The pt-organometallic version of perigraniline: going blue

Four conjugated push-pull organometallic polymers ([Pt]-AQ)n ([Pt] = trans-bis(phenylacetylene)bis(tributylphosphine)platinum(II); AQ = 2-bromo-, 2,6-dibromo-, 2,6-diamino-, and unsubstituted anthraquinone diimine) were prepared and characterized by UV-vis spectroscopy and electrochemistry. A low-energy charge transfer, CT, band ([Pt]*→AQ; confirmed by density functional theory calculations), was found in the 445-500 nm window rather than the expected red-shifted range above 630 nm. X-ray structures of four model compounds reveal that steric hindrance induces large dihedral angles between the C6 H4 and NCC2 planes, rendering π-orbital overlap difficult between the [Pt] and AQ units. The position of the CT band is mainly driven the reduction potential of the anthraquinone diimine unit.