Solid-state Emission Properties Research Articles

Spin-Vibronic Intersystem Crossing and Molecular Packing Effects in Heavy Atom Free Organic Phosphor.

We present a detailed investigation into the excited state properties of a planar D3h symmetric azatriangulenetrione, HTANGO, which has received significant interest due to its high solid-state phosphorescence quantum yield and therefore potential as an organic room temperature phosphorescent (ORTP) dye. Using a model linear vibronic coupling Hamiltonian in combination with quantum dynamics simulations, we observe that intersystem crossing (ISC) in HTANGO occurs with a rate of ∼1010 s-1, comparable to benzophenone, an archetypal molecule for fast ISC in heavy metal free molecules. Our simulations demonstrate that the mechanism for fast ISC is associated with the high density of excited triplet states which lie in close proximity to the lowest singlet states, offering multiple channels into the triplet manifold facilitating rapid population transfer. Finally, to rationalize the solid-state emission properties, we use quantum chemistry to investigate the excited state surfaces of the HTANGO dimer, highlighting the influence and importance of the rotational alignment between the two HTANGO molecules in the solid state and how this contributes to high phosphorescence quantum yield.

Perylenemonoimide-based superstable radical anions and dianions with solid-state emission properties

The ambient stable radical anions originated from perylenemonoimide via sulfur oxidation was explored in this investigation.

Substituent-Controlled Photophysical Responses in Dihydropyridine Derivatives and Their Application in the Detection of Volatile Organic Contaminants.

In the ever-expanding realm of organic fluorophores, structurally simple and synthetically straightforward molecules with unique photophysical properties have received special attention. Among these, 1,4-dihydropyridine (DHP) is an important scaffold that permits fine-tuning of their photophysical properties through substituents on the periphery. Herein, we describe a series of solid-emissive N-substituted 2,6-dimethyl-4-methylene-1,4-dihydropyridine derivatives appended with electron-withdrawing substituents (dicyanomethylene or 2-dicyanomethylene-3-cyano-2,5-dihydrofuran) at the C-4 position and alkyl or alkylaryl groups on the DHP nitrogen. Electronic and steric tuning exerted by these substituents resulted in interesting photophysical properties such as negative solvatochromism, solidstate, and aggregation-induced emission (AIE). Theoretical calculations were carried out to explain the solvatochromic properties. Insight into the AIE properties was obtained through variable-temperature nuclear magnetic resonance and viscosity- and temperature-dependent emission studies. The variations in molecular packing in the crystal lattice with changes in the N-substituents contributed to the tuning of solid state emission properties. Detection of aromatic volatile organic compounds (VOCs) was achieved using the aggregates of the DHP derivatives. Among the VOCs, p-xylene elicited a significant enhancement in emission, allowing its detection at submicromolar levels.

Aroyl-S,N-Ketene Acetals: Luminous Renaissance of a Class of Heterocyclic Compounds.

Aroyl-S,N-ketene acetals represent a peculiar class of heterocyclic merocyanines, compounds bearing pronounced and rather short dipoles with great push-pull characteristics that define their rich properties. They are accessible via a wide array of synthetic concepts and procedures, ranging from addition-elimination and condensation procedures up to rearrangement and metal-mediated reactions. With our work from 2020, aroyl-S,N-ketene acetals have been identified as powerful and promising dyes with pronounced and vastly tunable solid-state emission and aggregation-induced emission properties. One characteristic trademark of this class of dye molecules is the level of control that could be exerted and which was thoroughly explored. Based on these results, the field was opened to extend the system to bi- and multichromophoric systems by the full toolkit of synthetic organic chemistry thus giving access to even more exciting properties and manifolded substance libraries capitalizing on the AIE properties. This review aims at outlining the reaction-based principles that allow for a swift and facile access to aroyl-S,N-ketene acetals, their methodological and structural evolution and the plethora of fluorescence and aggregation properties.

Alkynylated and triazole-linked aroyl-S,N-ketene acetals: one-pot synthesis of solid-state emissive dyes with aggregation-induced enhanced emission characteristics

Alkynylated aroyl-S,N-ketene acetals are readily synthesized in mostly excellent yields by a Sonogashira reaction resulting in a substance library of more than 20 examples. Upon expansion of the reaction sequence by deprotection and concatenating of the copper-click reaction in a one-pot fashion, a library of 11 triazole-ligated aroyl-S,N-ketene acetals is readily accessible. All derivatives show pronounced solid-state emission and aggregation-induced emission properties depending on the nature of the alkynyl or the triazole substituents.

