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• 92-67-1 4-phenylalanine 

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The synthesis, X-ray structure analysis, and photoisomerization assessment of the acyclic triazenes 4-[(E)-2-(biphenyl-4-yl)diazenyl]-morpholine and 1,3-Bis(biphenyl-4-yl)triazene

The acyclic triazenes 4-[(E)-2-(biphenyl-4-yl)diazenyl]-morpholine (1) and 1,3-bis(biphenyl-4-yl)triazene (2) were prepared and their X-ray crystal structures determined. Compound 1 crystallized in the monoclinic space group P21/c with a = 29.153 (5) ?, b = 6.0444 (14) ?, c = 7.5997 (15) ?, and β = 96.03 (1). Compound 2 crystallized as the 1/4 cyclohexane solvate in the triclinic space group P 1? 1 ? with a = 10.3228 (10) ?, b = 13.4541 (14) ?, c = 15.4323 (15) ?, α = 87.158 (4), β = 76.030 (4) and γ = 71.492 (5). The N-N double bond in 1 and 2 adopted an (E)-configuration and had bond angles that ranged from 112.19 (9) to 114.01 (13), which deviated from optimal trigonal planar geometry by 6 -8. A degree of π-conjugation across the acyclic triazene moieties in compounds 1 and 2 was indicated by N-N double and single bond lengths that were respectively longer and shorter than the literature values for these types of bonds. The room temperature electronic absorption spectra of 1 and 2 in various solvents were both dominated by an intense band above 300 nm that was assigned to a combination of π → π*and n → π*transitions. Compounds 1 and 2 in acetonitrile and methanol solution were found to undergo trans → cis photoisomerization. The magnitudes of trans → cis rate constants were rationalized in terms of the degree of solvent stabilization of the dipolar resonance hybrid structure of the acyclic triazene subunits in 1 and 2. Irradiation of chloroform solutions of 1 and 2 caused trans → cis photoisomerization and radical decomposition to occur. Graphical Abstract: The X-ray structures of compounds 1 and 2 were determined and their photoisomerization kinetics explored.[Figure not available: see fulltext.]