Spectral properties of an indotricarbocyanine dye upon self-assembly of its $H^{*}$- and $J$-aggregates

Self-assembly of $H^{*}$- and $J$-aggregates of an indotricarbocyanine dye in phosphate buffered saline was investigated. At pH value of 7.0 the dye studied was shown to form non-luminescent $H^{*}$-aggregates with the absorption band peaked at 516 nm, its FWHM being 35 nm (1303 cm$^{-1}$), whereas, $J$-aggregates are absent. At pH value of 7.4 the $H^{*}$-aggregates are not formed, whereas, the $J$-aggregates are observed. The absorption band of the $J$-aggregates is peaked at 777 nm, its FWHM being 30 nm (497 cm$^{-1}$). Photoluminescence quantum yield of the $J$-aggregates does not exceed 10$^{-6}$. An increase in the solution temperature from 20 to 31$^\circ$C results in a 25-fold decrease in the self-assembly time of the $H^{*}$-aggregates. An increase in the solution temperature from 20 to 80$^\circ$C is followed by a reversible decay of both the $H^{*}$- and $J$-aggregates. The $H^{*}$-aggregate ($J$-aggregate) absorption band is reduced two-fold at the solution temperature of 37$^\circ$C (32$^\circ$C). Thansitions of the dye aggregates to high-lying electronic excited states were evidenced in the steady-state absorption in the spectral range between 400 and 480 nm.