RESUMEN
The physics of aggregates of polar and polarizable donor-acceptor dyes is discussed, extending a previous model to account for the coupling of electronic and vibrational degrees of freedom. Fully exploiting translational symmetry, exact absorption and fluorescence spectra are calculated for aggregates with up to 6 molecules. A two-step procedure is presented: in the first step, a mean-field solution of the problem is proposed to define the excitonic basis via a rotation of the electronic basis. The rotation is also accompanied by a Lang-Firsov transformation of the vibrational basis. In the second step, the aggregate Hamiltonian, written on the exciton basis, is diagonalized towards exact results. The procedure leads to a reduction of the dimension of the problem, since, at least for weak coupling, only states with up to 3 excitons are needed to obtain reliable results. More interestingly, the mean-field solution represents the proper reference state to discuss excitonic and ultraexcitonic effects. The emerging picture demonstrates that the exciton model offers a reliable description of aggregates of polar and polarizable dyes in the weak coupling regime, while ultraexcitonic effects are important in the medium-strong coupling regimes, and particularly so for J-aggregates where ultraexcitonic effects show up most clearly with multistability and multiexciton generation.
RESUMEN
A multiscale approach to the dynamics of resonant energy transfer (RET) is presented, combining DFT and TD-DFT results on the energy donor (D) and acceptor (A) moieties with an extensive equilibrium and non-equilibrium molecular dynamics (MD) analysis of a bound D-A pair in solution to build a coarse-grained kinetic model. We demonstrate that a thorough MD study is needed to properly address RET: the enormous configuration space visited by the system cannot be reliably sampled accounting only for a few representative configurations. Moreover, the conformational motion of the RET pair, occurring in a similar time scale as the RET process itself, leads to a sizable increase of the overall process efficiency.
RESUMEN
Delivery of hydrophobic materials in biological systems, for example, contrast agents or drugs, is an obdurate challenge, severely restricting the use of materials with otherwise advantageous properties. The synthesis and characterization of a highly stable and water-soluble nanovesicle, referred to as a quatsome (QS, vesicle prepared from cholesterol and amphiphilic quaternary amines), that allowed the nanostructuration of a nonwater soluble fluorene-based probe are reported. Photophysical properties of fluorenyl-quatsome nanovesicles were investigated via ultraviolet-visible absorption and fluorescence spectroscopy in various solvents. Colloidal stability and morphology of the nanostructured fluorescent probes were studied via cryogenic transmission electronic microscopy, revealing a "patchy" quatsome vascular morphology. As an example of the utility of these fluorescent nanoprobes, examination of cellular distribution was evaluated in HCT 116 (an epithelial colorectal carcinoma cell line) and COS-7 (an African green monkey kidney cell line) cell lines, demonstrating the selective localization of C-QS and M-QS vesicles in lysosomes with high Pearson's colocalization coefficient, where C-QS and M-QS refer to quatsomes prepared with hexadecyltrimethylammonium bromide or tetradecyldimethylbenzylammonium chloride, respectively. Further experiments demonstrated their use in time-dependent lysosomal tracking.
