Solvent‐Polarity‐Tunable Dimeric Association of a Fullerene (C₆₀)–N,N‐Dimethylaminoazobenzene Dyad: Modulated Electronic Coupling of the Azo Chromophore with a Substituted 3D Fullerene

Abstract

The tunable self-assembly of a fullerene (C(60))-N,N-dimethylaminoazobenzene (DPNME) molecular system as a function of solvent polarity in THF/water binary solvent is reported. Gradual increase of the volume fraction of the nonsolvent water in a 1×10(-5) M THF solution of DPNME at a mixed dielectric constant ε(mix)≈42 resulted in initial redshifting of the (1)(π→π(*)) absorption band, which signified the 1D head-to-tail or J-type arrangement of the DPNME molecular system. Further increase in the solvent polarity to ε(mix)≈66 evidenced formation of an antiparallel head-to-tail or H-type molecular arrangement in conjunction with the J-aggregates, thereby establishing a solvent-polarity-dependent dynamic equilibrium between the monomer ↔ J-aggregate ↔ H-aggregate. The controlled aggregation was governed by the synergetic effect of intermolecular donor-acceptor interaction between the electron-deficient fullerene ring and the electron-rich N,N-dimethylamino-substituted aromatic ring; typically, van der Waals and π-π interactions between the molecules constituting a pair of dimers were envisaged. An agreement between the semiempirically calculated drastically reduced oscillator strength of the DPNME H-dimer in the antiparallel configuration (0.69 vs. 1.29 in the monomeric DPNME) and the experimental electronic absorption spectra beyond ε(mix)=66 further strengthened this assignment to the hitherto forbidden antiparallel H-dimer. Complementing the above, the periodicity of molecular self-assembly dictated a monoclinic unit cell in the single-crystal XRD packing pattern with a C2/c space group; the molecules packed laterally with mutual interdigitation with the donor (E)-N,N-dimethyl-4-(p-tolyldiazenyl)aniline (AZNME) parts in an antiparallel fashion (contrary to the usual expectation for H-aggregates) with strong inter- and intrapair van der Waals and π-π interactions between the constituent fullerene moieties. Unlike those of porphyrin/phthalocyanine bowl-like donor-initiated architectures, a rare class of DPNME dyadic supramolecular self-assemblies was realized with π-extended 2D fullerene networks, in which the linear geometry of the AZNME donor and the conformational rigidity of the fullerene acceptor played crucial roles.

Synthesis, characterization and optical properties of novel dendronized azo-dyes containing a fullerene C60 unit and well-defined oligo(ethylene glycol) segments

“…Six different fullerene C 60 -azobenzene derivatives (15, 16, 17, 18, 19 and 20) were successfully synthesized and fully characterized by 1 H, 13 C NMR and MALDI-TOF. The optical properties of the fullerene C 60 -azobenzene dyes were studied by UV-vis spectroscopy and compared to those of their precursor malonic azodyes without fullerene (9, 10, 11, 12, 13 and 14).…”

“…On the other hand, in the aromatic region of the 13 ) at 71.40 and 52.15 ppm, respectively. The structure and purity of these compounds were conrmed by MALDI-TOF mass spectrometry.…”

“…4b, Table 1). On the other hand, malonic azo-dyes bearing NO 2 as acceptor group (13,14) exhibited a maximum absorption band at l max ¼ 478 nm in MeOH solution, showing slight shis of 10 and 6 nm in CHCl 3 and DMF solution, respectively (Table 1).…”

“…Yield: 65%. 1 (13). Procedure described for the synthesis of 9, using 7 (0.208 g, 0.5 mmol), DMAP (0.009 g, 0.8 mmol), 2 (0.352 g, 0.6 mmol) and DCC (0.129 g, 0.62 mmol) to give compound 13 (Scheme 1e).…”

A series of novel indium complexes derived from aromatic carboxylic acids: Hydrothermal syntheses, crystal structures, supramolecular networks and fluorescent properties

“…S25). The observed red-shift (118 nm) phenomenon might be attributed to the presence of a high polarized excited state [13]. Although CH 3 OH possesses a similar polarity to CH 3 CN, the fluorescence spectrum is red shift ca.…”