Electron impact excitation of the merocyanine molecule in the gas phase

Design and Photonics of Merocyanine Dyes

Merocyanines, thanks to their easily adjustable electronic structure, appear to be the most versatile and promising functional dyes. Their D-π-A framework offers ample opportunities for custom design through variations in both donor/acceptor end-groups and the π-conjugated polymethine chain, and leads to a broad range of practical properties, including noticeable solvatochromism, high polarizability/hyperpolarizabilities, and the ability to sensitize various physicochemical processes. Accordingly, merocyanines are applied and extensively studied in various fields, such as light-converting materials for optoelectronics, nonlinear optics, optical storage, solar cells, fluorescent probes, and antitumor agents in photodynamic therapy. This review encompasses both classical and novel more important publications on the structure-property relationships in merocyanines, with particular emphasis on the results by A.  I. Kiprianov and his followers in Institute of Organic Chemistry in Kyiv, Ukraine.

On-the-Fly Femtosecond Action Spectroscopy of Charged Cyanine Dyes: Electronic Structure versus Geometry

Understanding optical properties of molecular dyes is required to drive progress in molecular photonics. This requires a fundamental comprehension of the role of electronic structure, geometry, and interactions with the environment in order to guide molecular engineering strategies. In this context, we studied charged cyanine dye molecules in the gas phase with a controlled microenvironment to unravel the origin of the spectral tuning of this class of molecules. This was performed using a new approach combining femtosecond multiple-photon action spectroscopy of on-the-fly mass-selected molecular ions and high-level quantum calculations. While arguments based on molecular geometry are often used to design new polymethine dyes, we provide experimental evidence that electronic structure is of primary importance and hence the decisive criterion as suggested by recent theoretical investigations.