Effect of Donor-Acceptor Interaction

A new family of Pt(II) polyyne polymers functionalized with substituted 1,4-diethynylbenzene derivatives 8—14 were synthesized and optically characterized by absorption and PL studies.20 In regard to the emission properties, it is interesting to see that the relative intensity of triplet emission increases strongly with the electronegative fluorine content in such system. 

FIGURE 10. A plot of Eg against 1/m2 for complexes with different acetylenic chain length. 

Two interesting Pt(II) polyynes that possess mixed heterocyclic groups consisting of both thienyl and pyridyl rings 42 and 43 were also reported.43 The Eg values for 42 and 43 are 2.67 and 2.55 eV, respectively, which can be compared to the gaps of 2.55 and 2.40 eV for 29 and 30, and the corresponding blue shifts of 0.12 and 0.15 eV are consistent with a reduction in the D-A interaction between the metal and ligand. 

A soluble silole-containing polyplatinayne 51 was prepared.47 As compared to 2,5-dibromo-l,l-diethylsilole (Xmax = 326 nm), the positions of the low-lying shoulder bands (Xmax = 504 nm in CH2C12) are remarkably red-shifted by 178 nm for 51 after the inclusion of heavy-metal chromophores. This is possibly due to the intramolecular D-A interaction between the electron-rich metal ethynyl unit and the electron-poor silole ring. The Ee value is impressive at 2.10 eV for 51, and it is significantly lowered by 1.0 eV relative to 53 (3.10 eV).48 Compound 51 is photoluminescent with the singlet emission band at 537 nm. No room temperature emission from the Ti state was detected over the measured spectral window. 

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In case of short hydrogen bonds the effect of donor-acceptor interaction should be much greater. 

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