Superintermolecular orbitals in the C$_{60}$/pentacene complex

TL;DR

This paper discovers superintermolecular orbitals (SIMOs) in the C60/pentacene complex, which are highly delocalized, optically dark, and potentially crucial for charge generation in photovoltaics.

Contribution

It introduces the concept of SIMOs, a new type of delocalized orbital in C60/pentacene, characterized by their large spatial extension and weak Coulomb interactions.

Findings

SIMOs are highly delocalized over C60 and pentacene.

SIMOs are optically dark with weak Coulomb interactions.

SIMOs resemble superatomic orbitals in C60, with specific angular momentum characteristics.

Abstract

We report a group of unusually big molecular orbitals in the C60/pentacene complex. Our first-principles density functional calculation shows that these orbitals are very delocalized and cover both C60 and pentacene, which we call superintermolecular orbitals or SIMOs. Their spatial extension can reach 1 nm or larger. Optically, SIMOs are dark. Different from ordinary unoccupied molecular orbitals, SIMOs have a very weak Coulomb and exchange interaction. Their energy levels are very similar to the native superatomic molecular orbitals in C60, and can be approximately characterized by orbital angular momentum quantum numbers. They have a distinctive spatial preference. These features fit the key characters of charge-generation states that channel initially-bound electrons and holes into free charge carriers. Thus, our finding is important for C60/pentacene photovoltaics.