Get access

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

Authors

  • K. Senthil Kumar,

    1. Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036 (India), Fax: (+91) 44-2257-4202
    Search for more papers by this author
  • Prof. Archita Patnaik

    Corresponding author
    1. Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036 (India), Fax: (+91) 44-2257-4202
    • Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036 (India), Fax: (+91) 44-2257-4202
    Search for more papers by this author
    • Currently Fulbright–Nehru Visiting Research Professor at the Lawrence Berkeley National Laboratory, Berkeley, CA (USA).


Abstract

The tunable self-assembly of a fullerene (C60)–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 1×10−5M THF solution of DPNME at a mixed dielectric constant εmix≈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 εmix≈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 εmix=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.

Get access to the full text of this article

Ancillary