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All transitions in the experimentally designated and numbered Q, B, and N bands (< 4.8 eV) of the electronic absorption spectrum of zinc phthalocyanine (ZnPc) are assigned on the basis of one-to-one agreement between calculated and experimentally observed transition energies and oscillator strengths. Each band in this range of the spectrum represents a ligand-based transition that originates from a combination of occupied orbitals and terminates in the lowest unoccupied molecular orbital (LUMO [ABSTRACT FROM AUTHOR]

The assignment of experimental optical absorption spectra of protonated anthracene has been under debate for years. It is complicated by the presence of rich vibronic spectral features and the possible co-occurrence of two isomers, 9H-An+ and 1H-An+. In this study, the vibrationally resolved absorption spectra of 9H-An+ and 1H-An+ have been calculated using time-dependent density functional theory. The calculated vibronic spectra profiles of 9H-An+ and 1H-An+ are in excellent agreement with the corresponding experimental results and provide unambiguously spectra assignments. It shows that the previously reported assignments based on vertical excitation energy are largely wrong. The onset located at 493.8 nm of the experimental spectrum can be assigned to the S 0 → S 1 transition of 9H-An+, while the origin band located at 453.5 nm corresponds to the S 0 → S 2 transition of 1H-An+. Unlabelled Image • The population of two two isomers 9H-An+ and 1H-An+ in hot source were discussed with Boltzmann distribution. • The calculated vibronic spectra of 9H-An+ and 1H-An+ are in good agreement with the experimental spectra. • The correct assignments for the vibronic spectra of 9H-An+ and 1H-An+ were given in this work. [ABSTRACT FROM AUTHOR]