Control of polymorphism by ‘tailor‐made’ polymeric crystallization auxiliaries. Preferential precipitation of a metastable polar form for second harmonic generation

Polar crystals can display pyroelectricity, piezoelectricity and frequency doubling leading to second harmonic generation. These metastable polar polymorphs can be selectively precipitated to the exclusion of stable, non‐polar forms by the use of polymeric crystallization auxiliaries. The approach is based on the hypothesis that crystal nuclei assume structures very similar to those of the crystals into which they develop.