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Pure organic two-photon excited room temperature phosphorescent (RTP) materials have attracted great attention for time-resolved imaging due to their long emission lifetime and high resolution. The materials with an aromatic carbonyl group exhibit aggregation-induced emission (AIE) and RTP characteristics simultaneously. Here, we deeply explored the nature of aggregation-induced phosphorescence (AIP), especially the relationship between molecular configuration and optical properties. It was found that aggregation effect can suppress geometrical vibrations and regulate energy difference between S

Tyrosinase is crucial to regulate the metabolism of phenol derivatives, playing an important role in the biosynthesis of melanin pigments, whereas an abnormal level of tyrosinase would lead to severe diseases. It is rather necessary to develop a sensitive and selective imaging tool to assess the level of tyrosinase in vivo. We thoroughly researched the luminous mechanism of the existing TPTYR probe and provided design strategies to improve its two-photon excited fluorescence properties. The designed probes benza2-TPTYR and product benza2-TPTYR-coumarin have large two-photon absorption cross sections at the NIR spectral region (41 GM/706 nm, 71 GM/852 nm), while benza2-TPTYR-coumarin possesses easily distinguishable spectrum in the visible region and a high fluorescence efficiency (Φ

Profound understanding of the luminescence mechanism and structure-property relationship is vital for Cu(I) thermally activated delayed fluorescence (TADF) emitters. Herein, we theoretically simulated luminescent behavior in both solution and solid phases for two Cu(I) complexes and found the following: (i) The strengthened spin-orbit coupling (SOC) effect by more dx2-y2 orbital contributions and well-restricted structural distortion via remarkable intramolecular interaction in [Cu(dmp)(POP)]+ enable the emission at room temperature to be a mixture of direct phosphorescence (10%) and TADF (90%). (ii) Benefiting from enhanced steric hindrance and the electron-donating ability of the paracyclophane group, the narrowed S1-T1 energy separation (ΔEST) in [Cu(dmp)(phanephos)]+ accelerates the reverse intersystem crossing, promoting the TADF rate (1.88 × 105 s-1) and intensity ratio (98.3%). These results indicate that the small ΔEST is superior for reducing the lifetime and that the strong SOC stimulates the phosphorescence to compete with TADF, which are both conducive to avoiding collision-induced exciton quenching and reducing the roll-off in devices.

Investigation of the clear structure–property relationship and microscopic mechanism of thermally activated delayed fluorescence (TADF) emitters with high emission quantum yield is a direction wort...

Hypochloric acid (HOCl) plays a vital role in the natural defense system, but abnormal levels of it can cause cell damage, accelerated human aging, and various diseases. It is of great significance to develop new probes for detecting HOCl in biosystems nondestructively and noninvasively. The purpose of this work is to explore new chemical modification strategies of two-photon excitation fluorescence (TPEF) probes to improve the poor water solubility and low efficiency in imaging applications. Nil-OH-6 has a two-photon absorption cross-section value as high as 243 GM and attains a good quantum yield of 0.49. In addition, the modification of terminal groups with different azetidine-heterospirocycles or N,N-dialkyl fused amino groups to Nile Red can effectively improve the fluorescence efficiency as well as increase the solubility to some extent. This study provides some strategies to simultaneously improve the fluorescence performance and solubility of these two-photon probes and, hence, reliable guidance and a foundation for the subsequent synthesis of TPEF probes based on Nile Red.

Hypochlorous acid (HOCL) plays a critical role in the natural defense system, but excessive production of HOCL leads to many diseases. It is very essential to monitor the distribution and level of ...

The biological fluorescence imaging for nucleic acid has attracted attention because of the essential role of nucleic acid in a living system. Two-photon (TP) fluorescent probes are important molec...

