Journal
ACS OMEGA
Volume 4, Issue 12, Pages 14669-14679Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsomega.9b00718
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Funding
- National Science Foundation [CBET-1517273, CHE-1726345, DMR-1609895]
- National Academy of Sciences of Ukraine [V/180, VC/188, V/201]
- Army Research Laboratory [W911NF-15-2-0090]
- Act 211 by the government of the Russian Federation [02.A03.21.0011]
- Russian Science Foundation [14-43-00052]
- National Research Nuclear University MEPhI
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The electronic properties of neutral 2,4-bis(4-bis(2-hydroxyethyl) amino-2-hydroxy-6-(2-(2-(2-methoxyethoxy)ethoxy)-ethoxy)phenyl)squaraine (1) and charged 2-((3-octadecylbenzothiazol-2(3H)-ylidene)methyl)-3-oxo-4-((3-(4-(pyridinium-1-yl)butyl)benzothiazol-3-ium-2-yOmethylene)cyclobut-I-enolate iodide (2) squaraine derivatives were analyzed based on comprehensive linear photophysical, photochemical, nonlinear optical studies (including two-photon absorption (2PA) and femtosecond transient absorption spectroscopy measurements), and quantum chemical calculations. The steady-state absorption, fluorescence, and excitation anisotropy spectra of these new squaraines revealed the values and mutual orientations of the main transition dipoles of 1 and 2 in solvents of different polarity, while their role in specific nonlinear optical properties was shown. The degenerate 2PA spectra of 1 and 2 exhibited similar shapes, with maximum cross sections of similar to 300-400 GM, which were determined by the open aperture Z-scan method over a broad spectral range. The nature of the time-resolved excited-state absorption spectra of 1 and 2 was analyzed using a femtosecond transient absorption pump-probe technique and the characteristic relaxation times of 4-S ps were revealed. Quantum chemical analyses of the electronic properties of 1 and 2 were performed using the ZINDO/S//DFT theory level, affording good agreement with experimental data. To demonstrate the potential of squaraines 1 and 2 as fluorescent probes for bioimaging, laser scanning fluorescence microscopy images of HeLa cells incubated with new squaraines were obtained.
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