Monomers and their use for the production of a laser-optical recording element which can be repeatedly erased and recorded on

A method for repeated recording, reading, and erasing of data, comprising the steps of

• (1) recording digital or analog data with the aid of a write laser beam of sufficient luminous power, if necessary with the application of an external electric field, in the ferroelectric smectic liquid crystalline (S.sub.c*) recording layer (a) having a thickness (d) of a laser-optical recording element in the form of optically detectable regions which are stable at room temperature and which are ferroelectric smectic liquid crystalline S.sub.c* phases, smectic liquid crystalline S.sub.A* phases, disordered microdomains (scattering centers) or isotropic i phases, the said ferroelectric smectic liquid crystalline (S.sub.c*) recording layer (a) containing at least one polymer I having chiral mesogenic side groups exhibiting ferroelectric smectic liquid crystalline behavior and comprising monomer units derived from monomers of the structure I ##STR140## where is hydrogen, chlorine or methyl,
• A is a flexible space-maintaining long-chain molecular moiety having the formula --(--CH.sub.2 --).sub.R -- where R is an integer from 1 to 30,
• is an optically active chiral molecular moiety and B is a mesogenic molecular moiety which consists of three or more aromatic nuclei bonded linearly or virtually linearly to one another and which is selected from the group consisting of
• i) moieties B which contain one or more napth-2,6-ylene groups,
• ii) moieties B of the formula III ##STR141## where B.sup.2 is a p-phenylene, a biphenyl-4,4'-diyl or a napth-2,6-ylene group
• Y is an ether, an ester a thioester group
• or a carbon-carbon single bond and
• m and n are each 0 or an integer .gtoreq.1;
• iii) moieties b of the formula IV ##STR142## where m and n and Y have the abovementioned meanings and B.sup.3 is selected from the group consisting of the p-phenylene, the biphenyl-4-4'-diyl and the napth-2,6-ylene group and the group III-1 ##STR143## where Y has the abovementioned meanings;
• and iv) moieties B, selected from the group consisting of the groups X-1 to X-4 ##STR144## where Y has the abovementioned meanings and the groups X-1 to X-4 are bonded via the ether group to moiety A, with the proviso that the moiety C of the molecule is exclusively selected from the group consisting of the pinan-3-yl, the camphan-2-yl and the p-menthan-3-yl group and the group of the formula VII ##STR145## where R.sup.3 is methyl or trifluoromethyl, x and r independently of one another are each 0 or 1 and s is an integer from 1 to 3, the group of the formula VIII ##STR146## where s has the abovementioned meaning, and the group of the formula IX ##STR147## where t, u and v independently of one another are each an integer of from 1 to 10, t and u independently of one another may furthermore be 0, and y is 0 or 1, whenever one of the said groups X-1 to X-4 is selected for moiety B of the molecule,
• (2) detecting the recorded data or regions with the aid of a read laser beam by means of the birefringence contrast, the dichroic contrast, light scattering at scattering centers and/or interference of reflected laser light waves of different phase velocities, the light reflected by the recording element being analyzed, and then
• (3) erasing the recorded data or regions completely or sector by sector by heating the entire surface or individual sectors of the recording layer (a) in an external electric field, and
• (4) repeating process steps (1) and (2).