Accurate Prediction of the Excited States in the Fully Conjugated Porphyrin Tapes across the Full Spectral Range: A Story of the Interplay between π-π* and Intramolecular Charge-Transfer Transitions in Soft Chromophores

The ability of density functional theory (DFT) and time-dependent DFT (TDDFT) methods for the accurate prediction of the energies and oscillator strengths of the excited states in a series of fully conjugated meso-meso beta-beta beta-beta triple-linked porphyrin oligomers (porphyrin tapes 2-12) was probed in the gas phase and solution using several exchange-correlation functionals. It was demonstrated that the use of the hybrid B3LYP functional provides a good compromise for the accurate prediction of the localized pi-pi* and intramolecular charge-transfer transitions, thus allowing confident interpretation of the UV-vis-NIR spectra of porphyrin oligomers. The TDDFT-based sumover-state (SOS) calculations for the porphyrin tape dimer 2 and trimer 3 as well as parent monomer 1 correctly predicted the signs and shapes of the magnetic circular dichroism (MCD) signals in the low-energy region of the spectra.

Automated summary

The study demonstrated that the hybrid B3LYP functional provides a good compromise for accurate prediction of localized pi-pi* and intramolecular charge-transfer transitions in fully conjugated porphyrin oligomers, allowing confident interpretation of UV-vis-NIR spectra. TDDFT-based sum-over-state calculations correctly predicted the signs and shapes of magnetic circular dichroism signals in the low-energy region of the spectra for porphyrin tape dimers and trimers, along with parent monomers.