Redox-Active PTM Radical Dendrimers as Promising Multifunctional Molecular Switches

Nowadays there is a great interest in using individual molecules as nanometer-scale switches and logic devices, with the aim of reaching higher power and smaller size. Demonstrating that one molecular switch can be turned on and off at room temperature simply by applying a current to a neighboring molecule has interesting implications. Herein, we report the synthesis, characterization, and behavior of three generations of polyphosphorhydrazone dendrimers, fully functionalized with 6, 12, and 24 redox-active perchlorotriphenylmethyl (PTM) radicals in the periphery, capable of undergoing an electrochemical reversible switching by multielectron reduction and oxidation. An electrical input was used to trigger the physical properties of these radical dendrimers in a reversible way, modifying their optical, magnetic, and electronic properties. Our Gn(PTM• )x radical dendrimers are paramagnetic, exhibit an absorbance band at 386 nm, and have a red fluorescence emission, if in the radical state. When they are switched to their anion state, these dendrimers convert to diamagnetic species with a maximum absorbance band at ca. 520 nm and no fluorescence emission. Due to two different molecular states, the switch undergoes a reversible and important color change, from light brown for G0(PTM• )6 and bright yellow for G1(PTM• )12 and G2(PTM• )24 dendrimers, when in the radical state, to either a deep wine color for G0(PTM−)6 or purple colors for G1(PTM−)12 and G2(PTM−)24 dendrimers, when in the anion state. Furthermore, there exists a viable opportunity to control the exact number of electrons transferred during the switching process, which could lead not only to a two-state but also to a multistate switch in the near future. This is the first molecular switch based on organic radical dendrimers, to our best knowledge. Moreover, these species can act as electron accumulative molecules able to accept and release up to 24 electrons per molecule at very accessible potentials and in a reversible way.This work was supported by DGICT-MINECO (MAT2016- 80826-R and CTQ2017-90596-REDT), AGAUR (2017 SGR 918), Intramural CSIC project (201760E080), and Severo Ochoa FUNMAT-FIP-2018. ICMAB acknowledges Spanish MINECO through the Severo Ochoa Centres of Excellence Programme Grant SEV- 2015-0496.Peer reviewe