Mysterious Blue Molecule Allows Light To Be Squeezed Out; How Does Azulene Help in Efficient Energy Management?

Scientists discovered a new type of blue molecule with a unique structure that allows it to absorb light in a way that can be useful for different applications.

Rule-Breaking Molecule

In the deciduous and coniferous forests in North America, East Asia, and Central America, a type of mushroom can easily catch someone's attention with its striking blue color. Known as Indigo Milk Cap (Lactarius indigo), this mushroom contains (7-isopropenyl-4-methylazulen-1-yl) methyl stearate derived from the azulene compound.

For many years, azulene has captured the interest of scientists, especially the reason why it is blue, even if there is no apparent reason for it. The tiny molecule was also found to violate Kasha's universal rule.

This rule explains the behavior of molecules in emitting light while moving into various excited states. Like in an ascending ladder, the first step refers to the first excited state of the molecule. This step is high, and each subsequent step is lower and closer to the previous one. The shorter the distance between the steps, the faster the molecule falls from the stage to lower levels. From here, the molecule waits longer in the first step before returning to the base level upon emitting light. Azulene, however, behaves differently.

Exploring the Unusual Behavior of Azulene

At the Institute of Organic Chemistry and Biochemistry (IOCB) in Prague, Czechia Republic, Dr. Tomás Slanina led a group of chemists in describing the causes of the behavior of azulene as a fundamental aromatic molecule. They believe that their study can influence the foundations of organic chemistry and help harness the potential of captured light energy.

To explain the behavior of azulene, the researchers conducted an experiment that used the concept of anti-aromaticity. It refers to an unstable substance with molecules that try to escape from the excited state as quickly as possible, trying to leave the higher energy state and decay. The researchers analyzed its ground- and excited-state anti-aromaticity in increasing order of complexity to understand the ways its electronic structure leads to its anti-Kasha behavior.

Azulene is unsatisfied in the first step of the ladder, which means it decays on the order of picoseconds without emitting light. In the second step, it behaves like a satisfied aromatic substance, existing in the excited state for a full nanosecond, which is enough to emit light. This means that the energy of this excited state is not lost anywhere but is completely converted into a high-energy photon.

With this research, Slanina considered responding to the current need to ensure that the captured photon energy from a source like the Sun is not lost and can be further used in various applications. Slanina and his team aim to create molecules that can manage light energy most efficiently.