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Snyder JA, Grüninger P, Bettinger HF, et al. BN Doping and the Photochemistry of Polyaromatic Hydrocarbons: Photocyclization of Hexaphenyl Benzene and Hexaphenyl Borazine. J Phys Chem A. 2017;121(44):8359-8367doi: 10.1021/acs.jpca.7b08190.
Snyder, J. A., Grüninger, P., Bettinger, H. F., & Bragg, A. E. (2017). BN Doping and the Photochemistry of Polyaromatic Hydrocarbons: Photocyclization of Hexaphenyl Benzene and Hexaphenyl Borazine. The journal of physical chemistry. A, 121(44), 8359-8367. https://doi.org/10.1021/acs.jpca.7b08190
Snyder, Joshua A, et al. "BN Doping and the Photochemistry of Polyaromatic Hydrocarbons: Photocyclization of Hexaphenyl Benzene and Hexaphenyl Borazine." The journal of physical chemistry. A vol. 121,44 (2017): 8359-8367. doi: https://doi.org/10.1021/acs.jpca.7b08190
Snyder JA, Grüninger P, Bettinger HF, Bragg AE. BN Doping and the Photochemistry of Polyaromatic Hydrocarbons: Photocyclization of Hexaphenyl Benzene and Hexaphenyl Borazine. J Phys Chem A. 2017 Nov 09;121(44):8359-8367. doi: 10.1021/acs.jpca.7b08190. Epub 2017 Oct 26. PMID: 28949535.
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J Phys Chem A. 2017 Nov 09;121(44):8359-8367. doi: 10.1021/acs.jpca.7b08190. Epub 2017 Oct 26.

BN Doping and the Photochemistry of Polyaromatic Hydrocarbons: Photocyclization of Hexaphenyl Benzene and Hexaphenyl Borazine.

The journal of physical chemistry. A

Joshua A Snyder, Peter Grüninger, Holger F Bettinger, Arthur E Bragg

Affiliations

  1. Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States.
  2. Institut für Organische Chemie, Universität Tübingen , Auf der Morgenstelle 18, 72076 Tübingen, Germany.

PMID: 28949535 DOI: 10.1021/acs.jpca.7b08190

Abstract

Boron-nitrogen doping of polyaromatic hydrocarbon (PAH) materials can be used to tune their electronic properties while preserving the structural characteristics of pure hydrocarbons. Many multicycle PAHs can be synthesized photochemically; in contrast, very little is known about the photochemistry of their BN-doped counterparts. We present results of fs, ns, and μs time-resolved spectroscopic studies on the photoinduced dynamics of hexaphenyl benzene and hexaphenyl borazine in order to examine how BN doping alters photochemical C-C bond formation via 6π electrocyclization as well as the stability of resulting cyclized structures. Ultrafast measurements reveal photoinduced behaviors reflecting differences in excited-state decay pathways for the two molecules, with hexaphenyl borazine relaxing from its excited state with a rate that is 2 orders of magnitude faster than that of hexaphenyl benzene (3.0 vs 428 ps). Tetraphenyl dihydrotriphenylene generated from hexaphenyl benzene is observed to reopen with a ∼2 μs lifetime controlled by entropic stabilization of the cyclized structure; in contrast, photoinduced dynamics appear to be complete within 100 ps after excitation of hexaphenyl borazine. This significant difference in photochemical dynamics is reflected in the cyclodehydrogentation yields obtained for the two reactants (25 vs 0% for hexaphenyl benzene and borazine, respectively). Quantum-chemical computations predict that BN doping gives rise to energetic destabilization and increased singlet diradical character in cyclized structures. These findings indicate that the polarized BN bonds of the borazine core adversely impact photochemical bond formation relative to analogous hydrocarbons.

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