Introduction of steric para-tert-butyl substitutes was shown to stabilize the structure of molecules in the near-planar trans-form. The symmetrical introduction of two tert-butyl substitutes led to changes of fluorescent and lasing properties of molecules. In that case, the probability of trans-> cis-isomerization in III molecule decreased, but cis -> trans-isomerization probability in IV increased conversely, and the molecule fluoresced. The emitting property of stilbene was improved several times at such substitutes.