Quantum mechanics helps with photosynthesis

First author Erika Keil and Prof. Jürgen Hauer in the lab.
Photo Credit: Andreas Heddergott / TUM

Scientific Frontline: Extended "At a Glance" Summary: Quantum Mechanics in Photosynthesis

The Core Concept: Photosynthesis relies on quantum mechanical processes to capture and transport solar energy with remarkable, nearly loss-free efficiency.

Key Distinction/Mechanism: Unlike classical models of energy transfer, light absorbed by a leaf causes electronic excitation energy to be distributed simultaneously over several states of each chlorophyll molecule—a phenomenon known as quantum superposition.

Major Frameworks/Components: 

• Superposition of Excited States: The foundational stage where absorbed light energy exists in multiple states across chlorophyll molecules simultaneously.
• Low-Energy Q Region: A specific segment of the spectrum (yellow to red) where chlorophyll absorbs light, featuring two distinct, quantum mechanically coupled electronic states.
• High-Energy B Region: The blue to green spectral range involved in light absorption.
• Thermal Relaxation ("Cooling"): The subsequent process where the molecular system relaxes by releasing excess energy as heat.

Branch of Science: Quantum Biology, Physical Chemistry, and Biophysics.

Future Application: Insights from this research can be applied to the engineering of artificial photosynthesis units, potentially creating systems that harness solar energy for electricity generation and photochemistry with unprecedented efficiency.

Why It Matters: By unravelling the billions-of-years-old biological mechanisms that make plant energy conversion perfectly efficient, scientists can overcome current engineering limitations and revolutionize sustainable solar technology.

Examination of a sample with plant chlorophyll obtained from frozen spinach.
Photo Credit: Andreas Heddergott / TUM

Photosynthesis - mainly carried out by plants - is based on a remarkably efficient energy conversion process. To generate chemical energy, sunlight must first be captured and transported further. This happens practically loss-free and extremely quickly. A new study by the Chair of Dynamic Spectroscopy at the Technical University of Munich (TUM) shows that quantum mechanical effects play a key role in this process. A team led by Erika Keil and Prof. Jürgen Hauer discovered this through measurements and simulations.

The efficient conversion of solar energy into storable forms of chemical energy is the dream of many engineers. Nature found a perfect solution to this problem billions of years ago. The new study shows that quantum mechanics is not just for physicists but also plays a key role in biology.

Photosynthetic organisms such as green plants use quantum mechanical processes to harness the energy of the sun, as Prof. Jürgen Hauer explains: “When light is absorbed in a leaf, for example, the electronic excitation energy is distributed over several states of each excited chlorophyll molecule; this is called a superposition of excited states. It is the first stage of an almost loss-free energy transfer within and between the molecules and makes the efficient onward transport of solar energy possible. Quantum mechanics is therefore central to understanding the first steps of energy transfer and charge separation.”

This process, which cannot be understood satisfactorily by classical physics alone, occurs constantly in green plants and other photosynthetic organisms, such as photosynthetic bacteria. However, the exact mechanisms have still not been fully elucidated. Hauer and first author Erika Keil see their study as an important new basis in the effort to clarify how chlorophyll, the pigment in leaf green, works. Applying these findings in the design of artificial photosynthesis units could help to utilize solar energy with unprecedented efficiency for electricity generation or photochemistry.

For the study, the researchers examined two specific sections of the spectrum in which chlorophyll absorbs light: the low-energy Q region (yellow to red spectral range) and the high-energy B region (blue to green). The Q region consists of two different electronic states that are quantum mechanically coupled. This coupling leads to loss-free energy transport in the molecule. The system then relaxes through “cooling”, i.e. by releasing energy in the form of heat. The study shows that quantum mechanical effects can have a decisive influence on biologically relevant processes.

Published in journal: Chemical Science

Title: Reassessing the role and lifetime of Qx in the energy transfer dynamics of chlorophyll a

Authors: Erika Keil, Ajeet Kumar, Lena Bäuml, Sebastian Reiter, Erling Thyrhaug, Simone Moser, Christopher D. P. Duffy, Regina de Vivie-Riedle, and Jürgen Hauer

Source/Credit: Technische Universität München

Reference Number: qs020425_01

Privacy Policy | Terms of Service | Contact Us