Photophysical properties of pyrene-functionalized poly(propylene imine) dendrimers

:Four generations of poly(propylene imine) dendrimers have been covalently modified with pyrene moieties and examined by fluorescence spectroscopy. Em ission and excitation spectra were obtained so that the generational depend ence of the dendrimers, especially the extent of steric crowding, could be correlated to the photophysical properties of pyrene. In particular, the ef fect of dendrimer concentration and generation on pyrene-pyrene interaction s was evaluated. More excimer emission was observed for higher generation d endrimers, while little or no evidence for interdendrimer interactions was observed over more than 2 orders of magnitude in dendrimer concentration. E xcitation spectra revealed the presence of preassociated pyrene moieties. P rotonation of the tertiary amine units was shown to increase monomer fluore scence significantly, while only slightly increasing the observed excimer f luorescence.