Synthesis and light absorption/emission properties of novel squarylium dimers bearing a ferrocene spacer

Abstract

The squarylium (SQ) dimer 1 bearing a ferrocene spacer was synthesized, and its electronic absorption and fluorescence properties were investigated. The dimer 1a, in which the ferrocene moiety and each SQ chromophore are separated by an ethylenoxycarbonyl liking unit, exhibited an electronic absorption band with a large half-bandwidth compared to an analogous monomeric SQ dye, indicating that the two squarylium chromophores in 1a electronically perturb each other. On the other hand, the dimer 1c, bearing the longer undecamethylenoxycarbonyl linking unit than 1a, did not exhibit any significant interaction between the SQ chromophores. Significant fluorescence quenching was observed in the dimer 1a as well as the ferrocene-SQ dyad 2a bearing the same linking unit as that in 1a, compared to 1c and the reference SQ dye 3. This result indicated that photoinduced electron transfer from the ferrocene moiety to the SQ chromophore occurs. In particular, the fluorescence emission of 1a was quenched more effectively than that of 2a, and thus, intramolecular chromophoric interaction in 1a facilitates ferrocene-SQ photoinduced electron transfer.