Spectral Properties of Indotricarbocyanine Dye during Self-Assembly of Its H*- and J-Aggregates

The results of studying the self-assembly of H*- and J-aggregates of indotricarbocyanine dye in a phosphate-buffered saline are given. The formation of nonluminescent H*-aggregates with an absorption band at 516 nm and a full width at half maximum of 35 nm (1303 cm–1) is observed for the dye under study at pH 7.0, while J-aggregates are practically absent. At pH 7.4, H*-aggregates of the dye are not formed, but the self-assembly of J-aggregates with an absorption band at 777 nm and a full width at half maximum (FWHM) of 30 nm (497 cm–1) is observed; their photoluminescence quantum yield does not exceed 10–6. It was found that a change in the solution temperature from 20 to 31°C reduces the time of self-assembly of H*‑aggregates by a factor of 25. An increase in the solution temperature from 20 to 80°C leads to the decomposition of both H*- and J-aggregates; the temperature, at which the absorbance at the band maximum decreases by half, is 37°C for the bands of H*-aggregates and 32°C for the band of J-aggregates. It is shown that the absorption bands that appear in the spectral range of 400–480 nm are attributed to electronic transitions to high excited states of dye aggregates.