Electronic Spectroscopy of Phthalocyanine and Porphyrin Derivatives in Superfluid Helium Nanodroplets.

Alkwin Slenczka

doi:10.3390/molecules22081244

Abstract

Phthalocyanine and porphyrin were among the first organic compounds investigated by means of electronic spectroscopy in superfluid helium nanodroplets. Superfluid helium nanodroplets serve as a very gentle host system for preparing cold and isolated molecules. The uniqueness of helium nanodroplets is with respect to the superfluid phase which warrants the vanishing viscosity and, thus, minimal perturbation of the dopant species at a temperature as low as 0.37 K. These are ideal conditions for the study of molecular spectra in order to analyze structures as well as dynamic processes. Besides the investigation of the dopant species itself, molecular spectroscopy in helium droplets provides information on the helium droplet and in particular on microsolvation. This article, as part of a special issue on phthalocyanines and porphyrins, reviews electronic spectroscopy of phthalocyanine and porphyrin compounds in superfluid helium nanodroplets. In addition to the wide variety of medical as well as technical and synthetical aspects, this article discusses electronic spectroscopy of phthalocyanines and porphyrins in helium droplets in order to learn about both the dopant and the helium environment.

Highlights

The physical properties of liquid helium, and in particular the superfluid phase, qualify as an ideal host system for preparing cold and isolated molecules [1,2,3,4,5,6]
When dissolved into liquid helium, molecules tend to coagulate among each other and stick to the walls of the helium dewar. These problems have been overcome by generating a beam of superfluid helium droplets inside a vacuum machine in which each carries a single particle of the species of interest [1,2,3]
Similar purpose, we have extended our experimental work by studying porphyrin derivatives and in addition some phthalocyanine derivatives [49]

Summary

Introduction

The physical properties of liquid helium, and in particular the superfluid phase, qualify as an ideal host system for preparing cold and isolated molecules [1,2,3,4,5,6]. An extensive investigation of electronic spectra of bare phthalocyanine in helium droplets will be presented, revealing both information on the dopant species as well as on the helium environment. Starting from this example, phthalocyanine derivatives and porphyrin derivatives are added to the discussion. Any molecular species embedded into a superfluid helium droplet is immediately (within ps) cooled down to a temperature of only 0.37 K This is fortunate if not mandatory in particular for the interpretation of electronic spectra of larger molecules such as phthalocyanine and porphyrin derivatives. We will cross-check the interpretations of the phthalocyanine spectra with data obtained for other phthalocyanine and porphyrin derivatives

Vibronic Frequencies

Line Shape Analysis

Findings

Summary