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COMPUTATIONAL AND SPECTROSCOPIC STUDIES OF THE PHOTOCHEMISTRY AND PHOTOPHYSICS OF DIPHOSPHENES

Peng, Huo-Lei
http://rave.ohiolink.edu/etdc/view?acc_num=case1174432257

Abstract Details

2007, Doctor of Philosophy, Case Western Reserve University, Chemistry.
Diphosphenes exhibit a rich diversity of photochemical processes, including isomerization about the –P=P– double bond, which can be exploited to make molecular switches and storage materials and so on, by analogy to azobenzenoid and stilbenoid compounds. Understanding diphosphene photochemistry and photophysics will allow exploration of these practical possibilities. We report results from concerted experimental and computational study of real and model diphosphene systems. A series of DFT studies focused on the structural and electronic effects of substituents upon the frontier orbitals indicated that twisting of the phenyl rings relative to the central double bond alters the occupied frontier orbitals profoundly. A HOMO that is pi in nature at small phenyl twists shifts to one that is clearly n+ as the phenyl twist angles increased. A hypsochromic effect was induced by the phenyl twist and by substitution with electron-withdrawing groups. Femtosecond transient absorption spectroscopy into both the pi-pi* (S2) and n+-pi* (S1) states of DmpP=PDmp show two component decays, in the range of 450-650 nm, with lifetimes of 10's and a few 100's of picoseconds. Above 700 nm, the transient absorption also exhibits a 300 fs component upon S2 excitation. The photodynamics are complete within a nanosecond. DmpP=PDmp diphosphene undergoes no detectable xviii reversible photochemistry, unlike the related compound Mes*P=PMes*. The photodynamics in this later compound were found to be faster, with two lifetimes of ca. 1 and ca. 5 ps. Neither DmpP=PDmp nor Mes*P=PMes* show appreciable fluorescence (quantum yield < 10-4), consistent with these very rapid electronic dynamics. Dependence of the DmpP=PDmp dynamics upon solvent polarity was observed, but solvent viscosity appeared to have little impact. Initial experimental studies using alfa-diketone as a triplet sensitizer have strongly suggested a role for the triplet manifold in diphosphene photochemistry. Also there is evidence in the computational results for the role of a triplet state in the photochemistry. DFT and TDDFT calculation at B3LYP/6-31+g(d,p) level, of the excited states of a model compound: diphenyldiphosphene, were performed. Using these new computational results as a guide, a picture of diphosphene photochemistry and photophysics has been shown up.
Cather Simpson (Advisor)
Chemistry, Physical
diphosphene; phenyl twist; transient absorption; photochemistry; substituent effect; DFT

Recommended Citations

Citations

  • Peng, H.-L. (2007). COMPUTATIONAL AND SPECTROSCOPIC STUDIES OF THE PHOTOCHEMISTRY AND PHOTOPHYSICS OF DIPHOSPHENES [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1174432257

    APA Style (7th edition)

  • Peng, Huo-Lei. COMPUTATIONAL AND SPECTROSCOPIC STUDIES OF THE PHOTOCHEMISTRY AND PHOTOPHYSICS OF DIPHOSPHENES. 2007. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1174432257.

    MLA Style (8th edition)

  • Peng, Huo-Lei. "COMPUTATIONAL AND SPECTROSCOPIC STUDIES OF THE PHOTOCHEMISTRY AND PHOTOPHYSICS OF DIPHOSPHENES." Doctoral dissertation, Case Western Reserve University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1174432257

    Chicago Manual of Style (17th edition)

case1174432257
679
© 2007, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.