Resonance Raman investigation of the .pi. antibonding distribution in excited triplet aqueous p-benzoquinone

Abstract

The time-resolved resonance Raman spectra of triplet p-benzoquinone in water have been investigated at 266, 315,355, and 416 nm. Recent improvements in the apparatus are described. The C-C ring stretch (Wilson's 8a) and the symmetric C--O stretch are tentatively identified, using the isotopic shift for ring deuteration and comparison with the semiquinone radical anion. The symmetric carbonyl stretch at 1496 cm-' is unusally high for an nlr* excited state. The C=C ring stretch at 1552 cm-' is unusually low for a quinoid type species. These results indicate that there is a* antibonding density on the ring as well as on the carbonyl groups. Comparison is made with previous So -T1 vibronic electronic absorption studies in neon matrices.(7) Beck, S. M.; Brus, L. E.

A Time-Resolved Infrared Vibrational Spectroscopic Study of the Photo-Dynamics of Crystalline Materials

“…10 We also consider it to be unlikely that the triplet state is formed in the solid state despite the long lifetimes 44 observed; this conclusion is drawn from the fact that we would expect to see large changes in the carbonyl frequency commensurate with those observed in time-resolved Raman spectra of the triplet state of aromatic molecules with carbonyl groups such as benzoquinone. 45 Of course the very symmetric nature of these molecules may be a contributing factor whereby the infrared activity of these modes is very weak. But again the astounding similarities in the intensities of the bleach versus the transients suggest that there is complete conversion of the ground state to the transient state observed.…”

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

“…In this context, akin to bromanil, in benzoquinone and fluoranil the semiquinone radical and the radical anion have been observed (in methanol and water solutions). [8][9][10][11]24 4.2. Structure and Vibrational Assignment.…”

“…[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.…”

“…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.…”

The many aspects of quantum dots

“…Colloidal quantum dots emerged from a number of research labs in the early 1980s, with Louis Brus (then at Bell Labs, now at Columbia University) being singled out to receive the first Kavli Prize in Nanoscience in 2008 for his pioneering efforts in this field 7,8 . They have been widely used in bio-imaging applications for a number of years, and researchers have recently developed methods to stop the fluorescence from quantum dots switching on and off in a random manner (a problem known as 'blinking') 9 .…”