Aligned Inclusion of Dipolar Dyes into Zeolite Channels by Inclusion in the Excited State

Abstract

Unlike octadecyl-tethering hemicyanine (HC-18), nonyl-tethering hemicyanine (HC-9) entered the hydrophobic channels of silicalite-1 with a very small preference to the inclusion with the alkyl part first. Accordingly, while the degree of uniform orientation (DUO) of HC-18 in the channels was 0.67, that of HC-9 was only 0.08. This phenomenon was ascribed to the fact that HC-9 has a hydrophilic part at the center and two hydrophobic parts on both sides with almost equal hydrophobicities. Upon irradiation of the HC-9 dyes oriented parallel to the channel direction of silicalite-1 on the surface of the silicalite-1 film at 5 °C with a laser beam derived from an Ar+-ion laser (488 nm, 1.6 W), the DUO of the included HC-9 increased to 0.27. This phenomenon was attributed to the inclusion of HC-9 into the silicalite-1 channels in the excited-state in accordance with the phenomenon that the hydrophilic center shifts to the very end of the molecule (dimethyl amino group) in the excited state, giving rise to lengthening of the relatively hydrophobic region.