The phosphorescence properties of a series of diarylethene-containing platinum complexes: the effect of ligand photoisomerization

A theoretical comparison of the photophysical and photochemical properties has been made among a series of diarylethene-containing Pt(II) complexes that have two kinds of isomers exhibiting different optical behaviors. It is found that the extension of conjugated systems and electron-withdrawing substituents on a host-ligand promotes the rigidity of structures, which is beneficial to electron transfer during excitation. Moreover, the phosphorescence emission and quenching of complexes can be controlled by utilizing the contrasting optical performance of their two isomers. In closed-ring forms, the complexes suffer phosphorescence quenching due to the inefficient involvement of Pt in the excitation and the low energy gap between the first triplet excited state and the ground state. In open-ring forms, the shift of conjugated systems makes the excitation switch from diarylethene to Pt so that the spin–orbit coupling effect can be achieved, which leads to an effective phosphorescence emission. In addition, the calculation of the radiative decay rate constant kr is proposed to give an evaluation of the radiative decay process of open-ring forms. And the analysis of the potential energy surface of the triplet-excited state presents an in-depth description of the role of isomerization in its non-radiative decay process. All the above results show the tunability and applicability of diarylethene in organometallic materials. Based on these results, new complexes have been designed as promising candidates with better photoresponsive and phosphorescence performance.