A guest-dependent dynamic fivefold interpenetrated 3D porous metal-organic framework (MOF) of Zn ions has been synthesized that exhibits selective carbon dioxide adsorption. Furthermore, the MOF shows excellent luminescence behavior, which is supported by a systematic study on the guest-responsive multicolor emission of a suspension of the MOF. The dual-emission behavior arises from the excited-state intramolecular proton transfer (ESIPT), and the compound also shows remarkable potential to detect traces of water in various organic solvents. The experimental observations were also painstakingly authenticated by using time-dependent density-functional-theory (DFT) calculations.

We report theoretical results on the possible violation of Kasha's rule in the phosphorescence process of (acetylacetonato)bis(1-methyl-2-phenylimidazole)iridium(III) and show that the anomalous emission from both the T and T states is key to its white-light phosphorescence. This analysis is supported by the calculated Boltzmann-averaged phosphorescence lifetime of 2.21 μs, estimated including both radiative and nonradiative processes and in excellent agreement with the experimentally reported value of 1.96 ± 0.1 μs. The T state is found to be of metal-to-ligand charge-transfer character (dπ → nπ), and the d orbital contribution comes from 5d and 5d, whereas the S and T states both have dπ-pπ character with significant 5d orbital contribution, allowing for efficient intersystem crossing from the S to the T state and, in turn, phosphorescence from the T state. Our results open new opportunities for tailoring the phosphorescence wavelength and thus the design of molecules with improved photovoltaic properties.

We present the novel observation that Duschinsky mixings can lead to the breakdown of Kasha’s rule in a white light phosphor molecule, dibenzo­[b,d]­thiophen-2-yl (4-chlorophenyl)­methanone. Our theoretical analyses show the energy gap between the T1 and T2 states (0.48 eV) is too large to allow for any significant population of the T2 state at room temperature and instead the faster intersystem crossing (ISC) between the S1 and T2 states is rather due to strong Duschinsky mixing, leading to the emission from the T2 state as well. A second-order cumulant-based method has been used for the calculation of the ISC rate, which suggests 2 orders of magnitude faster ISC rates for S1 → T2 compared to those for S1 → T1. We found that the carbonyl moiety of the S1 and T2 states of the molecule is significantly different with respect to bond angle and dihedral angles, engendering large displacements in selective normal modes, thus giving rise to strong Duschinsky mixing.

We present a heuristic mechanism for the origin of the unusual triplet lasing from (E)-3-(((4-nitrophenyl)imino)methyl)-2H-thiochroman-4-olate·BF.We demonstrate that whereas the moderate lifetime (1.03 μs) of the first triplet state (T) prohibits triplet-triplet annihilation, the relatively faster S → T intersystem crossing and the 10 times smaller reverse intersystem crossing effectively help achieve population inversion in the T state. Furthermore, the triplet lasing wavelength (675 nm) for the tetramer does not overlap with the triplet-triplet absorptions wavelength, indicating that the spin-forbidden emission cross section is very large. Additionally, the almost complete absence of a vibrational progression in the vibronic phosphorescence spectrum of the monomer plays an important role in ensuring efficient triplet-state lasing from this organic material. Our results show that controlling the triplet-state lifetimes combined with lowering of the triplet-triplet absorption in the emission region and small vibronic coupling will be the key steps when designing novel organic triplet-lasing materials.

Recently, ultralong phosphorescence lifetime has been observed in 4,6-diethoxy-2-carbazolyl-1,3,5-triazine, and H-aggregation induced stabilization of the T state was suggested as its source. The response theory calculations demonstrate that the Davydov stabilization of the T state of the dimer is marginal with respect to the monomer and the corresponding transition moments are virtually the same. Moreover, the calculated radiative rate constant is far from the experimental value, indicating that the ultralong lifetime is not likely to be of electronic origin only. Our calculations reveal that the dual-peak emission from the T state is due to strong vibronic coupling between the T and S states along selected normal modes. Interestingly, the calculated vibronic radiative rate constant of the dimer (2.33 × 10 s) is comparable to the experimental value (4.7 × 10 s), supporting the notion that vibronic contributions to the transition moment are responsible for the ultralong lifetime observed in the bulk system.