Isolated Dimers Versus Solid‐State Dimers of N‐Heteropolycycles: Matrix‐Isolation Spectroscopy in Concert with Quantum Chemistry

In this work, matrix‐isolation spectroscopy and quantum‐chemical calculations are used together to analyse the structure and properties of weakly bound dimers of the two isomers benzo[a]acridine and benzo[c]acridine. Our measured experimental electronic absorbance spectra agree with simulated spectra calculated for the equilibrium structures of the dimers in gas‐phase, but in contrast, disagree with the simulated spectra calculated for the structures obtained by optimising the experimental solid‐state structures. This highlights the sensitivity of the electronic excitations with respect to the dimer structures. The comparison between the solid‐state and gas‐phase dimers shows how far the intermolecular interactions could change the geometric and electronic structure in a disordered bulk material or at device interfaces, imposing consequences for exciton and charge mobility and other material properties. Dimer contest: A combined matrix‐isolation spectroscopic and theoretical study provides unprecedented insight into isolated dimers of two constitutional benzoacridine isomers and the differences to dimeric structures in the crystalline solid state.