The direct observations of delayed fluorescence and phosphorescence from the cyanine dye Cy5 are reported. The delayed fluorescence is generated from the S-1 state of trans-Cy5 through a reserve intersystem crossing from the cis-triplet state T-1 to the trans-singlet state S-1 via thermal activation. The lowest cis-triplet state is evidenced to be involved in the,formation of the isomer. The back-isomerization from cis-triplet state to trans-singlet state crossing, a remarkably back-isomerization pathway that has not been reported before, plays a significant role in this unusual delayed fluorescence.