3986-53-6Relevant academic research and scientific papers
Trans–cis isomerization energies of azopyridines: a calorimetric and computational study
Zhu, Men,Yu, Lian
, p. 463 - 469 (2018/03/13)
Azobenzenes undergo reversible trans–cis photo-isomerization and have been studied extensively as photo-responsive materials. Despite their similar photochemistry, azopyridines have received relatively little attention; for example, their isomerization energies are presently unknown. In comparison with azobenzenes, azopyridines offer additional opportunities for materials design through hydrogen bonding and coordination chemistry. Here we report the isomerization energies for all three symmetrical azopyridines (i.e., the 2,2′-, 3,3′-, and 4,4′-isomers) through a combined experimental and computational study. Heat of isomerization was measured in the liquid state, with o-terphenyl introduced to suppress crystallization. We obtain ?Eiso?=?25.2?±?0.6, 42.6?±?0.6, and 35.0?±?1.8?kJ?mol?1 for 2,2′, 3,3′, and 4,4′-azopyridine, respectively. For azobenzene, we obtain ?Eiso?=?47.0?±?1.3?kJ?mol?1, in agreement with the literature value and validating our method. Theoretical calculations yielded gas-phase ?Eiso in reasonable agreement with experiment and explain the low isomerization energy of 2,2′-azopyridine on the basis of a low-energy cis conformer. Because of the smaller van der Waals volume of the pyridine N relative to the phenyl CH, the two aromatic rings in the cis isomer can approach closer to coplanarity, leading to greater π-conjugation and lower conformational energy.
Light-induced spin change by photodissociable external ligands: A new principle for magnetic switching of molecules
Thies, Steffen,Sell, Hanno,Schuett, Christian,Bornholdt, Claudia,Naether, Christian,Tuczek, Felix,Herges, Rainer
supporting information; experimental part, p. 16243 - 16250 (2011/12/01)
Magnetic bistability in spin-crossover materials generally is a collective phenomenon that arises from the cooperative interaction of a large number of microscopic magnetic moments within the crystal lattice in the solid state. We now report on individual molecules in homogeneous solution that are switched between the diamagnetic and paramagnetic states at room temperature by light-driven coordination-induced spin-state switching (LD-CISSS). Switching of the coordination number (and concurrently of the spin state) was achieved by using Ni-porphyrin as a square-planar platform and azopyridines as photodissociable axial ligands. The square-planar Ni-porphyrin is diamagnetic (low-spin, S = 0), and all complexes with axial ligands are paramagnetic (high-spin, S = 1). Association constants were determined for all conceivable 1:1 and 1:2 porphyrin/azopyridine complexes. The binding constants of the trans azopyridines are larger than those of the corresponding cis isomers. Thus, upon irradiation with UV light (365 nm, trans → cis) and visible light (455 nm, cis → trans), switching of the magnetic properties was achieved. Upon substitution of the azopyridines at the 4- and 4′-positions with larger substituents, the difference in trans and cis association constants, and thus the switching efficiency, was increased. A photoinduced, reversible switching between 20 and 68% paramagnetic Ni species in solution was achieved with isopropyl substituents at room temperature.
