Deep blue emitting dual state fluorescent triphenylamine-dicyclohexylurea derivative: Multi-stimuli responsive fluorescence switching and methanol/water sensing

A new deep blue emissive organic fluorophore (N-cyclohexyl-N-(cyclohexylcarbamoyl)-4-(diphenylamino)benzamide (NCDPB)) was designed and synthesized, which showed strong fluorescence both in solution and solid-state. Solid-state structural analysis of NCDPB revealed non-planar twisted molecular conformation with extended hydrogen bonding between the amide functionalities. The propeller shaped triphenylamine (TPA) and non-planar cyclohexyl unit prevented close π…π stacking and produced strong deep blue emission in the solid state (λmax = 400 nm, quantum yield (Φf) = 12.6 %). NCDPB also exhibited strong solvent polarity dependent tunable emission in solution (λmax = 402-462 nm, Φf = 1.15 (compared to quinine sulphate)). NCDPB showed reversible fluorescence switching between two fluorescence states upon mechanical crushing and heating/solvent exposure. Mechanical crushing caused red shifting of fluorescence from 400 to 447 nm and heating/solvent exposure reversed the fluorescence. Further, NCDPB also displayed off-on reversible/self-reversible fluorescence switching upon exposure to trifluoracetic acid (TFA) and NH3. The repeated fluorescence switching cycles indicated high reversibility without any significant change of fluorescence intensity. The drastically different fluorescence of NCDPB in CH3OH and EtOH was utilized to distinguish them and monitor CH3OH contamination in ethanol and benzene. It showed limit of detection (LOD) of methanol up to 0.25 % and 7 % in benzene and ethanol, respectively. The water sensitive fluorescence modulation of NCDPB in organic solvents was used to sensing water contamination in common organic solvents. Thus, integration of twisted TPA with H-bonding urea produced dual state emitting organic fluorophore with multi-responsive fluorescence switching and solvent sensing.

E- or Z-Isomers Arising from the Geometries of Ligands in the Mercury Complex of 2-(Anthracen-9-ylmethylene)-N-phenylhydrazine Carbothioamide

An anionic mercury(II) complex of 2-(anthracen-9-ylmethylene)-N-phenylhydrazine carbothioamide (HATU) and two isomers of a neutral mercury(II) complex of the anion of the same ligand (ATU) were reported. The anionic complex [Hg(HATU)2Cl2]·CH2Cl2 had a monodentate HATU ligand (a neutral form of the ligand) and chloride ligands. The two conformational isomers were of the neutral mercury(II) complex Hg(ATU)2·2DMF. The two isomers were from the E or Z geometry of the ligands across the conjugated C=N-N=C-N scaffold of the coordinated ligand. The two isomers of the complex were independently prepared and characterized. The spectroscopic properties of the isomers in solution were studied by 1H NMR as well as fluorescence spectroscopy. Facile conversion of the E-isomer to the Z-isomer in solution was observed. Density functional theory (DFT) calculations revealed that the Z-isomer of the complex was stable compared to the E-isomer by an energy of 14.35 kJ/mol; whereas, E isomer of the ligand was more stable than Z isomer by 8.37 KJ/mol. The activation barrier for the conversion of the E-isomer to the Z-isomer of the ligand was 167.37 kJ/mol. The role of the mercury ion in the conversion of the E-form to the Z-form was discussed. The mercury complex [Hg(HATU)2Cl2]·CH2Cl2 had the E-form of the ligand. Distinct photophysical features of these mercury complexes were presented.

Novel star-shaped D-π-D-π-D and (D-π)2-D-(π-D)2 anthracene-based hole transporting materials for perovskite solar cells