Push-Pull Bridged Distyrylbenzene with Highly Bright Solid-State Red-Orange Aggregation-Induced Emission.

Multiple emission colors in solid-state organic fluorophores with the same main skeleton are essential for improving the performance of light-emitting devices/materials. Specifically, emission in the red/near-infrared region is of great importance in the biological field. Previously, we developed di-bridged-distyrylbenzene DBDB[7] with high-brightness solid-state blue and aggregation-induced emissions (AIE) by introducing the bridging structures of a seven-membered ring into the vinylene groups of distyrylbenzene (DSB). Herein, we synthesize MNDBDMeODB[7] (1), which features substituted methoxy and malononitrile groups as donor and acceptor groups, respectively, in DBDB[7]. In solvents more polar than THF, MNDSDMeOB (3), which has the same main skeleton as 1 but without bridges, shows no emission in the solid state, whereas 1 exhibits highly bright red-orange emission in the solid state owing to the suppression of intermolecular electronic interactions by the bridges and the AIE property. We also synthesize MNDSD(EHO)B (2) in which the methoxy groups of 3 are replaced by ethylhexyloxy groups, thus disrupting the crystallinity of the molecule. 2 exhibits positive fluorescence solvatochromism and has a high fluorescence quantum yield in the solid state as a red-emitting DSB derivative. The solid-state emission properties of 1 and 2 will improve the applicability of DSBs and functionalities of light-emitting devices/materials.

Brønsted Base Prompted sp3 C-H Latent Nucleophiles to Access α-Branched Amines Bearing β-Carbonyl by Cleaving Amide and Ester Bonds.

α-Branched amines are key motifs that exist in a plethora of natural products and pharmaceuticals. Herein we disclose the first convergent synthesis of α-branched amines bearing β-carbonyl in isoindolinones by employing unactivated tertiary amides and unactivated alkyl esters as benign electrophile sources. The reaction proceeds by the direct aroylation of a C(sp3)-H carbon adjacent to the nitrogen atom in core isoindolinones. Several amides and esters were screened to choose the potential acyl source for the substrate scope. The reaction is carried out with a repertoire of substrates under mild conditions and shows high functional group compatibility. Remarkably the reaction is amenable to organometallic ferrocenyl ester and indole methyl esters bearing an acidic NH moiety. Strikingly no trace of amidation product 8 is observed. In particular α-branched amines bearing β-carbonyl synthesized from indole methyl esters are considered important targets, as both motifs are prevalent in many drugs. This protocol is scalable, and products obtained from indole methyl esters show strong solid-state emission properties which are complementary with DFT calculations.

Experimental and Theoretical Exploration of ESIPT in a Systematically Constructed Series of Benzimidazole Based Schiff Base Probes: Application as Chemosensors.

Herein, we have utilized 2-(2-hydroxyphenyl)benzimidazole (HBI) to synthesize 3-(1H-benzoimidazol-2-yl)-2-hydroxy-5-methyl-benzaldehyde (HBIA) followed by three Schiff bases by using -ortho (H2 BIo), -meta (H3 BIdm) and -para (H2 BIp) substituted amino benzoic acids and studied their photophysical properties. We have successfully derived molecular structures of HBI, HBIA and H3 BIdm which reveals that in HBI and HBIA, the phenolic -OH is intramolecularly hydrogen bonded with sp2 N of benzimidazole group whereas in H3 BIdm, it is hydrogen bonded with imine C=N of Schiff base moiety, which is responsible for different solid state emission properties of the reported compounds. Extensive experimental and theoretical studies show that for all three Schiff bases, in solution due to activation of C=N isomerization, ESIPT operates through benzimidazole site and displays different emission from the solid state. Furthermore, H2 BIo, H3 BIdm and H2 BIp selectively sense Cu2+ in semi aqueous medium with nano-molar detection limit and in HuH-7 cells through the inhibition of ESIPT of process.

Deoxyestrone-based lipofection agents with solution- and solid-state emission properties.

In this contribution, three deoxyestrone-based emissive lipofection agents are reported. Because of a centrally incorporated terephthalonitrile motif, these ligands can be classified as solution and solid-state emitters (SSSEs). With the attachment of tobramycin, these amphiphilic structures are able to form lipoplexes, mediating gene transfection of HeLa and HEK 293T cells.

