Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets

Abstract

Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broad (Δν > 100 cm(-1)) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time.

Anthracene–Argon Clusters Generated in Superfluid Helium Nanodroplets: New Aspects on Cluster Formation and Microsolvation

“…In order to solve the problem of microsolvation and to understand the influence of the helium droplet on its guest molecule, the spectral shapes of the ZPL and PW have to be deciphered. In addition to numerous such studies for various dopant species, which are most detailed for tetracene (TC) − and phthalocyanine (Pc), ,,,− systematic investigations of a series of derivatives of certain dopant species such as pyrromethene dyes, , porphyrine, ,, and anthracene ,,− have been reported. For some of these studies, the corresponding gas phase spectra were also measured for comparison.…”

“…It is commercially available, as such and in numerous derivatives with various substituents such as methyl, butyl, ethyl, propyl, phenyl, cyano, and chloro moieties. So far, we have reported on high resolution spectra in helium droplets of bare AN and of its derivatives 9,10-dichloro-AN, 9-chloro-AN, 9-cyano-AN, 9-phenyl-AN, 9-methyl-AN, 2-methyl-AN, and 1-methyl-AN. ,− The variation of the spectral shape of the helium-induced fine structure among these derivatives is surprisingly large. The low energy modes of the different substituents can be seen as well as their perturbation by the helium environment.…”

Electronic Spectroscopy in Superfluid Helium Droplets

“…Various derivatives of anthracene have been investigated by means of electronic spectroscopy in helium droplets. Among them are 9-phenylanthracene, 9-cyanoanthracene, 9-chloroanthracene, 9,10-dichloroanthracene, and three methylated derivatives, namely, 9-methylanthracene, 1-methylanthracene, and 2-methylanthracene [50,51,52,53]. For some of these derivatives corresponding gas phase data have been published [54][55][56][57][58][59][60][61][62][63].…”

“…Vertical lines mark the origin and two prominent vibronic transitions of non-substituted anthracene. Adapted from [50][51][52] electronic excitation. Remarkably, however, in helium droplets significant line broadening throughout the low energy progressions for 2-methylanthracene was observed.…”

“…Vertical lines mark the origin and two prominent vibronic transitions of non-substituted anthracene. Adapted from[50][51][52]…”