The Ultraviolet Absorption Spectra of Substituted Pyrazoles

Abstract

The ultraviolet spectra of several simple alkyl substituted pyrazoles have been examined. It is found that there is a pronounced bathochromic shift induced by the introduction of an alkyl group at the 4 position of the pyrazole ring, and a lesser shift by substitution at the 3 or the 5 position. In acid solution, similar shifts are observed.Berkeley 4, California

Lanthanide Cerium(III) Tris(pyrazolyl)borate Complexes: Efficient Blue Emitters for Doublet Organic Light-Emitting Diodes

“…The photophysical properties of these complexes in dichloromethane solution are shown in Figure S16. Ultraviolet–visible (UV–vis) absorption spectra indicate that all of the complexes exhibit a high molar extinction coefficient at a wavelength around 240 nm, which could be attributed to the π–π* transition of the pyrazole ring, , and the absorption bands between 250 and 450 nm could be assigned to the 4f–5d absorption of the Ce­(III) cation (Figure S16a). The excitation and emission spectra have similar features with those of the solid powder, and the fitted excited-state lifetimes are 53–73 ns (Table , Figures S16b–d and S3–S8, and Table S4).…”

Volatility, High Thermal Stability, and Low Melting Points in Heavier Alkaline Earth Metal Complexes Containing Tris(pyrazolyl)borate Ligands

“…Hexane was distilled from P 2 O 5 . KTp, KTp Me2 , MTp 2 (M = Sr, 1 ; Ba, 2 ), MTp Me2 2 (M = Sr, 3 ; Ba, 4 ), 3,5-diethylpyrazole, 3,5-di- n -propylpyrazole, and the β-diketones used for the pyrazole syntheses were prepared according to literature procedures. BaI 2 (THF) 3 was prepared by treating a slight excess of barium (1.1 equiv) with iodine (1.0 equiv) in refluxing THF.…”

Investigation of the “bent sandwich-like” divalent lanthanide hydro-tris(pyrazolyl)borates Ln(TpiPr2)2 (Ln = Sm, Eu, Tm, Yb)

“…The pp* transitions of the pyrazole units leading to a LMCT are typically located in the range of 220 nm and thus beyond the range of measureable wavelengths of the used spectrometer. 24 The photoluminescence excitation spectrum reveals the presence of a raw fine structure that is characteristic for the 7 F J levels arising from the 4f 6 core of the excited 4f 6 5d 1 configuration assuming a weak Coulomb interaction between the 4f and 5d electrons and rarely observed. 25 This feature is another evidence for the presence of Eu(II) in the compound and justifies the assignment of the respective emissive transition.…”