Photoluminescence Switching of Azobenzene-Conjugated Pt(II) Terpyridine Complexes by Trans−Cis Photoisomerization

Pt(II) complexes with a terpyridylazobenzene ligand (tpyAB) were newly synthesized, and their photoluminescence
properties by trans−cis isomerization of the azo moiety were investigated. In these complexes, upon excitation with
366-nm light in polar solvents such as DMF, DMSO, and propylene carbonate, trans-to-cis isomerization with
significant UV−vis spectral changes occurred almost completely. Cis-to-trans isomerization was observed both by
irradiation with visible light and by heat. The reduction peaks due to the terpyridine and the azo group in the cyclic
voltammograms of the Pt complexes were shifted in the positive direction by trans-to-cis isomerization. Emission
spectral changes due to trans−cis isomerization were observed for both the tpyAB and the Pt complexes. The
significant differences in the emission properties of the complex compared to tpyAB include the observation that
both the excitation and emission wavelengths were shifted to lower energy, located in the visible region. Moreover,
the change in emission intensity between the trans and cis forms was more significant upon excitation with UV
light, because the trans form of the complexes showed absolutely no emission. Accordingly, the azobenzene-conjugated Pt(II) terpyridine complexes promise to be doubly photofunctional materials, showing complete off−on
switching of emission linked to the trans−cis conformation change.