Bis-, Tris-, and Tetrakis(squaraines) Linked by Stilbenoid Scaffolds

Abstract

Keywords: Conjugation / Donor-acceptor systems / Squaraines / UV/Vis spectroscopy The oligosquaraines 1−5, with stilbenoid scaffolds, were prepared by multistep syntheses in which the final steps consisted of condensation reactions between the semisquaric acid 21 and multiple resorcinols 12b−15b and 17b. The target compounds exhibit intense (ε Ͼ 250000 L·mol −1 ·cm −1 ) and sharp absorption bands with maxima between 687 to 778 nm, Results and DiscussionScheme 1 provides an overview of the two-, three-, and fourfold squaraines 1Ϫ5 described here, together with the model compound 6. The bis(squaraines) 1 and 2 have linear [a] 2757 depending on the conjugation in the stilbenoid scaffold. Comparison with the monosquaraine 6 as a model compound reveals intramolecular interactions between different donor−acceptor−donor moieties, which give rise to increased absorption intensities.

Synthesis of Tetrastilbenylmethanes by Wittig−Horner Reactions

“…In the context of the generation of a tetrakis(squaraine), we recently prepared the fourfold phosphonate 1, [2] which proved to be suitable for the synthesis of the tetrastilbenylmethanes 3aϪe (Scheme 1). The WittigϪHorner reactions of 1 and the aldehydes 2aϪe give the target compounds in good yields and with very high trans stereoselectivities.…”

“…A suspension of KOH (100 mg, 1.78 mmol) in DMF (20 mL) was warmed to 60°C in a flask, which was carefully flushed with Ar. 4-Hexyloxybenzaldehyde (2a) (1.12 g, 5.43 mmol) and diethyl 4-(tris-{4-[(diethoxyphosphoryl)methyl]phenyl}methyl)benzylphosphonate (1) [2] (1.0 g, 1.09 mmol) in DMF (20 mL) were added dropwise at 0°C to the suspension. After 24 h at room temperature, crushed ice (100 g) was added.…”

“…The preparation was performed according to the procedure described for 3a. Aldehyde 2c [13] and 1 [2] yielded 80% of 3c (1.33 g from 1.0 g 1) as colorless crystals, m.p. 90°C (CHCl 3 /C 2 H 5 OH).…”

“…ϭ 363 nm, ε ϭ 100348 cm 2 ·mmol Ϫ1 . 13 C NMR (CDCl 3 ): [12] Tetrakis{4-[2-(4-{2-[3,4,5-tris(hexyloxy)phenyl]vinyl}phenyl)vinyl]phenyl}methane (5a): The preparation was performed according to the procedure described for 3a, but the reaction time at room temperature was extended to 48 h. Aldehyde 4a [15] and 1 [2] yielded 45% of 5a (1.15 g from 1.0 g 1) as yellow crystals, m.p. 130°C…”

Twists and Turns Around a Square: The Many Faces of Squaraine Chemistry

“…[68][69][70] For example, the bisemisquaraine 24 can be easily converted into the bissquaraine 25 by the method shown in Scheme 7. 59 From the standpoint of optical properties, bis-squaraines show a broader absorption than do simple squaraines.…”