Resonance Raman studies of the p-benzosemiquinone and p, p′-biphenylsemiquinone free-radical anions

Abstract

The p-benzosemiquinone and p,p'-biphenylsemiquinone free-radical anions have been produced by both chemical and photochemical methods. Resonance Raman spectra recorded from these free radicals are compared with those of the neutral parent compounds. The observed parent-to-radical Raman wavenumber shifts have been interpreted in terms of the structural changes that occur upon radical formation. Electronic absorption spectra of both radical species have been recorded and analysed. These have been used in conjunction with the resonance Raman data and excitation profiles to elucidate the excited-state geometries of the radicals. The resonance Raman spectrum of the p,p'-biphenylsemiquinone radical-anion dimer also is reported, as is its electronic absorption spectrum.

Vibronic spectra of the p-benzoquinone radical anion and cation: a matrix isolation and computational study

“…Raman spectra which revealed some of the totally symmetric fundamentals, [11][12][13][14][15] but only the strongest band in the IR spectrum, at around 1500 cm…”

“…The vibrational structure of PBQ À has stood at the focus of several studies, most of which have probed the totally symmetric fundamentals by (resonance) Raman spectroscopy. [11][12][13][14] In the IR spectrum only the most intense band at around 1500 cm À1 had been unambiguously pinpointed. 14,16 The vibrational structure of PBQ À has been investigated computationally by different groups, 35,36 but since they had done this in view of assigning the Raman spectra, they did not list the predicted IR intensities.…”

Mimicking the antenna-electron transfer properties of photosynthesis

“…2 for polymer assembly 4, homopolymer 5, and unbound chromophorequencher assembly 3. The characteristic features for 3 are the appearance of absorption bands for reduced MV 2ϩ at 398 and 608 nm (54) and oxidized PTZ at 517 nm (55). The difference spectrum of 4 is more complex because of an overlapping contribution from unquenched antenna excited states, which have a characteristic absorption at 380 nm and a bleach at Ϸ460 nm.…”

Time-Resolved Resonance Raman and Density Functional Studies on the Ground State and Short-Lived Intermediates of Tetrabromo-p-benzoquinone

“…26 Several approaches have been used to obtain a better understanding of the structure and spectra of various substituted quinones such as ubiquinones, 27-31 methoxy quinones, 27,32,33 plastoquinones, [34][35][36] and p-benzoquinone [7][8][9][10][11][12][13][14][15][16][17][18][19][37][38][39] and its halogen-substituted analogues, [20][21][22][23][24]40 etc. We have been involved in systematically investigating structures of quinones 24,31,39,[41][42][43] and their shortlived transient states with the specific objective of elucidating their structure-reactivity correlations.…”

“…[3][4][5] Further, because of their extensive use as electron acceptors in charge-transfer salts, they are subjects of several studies for their unique conduction properties. 6 Although the four haloanils and the parent benzoquinone show very different properties, experimental efforts have largely concentrated on the parent quinone [7][8][9][10][11][12][13][14][15][16][17][18][19] and its fluorinated and chlorinated analogues. [20][21][22][23][24] Since their electron affinities vary from 1.86 eV for p-benzoquinone to 2.95 eV for fluoranil, 25 the effect of different substitutions on the reactivities of these quinones is expected to be significant.…”