The molecular orientation of ellipsoidal C-70 in single-walled carbon nanotubes (SWCNTs) depends on the tube diameter (Go. Photoluminescence (PL) studies reveal that the fullerene encapsulation effects on the optical transition energy of SWCNTs are significantly different for C70 and C-60 at d(t) = 1.405-1.431 nm. This indicates that the transition from the "lying" alignment to the "standing" alignment occurs at d(t) approximate to 1.41 nm and the electronic states of SWCNTs are very sensitive to the interspacing between the encapsulated molecules and the SWCNTs. The present findings suggest that the electronic structure of SWCNTs is tunable not only by alternating the encapsulated molecules but also by controlling their molecular orientations, thus paving the way for development of novel SWCNT-based devices.