RESUMEN

Light-driven changes in supramolecular interactions in perylene bisimides (PBIs) with pendant sulfur-containing functional groups at the bay position are demonstrated. In the ground state, a noncovalent S···X interaction between the σ-hole on sulfur and a heteroatom, X (X = O, N, S), of a neighboring molecule is the main driving force for intermolecular interactions, while in the excited state it is the π-π interaction between PBI scaffolds which drives assembly. The presence of heteroatoms in the solvent results in acceleration of the π-stacking process via the formation of a PBI-solvent complex. The excited-state dynamics involved in the assembly process were revealed via time-resolved fluorescence and transient absorption spectroscopies, while steady-state spectroscopy was used to evaluate the structure of the supramolecular assembly.

RESUMEN

It has been demonstrated that the direction and magnitude of transition dipole moments, and hence rates in the excitation energy hopping in the self-assembled porphyrin boxes can be tuned by insertion of ethynyl groups as well as the dielectric constant of solvent.

RESUMEN

The conformation of embedded molecule in a polymer matrix is sensitive to the local nano-environment that the molecule experiences. Particularly, single molecule spectroscopic methods have been utilized to visualize each molecular conformation in local sites of the polymer matrix by monitoring rotational diffusion and fluctuating fluorescence of the molecule. Here, we have performed single molecule spectroscopic experiments on a π-stacked perylenediimide (PDI) dimer and trimer, in which enhanced π-π interaction in π-stacked PDIs makes the fluorescence lifetime longer, embedded in two different polymers, namely poly(methyl methacrylate) (PMMA) and poly(butyl methacrylate) (PBMA), to reveal the conformational change depending on the polymer matrix. The fluorescence lifetimes of π-stacked PDIs are influenced by polymer surroundings because their molecular conformations are dependent on their interactions with the local environment in the polymer matrix. Furthermore, from an in-depth analysis of autocorrelation functions of fluorescence intensity trajectories, we could assign that the first autocorrelation value (lag 1) is larger as the intensity trace becomes more fluctuating. Thus, we expect that π-stacked PDIs, a model system for the formation of PDI excimer-like states, can be utilized to probe the surrounding nano-environment by monitoring the conformational change in real time.

RESUMEN

1,3-Phenylene-bridged perylenebisimide dimer (PBI2) and trimer (PBI3) were prepared along with monomer reference (PBI1) using perylene imide-anhydride 5 as a key precursor. 3,3-Dimethylbut-1-yl substituents were introduced at the 2,5-positions of perylenebisimide (PBI) to improve the solubilities of PBI oligomers. Actually, no serious aggregation of PBI2 and PBI3 was detected in their dilute CH(2)Cl(2) solutions. Under these conditions, intramolecular electronic interactions among PBI chromophores have been revealed by measuring the photophysical properties at their ensemble and single-molecule levels. The excitation energy transfer times of PBI2 (0.16 ps) and PBI3 (0.60 ps) were determined from the two different observables, anisotropy depolarization, and singlet-singlet annihilation, respectively, which are considered as the incoherent Förster-type energy hopping (EEH) times as compared with the EEH time constant (1.97 ps) calculated on the basis of the Förster mechanism. The relatively short EEH times compared to similar PBI oligomers can be attributed to 1,3-phenylene linker, which assures a short distance between the chromophores and, as a consequence, makes it hard to treat the PBI unit as a point dipole. The limitation of point-dipole approximation to describe the PBI oligomers and additional through-bond type interactions can be attributed as the causes of the discrepancies in excitation energy transfer times. Considering these photophysical properties, we can suggest that 1,3-phenylene-linked PBI oligomers have potentials as molecular photonic devices including the artificial light-harvesting system.

Asunto(s)

RESUMEN

Doubly and triply N-confused hexaphyrins revealed quite unique photophysical properties arising from confusion of pyrrole rings in the macrocycle, and the molecular shape when compared with their parent regular hexaphyrin molecules.