On the role of torsional dynamics in the solid-state fluorescent properties of a new bifluorene–tetracarboxylic acid and its supramolecular assemblies: a structural and TD-DFT investigation

The solid-state emission properties of bifluorene–tetracarboxylic acid were reported and rationalised on the basis of fluorene torsional dynamics by SC-XRD and DFT calculations.

Synthesis and in-depth investigation of the photophysical and electrochemical properties of novel pyrazole cored D-A-D molecules

The synthesis of a novel pyrazole-cored push-pull system (Donor-Acceptor-Donor/D-A-D) in which thiophene serves as the donor and N-substituted pyrazole ring serves as the acceptor moieties is reported. The photophysical and electrochemical properties of the synthesised compounds were investigated using UV–Visible spectroscopy, photoluminescence spectroscopy, and cyclic voltammetry (CV). The photophysical results indicate that all four compounds have unique absorption and emission behaviour in the solid-state compared with the solution (in CHCl3). The optical band gap was calculated from the absorption curve and ranged from 2.75 eV to 3.81 eV. According to the CIE colour coordinates, each compound can emit different colour ranges. The estimated electrochemical results (HOMO and LUMO energy values) by CV and the possibility of adaptable tuning of these results demonstrate that the target compounds can be used as a fresh emissive candidate for organic optoelectronics applications. The significance of push-pull architecture and the solid-state emission properties of the targeted compounds were also highlighted in this work.

Cover Feature: Solid‐State Emission and Aggregate Emission of Aroyl‐ S,N‐Ketene Acetals Are Controlled and Tuned by Their Substitution Pattern (Chem. Eur. J. 61/2022)

Aroyl-S,N-ketene acetals put a novel, promising class of dyes on the stage of AIEgens. Like a puppet on a string, all their photophysical properties like AIE and solid-state emission properties, the starting point of aggregation and, as shown by Hirshfeld analysis, the solid-state quantum yield can easily be fine-tuned and completely controlled by the choice and interplay of substituents at the aroyl-S,N-ketene acetal. More information can be found in the Research Article by T. J. J. Müller and co-workers (DOI: 10.1002/chem.202202579).

Two distinctly fluorescent BioAIEgens originated from the combination of natural rosin and chromophoric triphenylamine

Aggregation-induced emission (AIE) luminogens have been widely used in various fields. Among them, BioAIEgens (AIEgens from natural resources) have been highly concerned by researchers because of their unique advantages. However, the number of BioAIEgens directly derived from nature is limited. Therefore, chemical modification on natural resources may be an effective way to obtain more BioAIEgens. In this paper, because the rigid alicyclic ring of dehydroabietic acid (DA) has the effect of restricting molecular motion, we successfully obtained two rosin-based BioAIEgens (DAA-TPA and DAMBA-TPA) by combining DA with triphenylamine. Interestingly, DAA-TPA obtained by connecting TPA with the aliphatic ring of DA has TICT-AIE and strong solid-state emission properties, while DAMBA-TPA obtained by connecting TPA with the aromatic ring of DA shows an atypical AIE and weak solid emission effect. Two control molecules were designed to investigate the influence of the introduction of aliphatic ring and aromatic ring on the photophysical properties of TPA. The results showed that DA containing both aliphatic ring and aromatic ring may be used as a precursor to construct BioAIEgens with different AIE properties. In addition, based on the fluorescence performance of DAA-TPA, we applied it to the detection of trace water in acetonitrile (ACN).

Rational design of state-depending photoactivatable and photoconvertible fluorescent AIEgens through a rapid photocyclodehydrogenation reaction

Photosensitive fluorophores have grand value and bright prospective in diverse photo-controlled applications including super-resolution imaging and advanced patterning; however, photoactivatable and photoconvertible small fluorophores encounter great challenges in comparison to their fast-growing protein-based counterparts. Herein, we proposed a general design strategy to achieve state-depending photoactivatable and photoconvertible fluorophores based on an AIE-active molecular skeleton through introducing a dipyridinylethene unit which easily undergoes a rapid photocyclodehydrogenation reaction. It is found that introducing a photoactive dipyrinylethene unit into an AIE-active tetraarylethene molecule can effectively regulate its dominant photophysical emission and photochemical reaction in a controllable way, and these combined compounds show predominant aggregation-induced emission properties in solid state but exhibit dominant photoactivatable and photoconvertible fluorescence behaviours in dispersed state. The photoactivatable and photoconvertible fluorescence is attributed to the rapid photo-induced cyclodehyrogenation reaction and AIE nature of the species involved in the photochemical processes. These findings outline a general design strategy to achieve photoactivatable and photoconvertible fluorescence systems by introducing a specific subunit easily undergoing rapid and efficient photocyclodehyrogenation reaction, and demonstrate exciting use of these state-dependent photosensitive fluorophores in diverse photo-controlled practical applications.

