Spectroelectrochemical and Computational Analysis of a Series of Cycloaddition–Retroelectrocyclization-Derived Donor–Acceptor Chromophores

Abstract

The [2+2] cyclcoaddition (CA) and subsequent retroelectrocyclization (RE) reactions are useful in constructing nonplanar donor–acceptor chromophores that exhibit nonlinear optical properties and intramolecular charge-transfer transitions. However, both the infrared (IR) and visible–near IR (vis–NIR) spectroelectrochemical responses of CA-RE-derived chromophores are rarely explored in depth. Reported in this contribution is a comprehensive IR and vis–NIR spectroelectrochemical study of the CA-RE adducts of DMAP-C2n -NAPiPr of both tetracyanoethene (TCNE) and tetracyanoquinodimethane (TCNQ) and companion time-dependent density functional theory (TD-DFT) analysis of the bands observed. Specifically, DMAP-C2n -NAPiPr (1a, n = 1; 1b n = 2; DMAP = N,N-dimethylaniline; NAPiPr = N-isopropyl-1,8-naphthalimide) react with TCNE to yield the tetracyanobutadiene (TCBD) derivatives (2a and 2b, respectively) and with TCNQ to yield the dicyanoquinodimethane (DCNQ) derivatives (3a and 3b, respectively). IR spectroelectrochemical studies showed the emergence/intensification of new CN stretches upon reductions. Ultraviolet–vis–NIR (UV–vis–NIR) spectroelectrochemical study of 3 revealed a partial bleach of the charge-transfer (CT) bands, originally appearing in the neutral species, and the emergence of new CT bands originating from NAPiPr to the reduced DCNQ moiety. UV–vis–NIR spectroelectrochemical study of 2, surprisingly, indicated a very minimal change upon reductions. Dynamic changes were observed in the mid-IR absorption for CC and CN for both 2 and 3, indicative of enhanced asymmetry and the formation of ion pairs on the dicyano bridge. DFT and TD-DFT analyses were used to obtain the semi-quantitative pictures of the frontier orbitals of 1–3 and elucidate the origin of the transient features observed spectroelectrochemically for the 1e– and 2e– reduced species.

Synthesis and Characterization of Tetraphenylethene AIEgen-Based Push-Pull Chromophores for Photothermal Applications: Do the Cycloaddition – Retroelectrocyclization Click Reaction Could Make any Molecule Photothermally Active?

“…Generally speaking, it is interesting to note that almost all the CA-RE derivatives described in the literature to date have spectral characteristics extremely close to those described in this paper when the electron donating group is a dialkyl or a diphenyl aniline. [54,57,59,62,[69][70][71][72][73][74]76,[83][84][85][86][101][102][103][104][105][106][107][108][109][110][111][112] In all cases, the ICT bands are found in the same regions within a few nm. The CT band A is between 450 and 470 nm and the CT band B between 680 and 710 nm for TCNQ and between 830 and 860 nm for F4-TCNQ.…”

Electron transfer rate modulation with mid-IR in butadiyne-bridged donor–bridge–acceptor compounds

“…20 mM concentration. Full details of the synthesis, structure and electrochemistry of the D-C4-NAP compound can be found in ref. 43 and 44.…”

Dimethylaniline-Tetracyanobutadiene and Dimethylaniline-Extended-Tetracyanobutadiene Functionalized BODIPYs Witnessing Ultrafast Charge Transfer

“…36−38 The push− pull molecular systems based on tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded-TCBD (DCNQ) exhibit strong intramolecular charge transfer (ICT) revealing new optical transitions at higher wavelengths. 35,39,40 Consequently, the TCBD and DCNQ-carrying push−pull systems have emerged as potential candidates in optoelec- tronics. 41,42 Diederich, Michinobu, Shoji, Trolez, and Butenschon et al have explored the synthesis, photophysical, and redox properties of TCBD and DCNQ functionalized push− pull chromophores as redox-active ICT systems for optoelectronic applications.…”

“…The [2 + 2] cycloaddition-retroelectrocyclization is a catalyst-free reaction known for good reaction yields . In this reaction, the electron-rich alkynes react with the strong acceptors, tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ), resulting in the nonplanar push–pull molecules with low HOMO–LUMO gaps. − The push–pull molecular systems based on tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded-TCBD (DCNQ) exhibit strong intramolecular charge transfer (ICT) revealing new optical transitions at higher wavelengths. ,, Consequently, the TCBD and DCNQ-carrying push–pull systems have emerged as potential candidates in optoelectronics. , Diederich, Michinobu, Shoji, Trolez, and Butenschön et al have explored the synthesis, photophysical, and redox properties of TCBD and DCNQ functionalized push–pull chromophores as redox-active ICT systems for optoelectronic applications. − Recently, our groups reported the TCBD and DCNQ functionalized push–pull systems and explored their photophysical and redox properties for optoelectronic applications (Chart ). …”