The impact of the alkyne substitution pattern and metalation on the photo-isomerization of azobenzene-based platinum(II) diynes and polyynes

Rayya A. Al-Balushi, Ashanul Haque, Maharaja Jayapal, Mohammed K. Al-Suti, John Husband, Muhammad S. Khan, Jonathan M. Skelton, Kieran C. Molloy, Paul R. Raithby

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Abstract

Trimethylsilyl-protected di-alkynes incorporating azobenzene linker groups, Me3Si─C≡C─R─C≡C─SiMe3 (R = azobenzene-3,3’-diyl, azobenzene-4,4’-diyl, 2,5-bisoctylazobenzene-4,4’-diyl), and the corresponding terminal dialkynes, H─C≡C─R─C≡C─H, have been synthesised and characterized. The CuI-catalyzed dehydrohalogenation reaction between trans-[Ph(Et3P)2PtCl] and the deprotected dialkynes in a 2:1 ratio in iPr2NH/CH2Cl2 gives the Pt(II) di-ynes trans-[Ph(Et3P)2Pt─C≡C─R─C≡C─Pt(PEt3)2Ph], while the dehydrohalogenation polycondensation reaction between trans-[(nBu3P)2PtCl2] and the dialkynes in a 1:1 molar ratio under similar reaction conditions affords the Pt(II) poly-ynes, [─Pt(PnBu3)2─C≡C─R─C≡C─]n. The materials have been characterized spectroscopically, with the di-ynes also studied using single-crystal X-ray diffraction. The Pt(II) di-ynes and poly-ynes are all soluble in common organic solvents. Optical-absorption measurements show that the compounds incorporating the para-azobenzene spacer have a higher degree of electronic delocalisation than their meta-azobenzene counterparts. Reversible photoisomerization in solution was observed spectroscopically for the alkynyl-functionalised azobenzene ligands and, to a lesser extent, for the Pt(II) complexes. Complementary quantum-chemical modelling was also used to analyse the optical properties and the isomerisation energetics.
Original languageEnglish
Pages (from-to)10955–10967
Number of pages13
JournalInorganic Chemistry
Volume55
Issue number21
Early online date18 Oct 2016
DOIs
Publication statusPublished - 7 Nov 2016

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Keywords

  • Azobenzene
  • Pt(II) acetylide complexes
  • Photoisomerisation
  • Time-dependent Density Functional Theory

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