Twisting the phenyls in aryl diphosphenes (Ar-P=P-Ar). Significant impact upon lowest energy excited states

Huo Lei Peng, John L. Payton, John D. Protasiewicz, M. C. Simpson

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

Aryl diphosphenes (Ar-P=P-Ar) possess features that may make them useful in photonic devices, including the possibility for photochemical E-Z isomerization. Development of good models guided by computations is hampered by poor correspondence between predicted and experimental UV/vis absorption spectra. A hypothesis that the phenyl twist angle (i.e., PPCC torsion) accounts for this discrepancy is explored, with positive findings. DFT and TDDFT (B3LYP) were applied to the phenyl-P=P-phenyl (Ph-P=P-Ph) model compound over a range of phenyl twist angles, and to the Ph-P=P-Ph cores of two crystallographically characterized diphosphenes: bis-(2,4,6-iBu 3C 6H 2)-diphosphene (Mes*-P=P-MeS*) and bis-(2,6-Mes 2C 6H 3)diphosphene (Dmp-P=P-Dmp). A shallow PES is observed for the model diphosphene: the full range of phenyl twist angles is accessible for under 5 kcal/mol. The Kohn-Sham orbitais (KS-MO s) exhibit stabilization and mixing of the two highest energy frontier orbitais: the n- and π localized primarily on the -P=P- unit. A simple, single-configuration model based upon this symmetry-breaking is shown to be consistent with the major features of the measured UV/vis spectra of several diphosphenes. Detailed evaluation of singlet excitations, transition energies and oscillator strengths with TDDFT showed that the lowest energy transition (S; -S 0) does not always correspond to the LUMO -HOMO configuration. Coupling between the phenyl rings and central -P=P- destabilizes the π-π dominated state. Hence, the Si is always n+-π* in nature, even with a π-type HOMO. This coupling of the ring and -P=P- π systems engenders complexity in the UV/vis absorption region, and may be the origin of the variety of photobehaviors observed in diphosphenes.

Original languageEnglish (US)
Pages (from-to)7054-7063
Number of pages10
JournalJournal of Physical Chemistry A
Volume113
Issue number25
DOIs
StatePublished - Jun 25 2009
Externally publishedYes

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phenyls
twisting
Excited states
excitation
Photonic devices
energy
rings
Isomerization
configurations
Discrete Fourier transforms
oscillator strengths
Torsional stress
isomerization
torsion
Absorption spectra
broken symmetry
Stabilization
stabilization
photonics
absorption spectra

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Twisting the phenyls in aryl diphosphenes (Ar-P=P-Ar). Significant impact upon lowest energy excited states. / Peng, Huo Lei; Payton, John L.; Protasiewicz, John D.; Simpson, M. C.

In: Journal of Physical Chemistry A, Vol. 113, No. 25, 25.06.2009, p. 7054-7063.

Research output: Contribution to journalArticle

Peng, Huo Lei ; Payton, John L. ; Protasiewicz, John D. ; Simpson, M. C. / Twisting the phenyls in aryl diphosphenes (Ar-P=P-Ar). Significant impact upon lowest energy excited states. In: Journal of Physical Chemistry A. 2009 ; Vol. 113, No. 25. pp. 7054-7063.
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