D–A systems based on oxazolone–coumarin triazoles as solid-state emitters and inhibitors of human cervical cancer cells (HeLa)

D–A systems with solid-state emission and anticancer properties have been synthesized in three steps via the MCR-Click protocol.

Excellent and reversible mechanofluorochromism in donor–acceptor π-systems based on bisarylic methanone derivatives

Mechanofluorochromic (MFC) materials characterized by high-contrast fluorescent colors and/or high intensities have rarely been reported. This can be attributed to the complex mechanism and molecular design associated with MFC phenomenon. Herein, the route followed for the preparation of two D–A type bisarylic methanone fluorescent molecules CAR-BZ-POZ and CAR-BZ-PTZ, has been presented. Results obtained from systematic photophysical experiments reveal that CAR-BZ-POZ and CAR-BZ-PTZ are characterized by twisted intramolecular charge-transfer (TICT) states, highly distorted molecular conformations, good solid-state emission properties, and high-contrast reversible mechanofluorochromism. The as-prepared CAR-BZ-POZ and CAR-BZ-PTZ solids emitted intense yellow-green fluorescence (531 and 550 nm, respectively), and the solid-state luminescence efficiencies recorded were 32.54% and 24.92%, respectively. When the samples were ground, orange-red fluorescence was emitted (602 and 594 nm, for CAR-BZ-POZ and CAR-BZ-PTZ, respectively). Results obtained by conducting mechanistic studies suggest that the MFC phenomenon can be attributed to the phase transition (from crystalline to amorphous phase) of the molecules. The red-shift in the PL spectral profiles, achieved following the process of grinding, could be attributed to the extension of the molecular conjugation length and the planar intramolecular charge transfer (PICT) properties.

Synthesis, structural, thermal, photophysical and vibrational spectroscopic studies of potassium-polynitrile based 3D coordination polymer.

Among various interactions (such as H-bonding, π-π stacking interaction) which are responsible for the fascinating metallo-architectures, cation - π interaction has emerged as a significantly important force. Moreover, it has now been observed that this interaction is found to be presented ubiquitous across several fields of contemporary interest, such as chemistry, material science, and biology. In this work, we have focused on the design and synthesis of a pentacyano organic anion and potassium cation based 3D coordination polymer (5CNP). The single-crystal XRD structure revealed fascinating structural arrangements due to the existence of several intra and interionic interaction. To the best of our knowledge, such polycyano aromatic system based 3D coordination polymer is not reported. In addition to single crystal X-ray diffraction (SCXRD), we have employed confocal Raman microscopic techniques to understand the structural aspects, particularly the pentacyano functional groups which are Raman active. Considering the prospect of 5CNP as a material, thermal stability, and structyral properties have been studied, in addition to detailed photophysical aspects. The photophysical responses in solid and in solution have been studied by steady and time-resolved fluorescence spectroscopy. Interesting photophysical observation is noted when studied in a binary mixture of THF-toluene. Scanning electron microscopy (SEM) studies have also been done for comprehensive understanding. In the end, cytotoxicity studies have been undertaken to evaluate the toxicity of 5CNP in our cells.

Copper(I) complexes with remotely functionalized phosphine ligands: Synthesis, structural variety, photophysics and effect onto the optical properties

