The self-assembly features of the bis-pyrene methyl amide functionalized pyridine and benzene "tweezers" 1 and 2 were studied in organic solution and in the solid state. These systems were found to display remarkably different self-association features and optical properties, which was rationalized by control experiments using compounds bearing pyrenemethyl esters, alkyl groups, or a single pyrene substituent (3-6). As dilute solutions in chloroform, tweezers 1 displays both pyrene monomer and excimer emission features reflecting intramolecular contacts between the pyrene subunits. At higher concentrations in chloroform, as well as in the solid state, tweezers 1 self-assembles to form a linear supramolecular polymer. In contrast, tweezers 2 does not interact in an intermolecular fashion and photoexcitation produces emission features characteristic of a pyrene monomer. DFT (density functional theory) and TDDFT (time dependent density functional theory) calculations revealed that the lowest vertical transitions are forbidden and that S 1 of 1 is an emissive state. In contrast to 1 and 2, both pyrene-free control systems 5 and 6 were found to form linearly self-assembled supramolecular arrays in the solid state, albeit of differing structure. Upon exposure to trinitrobenzene (TNB), the self-assembled structures formed from 1 undergo deaggregation to form TNB complexes. This change is reflected in both an easily discernible color change and a quenching of the fluorescence emission intensity. Changes in the optical features were also seen in the case of 2. However, notable differences between these two ostensibly similar systems were seen.
ASJC Scopus subject areas
- Colloid and Surface Chemistry