Dye-in-polymer (DIP) films consisting of Pr4VOPc dyes and PMMA polymer were prepared by spin-coating process. Pr4VOPc primarily precipitates as glassy solid phase I inside PMMA matrix during film formation. Upon exposure these films to organic solvent vapour, Pr4VOPc crystallines to a more stable phase Ⅱ, which has strong absorptivity in near-IR region. Orgsnic solvent vapour provides a medium for the soluhilization-crystullization process of the dyes, at the same time, plasticizes the polymer chains and makes all the dye migration motion feasible.