Profound understanding of the luminescence mechanism and structure-property relationship is vital for Cu(I) thermally activated delayed fluorescence (TADF) emitters. Herein, we theoretically simulated luminescent behavior in both solution and solid phases for two Cu(I) complexes and found the following: (i) The strengthened spin-orbit coupling (SOC) effect by more d

The level of hydrogen peroxide (H2O2) plays an essential role in regulating biological processes. The in vivo or in vitro detection of H2O2 in deep tissues by utilizing two-photon (TP) fluorescent probes can significantly alleviate the detection damage inflicted onto living organisms as well as facilitate high-resolution imaging when compared with one-photon (OP) fluorescent probes. However, few TP fluorescent probes possess both high fluorescence efficiency and easily distinguishable spectra for measuring H2O2. Therefore, an in-depth understanding of the relationship between the electronic structure and TP fluorescent properties and fabricating probes with excellent performance are still challenging. Consequently, we designed a series of benzocoumarin-based ratiometric TP fluorescent probes and corresponding product molecules for H2O2 detection. Thereafter, we theoretically evaluated the TP recognition performance of these compounds and studied the relationship between their molecular structure and TP performance by means of time-dependent density functional theory and quadratic response theory. Moreover, we determined their spectral properties and fluorescence efficiencies. Fortunately, in this study, we were able to propose an excellent TP probe BC-3 and the corresponding product molecule DCCA-3, which exhibit large TPA cross-sections in the NIR region (3420 GM/988 nm; 316 GM/939 nm) and large Stokes (116 nm; 60 nm) and emission (225 nm) shifts. Therefore, this probe enables the simultaneous NIR and TP imaging of H2O2, which is a unique ability and has never been previously reported. Moreover, we comprehensively investigated the effect of the benzene-fused position in the coumarin backbone on the transition dipole moment and nonradiative decay channels, explaining the fluorescence near-quenching mechanism of benzo[f]coumarin derivative DCCA-4 for the first time.

The development and utilization of two-photon fluorescent probes with large two-photon absorption (TPA) cross sections (δTPA) and strong TP-excited fluorescence are highly needed for monitoring the...

Correction for ‘New insight into the effects of N^N ligand isomerization and methyl modification on the phosphorescence properties of Cu(i) complexes with (1-(2-pyridyl)pyrazole/imidazole) ligands’ by Lu Shen et al., New J. Chem., 2018, 42, 3660–3670, https://doi.org/10.1039/C7NJ04879C.

Here we report that a covalent organic framework (COF), which contains 2,5-di(imine)-substituted 1,4-dihydroxybenzene (diiminol) moieties, undergoes color changes in the presence of solvents or solvent vapor that are rapid, passive, reversible, and easily detectable by the naked eye. A new visible absorption band appears in the presence of polar solvents, especially water, suggesting reversible conversion to another species. This reversibility is attributed to the ability of the diiminol to rapidly tautomerize to an iminol/cis-ketoenamine and its inability to doubly tautomerize to a diketoenamine. Density functional theory (DFT) calculations suggest similar energies for the two tautomers in the presence of water, but the diiminol is much more stable in its absence. Time-dependent DFT calculations confirm that the iminol/cis-ketoenamine absorbs at longer wavelength than the diiminol and indicate that this absorption has significant charge-transfer character. A colorimetric humidity sensing device constructed from an oriented thin film of the COF responded quickly to water vapor and was stable for months. These results suggest that tautomerization-induced electronic structure changes can be exploited in COF platforms to give rapid, reversible sensing in systems that exhibit long-term stability.

