Abstract: This study employs density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods at the M06-2X/def2-TZVP level to systematically reveal, for the first time, the regulatory mechanism of N-1 substituents on the photophysical properties and photocycloaddition reactions of ethyl 1,4-dihydropyridine-3,5-dicarboxylate derivatives (1a-1h). The results demonstrate that the type of N-1 substituent significantly influences the molecular excitation characteristics. Electronic excitations are predominantly characterized by π→π * transitions within the 1,4-dihydropyridine ring. The excited-state charge distribution is highly overlapping and localized in the C=C double bond region of the ring, exhibiting typical localized excitation features. This promotes a nearly planar molecular conformation in the excited state, accompanied by significant bond length changes at key reactive sites, both of which facilitate the occurrence of photocycloaddition reactions. This work establishes, for the first time, a systematic theoretical correlation between the photophysical properties and photocycloaddition reactivity of 1,4-dihydropyridine derivatives, providing important theoretical insights and innovative guidance for designing efficient photochemical reaction systems and constructing polycyclic frameworks.

Key words: 1,4-Dihydropyridine derivatives, Photophysical properties, Density functional theory, Photocycloaddition