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Cheng et al. Chem Synth 2023;3:13 https://dx.doi.org/10.20517/cs.2022.43 Page 7 of 13

Figure 5. Normalized emission spectra of 3-5 in degassed acetonitrile at 298 K.

conjugated polymers, the high-energy emissions are ascribed to the singlet [π→π*] excited state of the
polymer backbone, while the low-energy emissions of 3-5 are tentatively assigned to be originated from the
3
3 MMLCT excited states. To further validate the MMLCT origin of these low-energy emissions,
temperature-dependent emission studies have been performed [Supplementary Figures 16-18]. As a result,
3-5 exhibit a decrease in intensity of the low-energy emissions with significant blue shifts upon
increasing temperature.

On the other hand, distinctive thermo-responsive emission changes have also been observed for the
platinum(II)-containing conjugated polymers 3-5. Upon increasing the temperature of the solution of 3, the
high-energy emission from the polymer backbone is found to increase in intensity [Figure 6]. The reason
behind this can be attributed to the decrease in FRET efficiency from the polymer backbone to the
platinum(II) moieties. From the variable-temperature UV-vis absorption spectral traces of 3 [Figure 2],
there is a decrease in absorbance of the MMLCT band upon increasing temperature, leading to a decrease in
the spectral overlap and the enhanced recovery of the polymer fluorescence [Figure 6]. Moreover, 4 is found
to exhibit the largest recovery of the high-energy emission when compared to others upon increasing
temperature, as shown in Figure 7. Since 4 bears the least number of alkyl chains in each repeating unit, it is
believed that the energy would be less effectively dissipated through non-radiative decay pathways. As a
result, the FRET process dominates in 4, resulting in the greatest recovery of the polymer backbone
emission. Furthermore, both emission bands of 5 are found to be diminished with increasing temperature
[Figure 8], which can be attributed to the more dominating non-radiative process when compared to the
recovery of the fluorescence of the polymer backbone. The corresponding ratiometric emission intensity
plots of 3-5 have been depicted in Figure 9.

Due to the good spectral overlap between the absorption spectrum of the reference complex 2 and the
emission spectra of the conjugated polymers (PF-Br, PFP-Br and PFT-Br) [Figure 10], it is believed that the
intramolecular FRET process from the polymer backbone to the platinum(II) pendant would likely occur
upon photoexcitation. Although the emissions from the conjugated polymer backbones could still be
observed for 3-5, they are already effectively quenched when compared to their corresponding organic
-3
-4
polymers (Φ of PF-Br, PFP-Br and PFT-Br = 0.45-0.92; Φ of 3-5 = 8.4 × 10 -1.2 × 10 ). It is worth
lum
lum
noting that different extents of quenching efficiencies have been observed for 3-5. For example, the emission