doi:10.1038/nindia.2014.157 Published online 21 November 2014
Researchers have found that extremely short pulses of light can simultaneously induce ultrafast transfer of electrons and protons (i.e., hydrogen ions) in chemical reactions occurring inside a water-soluble nanosized molecular container1. Such light-induced ultrafast electron and proton transfer is potentially useful for carrying out photocatalysis in various industrially important chemical reactions, such as water oxidation for generating hydrogen gas.
Simultaneous transfer of electrons and protons frequently occurs in biological reactions in nature. One example of such a reaction is photosynthesis, which is powered by green plants harnessing energy from sunlight; many electrons and protons are transferred in the process of photosynthesis.
To better understand how the transfer of electrons and protons triggers such biological reactions and other chemical reactions, the researchers synthesized nanocages from palladium and triazine molecules. Acting as a host molecule, each nanocage trapped a guest organic molecule, an amine containing a phenyl group. The scientists then dipped this host–guest molecular system in water and exposed it to extremely short (40 femtoseconds) pulses of light.
Using an advanced analytical technique known as femtosecond broadband transient absorption spectroscopy, the researchers tracked how light induced electron and proton transfer in the host–guest molecular system in water. The short light pulses contained many energetic photons, which excited the host–guest molecular system, immediately transferring electrons from the guest molecule to the host molecule; this, in turn, spawned a radical cation. The host–guest molecular system reoriented itself after 890 femtoseconds, causing protons to hop from the guest molecule to the solvent water surrounding the nanocage.
“This highly efficient method will open up a new direction in visible-light-induced photocatalysis, especially for multi-electron catalysis of organic compounds and even water,” says lead researcher Jyotishman Dasgupta from the Tata Institute of Fundamental Research, Mumbai.
1. Gera, R. et al. Light-induced proton-coupled electron transfer inside a nanocage. J. Am. Chem. Soc. 136, 15909–15912 (2014)