Intramolecular Charge Transfer Transition Research Articles

Benzothiazole-quinoline based probe for simultaneous colorimetric detection of CN- and Cu2+ ions, with fluorescence sensing for Cu2+: Mechanistic insights and practical applications in environmental monitoring and cellular analysis

The development and synthesis of notably targeted and colorimetric sensor based on an azomethine compound for the distinct recognition of Cu2+ and CN− ion individually in an aqueous dimethyl formamide solution is performed. In the presence of CN− and Cu2+, the sensor BTZ showed impressive colorimetric changes, going from pale yellow to orange and pale yellow to dark yellow, respectively. In the meantime, FL spectrum (Cu2+) and UV–vis spectroscopy (CN−/Cu2+) were used to assess the sensing features. The plausible binding mechanisms of CN− and Cu2+ ions with sensor BTZ have been studied using the 1H NMR titration, Job's plot and DFT technique. The bathochromic shift produced by the intramolecular charge transfer (ICT) transition may have been the source of the phenomenon. Furthermore, CN− ion in the commercial substance is quickly identified and measured with the naked eye by using sensor BTZ. It was found that the BTZ's LOD for CN− and Cu2+ was 0.280 × 10−7 M and 1.153 × 10−7 M, respectively. Moreover, 1:1 binding ratio for the reaction of CN− and Cu2+ ions with sensor BTZ were demonstrated by Job's plot, which was dependent on analytical data. The findings show that BTZ is an easy-to-use and practical probe for concurrently sensing cyanide and copper ions in environmental samples and living cells that have less cytotoxicity.

Suzuki-Miyaura coupling reaction: Blue-yellow emitting AIE active dyes for organic electronics

A series of eight novel donor‒acceptor (D─A) based 2,3-di(thiophen-2-yl)quinoxaline derivatives 2–9 were prepared by modulating donor species on quinoxaline core with Palladium catalyzed Suzuki–Miyaura ‘C–C bond’ coupling reaction. The synthesized molecules were fully characterized and studied for impact of D–A interaction on opto-electrochemical properties. Absorption spectra of 2–9 display intramolecular charge transfer (ICT) transitions in the range of 388–414 nm. Dyes shows positive solvatochromism and emit in blue‒yellow region with emission maxima 444−550 nm on excitation at their respective ICT maxima in toluene, chloroform, DCM, DMSO and neat solid film. Further, solid state emission was studied for aggregation‒induced emission (AIE) effect in THF–water system due to the nanoparticles formation, as confirmed by FEG‒SEM technique. The HOMO and LUMO energy level for compounds 2–9 were measured by cyclic voltammetry and found in the range of −5.15 to −5.94 eV and −2.81 to −3.39 eV. Theoretical studies of molecules were also carried out by using DFT and TD‒DFT calculations. The comparable HOMO and LUMO energy levels with reported ambipolar materials and efficient solid-state emission make synthesized compounds potential candidate for solid state emissive, ambipolar charge transporting materials in organic electronics.

Achieving Controllable Thermochromic Fluorescence via Synergistic Intramolecular Charge Transfer and Molecular Packing

Thermochromic fluorescent materials (TFMs) have attracted significant attention due to their unique fluorescent colorimetric response to temperature. However, existing TFMs still suffer from weak stimulus responsiveness, broad temperature response ranges, uncontrollable emission color changes, and low quantum yields. In this study, we address these issues by designing and synthesizing three diketone‐boron complexes with distinct emission wavelengths (NWPU‐(2‐4)). Utilizing a molecular engineering strategy to manipulate intramolecular charge transfer transitions and molecular packing modes, our synthesized complexes exhibit efficient fluorescence emission in both solution and solid states. Moreover, their emission wavelengths are highly sensitive to environmental polarity. By incorporating these compounds into thermosensitive matrices of long‐chain alkanes, we produced TFMs with varied fluorescence emission peak variation ranges. Notably, the TFM based on NWPU‐4, owing to its strong charge transfer transitions and dense J‐aggregate packing configuration, not only exhibits intense fluorescence emission spanning the deep red to near‐infrared spectrum but also displays a remarkable 90 nm broad range of thermochromic properties. Ultimately, it was successfully applied to programmable, thermally controlled, multi‐level information encryption.

Achieving Controllable Thermochromic Fluorescence via Synergistic Intramolecular Charge Transfer and Molecular Packing.

