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 a-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 (C-60, C-70, 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 C-60 and C-70 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 C-60 or C-70 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 pi-system of BODIPY core, which correlates well with the experimental data.