To　investigate　the　wavelength-dependent　[2　+　2]　and　[3　+　2]　photocycloaddition　of　1,4-dihydropyridines　(1,4-DHPs),　the　combined　experimental　and　theoretical　studies　were　conducted　on　the　ethyl　1,4-diaryl-1,4-dihydropyridine-3-carboxylic　acid　under　different　wavelength　lights.　When　the　irradiation　wavelength　is　shorter　than　365　nm,　the　main　products　are　[2　+　2]　photocycloaddition　dimers　(3,9-diazatetraasteranes　and　3,6-diazatetraasteranes),　and　when　the　irradiation　wavelength　is　longer　than　395　nm,　the　main　products　are　[3　+　2]　photocycloaddition　dimers　(6,12-diazatetrakishomocubanes).　The　density　functional　theory　(DFT)　and　time-dependent　DFT　(TDDFT)　calculations　were　performed　to　gain　a　deeper　understanding　of　the　photocycloaddition　of　1,4-DHPs.　The　results　showed　that　both　the　[2　+　2]　and　[3　+　2]　photocycloadditions　are　two-step　mechanisms,　including　an　intermolecular　and　an　intramolecular　photocycloaddition,　and　the　chemoselectivity　is　mainly　caused　by　the　intramolecular　reaction.　The　intramolecular　[2　+　2]　photocycloaddition　was　proven　to　occur　in　a　short　wavelength　that　gives　the　higher　energy　to　overcome　the　reaction　energy　barriers.　The　intramolecular　[3　+　2]　photocycloaddition　was　proven　to　be　a　heat-induced　reaction,　which　can　occur　in　both　short　and　long　wavelengths.　Therefore,　depending　on　the　irradiation　wavelength,　the　dimers　of　[2　+　2]　and　[3　+　2]　photocycloaddition　can　be　selectively　obtained.　All　the　results　would　provide　a　theoretical　and　experimental　basis　for　the　synthesis　and　wide　applications　of　photocycloaddition　products　of　1,4-DHPs.　©　2024