Molecule-Light Complex: Dynamics of Hybrid Molecule-Surface Plasmon States

Synthesis and characterization of novel porphyrin-cinnamic acid conjugates

A series of novel porphyrin-cinnamic acid (porphyrin/CA) conjugates (4a-4c) have been synthesized by condensation of 5-(4-Hydroxyphenyl)-10,15,20-triphenyl- porphyrin (1) with different substituted cinnamic acids (CAs) through an alkyl linker due to the biological activities of CAs and the application of porphyrins in photodynamic therapy (PDT) of cancer. Their related zinc (II) complexes (5a-5c) were also prepared. These novel compounds have been fully characterized by ¹H NMR, Infrared (IR), Mass spectra (Ms) and Elemental analysis. The photophysical properties of these target molecules were studied by absorption and Fluorescence spectroscopy. In solution, the effect of pH, ionic strength in acid media and concentration on the aggregation behaviors of 4a has also been investigated by UV-Vis spectra. The broadened and red shifted Soret band indicated the formation of J-aggregates when the pH value was up to 2.0 in THF-aqueous solution. Furthermore, the higher ionic strength of 0.3 M NaCl in acid media resulted in the generation of J-aggregates in THF-aqueous solution. And the significant blue shift of Soret band also demonstrated the formation of H-aggregates of 4a at 1.1 × 10^-4 M in THF.

Bio-inspired Photocatalytic Ruthenium Complexes: Synthesis, Optical Properties, and Solvatochromic Effect

We report the synthesis, characterization, and photo-physical properties of two new ruthenium^II -phenol-imidazole complexes. These bio-mimetic complexes have potential as photocatalysts for water splitting. Owing to their multiple phenol-imidazole groups, they have a higher probability of light-induced radical formation than existing complexes. The newly synthesized complexes show improved overlap with the solar spectrum compared to other ruthenium^II -phenol-imidazole complexes, and their measured lifetimes are suitable for light-induced radical formation. In addition, we conducted solvatochromic absorption measurements, which elegantly follow Marcus theory, and demonstrate the symmetry differences between the two complexes. The solvatochromic measurements further imply electron localization onto one of the ligands. The new complexes may find applications in photocatalysis, dye-sensitized solar cells, biomedicine, and sensing. Moreover, their multiple chelating units make them promising candidates for light-activated metal organic radical frameworks, i.e. metal-organic frameworks that contain organic radicals activated by light.

The role of Rabi splitting tuning in the dynamics of strongly coupled J-aggregates and surface plasmon polaritons in nanohole arrays

We have investigated the influence of Rabi splitting tuning on the dynamics of strongly coupled J-aggregate/surface plasmon polariton systems. In particular, the Rabi splitting was tuned by modifying the J-aggregate molecule concentration while a polaritonic system was provided by a nanostructure formed by holes array in a golden layer. From the periodic and concentration changes we have identified, through numerical and experimental steady-state analyses, the best geometrical configuration for maximizing Rabi splitting, which was then used for transient absorption measurements. It was found that in transient absorption spectra, under upper band excitation, two bleaching peaks appear when a nanostructured polaritonic pattern is used. Importantly, their reciprocal distance increases upon increase of J-aggregate concentration, a result confirmed by steady-state analysis. In a similar manner it was also found that the lifetime of the upper band is intimately related to the coupling strength. In particular, we argue that with strong coupling strength, i.e. high J-aggregate concentration, a short lifetime of the upper band has to be expected due to the suppression of the bottleneck effect. This result supports the idea that the dynamics of hybrid systems is profoundly dependent on Rabi splitting.

Thermodynamics of molecules strongly coupled to the vacuum field

The thermodynamics of strong coupling between molecules and the vacuum field is analyzed and the Gibbs free energy, the enthalpy, and entropy of the coupling process are determined for the first time. The thermodynamic parameters are a function of the Rabi splitting and the microscopic solvation. The results provide a new framework for understanding light-molecule strong coupling.

Strong light-molecule coupling on plasmonic arrays of different symmetry

The strong coupling of porphyrin J-aggregates to plasmonic nanostructures of different symmetry is investigated. The nanostructures of higher symmetry show the strongest interaction with the molecular layer, suggesting that surface plasmon mode degeneracy plays an important role in the coupling efficiency. At high coupling strengths a new, weakly dispersive mode appears which has recently been predicted theoretically to be due to long-range energy transfer between molecules mediated by surface plasmons. These findings point to new ways for optimizing strong coupling and thereby realize its full potential for molecular and material science.

Polariton dynamics under strong light-molecule coupling

We present a comprehensive experimental study of the photophysical properties of a molecule-cavity system under strong coupling conditions, using steady-state and femtosecond time-resolved emission and absorption techniques to selectively excite the lower and upper polaritons as well as the reservoir of uncoupled molecules. Our results demonstrate the complex decay routes in such hybrid systems and that, contrary to expectations, the lower polariton is intrinsically long-lived.