Homoconjugated Push–Pull and Spiro Systems: Intramolecular Charge‐Transfer Interactions and Third‐Order Optical Nonlinearities

Abstract

Planar and non-planar push-pull chromophores (D-p-A), consisting of strong electron donors (D) and acceptors (A) connected by a p-conjugated spacer, feature intense intramolecular charge-transfer (CT) interactions [1, 2] and have recently received considerable attention as functional components in molecular electronics and nonlinear optics (NLO).[3] Transannular CT interactions between nonconjugated donors and acceptors in rigid molecular frameworks have also been extensively investigated. Through-space CT interactions in cyclophane derivatives, in which the donor and acceptor moieties are parallel to one another, were established by Staab and Rebafka [4] and Misumi and Otsubo, [5] and further explored by others.[6] When donor and acceptor are separated by appropriately aligned, rigid s-bond frameworks, long-range through-bond CT interactions were also observed in the UV/Vis spectra. [7] Only a few examples of transannular CT chromophores with a non-parallel arrangement, so-called homoconjugated push-pull systems, have been reported, [8][9][10][11] since Nakazawa and Murata published the first example of homoconjugated CT interactions in 9,10-dihydro-9,10-(1,2-tropylio)anthracene tetrafluoroborate in 1977. [8] In general, the reported homoconjugative CT interactions have been mostly restricted to bicyclic [2.2.2] p systems, and in particular triptycene derivatives.2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) is a popular strong oxidizing and dehydrogenating agent with many uses. [12, 13] We envisaged that thermal [2+2] cycloaddition between donor-activated electron-rich alkynes and the electron-deficient C=C double bonds in DDQ could take place to give new push-pull systems.[2b] Very recently, during the completion of the present study, Trofimov et al. indeed described [2+2] cycloadditions of DDQ with pyrrole-or indole-activated alkynes to give a variety of cycloadducts.[14]Herein, we describe a new class of homoconjugated push-pull chromophores (AE )-1 to (AE )-9 by [2+2] cycloaddition of N,Ndialkylanilino (DAA) and ferrocene (Fc)-substituted alkynes to DDQ. They feature surprisingly strong intramolecular CT interactions and, to the best of our knowledge, are the first homoconjugated push-pull chromophores with promising third-order nonlinear optical (NLO) properties. We also report the synthesis and characterization of spiro compound (AE )-10 by an electrocyclic ring-opening reaction of (AE )-1 followed by a transannular rearrangement.Good to excellent yields (63-94 %) of DAA-substituted chromophores (AE )-1 to (AE )-6 were obtained by [2+2] cycloaddition of DDQ with the acetylenic precursors 11 to 16 in 1,2-dichloroethane at 25 8C (Scheme 1). Analogously, the Fc-substituted chromophores (AE )-7 to (AE )-9 were formed in 62-90 % yield by reaction of DDQ with alkynes 17 to 19, respectively. The chromophoric products are deeply colored solids that are stable at ambient temperature in air. Thermal gravimetric analysis (TGA) did not show any significant weight loss (< 5 %) below 160 8C. However, upon heating...

Supramolecular dimeric structures of pyrazole-containing meso-oxo carbaphlorin analogues

“…Furthermore, during the synthetic attempt for the meso-aryl substituted analogues 11 containing a pyrazole unit, we found the unique tetrapyrrolic macrocycle 13 annulated with DDQ fragment. although the yield of this macrocycle is low under the present conditions, introduction of DDQ units into the intrinsic porphyrinoid skeleton renders the landscape for developing near Ir optical donor-acceptor materials (50).…”

The [2+2] Cycloaddition Reaction of Ethynylated 2H-Cyclohepta[b]furan-2-ones with 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone

“…2 These results show the DQQ-adducts have a potential as a new series of advanced organic materials.…”

“…They have also reported the unusual reactivities and properties of the DQQ-adducts, such as rearrangement of the carbon skeleton, 2,4 intramolecular charge-transfer absorption and third-order optical nonlinearities. 2 These results show the DQQ-adducts have a potential as a new series of advanced organic materials.…”

“…cycloaddition reaction of ethynyl substituted 2H-cyclohepta[b]furan-2-ones 1-9 with DDQ was examined according to the procedure described in the literature. 2,3 General experimental procedure was shown in the section of REFERENCE AND NOTES. 7 The yield of the products was summarized in Table 1.…”

Synthesis, Properties, and Crystal Structure of DDQ-Adducts of Ethynylated 2H-Cyclohepta[b]furan-2-ones

“…1 the adducts, such as carbon-skeleton rearrangement, 2,4 intramolecular charge-transfer absorption, third-order optical nonlinearities, 2 and so on. These results show the DQQ-adducts have a potential as a new series of advanced organic materials.…”