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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. [ABSTRACT FROM AUTHOR]

N‐Heteropolycycles are among the most promising candidates for applications in organic devices. For this purpose, a profound understanding of the low‐energy electronic absorbance and emission characteristics is of crucial importance. Herein, we report high‐resolution absorbance and fluorescence spectra of pentacene (PEN) and 6,13‐diazapentacene (DAP) in solid neon obtained using the matrix‐isolation technique. Accompanying DFT calculations allow the assignment of specific vibrationally resolved signals to corresponding modes. Furthermore, we present for the first time evidence for the formation of van der Waals dimers of both substances. These dimers exhibit significantly different optical characteristics resulting from the change of electronic properties evoked by the incorporation of sp2 nitrogen into the molecular backbone. [ABSTRACT FROM AUTHOR]

N‐Heteropolycycles are attractive as materials in organic electronic devices. However, a detailed understanding of the low‐energy electronic excitation characteristics of these species is still lacking. In this work, the matrix isolation technique is applied to obtain high‐resolution absorbance spectra for a series of tetracene and core‐substituted N‐analogues. The experimental electronic excitation spectra obtained for matrix‐isolated molecules are then analysed with the help of quantum‐chemical calculations. Additional lower energy excitation bands in the spectrum of the core‐substituted N‐derivatives of tetracene could be explained in terms of intensity borrowing from dipole‐forbidden transitions due to Herzberg–Teller vibronic coupling. In the case of tetracene, evidence for the additional formation of London dimers (J aggregates) is found at higher tetracene concentrations in the matrix. [ABSTRACT FROM AUTHOR]