Highly Functionalized Dimeric Tetraethynylethenes and Expanded Radialenes: Strong Evidence for Macrocyclic Cross-Conjugation

• Published in: Chemistry : a European journal Vol. 7; no. 15; pp. 3263 - 3280
• Main Authors: Nielsen, Mogens Brøndsted, Schreiber, Martin, Baek, Yong Gu, Seiler, Paul, Lecomte, Steve, Boudon, Corinne, Tykwinski, Rik R., Gisselbrecht, Jean-Paul, Gramlich, Volker, Skinner, Philip J., Bosshard, Christian, Günter, Peter, Gross, Maurice, Diederich, François
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag GmbH 03.08.2001; WILEY‐VCH Verlag GmbH; Wiley
• Subjects: alkynes; Chemistry; Chemistry, Multidisciplinary; conjugation; electrochemistry; expanded radialenes; nonlinear optics; Physical Sciences; Science & Technology; OPENING METATHESIS POLYMERIZATION; STRUCTURE-PROPERTY RELATIONSHIPS; electrochemistry; alkynes; expanded radialenes; OPTICAL 3RD-HARMONIC GENERATION; RODS; conjugation; ALL-CARBON; EXCITED-STATES; nonlinear optics; LIQUID-CRYSTAL POLYMERS; CHROMOPHORES; CHARGE SEPARATION; ELECTRONIC CHARACTERISTICS
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/1521-3765(20010803)7:15<3263::AID-CHEM3263>3.0.CO;2-3

A selection of dimeric tetraethynylethenes (TEEs) and perethynylated expanded radialenes, containing different donor/acceptor substitution patterns, have been prepared and fully characterized. The first X‐ray crystal structure of an expanded [6]radialene, with twelve peripheral 3,5‐di(tert‐butyl)phenyl substituents, is presented. This macrocycle, the all‐carbon core of which is isomeric with fullerene C60, adopts a non‐planar, “chair‐like” conformation. Also a TEE dimer, carrying N,N‐dimethylaniline donor substituents, has been subjected to an X‐ray crystallographic analysis. The electronic properties were studied by UV/Vis spectroscopy and electrochemistry, providing fundamental insight into mechanisms of π‐electron delocalization in the acyclic and macrocyclic chromophores. Donor or donor–acceptor‐substituted dimeric TEE derivatives show very strong absorptions extending over the entire UV/Vis region; their longest wavelength absorption bands have high charge‐transfer character. Macrocyclic cross‐conjugation in the expanded radialenes becomes increasingly efficient with increasing donor–acceptor polarization. A dual, strongly solvent‐polarity‐dependent fluorescence was observed for a tetrakis(N,N‐dimethylaniline)‐substituted dimeric TEE; this interesting emission behavior is explained by the twisted intramolecular charge‐transfer (TICT) state model. Donor‐substituted expanded radialenes display huge resonance‐enhanced third‐order nonlinear optical coefficients. Expanded radialenes exhibit remarkable electronic properties owing to a considerable degree of macrocyclic cross‐conjugation. An expanded [6]radialene (see figure, middle, m = 3) with a central C60 core adopts a chair‐like conformation as depicted according to an X‐ray analysis.