Fluorescent Self-Assembled Polyphenylene Dendrimer Nanofibers

Abstract

A second-generation polyphenylene dendrimer 1 self-assembles into nanofibers on various substrates such as HOPG, silicon, glass, and mica from different solvents. The investigation with noncontact atomic force microscopy (NCAFM) and scanning electron microscopy (SEM) shows that the morphology of the dendrimer nanofibers highly depends on substrate, solvent, and preparation method. Fluorescent nanofibers can be prepared from a polyphenylene dendrimer with chromophores either attached to the periphery of the dendrimer or incorporated in its core. Fluorescent nanofibers formed from polyphenylene dendrimer 4 with a perylenediimide core show isolated-chromophore emission due to the shielding of the rigid polyphenylene dendrons. Dendrimer 2 with one perylenemonoimide attached to its periphery self-assembles into fluorescent nanofibers, which exhibit a dimer like emission as a result of the interactions between peripheral chromophores. Dendrimer 3 with two perylenemonoimides at the rim does not form nanofibers by itself, but mixing of nonfluorescent dendrimer 1 with fluorescent dendrimers 2 or 3 leads to the formation of nanofibers with a homogeneous composition. Therefore, mixing can not only coassemble nonnanofiber-forming dendrimer 3 into nanofibers but also give rise to isolatedchromophore emission upon proper dilution.

Biomimetic materials for tissue engineering

“…Self-assembly has also been shown by molecules other than peptides or PAs [76]. For example, Liu et al reported the self-assembly of polyphenylene dendrimers into micrometer-long nano-fibers [77,78]. Perutz demonstrated the formation of nanotubes from polyglutamines [79][80][81].…”

The Chemistry of Organic Nanomaterials

“…[263,279,280] Dendrimers up to the fourth generation with biphenyl (for example, 106) or trans-azobenzene (for example, 89) cores have also been shown to give rise to such globular cluster or nanofibers. [281,282] The formation of nanofibers was found to be favored by lower dendrimer generations and more-separated dendrimer branches. The major driving forces for aggregation are p interactions between the dendrimers as a result of interdigitation of the branches.…”

“…Long fluorescent nanofibers have been obtained from such an assembly of the third-generation dendrimer analogue of 116 and the secondgeneration dendrimer 122 bearing one PMI unit. [282] The emission from 122 is red-shifted relative to that of the solution and indicates that aggregation of the chromophores is occurring. In contrast, the dendrimer 123 with two dye units (Scheme 31) does not form such nanofibers, only nanorods.…”

Organic Fluorescent Nanofibers and Sub-Micrometer Rods

“…When the fluorophore is embedded in the dendrimer core, the emission of the fiber is similar to that of the isolated chromophores, due to shielding effect. In contrast, when the fluorophore is attached to the surface of the dendrimer, it suffers interactions with other peripheral fluorophores (Liu et al, 2003).…”