Protonation-induced modulation of one- and two-photon absorption properties for quadripolar dyes

The time-dependent hybrid density functional theory (TD-DFT) in combination with analytical response theory is used to explore the one-photon absorption (OPA) and emission as well as two-photon absorption (TPA) properties of quadripolar compounds with hydroxyl, amino or pyridyl end groups upon (de)protonation process. Both their one-photon absorption and emission as well as two-photon absorption properties show obvious changes upon passing from their neutral to their doubly (de)protonated state. The intramolecular charge-transfer (ICT) analysis demonstrates the variation of the electronic properties of the terminal groups by the (de)protonation process. The computational results are in reasonable agreement with the experimental ones.