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Title: Photochemistry of highly excited states

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Journal Article: Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 52; Related Information: CHORUS Timestamp: 2018-01-12 15:49:17; Journal ID: ISSN 0027-8424
Proceedings of the National Academy of Sciences
Country of Publication:
United States

Citation Formats

Levine, R. D. Photochemistry of highly excited states. United States: N. p., 2017. Web. doi:10.1073/pnas.1718814114.
Levine, R. D. Photochemistry of highly excited states. United States. doi:10.1073/pnas.1718814114.
Levine, R. D. 2017. "Photochemistry of highly excited states". United States. doi:10.1073/pnas.1718814114.
title = {Photochemistry of highly excited states},
author = {Levine, R. D.},
abstractNote = {},
doi = {10.1073/pnas.1718814114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 52,
volume = 114,
place = {United States},
year = 2017,
month =

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  • Singlet and triplet excited states and the reduced and oxidized forms of two squaraine dyes, bis[4-(dimethylamino)-phenyl]squaraine (SQH) and bis[4-(dimethylamino)-2-hydroxyphenyl]squaraine (SQOH), have been investigated by picosecond and nanosecond laser flash photolysis. Both singlet and triplet excited states of SQH and SQOH have distinct and intense absorption maxima in the visible region. The lifetime of {sup 1}SQOH* ({tau}{sub s} = 3.0 ns) is considerably higher than {sup 1}SQH* ({tau}{sub s} = 1.5 ns) as the substituent OH group restricts rotational relaxation of the excited state. Both squaraine dyes exhibit poor intersystem crossing efficiency ({phi}{sub isc} < 0.001). However, the excited triplets ofmore » SQH and SQOH can be generated by triplet-triplet sensitization. The oxidized forms of these dyes, which were generated by photolytic and pulse radiolytic methods, exhibit absorption maxima in the vicinity of the ground-state absorption. The cation radical of SQOH can also be generated by charge transfer between excited dye and TiO{sub 2} semiconductor colloids.« less
  • Studies of the photophysical and photochemical properties of organometallic compounds have now been extensively performed for over 25 years. In considering the photoreactivity of such complexes, it has usually been assumed that their singlet excited states are extremely short-lived and unreactive as a consequence of effective intersystem crossing mechanisms facilitated by the heavy metal and rapid internal conversions to the ground state. In this paper the authors report quantitative photochemical measurements obtained for W(CO){sub 4}(en) (en = ethylenediamine) following excitation into the lowest energy LF absorption manifold at several wavelengths. This system is of particular significance because, unlike most othermore » substituted metal carbonyl complexes, its lowest lying LF absorption band is well removed from other electronic transitions and the lowest energy LF triplet absorption is a distinctive feature of the spectrum. Following excitation at various wavelengths, therefore, it is possible to populate the LF single and triplet energy levels exclusively and determine their quantitative photochemical reactivities directly. The results for W(CO){sub 4}(en) demonstrate conclusively that the LF excited states undergo separate photosubstitutional pathways and that reaction from the lowest lying LF triplet state takes place with a substantially reduced photoefficiency.« less
  • Study of reactive excited states of van der Waals complexes offers a link between the laser-assisted collision approach and the photodissociation approach to probing reaction dynamics. A cold complex of the reagent molecules with a defined geometry is formed in a supersonic jet and then optically excited to trigger the reaction. General features of this method are outlined and illustrated with experimental results for the Hg-H/sub 2/, Hg-Cl/sub 2/, and Xe-Cl/sub 2/ systems; these exemplify aspects of orbital specificity, selectivity in product state distributions, and observation of intermediate states.
  • Fluorescence from highly excited atomic states has been observed in cesium vapor irradiated by a dye laser tuned to either one of the 6/sup 2/S--7/sup 2/P transitions. The emission originated from levels as high as 1 eV above the state being pumped. The high-lying states are believed to be excited by an electronic energy transfer induced in a collision of two atoms occupying lower excited levels.