Figure 2. A-F) PL spectra of 0.1 M PBLG and 0.1 M DBU in DMF at
different excitation wavelengths (λ ex) and
different mixing time; H) 1H NMR spectrum of PBLG-DBU
complex (molar ratio 1:1) in CDCl3 at the different
mixing time.
Besides polyamide, polyester of PES was also investigated upon
complexation with equimolar DBU through excitation-dependent and
time-dependent PL spectra. As shown in Figure 3A, PES exhibited a quite
weak emission around 440 nm when it was dissolved in DMF with cof 0.1 M. When equimolar DBU was added, the emission was intensified,
meanwhile, an obvious EDE effect was observed (Figure 3B). However,
unlike PBLG, the maximum CL wavelength redshifted to 470 nm under 380 nm
excitation at the initial mixing. After standing for 1 day, an extra CL
peak at 510 nm was observed, and its intensity increased with time going
to 2 days. Interestingly, after 1 day, two distinct peaks
(λ em = 450 nm and 510 nm) are
excitation-wavelength independent (Figure 3C-F). Moreover, with the
increase in standing time, the intensity ratio of 510 nm / 450 nm
increased and the complexation-induced emission became dominant. These
results indicated that the complexation between PES and DBU is stronger
than polyamide and the formed complexes are more stable. Time-dependent1H NMR spectra revealed downfield chemical shifts of
the protons 1,5, and 8 in DBU and upfield chemical shifts of the ester
group protons in PES as the mixing time increased, which further
supports the complexation between PES and DBU (Figure 3H, Figure S10).