Impact of spatial topology and nitrogen atoms embedding in π-conjugated chromophores on their UV–VIS and IR spectra

A comparative study of π-conjugated chromophores of interest in astrochemistry is carried out using density functional theory (DFT) and time-dependent DFT. The point of the study is the simultaneous systematic evaluation of both UV/Visible and IR spectra by using of the same B3LYP functional and the same basis set of polarized triple-zeta quality. The main attention is paid to the impact of spatial topology and the number of substituted nitrogen atoms in the simplest polycyclic aromatic hydrocarbons and their N-heteroaromatic analogues with one and two nitrogen atoms, e.g. anthracene – acridine – phenazine and phenanthrene – 7,8-benzoquinoline – 1,10-phenanthroline, on relative energies and radiative properties of their lowest singlet and triplet ππ∗ and nπ∗ states as well as wavenumbers and intensities of vibrational transitions in the mid-frequency IR region. The estimated eigenvalues of the lowest singlet nπ* state in nitrogen-substituted polycyclic aromatic hydrocarbons are a valuable contribution to data available in a literature since they are usually unobserved if they are located above the lowest singlet ππ* state.