Optical properties of porphycenes in the regime of strong light-matter coupling

Interaction of molecules with light can be modified by placing the molecules in an optical microcavity. When the interaction between the properly oriented transition dipole moment of a molecule and the cavity mode occurs at a... [ view full abstract ]

Interaction of molecules with light can be modified by placing the molecules in an optical microcavity. When the interaction between the properly oriented transition dipole moment of a molecule and the cavity mode occurs at a rate faster than any competing dissipation process, the so-called strong coupling of light and matter develops, which results in a formation of hybrid light-matter states (polaritons). These new states have interesting optical and electronic properties possessed neither by the original molecule or the optical mode.

Because of their large transition dipole moment organic dyes have been extensively used for the strong coupling experiments. However, an interesting family of molecules, yet to be studied under strong light-matter coupling regime, is porphycenes. They possess an intriguing property of undergoing ultrafast (fs-ps) tautomerization reaction. As a result of this process, the electronic transition dipole moments significantly change their orientation. This leads to a fascinating situation where the degree of the strong coupling regime in a molecule embedded in a microcavity may vary following the reorientation of the transition dipole moment.

In the experiment, parent and substituted porphycene molecules, either in a solution or in a polymer matrix, are placed in a tunable, Fabry-Pérot type optical microcavity comprising of two silver coated mirrors. The cavity is then tuned to be resonant with different electronic transitions of the molecule. We study the effect of the cavity on both the absorption and emission properties of porphycenes. The preliminary experiments are carried out to check whether porphycene molecules indeed enter the strong coupling regime with the optical cavity modes. We want to demonstrate that by tuning the optical cavity and therefore controlling the coupling strength between the molecules and cavity modes, one can control the tautomerization rate. Coupling-induced splitting of the energy levels likely causes the asymmetry in the double-well potential for the tautomerization reaction. We thus hypothesise that inducing asymmetry in the otherwise symmetric double-well potential will affect the tautomerization rate and, in extreme conditions, may even stop it.