Origin of Substituent Effects in the Absorption Spectra of Peroxy Radicals:  Time Dependent Density Functional Theory Calculations

Abstract

We investigate the assignment of electronic transitions in alkyl peroxy radicals. Past experimental work has shown that the phenyl peroxy radical exhibits a transition in the visible region; however, previous high level calculations have not reproduced this observed absorption. We use time dependent density functional theory (TDDFT) to characterize the electronic excitations of the phenyl peroxy radical as well as other hydrocarbon substituted peroxy radicals. TDDFT calculations of the phenyl peroxy radical support an excitation in the visible spectrum. Further, we investigate the nature of this visible absorption using electron attachment/detachment density diagrams of the peroxy radicals and present a qualitative picture of the origin of the visible absorption based on molecular orbital perturbations. The peroxy radical substituent is also compared against isoelectronic radical groups. The visible absorption is determined to be dependent on mixing of the alkyl and radical substituent orbitals.

Radical Ions from 3,3′′′,3′′′″‐Tris(butylsulfanyl)‐2,2′:5′,2″:5″,2′′′,5′′′,2′′′′:5′′′′,2′′′″‐sexithiophene: An Experimental and Theoretical Study of the p‐ and n‐Doped Oligomer

“…Time-dependent DFT calculations [39] were performed to assign the absorption bands observed above 400 nm, since they reproduce well optical transitions not only in diamagnetic systems, [39] but also in radical species. [40,41] Table 2 shows that there is good agreement between theory and experimental results on going from the title compound to the positively charged species. However, the assignment of the two main peaks in the optical spectrum of the radical cation deserves some comments.…”

An experimental and theoretical study of the catalytic effect of quaternary ammonium salts on the oxidation of hydrocarbons

“…The hybrid functional B3LYP was chosen, since it had been previously shown to describe systems containing peroxyl radicals or ionic species accurately. [10][11][12] For H, C, N and O (atoms from the first and second rows) a 6-31G (d,p) or a 6-31CCG(d,p) basis set was chosen. For iodine 13 a 6-311GCC(3df) basis set was obtained from the EMSL 14 (the supplementary diffuse and polarization functions of reference 13 were added manually).…”

Quantum Chemical Methods for the Investigation of Photoinitiated Processes in Biological Systems: Theory and Applications

“…Very often these excited states are slightly shifted in energy by an almost constant value compared with the experimental electronic absorption spectrum, but the relative energies between the states are reproduced very favorably (see, for example, refs. [95,158,159]). Despite the success of TDDFT for valence excited states, it exhibits substantial errors for the calculation of Rydberg excited states, doubly excited states, [160,161] ionic states of systems with large p systems, [162,163] and charge-transfer excited states, [164][165][166][167] which are all well documented today.…”