posted on 2012-10-11, 00:00authored byJun-Sheng Chen, Guang-Jiu Zhao, Timothy R. Cook, Xiao-Fei Sun, Song-Qiu Yang, Ming-Xing Zhang, Ke-Li Han, Peter J. Stang
The 90° and 60° bimetallic platinum complexes
with special
structures are widely used in coordination-driven self-assembled metallosupramolecular
architectures, and these complexes are the key components of triangular,
rectangular, and polygonal metallacycle and metallocage supramolecules.
Therefore, spectroscopic techniques and quantum chemistry calculations
were employed in this article to investigate the photophysical properties
of these bimetallic platinum complexes. Compared with spectra for
the ligands, the absorption spectra of these Pt complexes are red-shifted,
and the fluorescence spectra become wider and are also red-shifted.
Moreover, the reasons for the low fluorescence quantum yields and
short fluorescence lifetimes of these compounds were investigated
using quantum chemistry calculations. We demonstrate that the fluorescent
states of the bimetallic platinum complexes can be considered as local
excited states, and that they possess a ligand-centered π–π*
transition feature. Meanwhile, the platinum metals act as perturbation
for these transitions, whereas the nonfluorescent states are classified
as intramolecular charge-transfer states. Furthermore, a new fluorescence
modulation mechanism is developed to explain the different emission
processes of these complexes with different ligands.