Stilbene-based materials, their preparation and use

A process for the preparation of a material of the formula I:

• ##STR5## in which R.sub.1, R.sub.2 and R.sub.3 in each case independently of another can be identical or different and are a hydrogen atom, halogen atom, hydroxyl group, nitro group, cyano group or monovalent, optionally substituted organic radical,
• R.sub.4 is a hydrogen atom, halogen atom, nitro group, cyano group or monovalent, optionally substituted organic radical and
• R.sub.5 can be identical or different and is a halogen atom, hydroxyl group, nitro group, cyano group or monovalent, optionally substituted organic radical,
• which process comprises the steps of
• alkylating an optionally substituted 1-indanone with an alkyl halide to produce an alkylated product;
• subsequently reacting the alkylated product with an optionally substituted benzylmagnesium halide in a Grignard reaction to produce a further product;
• and
• then subjecting the further product to acid workup.