Dendrimers with a pentaphenylene core: a photophysical study.

Novel dendrimers G2PC and G4PC consisting of a p-pentaphenylene core (PC) appended in the para position with two second-generation (G2) or two fourth-generation (G4) sulfonimide branches and two n-octyl chains, as well as a model compound of the pentaphenylene core (G0PC), are prepared. The photophysical properties (absorption, emission, and excitation spectra; fluorescence decay lifetime; and fluorescence anisotropy spectra) of the three compounds are investigated under different experimental conditions (dichloromethane solution and solid state at 293 K, dichloromethane/methanol rigid matrix at 77 K). In the absorption spectra contributions from both the branches and the core can be clearly identified. The fluorescence spectra show only the characteristic fluorescence of the pentaphenylene unit with lambda(max) around 410 nm in fluid solution and 420 nm in the solid state. In solution the fluorescence quantum yields are 0.78, 0.76, and 0.72 for G0PC, G2PC, and G4PC, respectively, and the fluorescence lifetime is about 0.7 ns in all cases. Energy transfer from the chromophoric groups of the dendrimer branches to the core does not occur. The three compounds show the same, high steady-state anisotropy value (0.35) in dilute rigid-matrix solution at 77 K. In dichloromethane at 293 K, the increasing anisotropy values along the series G0PC (0.17), G2PC (0.27), and G4PC (0.32), with increasing molecular volume of the three compounds, show that depolarization takes place by molecular rotation. In the solid state the anisotropy is very low (0.015, 0.017, and 0.035 for G0PC, G2PC, and G4PC, respectively), probably because of fast depolarization via energy migration.

Persulfonylation of amines applied to the synthesis of higher generation dendrimers.

Systematic analysis of the persulfonylation of branched aromatic oligoamines with different arylsulfonyl chlorides allowed optimization of the repetitive steps involved in the synthesis of the sulfonimide-based dendrimers. The optimized procedures afforded the fourth generation N- and pentaphenylene-centered dendrimers with 16 and 32 peripheral groups, respectively. Analysis of products of incomplete substitution showed that the amino groups in aromatic oligoamines are persulfonylated consecutively.

A photophysical study of terphenyl core oligosulfonimide dendrimers exhibiting high steady-state anisotropy.

The photophysical properties of three dendrimers containing a p-terphenyl core with appended sulfonimide branches of different size and n-octyl chains have been investigated in dichloromethane solution. In the dendrimer absorption spectra contributions from both the branches and the core are clearly identified. The fluorescence spectra show only the characteristic fluorescence of the terphenyl unit. Energy transfer from the appended chromophoric groups to the core does not occur. In the dendrimers, the terphenyl core exhibits a very high fluorescence quantum yield (ca. 0.75) and a short emission lifetime (0.8 ns). These properties allowed investigations of the fluorescence depolarization caused by rotation of the dendrimers. The dendrimers show a very high steady-state anisotropy in dichloromethane solution at room temperature (0.24 for the largest one), compared to that of the parent terphenyl under the same experimental conditions (<0.01) and in rigid matrix (0.33). Both the n-octyl chains and the sulfonimide branches play important roles to slow down the molecular rotation.

Designer dendrimers: branched oligosulfonimides with controllable molecular architectures.

The synthesis of "designer" dendrimers and dendrons with sulfonimide units at every branching point is reported. The synthesis is based on a series of (regio)selective functionalization reactions of amines and sulfonamides allowing precise control of the dendrimers' shape, the number of branches in each generation, and their peripheral decoration with functional groups. In principle, structurally different branches can be incorporated at any position within the dendrimer structure at will. Structurally perfect symmetrical and two-faced "Janus"-type dendrimers, as well as dendrimers and dendrons with intended interstices were synthesized on a preparative scale and fully characterized. Oligosulfonimide dendrons of various generations bearing an aryl bromide functional group at their focal points were attached to a p-phenylene core with the aid of Suzuki cross-coupling reactions resulting in dendrimers with photoactive terphenyl cores. The structure and the high purity of all dendritic sulfonimides were confirmed by means of (1)H and (13)C NMR, electrospray ionization mass spectrometry (ESI-MS), and elemental analysis. The utility of MALDI-TOF mass spectrometry for the analytical characterization of these dendrimers was evaluated in comparison to electrospray ionization. Two model branched oligosulfonimides were characterized in the solid state by single-crystal X-ray analysis. Reaction selectivities and conformation of sulfonimide branching points were rationalized by DFT calculations.