Thermochromic fluorescent materials (TFMs) have attracted significant attention due to their unique fluorescent colorimetric response to temperature. However, existing TFMs still suffer from weak stimulus responsiveness, broad temperature response ranges, uncontrollable emission color changes, and low quantum yields. In this study, we address these issues by designing and synthesizing three diketone-boron complexes with distinct emission wavelengths (NWPU-(2-4)). Utilizing a molecular engineering strategy to manipulate intramolecular charge transfer transitions and molecular packing modes, our synthesized complexes exhibit efficient fluorescence emission in both solution and solid states. Moreover, their emission wavelengths are highly sensitive to environmental polarity. By incorporating these compounds into thermosensitive matrices of long-chain alkanes, we produced TFMs with varied fluorescence emission peak variation ranges. Notably, the TFM based on NWPU-4, owing to its strong charge transfer transitions and dense J-aggregate packing configuration, not only exhibits intense fluorescence emission spanning the deep red to near-infrared spectrum but also displays a remarkable 90 nm broad range of thermochromic properties. Ultimately, it was successfully applied to programmable, thermally controlled, multi-level information encryption.

Two Aggregation‐Induced Emission Actives Triphenylamine‐Based Salicylaldimine Compounds for Latent Fingerprints Detection

AbstractTo further explore the candidate materials for latent fingerprints detection, two triphenylamine‐based salicylaldimine compounds containing phenoxazine moiety (TPA‐PXZ) and carbazole unit (TPA‐Cz) were designed and successfully synthesized, respectively. They exhibited intramolecular charge transfer transitions and aggregation‐induced emission properties. Based on quantum chemical calculation results, it was found that compounds TPA‐Cz and TPA‐PXZ had twisted spatial configuration, which were responsible for aggregation‐induced emission. Meanwhile, the morphology of two compounds nano‐aggregates in the THF/water mixtures with 60 % and 80 % water content was tested. To our delight, the developers that prepared by compounds TPA‐Cz and TPA‐PXZ both were used for latent fingerprints detection on the surface of glasses, and they emitted purple fluorescence, as well as the distinct fingerprint imaging could be easily distinguished fingerprint level 1–3 details. We believe that TPA‐Cz and TPA‐PXZ both are the promising candidate for latent fingerprints detection.

Influence of Intermolecular Structural Effects on Radiative Efficiency in Xanthene-Based Carboranyl Luminophores.

Two o-carboranes with (i) 9,9-dimethyl-9H-xanthene and (ii) spiro[fluorene-9,9'-xanthene] moieties (XTC and sXTC, respectively) were prepared and characterized. Single X-ray crystallography analysis revealed the presence of intermolecular hydrogen bonds in XTC crystals. Although both compounds did not exhibit emission in tetrahydrofuran solutions at 298 K, intense bluish emission was observed in the solid states and frozen tetrahydrofuran solutions at 77 K. According to the results of theoretical calculations, this emission originated from an intramolecular charge transfer (ICT) transition with the o-carborane moiety. The absolute quantum efficiency (Φem) of the ICT-based emission in the film state equaled 49% for XTC and 20% for sXTC but was as high as 90% for the crystals of both compounds. The crystal structures of XTC and sXTC revealed that the o-carboranyl-appended phenyl plane was orthogonal (85-89°) to the carbon-carbon bonding axis in the o-carborane, indicating the existence of a strong exo-π-interaction, which was identified as the structural basis for the ICT-based transition. These results implied that the intermolecular structural effect of XTC in the randomly aggregated solid state (film) helped maintain the above orthogonality and, hence, the high efficiency from the ICT radiative mechanism. Thus, we concluded that the ICT radiative efficiency of o-carboranyl luminophores in the aggregated solid state can be controlled by specific intermolecular interactions and that the molecular geometric design inducing this feature can be important for developing highly efficient carboranyl luminophores.

Theoretical study on the atomic substitution effect on the aromaticity and ESIPT behavior of a novel chalcone-based fluorophore

Recently, a new ESIPT-based fluorophore (E)-2-(4-(dimethylamino) benzylidene)-7-hydroxy-1-indanone (7HIN) was designed and obtained experimentally. We investigated the excited state intramolecular proton transfer (ESIPT) behavior and photophysical properties of 7HIN based on density functional theory (DFT) and time-dependent DFT. Two derivatives of 7HIN (4HID and 4HBF) were obtained by replacing the CH2 group in the five-membered ring with NH group and O atom to study the atomic substitution effect on the proton transfer reactions and fluorescent features of 7HIN. All data from structural parameters, infrared frequencies and electron density showed that the intramolecular hydrogen bonds (IHB) in 7HIN and its derivatives were strengthened in the excited state (S1), which will accelerate the ESIPT process. The potential energy curves (PECs) indicated that the proton transfer can easily occur in the S1 state because of the lower energy barrier. The electron-hole analysis revealed that the S0 → S1 transition is an intramolecular charge transfer transition. The NH- and O-substitution led to a weakening of IHB, increased the ESIPT barrier and red-shifted the absorption/emission wavelength of 7HIN. The PBE38 functional in this work is very reliable since the experimental absorption/fluorescence wavelength of 7HIN was reproduced well.

