ИСТИНА

Weakly bound homo- and heterodimers of organic chromophores serve as building blocks for electron/energy transfer in biological structures, amorphous organic semiconductor films and solar cells. In these multi-chromophoric systems optical properties are governed by the distance and relative orientation of the photoactive units. The inherent rigidity of the environment confines the system conformational space and consequently controls their vibronic profiles. Using molecular dynamics sampling we computationally investigate the effect of a restricted conformational space on the absorption lineshape of a weakly bound rhodamine heterodimer tethered on a DNA scaffold. The absorption profiles are compared with experimental spectra and with the spectra computed for pi- stacking conformations of the bare dimers in solution. A substantial increase in the intensity of the initially low-intense S0-S1 transition of the bare dimers is explained by the local character of the excitation in the conformationally restricted supramolecular hetero dimer-DNA complexes. Explicit sampling of the relative orientations of monomers provides an absorption lineshape which is in good agreement with the experimental spectrum.