Probing the in‐plane dipole moment vector between ground and excited state of single molecules by the Stark effect

Abstract

Single molecules, embedded inside a well‐defined insertion site of a single‐crystalline host matrix, are sensitive probes of electric field via the induced Stark shift on their lifetime‐limited electronic transition. Though the response of molecules to electric field has been shown to be relatively homogeneous, crystal symmetry allows for several, spectroscopically‐indistinguishable, orientations of the net permanent dipole moment between the ground and excited state ‐ the dipole vector – and this is problematic for measuring field orientation and magnitude. In this work, we measure for each terrylene molecule, embedded inside a new host matrix, the dipole vector independently by an electric field that we can rotate in the plane of the crystal. This single crystal host matrix, called [1]BenzoThieno[3,2‐b]BenzoThiophene, induces a moderate symmetry breaking of the embedded centrosymmetric terrylene molecule, and gives rise to a net dipole moment of 0.28 ± 0.09 Debye. Based on quantum chemistry calculations we propose an insertion site that best matches the experimental findings.