Assignment and vibrational analysis of the 600 nm absorption band in the phenoxyl radical and some of its derivatives

Abstract

. 71, 1655 (1993).An experimental and theoretical study is reported of the 600 nm band system of phenoxyl and several methoxy substituted phenoxyls. These radicals, generated in freon, show a diffuse band in this region with a vibrational structure that is incompletely resolved but consistent with the 500 cm-I "progression" observed earlier for phenoxyl in the vapour and in a rigid matrix. The low intensity of this band is considerably enhanced by ortho-methoxy substitution. To establish its assignment and analyze its structure, semi-empirical and nb initio quantum chemical calculations have been performed. It is found that, on the basis of the ordering of the states and the magnitude of their transition moments, all calculations favour a TT* ('B~ + 'A~) rather than the earlier proposed nn* assignment for this band. Of the methods used, only the (nb initio) CASSCF method is found to be able to simulate the observed vibrational structure adequately. This simulation is based on optimized structures and vibrational force fields calculated for the lB, and 1A2 states of phenoxyl. It identifies the dominant mode of about 500 cm-' as vki, the characteristic deformation mode of phenyl rings, but shows that higher members of the "progression" receive large intensity contributions from higher frequency modes. The chosen assignment and the assignments of higher-energy transitions reported in the literature are compared with those for the better known benzyl radical. It is shown that some of the phenoxyl assignments reported in the literature contain errors. Une etude experimentale et theorique est presentee concernant le systeme de bandes pres de 600 nm du phenoxyle et de plusieurs phenoxyles comportant un ou deux groupes methoxy. Ces radicaux, produit dans Ie frCon, montrent une bande diffuse dans cette region; la structure vibrationelle n'est pas completement resolue mais est en accord avec la "progression" de bandes de 500 cm-' observCe plus tat pour le phCnoxyle dans la vapeur et dans une matrice rigide. L'intensitC de cette bande faible est hausste considCrablement par des substituants ortho-methoxy. Pour etablir l'attribution de cette bande et pour analyser sa structure, on a fait des calculs avec des mCthodes de chimie quantique, non seulement semi-empirique mais aussi nb initio. On a trouve que, selon l'ordre des Ctats et la magnitude des moments de transition, tous ces calculs favorisent l'attribution de la bande a une transition TT* ('B, + 'A?) au lieu de l'attribution t z~" proposee prCcCdemment. De toutes les methodes utilisees, seule la methode (ab initio) CASSCF peut simuler d'une fason acceptable la structure vibrationnelle observCe. Cette simulation est basee sur les structures optimisCes et les champs de force vibrationnels calcults pour les Ctats 1B2 et 1A, du phCnoxyle. Elle mene l'identification du mode normal de 500 cm-I, qui domine le spectre, avec le mode v6,, c'est-a-dire le mode caracteristique pour la deformation des noyaux benzeniques; cependant, des modes normaux d'une frequence plus ClevCe cont...

Ultraviolet Absorption Spectra of Substituted Phenols: A Computational Study†

“…The Equation‐of‐Motion (EOM) approach has been used to investigate a wide range of molecular properties (23–25) and has yielded very accurate excited‐state results for benzene (26, 27). CASSCF has been used in electronic structure calculations for a broad range of molecules (28, 29). The only difficulty associated with CASSCF calculations lies in the judicious choice of the active space.…”

Laboratory Optical Spectroscopy of the Phenoxy Radical as a Candidate for Diffuse Interstellar Bands

“…Although they are the most fundamental benzene derivative radicals, the thiophenoxy (Araki et al 2014b), phenoxy, and methylphenoxy radicals were not able to explain DIBs. second excited state were calculated by Johnston et al (1993), the energy levels of the ground and excited states in their calculations were inverted compared with those in currently accepted energy level structures. Thus, we recalculated the frequencies of the B A 2 2 second excited state using TD-B3LYP/cc-pVTZ.…”

“…The electronically excited states of A B , and E B 2 1 have been characterized with absorption bands in the regions from 1140 nm to 1310 nm (Gunion et al 1992;Radziszewski et al 2001;Cheng et al 2008), 510 nm to 640 nm (Ward 1968;Pullin & Andrews 1982;Kesper et al 1991;Johnston et al 1993;Yu et al 1995;Radziszewski et al 2001;SpangetLarsen et al 2001), 370 nm to 400 nm (Porter & Wright 1955;Pullin & Andrews 1982;Kesper et al 1991;Radziszewski et al 2001;Spanget-Larsen et al 2001;Tonokura et al 2004), 270 nm to 300 nm (Porter & Wright 1955;Ward 1968;Kajii et al 1987;Berho & Lesclaux 1997;Platz et al 1998;Radziszewski et al 2001;Spanget-Larsen et al 2001;Bayrakceken et al 2003), and 220 nm to 250 nm (Kajii et al 1987;Berho & Lesclaux 1997;Platz et al 1998;Radziszewski et al 2001), respectively, where the z-axis isalong the C-O bond and the x-axis is perpendicular to the plane. Only the A B X B transitions show resolved vibrational structures (Johnston et al 1993;Radziszewski et al 2001;Spanget-Larsen et al 2001;Cheng et al 2008 transition. To compare this transition with DIBs, gas-phase, high-resolution observation of the transition is essential.…”

Mechanism of azo dye degradation in Advanced Oxidation Processes: Degradation of Sulfanilic Acid Azochromotrop and its parent compounds in aqueous solution by ionizing radiation

“…The phenoxy (naphthoxy) radicals characteristically have three absorption bands (Johnston et al, 1993;Steenken and Neta, 2003): an intense band between 300-400 nm (depending on the parent molecule) a weaker and often structured band in the 350-420 nm range (e max E4000 mol À 1 dm 3 cm À 1 ; Roder et al, 1999) and a weak, ill-defined wide band in the 500-700 nm range. Such radicals generally decay in slow second order reactions (as observed here).…”