Fully Conjugated Pyrene–BODIPY and Pyrene–BODIPY–Ferrocene Dyads and Triads: Synthesis, Characterization, and Selective Noncovalent Interactions with Nanocarbon Materials

Several pyrene–boron-dipyrromethene (BODIPY) and pyrene–BODIPY–ferrocene
derivatives with a fully conjugated pyrene fragment appended to the
α-position(s) of the BODIPY core have been prepared by Knoevenagel
condensation reaction and characterized by one-dimensional (1D) and
two-dimensional (2D) nuclear magnetic resonance (NMR), UV–vis,
fluorescence spectroscopy, high-resolution mass spectrometry as well
as X-ray crystallography. The redox properties of new donor–acceptor
BODIPY dyads and triads were studied by electrochemical (cyclic voltammetry
(CV) and differential pulse voltammetry (DPV)) and spectroelectrochemical
approaches. Formation of weakly bonded noncovalent complexes between
the new pyrene–BODIPYs and nanocarbon materials (C60, C70, single-walled carbon nanotube (SWCNT), and graphene)
was studied by UV–vis, steady-state fluorescent, and time-resolved
transient absorption spectroscopy. UV–vis and fluorescent spectroscopy
are indicative of the much stronger and selective interaction between
new dyes and (6,5)-SWCNT as well as graphene compared to that of C60 and C70 fullerenes. In agreement with these data,
transient absorption spectroscopy provided no evidence for any significant
change in excited-state lifetime or photoinduced charge transfer between
pyrene–BODIPYs and C60 or C70 fullerenes
when the pyrene–BODIPY chromophores were excited into the lowest-energy
singlet excited state. Density functional theory (DFT) and time-dependent
DFT (TDDFT) calculations suggest that the pyrene fragments are fully
conjugated into the π-system of BODIPY core, which correlates
well with the experimental data.