The one-photon and two-photon absorption properties of platinum acetylide complexes that feature hightly π-congugated ligands substituted with π-donor or π-acceptor moieties are investigated by use of the analytic response theory at DFT level. The numerical results show that these molecules have relatively strong two-photon absorption activities. While the platium insert into the ligands, TPA cross sections of the metal compounds are significantly enhanced. Metal clusters can also extend the π-conjugated length, which plays an important role in increasing the TPA cross section. Moreover, the NLO properties of metal clusters can be enhanced by the introduction of metal→ligand and ligand→metal charge-transfer states. The charge-transfer process is analyzed when the molecule is excited from the ground state to charge-transfer state.

In this work, using DFT and TDDFT methods, we investigated the excited-state intramolecular proton transfer (ESIPT) mechanism of a novel NIR-BODI system [Org Biomol Chem 15:4072, 2017.] in both toluene and acetonitrile $({\rm CH}_3{\rm CN})$ solvents theoretically. Comparing the prime structural variations of NIR-BODI involved in the intramolecular hydrogen bond, we can conclude that O-H∙∙∙N should be strengthened in the $S_1$ state, which may facilitate the ESIPT process. Concomitantly, infrared vibrational spectra analysis further verify the stability of hydrogen bond. In good agreement with previous experimental results, NIR-BODI reveals two kinds of excited-state structures (NIR-BODI-enol* and NIR-BODI-keto*). Analysis about charge redistribution reveals the tendency of ESIPT process. Our scanned potential energy curves according to variational O-H coordinate demonstrates that the proton transfer process should be more likely to occur in the $S_1$ state due to the inappreciable potential energy barriers. In addition, due to the minute differences of potential energy curves contrasting toluene (the NIR-BODI-keto could be not located) and ${\rm CH}_3{\rm CN}$ (the NIR-BODI-keto can be located) solvents in $S_0$ state, we deem that solvent effect could play roles NIR-BODI system. Given the $S_1$-state potential energy barriers, we confirm that the ESIPT process is easier in ${\rm CH}_3{\rm CN}$ solvent.

In this present work, the sensing mechanism of a novel fluoride chemosensor 2,2':6',2''-terpyridine (abbreviated as “2” according to previous experiment) has been investigated based on density functional theory (DFT) and time-dependent DFT (TDDFT) methods. The theoretical electronic spectra (vertical excitation energies and fluorescence peak) reproduced previous experimental results [RSC Adv. 2014, 4, 4041.], which confirms the rationality of our theoretical level used in this work. The constructed potential energy curve suggest that the non-barrier process could be responsible for the rapid response to fluoride anion. Analyses about binding energies demonstrate that only fluoride anion could be detected for 2 chemosensor in acetonitrile solvent. Comparing with other anions, we confirm the uniqueness of fluoride anion for 2 sensor. In view of the excitation process, the strong intramolecular charge transfer (ICT) process of $S_0→ S_1$ transition explain the redshift of absorption peak for 2 sensor with the addition of fluoride anion. This work not only presents a straightforward sensing mechanism of fluoride anion for 2 chemosensor, but also plays important roles in synthesizing and designing fluorescent sensors in future.

Algebraic approach to dynamical entanglement of triatomic molecules in laser fields are proposed. The effects of laser fields on dynamical entanglement are discussed. The researches show that the changes of two stretch vibrational entanglement along with the laser frequency are corresponding to vibrational transitions from different initial states to final states. The sustained entanglement will be implemented by using a two-step laser excitation.