Design of Isoindigo-Based Small-Molecule Donors for Bulk Heterojunction Organic Solar Cell Applications in Combination with Nonfullerene Acceptors.

The development of small-molecule organic solar cells with the required efficiency depends on the information obtained from molecular-level studies. In this context, 39 small-molecule donors featuring isoindigo as an acceptor moiety have been meticulously crafted for potential applications in bulk heterojunction organic solar cells. These molecules follow the D2-A-D1-A-D2 and D2-A-π-D1-π-A-D2 framework. Similar molecules considered in the previous experimental study (molecules R1 ((3E,3″E)-6,6″-(benzo[1,2-b:4,5-b']dithiophene-2,6-diyl)bis(1,1'-dimethyl-[3,3'-biindolinylidene]-2,2'-dione)) and R2 ((3E,3″E)-6,6″-(4,8-dimethoxybenzo[1,2-b:4,5-b']dithiophene-2,6-diyl)bis(1,1'-dimethyl-[3,3'-biindolinylidene]-2,2'-dione))) have been chosen as reference molecules. Molecules with and without π-spacers have been considered to understand the impact of the length of the π-spacer on intramolecular charge-transfer transitions and absorption properties. A detailed investigation is carried out to establish the relationship between the structure and photovoltaic parameters using density functional theory and time-dependent density functional theory methods. The newly developed molecules exhibit better electronic, excited-state, and charge transport properties than the reference molecules. Additionally, model donor-acceptor interfaces are constructed by integrating the designed donor molecules with fullerene/nonfullerene acceptors. The electronic and excited-state properties of these interfaces are rigorously evaluated. Results elucidate that the donor comprising of isoindigo-bithiophene-pyrroloindacenodithiophene (IIG-T2-PIDT) emerges as a promising candidate for bulk heterojunction solar cells based on nonfullerene acceptors. This research provides systematic design strategies for the development of small-molecule donors for organic solar cells.

Selective and Effective Sensing of Cyanide Ion with no Interference in Water by Phenothiazine-indolium Fused Optical Sensor.

The sensor with electron donor phenothiazine-2-carbaldehyde and electron acceptor indolium carboxylic acid, is developed with an intramolecular charge transfer transition between them. The synthesized molecule senses cyanide ion in water. The cyanide ion reacts with the molecule via nucleophilic addition in the indolium ring with a noticeable purple to colorless change in the solution observed. Also with the cyanide ion interaction, the sensor exhibits change in UV-visible absorption and fluorescence spectra. While the other ion does not show spectral and visual changes when interacts with the sensor molecule. Also the interference study reveals that the molecule is highly selective towards cyanide ion. Different source of water samples confirms the CN- ion sensing efficiency of the molecule. 1:1 interaction between the molecule PTI and cyanide ion is confirmed from the results of Jobs plot, 1H NMR and HRMS. Paper strips were prepared and this can act as a simple tool to sense cyanide ion in various water samples.

Near-IR Capturing N-Methylbenzene Sulfonamide-Phenothiazine Incorporating Strong Electron Acceptor Push-Pull Systems: Photochemical Ultrafast Carrier Dynamics.

