Photo-Physical Transformations in Pyrazoline Derivative Based Systems

Discovery of E / Z or trans – cis photoisomerization in the azobenzenes and their derivatives had tremendous impact on the whole domain of photochromic materials including photochromic polymers and liquid crystals. Here we show similar configurational photoinduced transformation in a simple derivative of pyrazoline. The X-ray crystallographic investigations of ( E )-3-(4-nitrostyryl)-1-phenyl-4,5-dihydro-1 H -pyrazole (abbreviated as PY-pNO 2 ) in grown crystals show two different structures comprising of either cis or trans molecules. The performed quantum chemical calculations confirm the existence of both configurations of PY-pNO 2 at the room temperature. Photophysical properties of this compound derived from quantum chemical calculations predict possibility of trans to cis switching of PY-pNO 2 by light. Indeed, molecules of PY-pNO 2 embedded in PMMA polymeric matrix when illuminated with 532 nm linearly polarized laser light show the induced optical anisotropy, i.e., birefringence characteristic for photoisomerizable molecules similar to that in the group of the azobenzene derivatives.