Effects of solvent environment on the spectroscopic properties of tylosin, an experimental and theoretical approach.

Tylosin is a commonly used antibiotic in animal medicine. However, it remains unclear how tylosin impacts the broader ecosystem once the host animal has excreted it. One of the main concerns is that it can lead to the development of antibiotic resistance. Therefore, there exists a need to develop systems that remove tylosin from the environment. Utilizing UV irradiation to destroy pathogens is one technique often deployed by scientists and engineers. However, for light-based techniques to be efficient, it is necessary to understand the spectral properties of the material being removed. Steady-state spectroscopy and density functional theory were used to analyze the electronic transitions of tylosin responsible for its strong absorbance in the mid-UV region. It was observed that the absorbance peak of tylosin stems from two transitions in the conjugated region of the molecule. Moreover, these transitions stem from an electronegative region of the molecule, which would allow them to be manipulated by changing solvent polarity. Finally, a polariton model has been proposed, which can be used to initiate the photodegradation of tylosin without the need for direct irradiation of the molecule with UV-B light.

Light Emission from Vibronic Polaritons in Coupled Metalloporphyrin-Multimode Cavity Systems.

In this study, we explore how one can use cavity polariton formation and a non-Condon vibronic coupling mechanism to form a type of hybrid light-matter state we denote as Herzberg-Teller (HT) vibronic polaritons. We use simple models to define the basic characteristics of these hybrid light-matter excitations including their dispersive energies. Experimentally, we find evidence of HT polaritons in the light emission spectra from copper(II) tetraphenylporphyrin (CuTPP) molecules strongly coupled to both single and multimode Fabry-Perot resonator structures. For specific resonator designs, we find evidence of significant enhancement of light emission from a short-lived sing-doublet state of CuTPP, which couples to a higher energy singlet state via a non-Condon vibronic mechanism. The results of a two-state model support the conclusion that this enhancement and the temperature-dependent dispersion of the light emission peak energy stem from radiative relaxation into cavity photon states dressed by collective vibrations of the molecules participating in polariton formation. These results show how researchers can leverage the complex interplay of electronic and nuclear degrees of freedom in light absorbing molecules to form a vaster array of coherent light-matter states and potentially transform platforms in optoelectronic and photocatalytic technologies.

Local molecular probes of ultrafast relaxation channels in strongly coupled metalloporphyrin-cavity systems.

The quantum control of ultrafast excited state dynamics remains an unachieved goal within the chemical physics community. In this study, we assess how strongly coupling to cavity photons affects the excited state dynamics of strongly coupled zinc (II) tetraphenyl porphyrin (ZnTPP) and copper (II) tetraphenyl porphyrin (CuTPP) molecules. By varying the concentration of each chromophore within different Fabry-Pérot (FP) structures, we control the collective vacuum Rabi splitting between the energies of cavity polariton states formed through the strong coupling of molecular electrons and cavity photons. Using ultrafast transient reflectivity and transmission measurements probing optical transitions of individual ZnTPP and CuTPP molecules, we find that the polaritonic states localize into uncoupled excited states of these chromophores through different mechanisms. For ZnTPP, we build a simple kinetic model including a direct channel of relaxation between the polaritonic states. We find that our models necessitate a small contribution from this interpolaritonic relaxation channel to explain both our steady-state and transient optical spectroscopic measurements adequately. In contrast, we propose that strong cavity coupling slows the internal conversion between electronic states of CuTPP not directly interacting with the photons of FP structures. These results suggest that researchers must consider the vibrational structure and excited state properties of the strongly coupled chromophores when attempting to use polariton formation as a tool to control the dynamics of molecules central to photo-sensitizing and light harvesting applications.

Quantum Control of Ultrafast Internal Conversion Using Nanoconfined Virtual Photons.

The rational control of nonradiative relaxation remains an unfulfilled goal of synthetic chemistry. In this study, we show how strongly coupling an ensemble of molecules to the virtual photons of an electromagnetic cavity provides a rational handle over ultrafast, nonradiative dynamics. Specifically, we control the concentration of zinc tetraphenyl porphyrin molecules within nanoscale Fabry-Perot cavity structures to show a variable collective vacuum Rabi splitting between cavity polaritons coincides with systematic changes in internal conversion rates. We find these changes deviate from the predictions of so-called gap laws. We also show that simple theories of structural changes caused by polariton formation cannot explain discrepancies between our results and established theoretical predictions. In light of these deficiencies, we explore other ways to explain the dependence of the internal conversion rate on polariton parameters. Our results demonstrate cavity polariton formation controls the photophysics of light harvesting and photocatalytic molecular moieties and the gap remaining in our fundamental understanding of mechanisms enabling this control.