Microsolvation of phthalocyanine molecules in superfluid helium nanodroplets as revealed by the optical line shape at the electronic origin

TL;DR

This study examines how phthalocyanine molecules behave in superfluid helium droplets using optical spectroscopy, revealing non-monotonous solvent shifts and size-dependent substructures that challenge previous assumptions about their solvation dynamics.

Contribution

It provides new experimental insights into the solvent effects on phthalocyanine in helium droplets, contradicting prior monotonic shift expectations and highlighting complex size-dependent behaviors.

Findings

Solvent shift does not increase monotonously with droplet size.

A size-dependent substructure is observed in the spectra.

Behavior inconsistent with freely rotating Pc-helium complexes.

Abstract

We investigate the solvent shift of phthalocyanine (Pc) doped into superfluid helium droplets and probed by optical spectroscopy at the electronic origin. Our present work complements extant studies and provides results that in part contradict previous conclusions. In particular, the solvent shift does not increase monotonously with droplet radius all the way up to the bulk limit, but exhibits a turnaround instead. Moreover, a substructure is resolved, whose characteristics depend on the droplet size. This behavior can hardly be reconciled with that of a freely rotating Pc-helium complex.