Indirect electrophotographic process with a nitro-phenolsultonephthalein

In a process of indirect electrophotographic copying wherein a sheet material comprising a dye-sensitized photoconductive layer is repeatedly exposed imagewise to form on said layer by each exposure an image which as such or upon being developed is transferred from said material, the improvement wherein said material comprises a photoconductive layer sensitized by at least one dye selected from the group consisting of dyes represented by the following formula and mesomeric and tautomeric forms thereof:

• ##STR4## in which M represents a hydrogen or metal atom or.sup.a methyl or ethylgroup, A.sub.1 or A.sub.2 or both A.sub.1 and A.sub.2 represent a nitro group in an ortho position with respect to the --OM and/or keto group, X represents a carbon atom or a SO group and Y.sub.1 and Y.sub.2 represent a substituent selected from the group consisting of hydrogen and halogen atoms and lower alkyl, lower alkoxy, nitro, hydroxyl and esterified hydroxyl groups and the remaining positions may be unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms and lower alkyl, lower alkoxy, nitro, hydroxyl and esterified hydroxyl groups.