For carries separation, kinetic factors are another very important point. From the electron distribution diagram in
Fig. 4a, it can be seen that the introduction of the pyridine ring makes the electron cloud more concentrated on the C atom on the pyridine ring, which results in a potential difference in the melon chain with or without pyrimidine rings. Such distinct electron densities at different sites can induce the generation of built-in electric field between the melon chains with or without pyrimidine rings. According to the plane charge density calculated in
Fig. 4b, APMCN has a larger difference between positive and negative charge densities, which can roughly be assumed that APMCN has a larger built-in electric field intensity. Moreover, the built-in electric field intensity is positively depended on the zeta potential and the surface potential [
33,
34]. As shown in
Fig. 4c and Table S5 (Supporting information), the absolute value of APMCN zeta potential (−49.3 mV) is the largest than the rest of the samples (CN: −27 mV; CCN: −44.7 mV and MCCN: −44.0 mV). And according to the surface potential measured by atomic force microscopy with a Kelvin probe (
Fig. 4d), it can be seen that the surface potential of APMCN (Δ
E = 67.2 mV) is higher than that of CN (Δ
E = 38.9 mV) and MCCN (Δ
E = 42.5 mV). The corresponding potential curve is provided in Fig. S19 (Supporting information). Besides, molecular dipole moment is also an important factor affecting the strength of the built-in electric field [
14]. As shown in Fig. S20 (Supporting information), the dipole of APMCN is 13.46 Debye, which is much larger than that of MCCN (6.49 Debye) and CN (0.26 Debye). The larger molecular dipole of the D–A system ensures a large enough built-in electric field, which benefits the photoinduced carrier separation. As a result, the stronger built-in electric field of D–A catalyst APMCN significantly enhanced the carries separation and transportation. Furthermore, based the surface photovoltage intensity (Fig. S21 in Supporting information) [
35,
36], it can be quantificationally obtained that the internal electric field intensity of APMCN is 5.94 times as high as that of CN (
Fig. 4e) [
14,
37]. Beyond that, it is well known that the built-in electric field is closely related to the dissociation of exciton. The key factor of exciton dissociation is exciton binding energy (
Eb) [
38–
40]. As shown in Fig. S22 (Supporting information), the temperature-dependent photoluminescence was used to evaluate exciton dissociation behavior. The increased temperature promotes the dissociation of excitons, which means that there are more free carriers and a decrease in PL intensity. The
Eb of APMCN is the lowest of all samples, only 21.4 meV (CN: 32.2 meV, CCN: 24.4 meV, MCCN: 21.7 meV). This result indicates that excitons of APMCN accelerated dissociation due to the formation of giant built-in electric field. As a result, more free carriers are available to participate in redox reactions, thereby promoting photocatalytic hydrogen production.