In　this　article,　we　have　investigated　the　photochemical　reactions　of　4-aryl-4H-pyran　and　found　that　the　structural　symmetry　had　a　significant　influence　on　its　photochemical　behavior.　When　symmetric　4-aryl-4H-pyran　was　used,　such　as　diethyl　2,6-dimethyl-4-aryl-4H-pyran-3,5-dicarboxylate,　mainly　underwent　[2　+　2]　photocycloaddition　reaction.　While　asymmetric　4-aryl-4H-pyran,　such　as　2-amino-3-cyano-4-aryl-4H-pyrans,　mainly　underwent　photocleavage　reactions.　To　speculate　the　reaction　mechanism,　density　functional　theory　(DFT)　and　time-dependent　density　functional　theory　(TDDFT)　calculations　were　carried　out　at　the　B3LYP-D3/def2TZVP//B3LYP-D3/6-31G(d)　level.　The　results　showed　that　diethyl　2,6-dimethyl-4-aryl-4H-pyran-3,5-dicarboxylate　underwent　a　two-step　[2　+　2]　photocycloaddition　to　give　3,9-dioxatetraasterane　derivatives　via　an　intermolecular　and　an　intramolecular　reaction.　And　the　2-amino-3-cyano-4-aryl-4H-pyran　underwent　a　ring　cleavage　to　produce　the　conjugated　diene　de-rivatives.　To　explain　the　different　photochemical　behaviors　of　4-aryl-4H-pyrans,　electron　spin　density,　frontier　molecular　orbitals　(FMOs)　analysis,　electron-hole　analysis　and　root-mean-square-deviation　(RMSD)　analysis　were　performed.　(c)　2022　Elsevier　Ltd.　All　rights　reserved.