Unraveling the intriguing aspects of the intramolecular charge transfer (ICT) phenomenon of multi-modular donor-acceptor-based push-pull systems are of paramount importance considering their promising applications, particularly in solar energy harvesting and light-emitting devices. Herein, a series of symmetrical and unsymmetrical donor-acceptor chromophores 1-6, are designed and synthesized by the Corey-Fuchs reaction via Evano's condition followed by [2+2] cycloaddition retroelectrocyclic ring-opening reaction with strong electron acceptors TCNE and TCNQ in good yields (~60-85 %). The photophysical, electrochemical, and computational studies are investigated to explore the effect of incorporation of strong electron acceptors 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) and dicyanoquinodimethane (DCNQ) with phenothiazine (PTZ) donor. An additional low-lying broad absorption band extended towards the near-infrared (NIR) region suggests charge polarization after the introduction of the electron acceptors in both symmetrical and asymmetrical systems, leading to such strong ICT bands. The electrochemical properties reveal that reduction potentials of 3 and 6 are lower than those of 2 and 5, suggesting DCNQ imparts more on the electronic properties and hence largely contributes to the stabilization of LUMO energy levels than TCBD, in line with theoretical observations. Relative positions of the frontier orbitals on geometry-optimized structures further support accessing donor-acceptor sites responsible for the ICT transitions. Eventually, ultrafast carrier dynamics of the photoinduced species are investigated by femtosecond transient absorption studies to identify their spectral characteristics and target analysis further provides information about different excited states photophysical events including ICT and their associated time profiles. The key findings obtained here related to excited state dynamical processes of these newly synthesized systems are believed to be significant in advancing their prospect of utilization in solar energy conversion and related photonic applications.

Coumarin Linked Cyanine Dye for the Selective Detection of Cyanide Ion in Environmental Water Sample.

A benzoxazole-coumarin-based probe BOC, was synthesized and validated for its anion sensing ability and found to be effective in recognizing cyanide ions. Upon addition of cyanide, a spontaneous color change was observed that was visible to the naked eye. The sensitization process takes place with nucleophilic addition, and the cyanide ion added to the probe disrupts the intra molecular charge transfer transition (ICT) between the donor and acceptor units, causing the pink colored probe to become yellow. Ultraviolet and fluorescence methods were applied to measure the detection limits of probes with added cyanide ions, which were found to be 3.47 µM and 2.48 nM. The stoichiometry of the probe with the cyanide ion was determined by the Job's method, NMR titration, and mass spectrometry and was found to be in a 1:1 ratio. The results obtained from the visual and UV-visible spectral studies are justified by theoretical calculations. The cyanide-loaded probe induced visual changes, which enabled the development of a test strip for field application, and the prepared strip can be used to detect the ppm level of cyanide in water samples. The developed probe, BOC, can be used to detect cyanide ions in various water samples.

A ferrocene-based chemo-dosimeter for colorimetric and electrochemical detection of cyanide and its estimation in cassava flour.

A simple chemo-dosimeter VDP2 bearing a ferrocene moiety was designed, synthesized, and characterized, and exhibited both chromogenic and electrochemical responses selectively for CN- in H2O-DMSO (9 : 1, v/v) medium. The probe VDP2 showed an instantaneous color change from colorless to yellow with CN- that can readily be observed visually. The deprotonation of the benzimidazole -NH, followed by nucleophilic addition of CN- to the olefinic C-atom, as evidenced by 1H and 13C NMR titration experiments, caused the colorimetric and electrochemical responses. The mass spectral study, CV, FTIR and Mulliken charges computed well supported the proposed mechanism. The electrochemical limit of detection was calculated to be 72 nM. The results of DFT and TD-DFT calculations suggested that the colorless nature of the probe VDP2 is due to weak intramolecular charge transfer (ICT) transition and the yellow color of the VDP2+CN adduct is due to through-space ICT transition. Above all, the probe could be an ideal candidate for monitoring cyanide in water samples and cassava flour with practical significance. A simple and convenient colorimetric method was developed to determine cyanide content in cassava flour.

D−A Based 2,3‐di(pyridin‐2‐yl)pyrido[2,3‐b]pyrazine Amine derivatives as Blue‐Orange Emitting Materials: Tuning of Opto‐electrochemical and Theoretical properties

AbstractA series of six new donor‐acceptor (D−A) type 2,3‐di(pyridin‐2‐yl)pyrido[2,3‐b]pyrazine amine derivatives as blue‐orange light emitting materials were designed, synthesized, characterized and their relevant opto‐electrochemical and theoretical properties have been fully investigated. Absorption spectra of dyes 2–7 possess intramolecular charge transfer (ICT) transitions (λmax=394–449 nm) and positive solvatochromism with emission in the blue‐orange region (λemm=477–582 nm) in solution and solid state. Further, the HOMO (−5.32 to −5.86 eV) and LUMO (−3.34 to −3.40 eV) energy levels were calculated by cyclic voltammetry (CV) and correlated by DFT/TD−DFT calculations. Moreover, computed singlet (S1) and triplet (T1) excitation energy difference (ΔEST=0.27–0.68 eV) were analyzed using the DFT/TD−DFT methods. Thus, potential applications of the dyes are proposed for organic electronics.

