Decoupling the artificial special pair to slow down the rate of singlet energy transfer

作者：Harvey Pierre D^*; Langlois Adam; Filatov Mikhail; Fortin Daniel; Ohkubo Kei; Fukuzumi Shunichi; Guilard Roger

来源：Journal of Porphyrins and Phthalocyanines, 2012, 16(5-6): 685-694.

DOI：10.1142/S1088424612500812

• singlet energy transfer
• DFT computations
• molecular orbital coupling
• fs transient absorption spectroscopy

Trimer 2, composed of a cofacial heterobismacrocycle, octamethyl-porphyrin zinc(II) and bisarylporphyrin zinc(II) held by an anthracenyl spacer, and a flanking acceptor, bisarylporphyrin free-base (Ar = -3,5-(tBu)(2)C6H3), has been studied by means of absorption spectroscopy, %26quot;steady state and time-resolved fluorescence%26quot; and fs transient absorption spectroscopy, and density functional theory (DFT) in order to assess the effect of decoupling the chromophores%26apos; low energy MOs on the rate of the singlet, S-1, energy transfer, k(ET), compared to a recently reported work on a heavily coupled trimeric system, Trimer 1, [biphenylenebis(n-nonyl) porphyrin zinc(II)]-bisarylporphyrin free-base (Ar = -3,5-(tBu)(2)C6H3). The position of the 0-0 peaks of the absorption and fluorescence spectra of Trimer 2 indicates that these porphyrin units are respectively energy donor 1, donor 2, and acceptor. The DFT computations confirm that the MOs of the cofacial donor 1-donor 2 dyad are decoupled, but significant MO coupling between donor 2 and acceptor 1 is still present despite the strong dihedral angle between their respective average planes (77.5 degrees: geometry optimization by DFT). The fs transient absorption spectra exhibit a clear S-1-S-n fingerprint of the bisarylporphyrin zinc(II) chromophore and the kinetic trace exhibits a slow rise time of 87 ps, due to a S-1 donor 1 -%26gt; donor 2 ET. The transient species donor 2 and acceptor decay respectively in the short (similar to 1.5) ns and 6 ns time scale.

• 出版日期2012-6