Optical and Photophysical Properties of Light-Harvesting Phenylacetylene Monodendrons Based on Unsymmetrical Branching

The optical and photophysical properties of phenylacetylene dendritic macromolecules based on unsymmetrical branching are investigated using steady-state and time-dependent spectroscopy. Monodendrons, up to the fourth generation, are characterized with and without a fluorescent perylene trap at the core. The higher generation monodendrons without the perylene trap exhibit high molar extinction coefficients (>105 M-1 cm-1) and high fluorescence quantum yields (65−81%). When a perylene trap is placed at the core, then the monodendrons typically exhibit high energy transfer quantum yields (∼90%), as well as subpicosecond time scale excited-state dynamics, as evidenced by ultrafast pump−probe measurements. The photophysical properties of the unsymmetrical monodendrons are compared to those of phenylacetylene monodendrons with symmetrical branching, which have been described recently. The high fluorescence quantum yields and large energy transfer quantum efficiencies exhibited by the unsymmetrical monodendrons suggest they have potential for applications in molecular-based photonics devices.