Ground-State Dimers in Excimer-Forming Bichromophoric Molecules. NMR and Single-Photon-Counting Data: 2. Racemic and Meso Dipyrenylpentanes and Dipyrenylalkanes

Article abstract of DOI:10.1021/j100373a036

1H-NMR spectra of the racemic and meso diastereomers of 2,4-di(1-pyrenyl)pentane (1DPP) in toluene-d8 and of the 1,n-di(1-pyrenyl)alkanes (1Py(n)1Py with n = 0-10 and 13) and 1,n-di(2-pyrenyl)alkanes (2Py(n)2Py with n = 1-10 and 14) in chloroform-d were measured at room temperature.The conformer distribution in both 1DPP molecules was determined from an analysis of the vicinal coupling constants between the methylene and methine protons.In meso-1DPP, an intramolecular sandwichlike ground-state dimer was detected, whereas in rac-1DPPP a dimer only overlapping at the aromatic protons H9 and H10 is formed.The presence of both dimers was confirmed by the time-resolved fluorescence measurements (single-photon counting (SPC)).With the dipyrenylalkanes, an analysis of the chemical shifts of the aromatic protons shows that sandwich dimers are not present.Only in the case of 1Py(3)1Py is partial-overlap dimer detected.These findings are supported by results from SPC measurements.