No abstract

A series of ethynylpyridine-appended nucleobases have been designed, synthesized, characterized and employed for the formation of crystalline molecular networks by hydrogen/coordination bonding.

A library composed of ten porphyrins bearing nucleobases is prepared, following two strategies: substitution or Sonogashira cross-coupling reactions. The former strategy led to the synthesis of four porphyrins (T 2 À Po1, A 2 À Po1, C 2 À Po1 and P 2 À Po1) bearing nucleobases (NBs) at two trans meso-positions. These 4 porphyrins were obtained by reacting 5,15-di(4-(bromomethyl)phenyl)-10,20-dimesitylporphyrin (Po1) with thymine (T), adenine (A), cytosine (C) and 2-amino-6-chloropurine (P), a precursor of guanine (G), respectively in the presence of a suitable base. A fifth porphyrin, 5,15-di(N9-meth-ylphenylguanine)-10,20-dimesitylporphyrin (G 2 À Po1) was obtained by hydrolysis of P 2 À Po1. A thymine tetra-functionalized porphyrin was also synthesized following the same strategy starting from T and 5,10,15,20-tetrakis[4-(bromomethyl)phenyl] porphyrin (Po2). The second strategy based on Sonogashira cross-coupling reactions between 5,15-dibromo-10,20-dipentylporphyrin (Po3) and ethynyl-substituted nucleobases resulted in four rigid porphyrins (U 2 À Po3, C 2 À ZnPo3, A 2 À ZnPo3, and G 2 À ZnPo3).

We report a ruthenium(II) bisacetylide complex bearing a photochromic dithienylethene (DTE) acetylide arm and a coordinating bipyridyl on the trans acetylide unit. Its coordination with Yb(TTA)3 centers (TTA = 2-thenoyltrifluoroacetonate) produces a bimetallic complex in which the dithienylethene isomerization is triggered by both ultraviolet (UV) light absorbed by the DTE unit and 450 nm excitation in a transition of the organometallic moiety. The redox behavior arising from the ruthenium(II) bisacetylide system is fully investigated by cyclic voltammetry and spectroelectrochemistry, revealing a lack of stability of the DTE-closed oxidized state preventing effective redox luminescence switching. On the other hand, the photoswitching of ytterbium(III) near-infrared (NIR) emission triggered by the photochromic reaction is fully operational. The electronic structure of this complex in its different states characterized by strong electronic coupling between the DTE and the ruthenium(II)-based moieties leading to metal-assisted photochromic behavior were rationalized with the help of time-dependent density functional theory (TD-DFT) calculations.