Unsymmetrical Cruciforms

Abstract

Five new, unsymmetrical 1,4-distyryl-2,5-bisphenylethynylbenzenes (cruciforms, XF) have been prepared by a sequential Horner reaction of the bisphosphonate of 2,5-diiodo-1,4-xylene with two different aromatic aldehydes. The obtained diiodide was coupled to phenylacetylene under Sonogashira conditions with (Ph(3)P)(2)PdCl(2) as catalyst. The resulting XFs carry dibutylamino, pyridyl, cyano, and diphenylamino residues on their styryl arms to give rise to donor-, acceptor-, and donor-acceptor-substituted XFs. The optical properties of these XFs were investigated. Titration studies using trifluoroacetic acid tracked changes in the electronic structure of the XFs upon protonation. Donor XFs display a blue shift in absorption and emission upon protonation, while the pyridyl-substituted XF displays red shift in absorption and emission upon protonation. In the case of the donor-acceptor XF carrying a pyridyl and an aminostyryl arm, the first protonation occurs either on the pyridine or on the dibutylamino arm; a red shift is seen in absorption (for the former) and a blue shift is observed in emission (for the latter). The titration studies indicate that the protonated XFs do not display kinetic photoacidity when operating either in dichloromethane or acetonitrile solutions. The trends observed for protonation were mirrored when the XFs bind to metal cations. While the binding constants of the metal cations to the XFs were lower than for that for protons, as in some cases full metalation of the XF could not be obtained, the results were qualitatively the same. We did not find dynamic excited-state decomplexation events in the XFs that we have investigated. The XFs, stilbene derivatives, are different from other reported, similarly structured fluorophores as they show significant ratiometric changes in emission upon metal complexation; thus, distyrylbenzene-derived fluorophores may be, in the end, viable choices as platforms for metal ion detection.

Aldehyde Cruciforms: Dosimeters for Primary and Secondary Amines

“…Using a single aldehyde-functionalized cruciform in seven different solvents allowed us to discern fourteen different amines by digital photography and statistical evaluation of the response patterns extracted as red, green, blue (RGB) values. hyde 2 [16] in triethylamine as a nonreactive auxiliary base to give the targets 3 a-d as solid crystalline materials in yields that range from 35-75 % yield after chromatography and crystallization. Figure 1 displays the X-ray crystal structure of 3 a.…”

Water‐Soluble Distyrylbenzenes: One Core with Two Sensory Responses—Turn‐On and Ratiometric

“…We explored the DSBs as metal-binding compounds in polar organic solvents and in water (Figure 4). [23] Compounds 1 a-3 a and 4 all show a distinct response towards addition of Zn 2 + in acetonitrile. This response is qualitatively identical to that observed towards TFA.…”

Synthesis of a Library of Fluorescent 2‐Aryl‐3‐trifluoromethylnaphthofurans from Naphthols by Using a Sequential Pummerer‐Annulation/Cross‐Coupling Strategy and their Photophysical Properties

“…Nitrogen-containing naphthofurans exhibit acidochromism. [25] The addition of trifluoroacetic acid to a solution of 2NAP09 in CH 2 Cl 2 effected blue-shifts of the absorption and emission bands, as well as a decrease in the intensity of the absorption band (Figure 4 a). The protonation would prohibit the dimethylaminophenyl group from serving as an electron donor to reverse the original donor-acceptor relationship.…”