Anisotropic observation of absorption and fluorescence transition dipoles in exciton–polariton properties of PIC J-aggregates

Abstract

Fibril-shaped J-aggregates of pseudoisocyanine dyes are prepared in thin-film matrices of polyvinyl sulfate and their microscopic fluorescence and reflectance imaging are investigated at room temperatures. Improved experiment, both in sample preparations and in microscope optics, allows us to resolve the higher-energy bands in the spectrum and to determine the directions of local absorption and fluorescence transition dipoles more precisely. Based on the anisotropies of the local transition dipoles, we have assigned the 540 nm middle band to be the upper exciton, Davidov split, transition and the higher 495 nm to its vibronic sub-band, while the J-band at 572 nm to be the lower Frenkel exciton transition. Assuming linear chain directions of individual J's to be parallel in average to the long axis of the fibril, the result also implies that a zigzag-type molecular conformation is most suitable for the model of PIC-J aggregates.