Fabrication and comprehensive investigations on NBD-based luminescent solar concentrator

The design and development of innovative chromophoric materials for luminescent solar concentrators (LSCs) is an emerging area of research in the pursuit of low-cost photovoltaic technology. In this study, we devised and developed the optically active fluorescent dye NBDNH2 based on the skeleton of a benzoxadiazole. In NBDNH2, the electron donating amino group and the electron-withdrawing nitro group are the responsible for intramolecular charge transfer transition as well as fluorescence upon photoexcitation. The structural and photophysical properties of NBDNH2 dye have been meticulously investigated. In addition, the solvent-property relationships also investigated through time-resolved fluorescence and 1H NMR measurements. The photophysical studies reveal that the dye has a moderate Stokes shift, a long fluorescence lifetime and provides guidance for the development of LSCs. NBDNH2 was doped in polymethyl methacrylate (PMMA) to fabricate LSC devices. Due to promising optical properties, the NBDNH2 based LSC (5 × 5 × 0.3 cm3) showed the internal and external photon efficiencies as high as 29.4 % and 3.84 %, respectively. When connected with the photovoltaic cell, the champion device yielded power conversion efficiency of 1.32 % and 0.64 % with scattering and black background, respectively. Based on the findings, we unequivocally envisaged that the benzoxadiazole-based ICT probe is a prospective optical material for LSC applications.

Theoretical and experimental investigation of exciplex-forming and electroluminescent properties of 4-ethyl-3,5-bis[40-(N, N-diphenylamine)biphenyl-4-yl]-4H-1,2,4-triazole

The recently synthesized 4-ethyl-3,5-bis [40-(N, N-diphenylamine)biphenyl-4-yl]-4H-1,2,4-triazole (TPA-TZ) is in this work thoroughly studied as an efficient luminophore with an account of density functional theory. The intense fluorescence is explained as an intramolecular charge-transfer transition from the diphenylamine (donor) moiety to the central part of the dye with a characteristic electron redistribution in the triazole ring (acceptor). The photoluminescence (PL) and phosphorescence (Ph) spectra of TPA-TZ in the film and in THF solution at 77 K were studied together with the well-known 2,4,6-tris [3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T) dye. The latter compound was used as an electron-withdrawing component of the investigated TPA-TZ: PO-T2T exciplex, which is characterized by a relatively high energy level of the excited lowest triplet state. The films of a solid-state mixture of TPA-TZ and PO-T2T showed exciplex-type emission being slightly red-shifted compared to the PL of the individual donor and acceptor compounds. Two OLED devices with emitting layers of TPA-TZ and of the exciplex-forming molecular mixture of TPA-TZ and PO-T2T were prepared. The exciplex–based OLED demonstrated 4 103 cd/m2 brightness, a current efficiency of 22 cd/A, a power efficiency of 6.77 lm/W, and an external quantum efficiency (EQE) of 7%. This confirms the possibility of triplet harvesting in the molecular mixture of TPA-TZ and PO-T2T, since the theoretical EQE limit for OLED based on the prompt fluorescence is 5%.

Synthesis of D−A based violet−red light emitting indolo[2,3-b]quinoxalin-2-yl(phenyl)methanone amine dyes: Opto-electrochemical, AIE, and theoretical properties

In this work, we have designed and synthesized seven new amine derivatives of indolo[2,3-b]quinoxalin-2-yl(phenyl)methanone through the use of palladium-catalyzed Buchwald−Hartwig (C−N) coupling amination reaction and characterized by spectroscopic methods. Molecules offers intramolecular charge transfer (ICT) transitions, which result in absorption spectra with longer wavelengths (λmax = 385−509 nm), resembling a donor−acceptor (D−A) assembly. Consequently, the dyes emit light in violet–red region (λemi = 406−637 nm) in solution and solid film. Moreover, dye 5 and 6 demonstrate aggregation–induced emission (AIE) in THF−Water system due to the formation of nanoaggregates. Electrochemical properties investigated using cyclic voltammetry. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were determined within the range from −4.91 to −5.76 eV and −3.03 to −3.45 eV, respectively, and comparable with reported ambipolar materials. Theoretical studies also conducted using density functional theory (DFT) and time–dependent density functional theory (TD–DFT) calculations, which agreeing with experimental data. The small energy difference between singlet (S1) and triplet (T1) states (∆EST = 0.24−0.45 eV) suggests that these dyes possess thermally activated delayed fluorescence (TADF) emitting properties. Thus, dyes propose their potential application in optoelectronic devices.

