Morphological Characterization of H Aggregates in Langmuir−Blodgett Films of Pyridinium−Dicyanomethanide Dyes

We investigated the aggregation of the pyridinium−dicyanomethanide dye 4-[5-(dicyanomethanido)thien-2-yl]-N-(n-hexadecyl)pyridinium (C16H33−PDCNT), in transferred films obtained with the Langmuir−Blodgett (LB) technique; this behavior is an example for the formation of H* aggregates, which show strongly blue-shifted and sharp electronic absorption bands. Surface pressure−area isotherms are reported at T = 291 K. LB films were investigated by UV−vis spectroscopy and optical and atomic force microscopy in order to obtain information about the molecular structure of the aggregates. The molecule strongly absorbs in the visible region because of a charge-transfer band; the sharp peak at 422 nm is attributed to the formation of H* aggregates.