Three types of novel star-shaped molecular architectures, D-π-D-π-D and (D-π)₂-D-(π-D)₂ anthracene (ANTTPA, AOME, AOHE) based hole transporting materials, are designed for hybrid perovskite solar cells using the Gaussian 09 computation program with the B3LYP/6-31g (d, p) basis set level. The HOMO energy level of the designed materials has a higher HOMO energy level compared to the perovskite HOMO energy level, which is more facile for hole transport from the hole transporting layer to the oxidized perovskite layer. Thereafter, anthracene-based derivatives were synthesized from Buchwald-Hartwig and Mizoroki-Heck cross coupling reactions. The behaviors of the transporting charges were determined by both UV-visible absorbance and emission spectroscopy through solvatochromism experiments. Furthermore, the electrochemical properties also proved that the synthesized compounds had an optimal HOMO energy level in the TiO₂/perovskite/HTM interface. Our hole transport materials (HTMs) have a good film formation compared to the spiro-OMeTAD, which was confirmed from scanning electron microscopy images. The obtained theoretical and experimental data show the suitability of designing anthracene-based derivatives with the potential to be used as hole transporting materials in organic-inorganic hybrid perovskite solar cells.

Anthracene based AIEgen for picric acid detection in real water samples

In this work, a new anthracene Schiff base derivative (AS) was successfully synthesized and characterized by pivotal analytical techniques. Based on the contented results, the AS molecule was employed for photophysical investigation using UV-Visible absorption, steady state and time resolved fluorescence techniques. The photophysical studies reveal that the AS possesses modest molar absorption coefficient (10⁴) and weak fluorescence (ϕ = 0.006). The weak fluorescence of AS is due to intramolecular photoinduced electron transfer (PET). Intriguingly, the weak fluorescence intensity of AS is enhanced dramatically by the gradual addition of water up to 90% as well as appearance of long lived fluorescence decay. The enhancement in the fluorescence intensity and lifetime clearly indicates that this molecule has aggregation-induced emission (AIE) property. Further, the AIE property of AS is utilized for sensitive detection of picric acid (PA). The fluorescence of aggregated AS is quenched regularly with the sequential addition of PA concentration. The higher Stern-Volmer constant (2.61 × 10⁵ M^-1) and excellent detection limit of 93 nM designate the AS aggregates as potential candidate for explosive detection. The mechanism behind the quenching of fluorescence can be ascribed to inner filter effect, which is supported by spectral overlap analysis and fluorescence lifetime measurements. The suitability of AS aggregates for practical applications is realized by the detection of trace amounts of PA in real water samples.

Anthracene dimer crosslinked polyurethanes as mechanoluminescent polymeric materials

The force-induced cleavage of anthracene dimer results in fluorescence and shows good sensitivity to mechano-stimuli such as pressure.

SnCl2-catalyzed synthesis of dihydro-5H-benzo[f]pyrazolo[3,4-b]quinoline and dihydroindeno[2,1-b]pyrazolo[4,3-e]pyridine with high fluorescence and their photophysical properties

A series of pyrazoloquinoline and pyrazolopyridine based derivatives bearing donor–acceptor (D–A) substituent groups on the phenyl ring, was synthesized by a mild reaction condition.

Role of Voluminous Substituents in Controlling the Optical Properties of Disc/Planar-Like Small Organic Molecules: Toward Molecular Emission in Solid State

Inspired by the role of coadsorbents in dye-sensitized solar cells, a pathway to disfavor aggregation in disclike luminophores was studied to enhance solid-state emission. By restricting the intense π-π stacking using a multicyclic aliphatic ring system, we brought the lithocholic ring system as bulky side substitution into the fluorophore design. Compared to the small-size cyclohexyl substitution in BC-CY6, which exhibited a bathochromic shift in solid-state emission owing to the intermolecular interactions, lithocholic-substituted BC-LTH had reduced intense intermolecular interactions. This very bulky/voluminous side substitution (lithocholic unit) helped us extract intermolecular interaction-free molecular emission in solid state. The cyclohexyl substitution provided solid-state emission, and the broad and high Stokes shift provided an insight into stacking interactions. Face-to-face stacking-originated dimerlike species was observed in the crystal packing, which was studied by theoretical geometry optimization. The dimer species exhibited an intermolecular distance of 3.5 Å. The molecular sizes of the developed chromophores were estimated by geometry optimization, and it was concluded that the dimeric interactions in BC-LTH may not be formed owing to the voluminous nature of the side substitution present. Hence, we have been able to successfully establish through molecular level understanding the role of lithocholic functionality in tuning the optoelectronic properties of various emissive materials for different applications.