It also implies that the correlation between peak 1 and peak 3 mainly comes from the intra-monomer correlations. In addition, the DQ correlation peak at around 13.5 ppm (i.e., auto-correlation of pyridine) is much stronger than the DQ peak at around 3.4 ppm (i.e., auto-correlation of aliphatic protons) in PLVP-3, however, these two peaks have similar intensity in the blend. It is because the intra-chain interactions between two monomers in PLVP can lead to better dispersion of monomers and thus avoid the aggregation of aliphatic groups. The solid-state NMR results indicate that the copolymer, PLVP, possesses a stronger intra-chain interaction between lactones and pyridines compared with the blend of PMLA and P2VP homopolymers. As evidenced in Figure , no emission can be observed in PMLA/P2VP blend. It indicates that the effective intra-chain interactions of PLVPs are critical to the intrinsic PL in solution. In this case, a single polymer chain can play a role as an individual luminophore, rather than the clusters of certain groups. This is also the reason that strong emissions and high quantum yield can be obtained even in a dilute solution of PLVPs. Furthermore, theoretical calculations were carried out for PLVP based on a single polymer chain with four alternant units (Figure ). As a comparison, P2VP and PMLA homopolymers with four repeating units were also investigated (Figure ). It is found that the pyridine and lactone rings could have a small distance (3.227 Å) under certain conformation. Note that the C-C backbones of PMLA are atactic, and different local conformations are expected to coexist. The HOMO energy levels of PLVP-1~PLVP-5 are -5.86 eV, -5.94 eV, -5.94 eV, -5.95 eV and -5.87 eV, respectively, as measured by photoelectron spectrophotometer (Figure ). Based on the corresponding UV absorption band edge, the LUMO energy levels of PLVP-1~PLVP-5 are calculated as -2.38 eV, -2.48 eV, -2.48 eV, -2.37 eV and -2.29 eV, respectively. In addition, the HOMO energy levels of PLVP-3L and PLVP-3M are -5.85 eV and -5.77 eV, respectively, and the LUMO energy levels are -2.47 eV and -2.39 eV, respectively. To evaluate the dependence of PL intensity of PLVPs on chain rigidity, the Tgs of PLVPs with different MLA concentrations were examined by DSC. Figure shows the DSC heating curves of P2VP, PMLA, and PLVPs. The Tgs of P2VP PMLA are 107 and 235 ℃, respectively, which are consistent with the previous reports. All the PLVPs exhibit single Tg in their DSC profiles, indicating the random and homogeneous distribution of two monomers along the main chains. The Tgs of PLVP-2, PLVP-3, PLVP-4, and PLVP-5 are 97, 107, 140, and 178 ℃, respectively. The Tg of PLVP-1, the one with the highest concentration of MLA, was unable to be detected, since its Tg is above the degradation temperature (Figure ). Figure shows the PL spectra of PLVPs in DMF solution at the same concentration (1 mg/mL), and the emission intensity of PLVPs is varied with the monomer ratio. It is found that the maximum emission is obtained as the MLA/2VP ratio is 3:1 (Figure ). This is because the emission intensity is a "trade-off" between the chain rigidity and the concentration of luminophores. Namely, the low content of MLA will reduce the chain rigidity, and the low content of 2VP will give to a low concentration of luminophores. Similar results were also observed in some previous reports. In addition, it is found that PLVPs with different monomer ratios have almost the same quantum yield and fluorescence lifetime, but distinct fluorescence intensities in solution. This is because the absorbance of PLVPs is varied with the monomer ratios. According to the absorption spectra of PLVPs shown in Figure , the molar extinction coefficients of PLVP-1 to PLVP-5 are calculated as 4.2×10 3 , 5.8×10 3 , 4.5×10 3 , 1.4×10 3 , 1.0×10 3 cm 2 /mol, respectively. As a result, the fluorescence intensity of PLVP-2 is higher than the others due to its larger value of molar extinction coefficient.