Cysteine is an essential amino acid in the synthesis of human protein. Therefore, the effective detection of cysteine in living organisms is of great significance. In this paper, first-principles are used to systematically study the fluorescence recognition mechanism and two-photon absorption properties of a series of novel two-photon (TP) fluorescent probes for cysteine. These probes are constructed based on coumarinocoumarin derivatives possessing the excellent fluorescence properties of coumarin molecules and the experimental fact that sporadic coumarinocoumarin can be used as a fluorescent probe, the recognition of which depends on enabled photo-induced electron transfer (PET) and intramolecular charge transfer (ICT) mechanisms toward cysteine. The results show that the transition dipole moments of coumarinocoumarin and monomer coumarin are significantly different, which allows the coumarinocoumarin to break the limit of the linear increase in the dipole moment vector of the monomer coumarin in the direction and magnitude. The magnitude of the two-photon cross-section value ( δ max T ) depends on the state dipole moment ( μ j j ( μ i i )) of the transition channel and the transition dipole moment ( μ i j ) of the coherent channel. Through the above research, we propose that (1) the length of the π conjugated chain can be increased along the 7-site of the coumarinocoumarin skeleton; (2) extend the π conjugated chain along different paths to change the state dipole moment of the transition channel of the target molecule and the direction of the transition dipole moment vector of the coherent channel to improve the TPA cross-section values of the probe molecule. Moreover, maximum TPA can be achieved in the range of 700–1000 nm for designed probe molecules, effectively avoiding factors such as the self-fluorescence of biological tissues and background interference. CCy-1-OH ∼ CCy-3-OH and CCy-7-OH molecules are designed to be excellent candidates for TP fluorescent probes. We hope the study can provide useful theoretical basis for cysteine imaging research.

Molecular stacking motifs in solid play a pivotal role on the charge transport properties of materials. The relationship between molecular structure and packing motifs in solid remains challenging. In the present work, the single crystal structures of PEN-O, PEN-N, PEN-CF3 and TPDO were predicted by evolutionary algorithm using the USPEX program. The stacking motifs, the electronic structures and the stabilities of pentacene (PEN) derivatives are systematically investigated by employing density functional theory. Our study expounded how the introduction of heteroatoms (oxygen-atom and nitrogen-atom) and substituent (trifluoromethyl) adjust their electronic structure effectively to improve the capability of carrier injection. Hirshfeld surface analysis was performed for the intermolecular close contact points to rationalize the molecular stacking patterns in solid. In addition, electrostatic potential and energy decomposition by symmetry adapted perturbation theory are analyzed to reveal the effects of heteroatoms and substituents on charge distribution and noncovalent interactions. Through introducing heteroatoms and substituents into PEN, the charge redistribution leads to non-uniform electrostatic potentials of conjugated molecular skeleton, which results in the change of the stacking patterns from herringbone to π-stacking. Furthermore, incorporating oxygen-atom or nitrogen-atom into PEN decreases dispersion energies, while modifying PEN with trifluoromethyl increases the dispersion energy. However, both of them lead to the decrease of the electrostatic and exchange-repulsion energy.

The level of hydrogen peroxide (H2O2) plays an essential role in regulating biological processes. The in vivo or in vitro detection of H2O2 in deep tissues by utilizing two-photon (TP) fluorescent probes can significantly alleviate the detection damage inflicted onto living organisms as well as facilitate high-resolution imaging when compared with one-photon (OP) fluorescent probes. However, few TP fluorescent probes possess both high fluorescence efficiency and easily distinguishable spectra for measuring H2O2. Therefore, an in-depth understanding of the relationship between the electronic structure and TP fluorescent properties and fabricating probes with excellent performance are still challenging. Consequently, we designed a series of benzocoumarin-based ratiometric TP fluorescent probes and corresponding product molecules for H2O2 detection. Thereafter, we theoretically evaluated the TP recognition performance of these compounds and studied the relationship between their molecular structure and TP performance by means of time-dependent density functional theory and quadratic response theory. Moreover, we determined their spectral properties and fluorescence efficiencies. Fortunately, in this study, we were able to propose an excellent TP probe BC-3 and the corresponding product molecule DCCA-3, which exhibit large TPA cross-sections in the NIR region (3420 GM/988 nm; 316 GM/939 nm) and large Stokes (116 nm; 60 nm) and emission (225 nm) shifts. Therefore, this probe enables the simultaneous NIR and TP imaging of H2O2, which is a unique ability and has never been previously reported. Moreover, we comprehensively investigated the effect of the benzene-fused position in the coumarin backbone on the transition dipole moment and nonradiative decay channels, explaining the fluorescence near-quenching mechanism of benzo[f]coumarin derivative DCCA-4 for the first time.