A Novel DR/NIR T-Shaped AIEgen: Synthesis and X-Ray Crystal Structure Study

Abstract

We developed a new benzodifuran derivative as the condensation product between 2,6-diamino -4-(4-nitrophenyl)benzo [1,2-b:4,5-b']difuran-3,7-dicarboxylate and 3-hydroxy-2-naphthaldehyde. The intramolecular hydrogen-bond interactions in the terminal half-salen moieties produce a sterically encumbered highly conjugated main plane and a D-A-D (donor-acceptor-donor) T-shaped structure. The novel AIEgen (aggregation-induced enhanced emission generator) fulfils the requirement of RIR (restriction of intramolecular rotation) molecules. DR/NIR (deep red/near infrared) emission was recorded in solution and in the solid state, with a noteworthy photoluminescence quantum yield recorded on the neat crystals which undergo some mechanochromism. The crystal structure study of the probe from data collected at a synchrotron X-ray source shows a main aromatic plane π-stacked in a columnar arrangement.Crystals 2020, 10, 269 2 of 15 law [20][21][22] the intrinsic low band-gap of such DR/NIR emitters makes them especially vulnerable to the ACQ effect [23] due to higher vibrionic coupling between the ground and excited states. Therefore, most of the AIEgens reported emit blue and green lights. Although they are highly sought after for red OLEDs (Organic Light Emitting Diodes), night-vision devices, secured displays, optical waveguides and in the wide field of bio and chemo-sensing [24][25][26][27][28], there are fewer efficient DR/NIR (deep red/near infrared) materials. Of particular interest are AIE fluorophores with intense emission at DR/NIR region owing to their deep tissue penetration, photo-stability and minimum interference in living systems [25,29,30]. Their applications are closely related to cell imaging and DNA and protein sensing [31][32][33].Novel molecular construction of DR/NIR AIEgens can be achieved with electron donor (D) and electron acceptor (A) blocks connected through π-conjugated frameworks. The most fundamental phenomenon governing the spectroscopic properties is the intramolecular charge transfer (ICT) process from the donor to the acceptor in the excited state [34][35][36]. Intercrossed excited state between the low-lying local exciton (LE) and charge transfer (CT) exciton results from the D-A interaction. Obviously, the molecular geometry is crucial for the process.Benzodifuran derivatives have drawn attention for a wide range of biological and pharmacological applications, including antimicrobial, antiviral, analgesic and antitumor [37][38][39][40] activity. This class of heterocyclic compounds are also employed in dyes industry as pigments and in different fields of optoelectronics and photonics. Due to the excellent semiconducting properties [41,42], benzodifuran scaffolds are used as nonlinear optical materials [43], for dye sensitized solar cells [44] and in organic solar cell and transistors. Finally, as electron-rich building blocks they have a potential in the constructing of photoluminescent materials [45][46][47] Herein, we developed a new benzodifuran derivative from 2,6-diamino-4-(4-nitrophenyl) ...

Facile Synthesis of Ultrastable Fluorescent Copper Nanoclusters and Their Cellular Imaging Application

“…In Figure 3 B, there is an obvious absorption peak around 600 nm, which may be attributed to the aggregation of Cu NCs@GSH (in Figure S3 ) and not the formation of large size Cu NPs. The location of emission peak remained unchanged even upon various excitation wavelengths ( Figure 3 C), implying that it was real fluorescence and not light scattering [ 43 , 44 , 45 ] and the relatively uniform surface state [ 46 , 47 ]. After freeze-drying, the lavender powder was obtained, which showed no fluorescence by irradiating at 365 nm while the strong blue-green fluorescence of Cu NCs@GSH can be recovered after their redispersion in water ( Figure S4 ).…”

Visual pH Sensors: From a Chemical Perspective to New Bioengineered Materials

“…Beginning with the pioneering studies of Tang and Park in 2001 a unique class of molecules called AIEgens (aggregation-induced emission) was developed [ 54 , 55 ]. Typically, AIEgens molecules contain multi-aromatic conjugated rings with potentially free rotating chemical groups.…”

“…Typically, AIEgens molecules contain multi-aromatic conjugated rings with potentially free rotating chemical groups. Although weakly or not emissive as isolated molecules, they become emissive in the solid state, or in concentrated solution, due to intermolecular processes and as consequence of their restriction of intramolecular rotation (RIR) [ 55 ]. AIEgens molecules have shown properties as fluorophores and exhibit aggregation-induced emission, or emission enhancement.…”

“…AIEgens molecules have shown properties as fluorophores and exhibit aggregation-induced emission, or emission enhancement. The aggregate state of the AIE molecules, often characterized by X-ray structural studies, is the result of hydrogen-bonding, p-stacking, or other Van der Waals interactions [ 55 ]. These unique characteristics differentiate AIEgens from conventional luminophores and are currently explored as optical sensors including specific interactions derived by samples pH changes.…”

Zinc (II) and AIEgens: The “Clip Approach” for a Novel Fluorophore Family. A Review

“…RACI model generally leads to a forecast on the fluorescence yield (PLQY, Φ). This fundamental parameter is defined as the ratio of the number of photons emitted to the number of photons absorbed and derives from evaluating both the radiative and the non-radiative channels activated in the AIE molecule [ 40 , 41 , 42 , 43 , 44 ].…”