Formation of fluorescent H-aggregates of a cyanine dye in ultrathin film and its effect on energy transfer

In this communication we report the formation of fluorescent H-aggregates of a cyanine dye 3,3-Dioctadecyloxacarbocyanine perchlorate (Oxa18) in ultrathin film and its effect on energy transfer between Oxa18 and Sulphorhodamine B monosodium salt (sRhb). Surface pressure–area per molecule isotherm revealed that Oxa18 forms stable Langmuir monolayer at air-water interface. Spectroscopic investigation revealed that Oxa18 forms H-aggregate in Langmuir–Blodgett (LB) film which is enhanced in presence of nano clay laponite. Ideally H-aggregate do not fluoresce. However, due to imperfect stacking of Oxa18 molecules in the aggregates, fluorescence occurred from Oxa18 H-aggregates. This H-aggregated band has substantial effect on the enhancement of energy transfer from Oxa18 to sRhb both in solution and in ultrathin film.