CHIRAL LUMINESCENT MATERIALS

Chirality is a fascinating phenomenon in nature, and it could be observed in natural objects like galaxies, seashells, human DNA, amino acids etc.(Fig 1) Chiral molecules are associated with a particular puzzle that they appeared to be identical chemically and physically, except that one form rotated the plane polarized light to right and another to the left.[1] Researchers all over the world are engaged in understanding physical, chemical and biological properties of chiral molecules. As a result of these investigations optical activity of molecules has found large applications in biological areas such as chemical biology and drug discovery. However, there are not many other areas of scientific development that have considered chirality for any serious applications. Most of the techniques used in the investigation of chiroptical properties have focused on the relaxed electronic ground state of chiral molecules.

Our proposal aims at the utilization of chiral materials in advanced technological applications. We design systems in which chiral emission can be employed as a powerful tool to replace the conventional luminescent materials for better performance and efficiency. We intend to utilize the advantages of the circularly polarized luminescence (CPL) in the field of anti-counterfeiting technology. CPL spectroscopy is the fluorescence analogue of CD (circular dichroism) (Fig 2) where the latter measures the differential absorption of right- and left- circularly polarized light by chiral systems and former deals with the differential emission of right- and left- circularly polarized light by chiral luminescent systems.[2] A convenient measure for the CPL signals is the luminescence dissymmetry factor glum(λ), given by the following formula:
glum(λ) = 2(IL − IR)/(IL + IR)
where, IL → intensity of the left-circularly polarized component of the emitted lightIR → intensity of the right-circularly polarized component of the emitted light

Materials that exhibit circularly polarized luminescence are being actively investigated in applications such as liquid crystal display backlights, 3D displays, holographic displays, light sources for controlling plant growth, and security systems for optical communications and printing. It is therefore important to identify molecules that emit one-handed circularly polarized light with high quantum yield. CPL spectra contain important information such as the stable structure of excited molecules, and the behavior of these molecules in chemical reactions that involve an intermediate excited state. However, fluorescence emission is generally weak and CPL signals are even weaker, making it difficult to detect.[3]
Various classes of molecules including chiral lanthanide complexes, polymers, higher-order assembly- induced chirality, liquid crystals, and small organic molecules (SOMs) have been exploited for different chiroptical applications. Among these lanthanide complexes found to have very high glum, [4] however, low ϕF, rarity and toxicity of metals makes them unsuitable for practical applications. Even though glum values attained are very low, the higher luminescence quantum yield and the tunability in emission make the organic systems superior to others in terms of practical applications.
Our research aims at the utilization of chiral materials in advanced technological applications. We design systems in which chiral emission can be employed as a powerful tool to replace the conventional luminescent materials for better performance and efficiency. We intend to utilize the advantages of the circularly polarized luminescence (CPL) in serious fields like anti-counterfeiting technology. For authentication purposes a very high glum value is not a requirement. Chiral luminescence, due to its specific phase, coherence and polarization can provide additional level of security that will help safeguard most of our valuable documents. It is therefore very important to identify molecules that emit one-handed circularly polarized light, which can be utilized as difficult-to-replicate security tags.

Jusaina
Eyyathiyil

Jusaina
Eyyathiyil

CHIRAL LUMINESCENT MATERIALS

Jusaina Eyyathiyil

CHIRAL LUMINESCENT MATERIALS

Jusaina
Eyyathiyil