In the s = 1/2 antiferromagnetic spin chain material TiPO4, the formation of a spin gap takes place in a
two-step process with two characteristic temperatures, T
∗ = 111 K and TSP = 74 K. We observe an unusual
lattice dynamics over a large temperature regime as well as evidence for an orbital instability preceding the
spin-Peierls transition. We relate different intrachain exchange interactions of the high temperature compared
to the spin-Peierls phase to a modification of the orbital ordering pattern. In particular, our observation of a
high-energy excitation of mixed electronic and lattice origin suggests an exotic dimerization process different
from other spin-Peierls materials.