Jin-Ting Ye

Spirooxazine molecular switches with nonlinear optical responses as selective cation sensors

Spirooxazine, a photochromic material, can transform into metallic open-form merocyanine by molecular switching, giving rise to large contrasts in its second-order nonlinear optical (NLO) properties. The switching properties are particularly large when various metal ions (Li+, Na+, K+, Mg2+, Ca2+, Fe2+, Zn2+, and Ag+) are introduced, as evidenced by density functional theory calculations, which show that the spirooxazine undergoes a pronounced change in geometry accompanied by formation of a larger π-conjugated system. The resultant merocyanine derivatives have 10–21-fold higher static second-order NLO responses. Spirooxazine can therefore be used as a powerful and multi-use detection tool. The large first hyperpolarizability (βtot) is shown to rely on the alkaline earth metal, causing βtot values to increase nearly 21-fold, as evidenced by the larger charge distribution, lower transition energy, and separate distribution of first hyperpolarizability density. In contrast, variation of βtot in the Fe2+ derivative is not obvious, owing to stronger complexation, a larger amount of charge transferred from the napthoxazine moiety to the metal, and the reduction in N⋯O distance between the ligand heads. Therefore, spiropyran-to-merocyanine molecular switching can be used to distinguish alkaline earth metals and determine the efficiency of cation detection.

The novel link between planar möbius aromatic and third order nonlinear optical properties of metal–bridged polycyclic complexes

Metal–bridged polcyclic aromatic complexes, exhibiting unusual optical effects such as near-infrared photoluminescence with particularly large Stokes shifts, long lifetimes and aggregation enhancement, have been established as unique “carbonloong chemistry”. Herein, the electronic structures, aromaticities, absorption spectra and third order nonlinear optical (NLO) responses of metal–bridged polcyclic aromatic complexes (M = Fe, Re, Os and Ir) are investigated using the density functional theory computations. It is found that the bridge–head metal can stabilize and influence rings, thus creating π–, σ– and metalla–aromaticity in an extended, π–conjugated framework. Interestingly, metal radius greatly influence the bond, aromaticity, liner and third order NLO properties, which reveals useful information to develop new applications of metal regulatory mechanism in NLO materials field. Significantly, the novel relationship between the aromaticity and third order NLO response has firstly been proposed, that the metal-bridged polycyclic complex with larger aromaticity will exhibit larger third order nonlinear optical response. It is our expectation that the novel link between aromaticity and NLO response could provide valuable information for scientists to develop the potential NLO materials on the basis of metal–bridged polycyclic complexes.

A cation-selective and anion-controlled benzothiazolyl-attached macrocycle for NLO-based cation detection: variational first hyperpolarizabilities

Recently, a benzothiazolyl group bearing the NO2S2-macrocycle L has been the subject of great interest due to its unique advantages in binding metal cations. Here, we systematically investigate the second-order nonlinear optical (NLO) properties of L, its metal cation derivatives L*M (M = Na+, K+, Mg2+, Ca2+, Zn2+, Cd2+, and Hg2+), and some anion-controlled complexes [Hg(L)(ClO4)2 and Hg(L)(Cl)2] by density functional theory (DFT). The results show that the addition of the transition metal cation Hg2+ leads to the increasing transition energy of the S0 → S1 transition, which induces a significant decrement in the NLO response (βtot = 8.2 × 10−30 esu) with respect to the corresponding macrocycle L (βtot = 125.8 × 10−30 esu). The depolarization ratio (DR) and anisotropy parameter (ρ) render it possible to control the NLO contribution. Further analysis of the charge transfer (CT) parameters, transferred electrons (qCT), CT distance (dCT), and t index indicates that L*Hg2+ reaches the minimum CT and spatial charge separation. Thus, the transition metal cation Hg2+ is distinguishable and easier to detect by utilizing the variations in the NLO response. Furthermore, the addition of ClO4− to the complex L*Hg2+ forms a distorted pentagonal bipyramid configuration, which drives the significant reduction of the first hyperpolarizability. Therefore, the obvious NLO contrasts can be switched by different metal cations and anions, which will broaden the scope of optical molecular detectors and further inspire us to investigate it.

Theoretical investigation on second-order nonlinear optical properties of ruthenium alkynyl–dihydroazulene/vinylheptafulvene complexes

Ru metal acetylide electron donor-acceptor complexes have important applications in the field of nonlinear optics. Herein, in this work, a series of half-sandwich ruthenium-based Cp*(dpe)Ru ([Ru*]) metal complexes with the dihydroazulene/vinylheptafulvene (DHA/VHF) have been investigated by density functional theory (DFT) calculations. The results showed that the position of the [Ru*] acetylide functionality, either para or meta on the phenylene ring to the DHA/VHF core (1c/1o and 2c/2o), and additional a p-phenylene spacer (3c/3o) had a great influence on the second-order nonlinear optical (NLO) responses. The systems 1 and 3 can significantly increased second-order NLO responses compared with system 2. It was attributed to the more obvious charge transfer along y-axis, which is from [Ru*] acetylide functionality to DHA, accompanied by a significant decrease of the transition energy according electron density difference maps and time-dependent DFT calculations. The βvec values of the open-ring complexes were larger than the corresponding closed-ring complexes owing to the smaller HOMO-LUMO gap in the open-ring complexes. It was also because of the smaller BLA values in open-ring complexes, which had stronger π-conjugation. Especially, the change ratio of βvec value of system 2 was the largest due to the fact that their charge transfers degree varied greatly. In addition, the frequency-dependent NLO properties of the studied complexes were evaluated at 0.0239 a.u. and 0.0340 a.u. The calculation results demonstrated that the magnitude of the frequency-dependent first hyperpolarizability increased with the increasing frequency. We believe that our present work will be beneficial for further theoretical and experimental studies on large second-order NLO responses of metal complexes.