  Nonlinear lattice relaxation of photoexcited diplatinum-halide chain
compounds is theoretically investigated within a one-dimensional extended
Peierls-Hubbard model. We first illuminate the whole relaxation scenario in
terms of variational wave functions and then visualize each relaxation channel
numerically integrating the Schr\"odinger equation. High-energy excitations
above the electron-hole continuum tend to relax into polarons, while excitons
pumped within the optical gap, unless luminescent, turn into solitonic states
nonradiatively. Neutral and charged solitons coexist as stable photoproducts,
which has never been observed in conventional platinum-halide chains, and they
are highly resonant on the occasion of their birth and geminate recombination.
