Donor-substituted octacyano[4]dendralenes: a new class of cyano-rich non-planar organic acceptors

Abstract

Double [2+2] cycloaddition/retro-electrocyclisation reactions between tetracyanoethene (TCNE) and various anilino-capped buta-1,3-diynes furnished a series of octacyano[4]dendralene derivatives featuring intense, low-energy intramolecular charge-transfer absorptions. These novel chromophores are strong electron acceptors and undergo facile one-electron reductions at potentials (-0.09 to -0.17 eV vs. Fc + /Fc, in CH 2 Cl 2 -0.1 M n Bu 4 NPF 6 ) lower than those reported for the benchmark organic acceptors, such as TCNE (-0.32 eV) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) (-0.25 eV). The electron-accepting power of one octacyano[4]dendralene, as expressed by the computed adiabatic electron affinity (EA), compares to that of the reference acceptor 2,3,5,6-tetrafluoro-7,7,8,8tetracyanoquinodimethane (F 4 -TCNQ) used as a p-type dopant in organic light-emitting diodes (OLEDs) and solar cells. Gas-phase density functional theory (DFT) calculations predict a stretchedout conformation as the global energy minimum for octacyano[4]dendralenes. In the solid state however, folded conformations were observed for two structures by X-ray analysis. Taking the solid state environment approximately into account calculations predict a energetical degeneracy between the stretched-out and folded conformation. Therefore conformational preference probably is a result of supramolecular dimer formation, mediated by two pairs of intermolecular, antiparallel dipolar CN/CN interactions.

Porphyrin Donor and Tunable Push–Pull Acceptor Conjugates—Experimental Investigation of Marcus Theory

“…We infer that stable radical species from non‐paired electrons exist centered on the F 4 ‐TCNQ‐based electron acceptors. We have previously shown that the push–pull chromophores with the strongest acceptors, such as those derived from F 4 ‐TCNQ, give EPR spectra in agreement with acceptor‐based radicals . Considering the fact that much sharper signals were observed for the porphyrin nuclei, the radical species is most likely confined to the electron acceptor rather than resulting from intramolecular single‐electron transfer.…”

Platinum(II) Acetylides in the Formal [2+2] Cycloaddition‐Retroelectrocyclization Reaction: Organodonor Versus Metal Activation

“…These findings were unambiguously confirmed by X‐ray crystallographic analysis and are in agreement with the expectation that the CA‐RE reaction occurs at the triple bond next to the strongest donor that is also the least sterically hindered activating group. No further addition products were observed even in the presence of excess of the alkene reagents, which reflects the deactivation of the remaining triple bonds by the newly introduced, strongly electron‐accepting tetracyanobutadiene and cyclohexadienyl‐expanded tetracyanobutadiene moieties, respectively, in the adducts 19…”

Donor–Acceptor (D–A)‐Substituted Polyyne Chromophores: Modulation of Their Optoelectronic Properties by Varying the Length of the Acetylene Spacer

“…Monoyne 3 a was prepared by Sonogashira cross‐coupling reaction of 4‐bromo‐ N,N ‐diisopropylaniline with terminal acetylene 4 in 58 % yield (see Scheme 2SI in the Supporting Information). Diyne 3 b and tetrayne 3 d were obtained by following well‐established synthetic protocols42, 43 by an oxidative homocoupling reaction of the corresponding terminal mono‐ and di‐acetylenes in 88 % and 45 % overall yield, respectively, based on 4 (see Scheme 3SI and 5SI in the Supporting Information). Triyne 3 c was prepared from 4 in 28 % yield over 4 steps; the last critical step included a Fritsch–Buttenberg–Wiechell (FBW) rearrangement44–47 of the corresponding symmetrical gem ‐dibromoolefin48 (see Scheme 4SI in the Supporting Information).…”

“…A further comparison between the UV/Vis spectra of these two series of chromophores revealed a small bathochromic shift of all ICT bands of 2 a – d with respect to those of 13 a , 1 and 13 c , d , accompanied by a small increase in intensity (see Figure 21SI in the Supporting Information). This effect should be ascribed to the stronger electron‐donating ability of the N , N ‐diisopropylanilino donor as compared to its dimethylanilino analogue 43…”