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Materials 2020, 13, 2646 9 of 24 The spectroscopic characterization of these squaraine cyanine dyes, to the best of our knowledge, is described and presented here for the first time (Section 2.1 and Figures S1–S15). Scheme 1. Synthetic routes of quinoline- and benzoselenazole-derived unsymmetrical squaraine cyanine dyes 9–12. Reaction conditions: (i) 1-iodohexane, acetonitrile, reflux (η = 85%); (ii) n-butanol, reflux (η = 63%); (iii) trimethylamine, ethanol, reflux (η = 63%); (iv) 1: sodium hydroxide aqueous solution (40%), 90 ◦C; 2: hydrochloric acid aqueous solution (2 M) (η = 75%); (v) 1-iodohexane, acetonitrile, reflux (η = 83%); (vi) n-butanol/pyridine (10% v/v), reflux (η = 33%); (vii) methyl trifluoromethanesulfonate, dry dichloromethane, nitrogen atmosphere, room temperature (r.t.) (η = 88%); (viii) 1: ammonia or methylamine solution (2 M), dry dichloromethane, nitrogen atmosphere, r.t.; 2: potassium iodide aqueous solution (14%), r.t. (η = 70% and 67%, respectively). 3.1.2. Nuclear Magnetic Resonance Particularities In Table 1, the most relevant NMR chemical shifts of dyes 9–12, the methynic protons and carbons signals are shown. For dyes 9, 10 and 11, the above-mentioned protons appear as two singlets of one proton each, at 6.00/5.77, 6.19/5.75 and 6.18/5.95 ppm, respectively. These two singlets that occur in the 1H NMR spectrum of each dye result from the fact that these specific dyes bear two different heterocycles and the chemical neighborhoods of each methynic proton, which are not precisely the same, cause two peaks with different chemical shifts. For the same reason, in the 13C NMR spectra of those dyes, two different peaks for methynic carbons appeared at 92.85/88.91, 92.84/89.13 and 93.89/89.15 ppm, respectively. In the 1H NMR of dye 12 (Figure S13), two extra singlets can be seen in that spectral area, namely at 6.15, 6.07, 5.94 and 5.85 ppm and also, in its 13C NMR spectrum (Figure S14), four signals appeared at 94.40, 93.99, 89.86 and 86.30 ppm. In addition to the protons and carbons of the methynic bridges, detailed here by way of example, all other protons and carbons of squaraine dye 12 are doubled in the NMR spectra. This signals’ duplication can be explained by the difficulty in the free rotation of thePDF Image | Photophysicochemical Light Antiproliferative vs cancer
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