The physical and chemical properties of PAMAM-AT dendrimers' interior were investigated using the fluorescent, solvatochromic probe phenol blue. In aqueous solutions of each generation studied except G0, two discrete dye populations were clearly observed. PAMAM-AT dendrimers were shown to form a tight, nonpolar association with the majority of available dye within the dendrimer interior, probably near its core. In the absorption and steady-state fluorescence emission spectra, a microenvironment of decreasing polarity in increasingly larger-generation PAMAM-AT dendrimers (up to G3) is seen for the associated probe. The remaining larger-generation dendrimers (G4−8) all provide a microenvironment of essentially equal polarity. Fluorescence anisotropy values for phenol blue in the PAMAM-AT dendrimers demonstrate the dye's sensitivity to the changing molecular volumes of the dendrimer generations. Model compounds that mimic PAMAM-AT's surface groups and branching moieties were used to better define the associated dye's location. The mimics further confirm that phenol blue is associated inside the dendrimer, where it does not interact with the dendrimer surface groups.

The physical and chemical properties of PPI dendrimers' interior were investigated using the fluorescent, solvatochromic probe phenol blue. In aqueous solutions of each generation studied, two discrete dye populations were clearly observed. PPI dendrimers were shown to form a tight, nonpolar association with the vast majority of available dye, within the dendrimer interior, near the core. In the steady-state fluorescence emission spectra, a microenvironment of decreasing polarity in increasingly larger-generation PPI dendrimers (up to G3) was seen for the associated probe. Each of the remaining larger-generation dendrimers provided a microenvironment of essentially equal polarity. Fluorescence anisotropy values for phenol blue in the PPI dendrimers demonstrated the dye's sensitivity to the changing molecular volumes of the dendrimer generations. Model compounds that mimicked PPI's surface groups and branching moieties were used to better define the associated dye's location. The mimics further confirmed that phenol blue was associated inside the dendrimer, where it did not interact with the dendrimer surface groups. The comparison of amine-terminated PPI and PAMAM dendrimers clearly demonstrated the effects of their structural differences and the ability of phenol blue to have sensed those differences, including the initiator core length, branching unit length, and branching unit chemical composition.