  The study of supramolecular interactions and aggregation behaviour of
functional materials is of great importance to tune and extend their spectral
sensitivity and, hence, improve the optoelectronic response of related devices.
In this study, we resolve spatially and spectrally the absorption and emission
features of a squaraine aggregate by means of confocal microscopy and
absorption/photoluminescence spectroscopy. We observe that the aggregate
affords both a broad absorption spectrum (centred at 670 nm), likely originated
by a dyes configuration with allowed J- and H- arrangements, and a strong and
relatively narrow emission in the near-infrared (NIR) part of the spectrum
(centred at 780 nm), with a remarkable Stokes shift of 110 nm that is among the
largest exhibited by squaraine dyes. These peculiarities would be beneficial
for extending the spectral sensitivity of bot photovoltaic and light-emitting
diodes, and extremely appealing for possible applications of these aggregates
as NIR fluorescent probes in biomedical applications.