NIR-Absorbing 1,1,4,4-Tetracyanobuta-1,3-diene- and Dicyanoquinodimethane-Functionalized Donor-Acceptor Phenothiazine Derivatives: Synthesis and Characterization.

A series of symmetrical and unsymmetrical donor-acceptor type phenothiazine derivatives 1-18 were designed and synthesized via Pd-catalyzed Sonogashira cross-coupling and [2 + 2] cycloaddition-retroelectrocyclization reactions. The incorporation of cyano-based acceptors 1,1,4,4-tetracyanobutadiene (TCBD) and dicyanoquinodimethane (DCNQ) in the phenothiazine derivatives resulted in systematic variation in the photophysical, thermal, and electrochemical properties. The electronic absorption spectra of the phenothiazine derivatives with strong acceptors 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, and 18 show red-shifted absorption as compared to phenothiazine derivatives 1, 4, 7, 10, 13, and 16 in the near-IR region due to a strong intramolecular charge transfer (ICT) transition. The electrochemical analysis of the phenothiazine derivatives 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, and 18 reveals two reduction waves at low potential due to the TCBD and DCNQ acceptors. The mono-TCBD-functionalized phenothiazine 2 shows higher thermal stability compared to other phenothiazine derivatives. The computational studies on phenothiazines 1-18 reveal the LUMO is substantially stabilized as acceptor strength increases, which lowers the HOMO-LUMO gap.

Acceptor engineering of semiconducting oligomers for improved NIR-II fluorescence imaging and therapy

Fluorescence imaging (FI) conducted over second near-infrared (NIR-II) window shows superior performance with deeper penetration, higher temporal and spatial resolution than that over the first near-infrared (NIR-I) window. Various attempts have been made to develop ideal fluorophores with high brightness, longer emission wavelength and good biocompatibility for NIR-II FI. Here, we design and synthesize three D-A-D type oligomers through acceptor engineering approach to compare their optical properties. The newly prepared oligomer (O3) based on thiadiazolobenzotriazole (TBZ) acceptor exhibits the highest NIR-II brightness compared with the counterparts because of the weakest intramolecular charge transfer transition. Water-dispersed O3 nanoparticles (NPs) are then fabricated via nanoprecipitation method, which demonstrate superior NIR-II imaging ability for in vivo vascular imaging and tumor-targeted imaging. Furthermore, O3 NPs exhibit significant photothermal performance, thus inducing obvious cancer cell elimination upon 808 nm light irradiation. Taken together, TBZ unit is a promising electron acceptor for constructing bright and functional NIR-II dyes. This acceptor engineering method has offered us a feasible strategy to develop versatile NIR-II fluorophores.

A Combination of B- and N-Doped π-Systems Enabling Systematic Tuning of Electronic Structures and Properties.

Doping heteroatoms into polycyclic aromatic hydrocarbons (PAHs) may alter their structures and thereby physical properties. This study reports the construction of B/N-codoped PAHs via combining the B- and N-doped π-systems. Two π-extended B/N-codoped PAHs were synthesized through the Mallory photoreaction. Both feature a C48 BN2 π-skeleton, which is assembled by linearly fusing three substructures including B-doped and sp2 -hybridized N-doped π-moieties and one pyrene unit. In comparison to the pristine B-doped analog, their intramolecular charge transfer (ICT) states are distinctly modulated by the fused N-doped π-system and the further incorporated cyano group, leading to their tunable optical properties, as revealed by detailed theoretical and experimental analysis. Furthermore, these three molecules have sufficient Lewis acidity and can coordinate with Lewis base to form Lewis acid-base adducts, and notably, such intermolecular complexation can further dynamically modulate their ICT transitions and thereby photophysical properties, such as producing blue, green and red fluorescence.

Tunable Yellow to Near-Infrared Fluorescent Boron-Amino-Chelating Complexes with Stokes Shifts >100 nm.

A series of diphenylboron-chelating N-substituent 8-aminoquinoline, 5-aminoquinoxaline, and 1-aminophenazine were prepared. They exhibit lowest energy absorption peaks of 444-766 nm, emission peaks of 563-820 nm, and quantum yields of up to 46.5%. Electrochemical and theoretical studies indicate that the N-substituent mainly determines the HOMO and the framework determines the LUMO, thus allowing for a wide-tuning of absorptions/emissions. Intramolecular charge transfer transition leads to large Stokes shifts of up to 166 nm. One selected compound showed satisfactory cytocompatibility and cytoplasm-targeting cell imaging ability.