Spectral Properties of Indotricarbocyanine Dye during Self-Assembly of Its H *- and J -Aggregates
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Spectral Properties of Indotricarbocyanine Dye during Self-Assembly of Its H*- and J-Aggregates N. V. Belkoa, b, *, M. P. Samtsovb, and A. A. Lugovskib a Belarusian
b Sevchenko
State University, Minsk, 220030 Belarus Institute of Applied Physical Problems, Belarusian State University, Minsk, 220045 Belarus *e-mail: [email protected] Received March 12, 2020; revised March 12, 2020; accepted May 29, 2020
Abstract—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. Keywords: polymethine dyes, phosphate-buffered saline, self-assembly, J-aggregates, H*-aggregates, electronic spectra DOI: 10.1134/S0030400X20110053
INTRODUCTION Polymethine (cyanine) dyes have unique properties, owing to which they can be used as biological fluorescent labels [1–5], photosensitizers for photodynamic therapy [6–11], components of nonlinear media [12–14], spectral sensitizers [15, 16], and in other fields [17–20]. The tendency to form molecular aggregates in aqueous media is a feature of polymethine dyes [21]. The optical properties of polymethine dye aggregates [22–40] differ from the properties of monomers and make the former suitable for practical applications in nanophotonics [41–45], photovoltaics [46–48], nanoplasmonics [49–51], and other fields [32, 34, 40, 52–55]. There are two main types of molecular aggregates: H-aggregates and J-aggregates [15, 17, 32]. For H-aggregates, an absorption band that is hypsochromically shifted relative to the absorption maximum of monomers is typical [15, 56]. In most cases, aggregates of this type do not exhibit fluorescence [15, 56], though there are exceptions [57–59]. As a rule, the H-band is characterized by approximately the same value of the full width at half maximum (FWHM) of the absorption band as the spectrum of monomers [15,
32, 48]. Along with H-aggregates, some compounds form absorbing species, the spectrum of which has an addit
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