Design and synthesis of nonconjugated monodendrons with triarylamine repeating units

Light harvesting dendrimers

Tree-like dendrimers with decreasing number of chromophores from periphery to core is an attractive candidate for light-harvesting applications. Numerous dendritic designs with different kinds of light-collecting chromophores at periphery and an energy-sink at the core have been demonstrated with high energy transfer efficiency. These building blocks are now being developed for several applications such as light-emitting diodes, frequency converters and other photonic devices. This review outlines the efforts that are based on both conjugated and non-conjugated dendrimers.

Energy and Electron Transfer in Bifunctional Non-Conjugated Dendrimers

Nonconjugated dendrimers, which are capable of funneling energy from the periphery to the core followed by a charge-transfer process from the core to the periphery, have been synthesized. The energy and electron donors involve a diarylaminopyrene unit and are incorporated at the periphery of these dendrimers. The energy and electron acceptor is at the core of the dendrimer, which involves a chromophore based on a benzthiadiazole moiety. The backbone of the dendrimers is benzyl ether based. A direct electron-transfer quenching of the excited state of the periphery or a sequential energy transfer-electron-transfer pathway are the two limiting mechanisms of the observed photophysical properties. We find that the latter mechanism is prevalent in these dendrimers. The energy transfer occurs on a picosecond time scale, while the charge-transfer process occurs on a nanosecond time scale. The lifetime of the charge separated species was found to be in the range of microseconds. Energy transfer efficiencies ranging from 80% to 90% were determined using both steady-state and time-resolved measurements, while charge-transfer efficiencies ranging from 70% to 80% were deduced from fluorescence quenching of the core chromophore. The dependence of the energy and charge-transfer processes on dendrimer generation is analyzed in terms of the backfolding of the flexible benzyl ether backbone, which leads to a weaker dependence of the energy and charge-transfer efficiencies on dendrimer size than would be expected for a rigid system.

Synthesis of nonconjugated dendrons with a redox gradient

Macromolecules with built-in redox gradients are of much interest due to their potential in a variety of optoelectronic and energy-harvesting applications. In this paper, the design and synthesis of nonconjugated dendrons with redox gradients to guide the charge flow from the core to the periphery is described. The dendrons reported here are based on benzyl ether connectivities. The repeat units of the dendrons are based on triarylamines, and the periphery units of the dendrons are based on N,N,N',N'-tetraarylbenzidine units. The presence of a redox gradient after incorporation of these charge-transporting units into the dendrons is supported by cyclic voltammetric studies.