Abstract. Intramolecular photochemical reactions of thiophene analogues of o-distyrylbenzene, 2,2'-(o-phenylenedivinylene)dithiophenes (1a,b), 3,3'-(o-phenylenedivinylene)dithiophene (2a) and 3,3'-(o-phenylenedivinylene)dibenzothiophene (2b), were studied in acidic media at low concentrations. A 1,6-and 1,5-ring closure of hexatriene system leading to dihydronaphthalene or indene derivatives, respectively, was observed. (doi: 10.5562/cca2120)