Upon S 0 −S 1 excitation, the pyrazoline derivative molecule (Z)-2-(4-nitrophenyl)-3-(1-phenyl-4,5-dihydro-1H-pyrazol-3-yl)acrylonitrile, abbreviated as PY-oCNNO 2 , can be transformed from its ground state trans (E) form to bended cis (Z) form. Similar to the case of the well-known family of the photochromic azobenzenes, such a molecular property can be employed to fabrication of photochromic polymers by suitable doping of the chromophores into polymer matrix. In this work, we prepared poly(methyl methacrylate) thin films doped with PY-oCNNO 2 and measured the characteristic for optical switchers dynamic and static photoinduced birefringence (PIB) phenomenon. Possible conformational states of PY-oCNNO 2 , energy barriers, and associated dipole moments were calculated using TD-DFT quantum chemical methods. The presented experiments show that pyrazoline derivatives constitute a prospective group of materials with a great potential for photonic applications.
Discovery of E/Z or trans-cis photoisomerization in the azobenzenes and their derivatives had the 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-1H-pyrazole (abbreviated as PYpNO 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 like in the group of the azobenzene derivatives.
2‐(2’‐Hydroxyphenyl)benzazole (HBX) fluorophores are well‐known excited‐state intramolecular proton transfer (ESIPT) emitters largely studied for their synthetic versatility, photostability, strong solid‐state fluorescence and ability to engineer dual emission, thus paving the way to applications as white emitters, ratiometric sensors, and cryptographic dyes. However, they are heavily quenched in solution, due to efficient non‐radiative pathways taking place as a consequence of the proton transfer in the excited‐state. In this contribution, the nature of the heteroring constitutive of these rigidified HBX dyes was modified and we demonstrate that this simple structural modification triggers major optical changes in terms of emission color, dual emission engineering, and importantly, fluorescent quantum yield. Investigation of the photophysical properties in solution and in the solid state of a series of ethynyl‐TIPS extended HBX fluorophores, along with ab initio calculations demonstrate the very promising abilities of these dyes to act as bright dual‐state emitters, in both solution (even in protic environments) and solid state.
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