The synthesis, chemical and photophysical investigation of a series of eight novel copper-halide derivatives with different nuclearity is herein presented. One mononuclear copper(I) complex with formula [CuI(pyridine)(P)2], where P is a functionalized phosphine, six dinuclear derivatives bearing the rhombic {Cu2I2} subunits and with general formula [Cu(μ-I)(P)(N)]2 (N = pyridine, quinoline and 4-cyanopyridine) as well as one tetranuclear copper-iodide clusters of general formula [Cu(μ-I)P]4 consisting of a cubane-like {Cu4X4} motif were straightforwardly prepared, also by means of mechano-chemical synthetic procedure. The phosphine ligands were prepared in excellent yield by using simple hydrophosphination reactions. For five of the investigated cuprous iodide derivatives their atom connectivity and solid-state crystalline packing was unambiguously confirmed by solving their single-crystal X-ray structure. All the investigated complexes resulted into photo- and thermally-stable luminescent species. In the solid state as microcrystalline powder samples, the complexes display intense photoluminescence ranging from the sky-blue to orange-red portion of the spectrum with PLQY values of 0.28–0.50 and 0.34–0.97 at room and low (77 K) temperature, respectively, depending on the nature of both the coordinated N-heteroaromatic ring and phosphine ligands. In spite of the remote location of the functionalization of the phosphine, profound effects are observed onto the solid-state emission properties highlighting the importance of microenvironment for the emitters in the aggregated phase.

Preparations of Core H2O-Bound 5, 10, 15, 20-Tetrakis-4-chlorophenyl Porphyrin, P 1 , and O-Methylation of Phenol and Its P-Substituted Analogues.

The treatment of a dichloromethane solution of 5, 10, 15, 20-tetrakis-4-chlorophenyl porphyrin, P1, with methanolic solutions of each of phenol, p-amino phenol, and p-nitro phenol for just 1 h results in the formation of water-molecule-bound amorphous solids of P1. In addition to the straightforward access to the H2O-molecule-coordinated species of P1 thus produced, the another chief advantage of this synthetic strategy is the successful recoveries of anisole, p-amino anisole, and p-nitro anisole at the end of the reactions. The present work therefore further reports the use of P1 as an efficient catalyst for the selective O-methylation of phenols using methanol as an environmentally friendly methylating agent. The H2O-bound amorphous solids of P1 exhibit higher-intensity absorption as well as photoluminescence emission bands in dichloromethane compared with the parent crystalline form. Further, the measurement of the solid-state emission properties of both the crystalline and amorphous forms indicates quenching of fluorescence bands corresponding to amorphous solids in comparison with that of parent crystalline form. The crystalline form of P1 and the H2O-bound amorphous solids were further studied by scanning electron microscope/transmission electron microscope (SEM/TEM), powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and thermal analysis techniques. The results of these studies indicate change in morphological and structural features, surface areas, porosities, and thermal robustness upon core coordination of water molecules with the macrocyclic rings of P1.

Synthesis, structures, luminescence and thermal stability of Visible/NIR emitting binuclear azomethine-Zn(II) complexes

A series of binuclear azomethine-Zn(II) complexes was successfully synthesized from 4,4-diaminodiphenylsulphide derived Schiff bases, N,N-bis-(3,4-dihydroxybenzaldehyde)-4,4-diaminodiphenylsulphide (L1), N,N-bis-(5-nitrosalicylidene)-4,4-diaminodiphenylsulphide (L2), N,N-bis-(5-chlorosalicylidene)-4,4-diaminodiphenylsulphide (L3). The compounds were characterized through single crystal X-ray diffraction analysis, FT-IR, 1H NMR,13C NMR, energy dispersive X-ray diffraction (EDX), UV–Visible and photoluminescence spectroscopy. Single crystal X-ray diffraction analysis manifested that in the binuclear ZnL3 complex, two zinc ions bridge two Schiff bases with each metal centre adopting a distorted tetrahedral geometry, through coordination with two phenolate oxygen atoms and two azomethine nitrogen atoms. Each L3 ligand bonds two Zn(II) centres on different sides of the metals where the ligand flipped over to the opposite side around the S atom creating a twist. Photophysical properties of the synthesized compounds were explored in solid and solution states at room temperature. In solid state, the complexes revealed emissive properties in the visible and near infra-red (NIR) regions, with large Stoke's shift (Δλ) of 260–385 nm with respect to absorption, exhibiting emission in visible region (585 nm) both for ZnL2 and ZnL3 and dual emissive peaks in the NIR region (710 nm, 1199 nm) for ZnL1. Whereas, emissions in solution state (DMF) with lower intensity occurred at 465–545 nm. All complexes were subjected to thermogravimetric analysis with ZnL2 showing the highest thermal stability of up to 342 °C before undergoing decomposition. The good solid state emission properties illustrated that the complexes featured their potential as promising cost effective solid state photoactive materials.