substantially larger RC-to-LH1 energy difference (ΔE = 630 cm-1) of 3-fold thermal energy (3kBT). The spectroscopic and kinetics results are discussed on the basis of the newly reported high-resolution structures of Tch. tepidum LH1-RC, which allow us to propose the existence of a passage formed by LH1 BChls that facilitates the LH1 → RC EET. The semilogarithmic plot of the EET rate against ΔE was found to be linear over a broad range of ΔE, which consolidates the mechanism of thermal activation as promoted by the spectral overlap between the LH1 fluorescence and the special pair absorption of RC.