Strong Charge‐Transfer Chromophores from [2+2] Cycloadditions of TCNE and TCNQ to Peripheral Donor‐Substituted Alkynes

Abstract

Peripheral donor‐substituted N,N‐dimethyl‐4‐[(7‐nitrobenzo[c][1,2,5]thiadiazol‐4‐yl)ethynyl]aniline (1a), 4‐(benzo[c][1,2,5]thiadiazol‐4‐ylethynyl)‐N,N‐dimethylaniline (1b), and 4,4′‐{benzo[c][1,2,5]thiadiazole‐4,7‐diylbis(ethyne‐2,1‐diyl)}bis(N,N‐dimethylaniline) (2) were prepared by Sonogashira cross‐coupling reactions. Compounds 1a, 1b, and 2 subsequently reacted with tetracyanoethylene (TCNE) or 7,7,8,8‐tetracyanoquinodimethane (TCNQ) to afford the charge‐transfer chromophores 3–8. X‐ray crystallographic analysis revealed the nonplanarity of these donor–acceptor (D–A) chromophores. Cyclic voltammetry (CV) exhibited a multistep reduction wave. UV/Vis spectra and theoretical calculations identified efficient intramolecular charge‐transfer interactions. Moreover, scanning electron microscopy (SEM) showed the morphology transition and reconstruction process of 5 from 0D hollow nanospheres to 1D tubular microstructures.

Ferrocene: An unrivaled electroactive building block for the design of push-pull dyes with near-infrared and infrared absorptions

“…Heterocyclic structures such as thiazoles, benzothiazoles and benzothiadiazoles are strong electron acceptors extensively studied in the literature for non-linear optical applications and organic photovoltaics [25][26][27][28][29][30][31][32][33]. When these acceptors are connected to electron donors by mean of a triple bond, their electron-withdrawing ability can be greatly improved by a [2 + 2] cycloaddition-retro-cyclization with tetracyanoethylene (TCNE).…”

Reversible mechanochromism in dipyridylamine-substituted unsymmetrical benzothiadiazoles

“…S19; ESI †). 9 There is a large red shi ($65 nm) in the low energy transition of BTD 3 compared to BTD 2, reecting strong electronic communication between dipyridylamine and BTD moiety. The BTDs 2 and 3 emit green and orange uorescence at the wavelength of $513 nm and $578 nm respectively.…”

Tuning the HOMO–LUMO gap of donor-substituted benzothiazoles

“…12d,17,18 The ICT band in BTs 5-8 exhibits red-shift, on increasing the solvent polarity indicating CT character (see ESI, Figure S19). 16 The presence of strong CT transition result in intense color solution of BTs 5-8 in dichloromethane (Figure 2). The optical energy gaps in donor-acceptor BTs were derived from the onset wavelength of UV/Vis absorption spectra in dichloromethane.…”

“…16 The reaction of TCNQ with BTs 3 and 4 were sluggish in nature. To overcome this barrier the reactions were carried out under the microwave irradiation.…”