Novel Organic CT Salts of 1,3-Bis(dicyanomethylidene)indan Anion and Viologen Cations with Different Linear Alkyl Chain Lengths

Abstract

Viologens with linear alkyl chains from propyl to hexyl were synthesized to complete a series from methyl to octyl viologens, together with commercial samples, to study formation of their co-crystals with 1,3-bis(dicyanomethylidene)indan anion (TCNIH-). Co-crystals in a (viologen)(TCNIH)2 composition were obtained for all the viologens without inclusion of any other ions or solvent molecule. A border was clearly found between pentyl and hexyl for the evolution of charge transfer (CT) band in the absorption spectrum for electron transfer from TCNIH- donor to viologen acceptor. Strong coulombic interaction for close packing of co-crystals obviously contributes to the evolution of CT, although it is suppressed when the side chain is bulkier than hexyl to weaken the donor/acceptor interaction, as supported by drastic decrease of melting point and drastic increase of the largest crystal lattice spacing, found by DSC and PXRD, respectively. An exception was the salt with propyl viologen which did not show the CT band, in spite of the relatively strong donor/acceptor interaction.

π-Electronic ion pairs: building blocks for supramolecular nanoarchitectonics viaiπ–iπ interactions

“…39a). [88][89][90] The ion pairs of triphenyl(thio)pyryliums 67a,b + with tetracyanoallyl anion 65 À were synthesized by ion-pair metathesis of the ClO 4 À salts of the cations with Na + -65 À . 88a In CHCl 3 , 67a,b + -65 À exhibits CT bands at 570 and 595 nm, respectively (Fig.…”

Formation of charge-transfer complexes in ionic crystals composed of 1,3-bis(dicyanomethylidene)indan anion and viologens bearing alkyl chains

“…Good packing and substantial CT properties can be achieved by selecting a combination of molecules with symmetric shapes and similar molecular sizes. 14 In this study, new organic CT ion-pair crystals consisting of viologen dications with alkyl chains ranging from methyl to octyl (C1–C8) and CMI − were synthesised 15 and their optical properties were characterised. The correlation between the crystal structure and the optical properties of the organic ion pairs was elucidated.…”

Various Ionic Crystals from the Combination of 1,3-Bis(dicyanomethylidene)indan Anion and π-Electronic Cations

“…To stabilize the π-electronic anions, π-extended anions and anions having electron-withdrawing groups (e.g., Kuhn’s anion, , pentacyanocyclopentadienide, and pentamethoxycarbonyl-substituted cyclopentadienide − ) were developed. Bis­(dicyanomethylidene)­indan anion (CMI – ), prepared by the self-deprotonation of 1,3-bis­(dicyanomethylene)­indan (CMI), − is also a fairly stable π-extended anion. It has been studied as a small near-infrared (NIR) dye, which shows light absorption and fluorescence in the red to the NIR region.…”