Synthesis and emission properties of 1,1,4,4-tetracyanobutadienes derived from ynamides bearing fluorophores

Abstract

A series of 1,1,4,4-tetracyanobutadienes (TCBD) bearing a large diversity of fluorophores was prepared following a multi-step synthesis. In a crucial last step, all compounds were obtained from the corresponding ynamides which were particularly suitable for the formation of the TCBDs in the presence of tetracyanoethylene via a [2+2] cycloaddition/retroelectrocyclization step (CA-RE). Fluorenyl derivatives including several variations on position 7 and 9, in addition to phenanthrenyl and terphenyl derivatives provided ynamide-based TCBD affording remarkable emission properties covering a large range of wavelengths. Those compounds emit both in solid state and in solution from the visible region to the NIR range, depending on the molecular structures. Quantum yields in cyclohexane reached unforeseen values for such derivatives, up to 7.8%. A huge sensitivity to the environment of the TCBDs has also been unraveled for most of the compounds since we observed a dramatic fall of the quantum yields when changing the solvent from cyclohexane to toluene, while they are almost non-emissive in dichloromethane.

Quadruple Functionalization of a Tetraphenylethylene Aromatic Scaffold with Ynamides or Tetracyanobutadienes: Synthesis and Optical Properties

“…[47][48][49][50] Therefore, the emission properties of compounds 4 and 13 where examined. While none of them showed a measurable luminescence in dichloromethane, which is in agreement with a previous study on TCBDs derived from ynamides [46] , the tetra-TCBD 4 exhibited a weak luminescence in toluene (quantum yield: 0.6 %). On the contrary, the mono-TCBD 13 did not show any emission in toluene at all.…”

“…TCBDs [43,44] have long been thought to be non‐emissive because of fast non‐radiative deactivation pathways [45] . However some groups, including ours, [20,21,46] recently showed that TCBDs could exhibit luminescence, depending on their nature and their environment [47–50] . Therefore, the emission properties of compounds 4 and 13 where examined.…”

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

“…Trolez et al investigated the photoluminescence properties of various fluorophore-containing TCBDs synthesized via reactions between ynamides and TCNE [139]. The study revealed that numerous fluorenyl derivatives and their phenanthrenyl and terphenyl counterparts exhibited noteworthy emission behavior in solid form and in solutions (Figure 6).…”

Enhancing Photophysical and Photosensitizing Properties of Nanoaggregates of Weakly Emissive Non-Planar Push-Pull Chromophore

“…However, largely, the synthesized 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs) have been found non-emissive/negligible due to radiation-less decay pathways mediated by photoinduced electron transfer (PET)/twisted intramolecular charge transfer (TICT) phenomena or charge separation [5][6][7][8]. Although emissive TCBD chromophores are rarely reported [9][10][11][12][13][14][15][16], their numerous applications continue to demand their synthesis.…”

“…To obtain emissive TCBDs, another approach was made by several groups, i.e., fluorophore conjugation with TCBDs, however, only a few reports have successfully shown luminescence behaviour for eg., Trolez and co-workers demonstrated that ynamide-TCBD with fluorophore achieved notable photoluminescence (PL) including NIR emission in an organic apolar solvent, i.e., cyclohexane with a remarkable quantum yield of 7.6% [12,15] and weak NIR emission in the solid-state due to AIE synthon of tetraphenyl ethene (TPE) [16]. Recently, similar TPE-based TCBD derivatives were demonstrated to exhibit photothermal effects [17].…”