Regioselectivity in the photocycloaddition of 9-substituted anthracenes incorporated within nafion membranes

The photocycloaddition of five 9-substituted anthracenes [AnCH(2)N(+)(CH3)(3)Br- (1), AnCH(2)COO(-)Na(+) (2), AnCH(2)OH (3), AnCOCH(3) (4), and AnCH(3) (5), An = 9-anthryl] incorporated within Nafion membranes has been investigated. While irradiation of the above compounds in homogeneous solutions, and 5 in Nafion also, mainly gave rise to their head-to-tail (h-t) photocyclomers, photoirradiation of the samples of 1-4 incorporated within Nafion membranes almost exclusively resulted in the head-to-head (h-h) photocyclomers. Furthermore, the h-h photocyclomers are significantly more stable in Nafion membranes than in homogeneous solutions. These observations can be explained in terms of the preorientation of the substrate molecules in the inverse micellelike clusters of Nafion.