Diindolocarbazole-Based Rigid Donor-Acceptor TADF Molecules for Energy and Electron Transfer Photocatalysis.

The design and synthesis of four twisted donor-acceptor (D-A) thermally activated delayed fluorescence (TADF) molecules CBZ-IQ, CBZ-2FIQ, DI-IQ and DI-2FIQ is reported in this work based on diindolocarbazole (DI) and phenyl carbazole as donor and indoloquinoxalines as acceptor. These compounds serve as photocatalysts for organic transformations. Theoretical calculations and experimental data showed reasonable singlet and triplet energy gaps of 0.17-0.26 eV for all compounds. All molecules showed increase in fluorescence quantum yields after degassing the solution and the transient photoluminescence decay showed two components: shorter prompt components (11.4 ns to 31 ns) and longer delayed components (36.4 ns to 1.5 µs) which further indicate the occurrence of TADF process. Cyclic voltammetry studies indicated well-suited excited state redox potentials of all compounds to catalyze organic transformations such as heteroarene arylation. Accordingly, photocatalytic C-H arylation of heteroarenes were performed using these compounds with excellent isolated yields of upto 80 %. Due to their suitable efficient triplet energy levels, all the emitters were also employed as energy transfer photocatalysts in E to Z isomerization of stilbene with the excellent conversion of ~90 %.

Tripodal Triazine and 1,8-Naphthalimide-based Small Molecules as Efficient Photocatalysts for Visible-light Oxidative Condensation.

Tripodal donor-acceptor (D-A) small molecules Tr-Np3 and Tr-T-Np3 consisting of triphenyl triazine and 1,8-naphthalimide, without and with a thiophene spacer have been synthesized. Their optical and redox properties were thoroughly investigated along with their utilization as photocatalysts in organic transformations. Compounds Tr-Np3 and Tr-T-Np3 showed broad absorption in the range of 290-480 nm in solutions and 300-510 nm in thin films. These tripodal molecules displayed wide optical bandgaps of (Eg opt ) 3.10 eV and 2.64 eV with very deep-lying HOMO energy levels (-6.60 eV and -6.03 eV) and low-lying LUMO levels (-3.50 eV and -3.40 eV). Appreciable electron mobilities of 5.24×10-4  cm2 /Vs and 6.14×10-4  cm2 /Vs were obtained for compounds Tr-Np3 and Tr-T-Np3 respectively by space-charge limited current (SCLC) measurements. Metal-free tripodal molecules Tr-Np3 and Tr-T-Np3 showed excellent photocatalytic abilities towards condensation of aromatic aldehydes and o-phenylenediamine followed by cyclization under visible light to yield benzimidazole derivatives that are of high medicinal value.

Functionalized Benzothiadiazole Non-Fused A-D-A'-D-A Small Molecules for Effective Electron Mobilities and Metal-free Photocatalysis.

Three non-fused A-D-A'-D-A π-conjugated metal-free small molecules BT-IT1, BT-IBT2 and BT2F-IBT3 have been synthesized and their absorption characteristics and redox properties, as well as charge carrier mobilities have been investigated. The resultant molecules exhibited broad absorption in the range of 325-600 nm in solutions and in thin films the absorption range is 350-700 nm. These new conjugated small molecules showed low-lying HOMO energy levels (-5.49 to -5.50 eV), deep LUMO energy levels (-3.67 to -3.69 eV) and narrow bandgaps of (Eg CV ) ∼0.79 eV. Appreciable electron mobilities for compounds BT-IBT2 and BT2F-IBT3 were 4.56×10-3 and 1.12×10-3  cm2 V-1 s-1 , respectively, obtained by space-charge limited current (SCLC) measurements. Additionally, excellent photocatalytic performances of BT-2T (6), BT2F-2T (10), BT-IT1, BT-IBT2 and BT2F-IBT3 for highly selective oxidation of thioanisole to desired sulfoxides under visible light irradiation were observed.

Discs to a 'Bright' Future: Exploring Discotic Liquid Crystals in Organic Light Emitting Diodes in the Era of New-Age Smart Materials.

With the advent of a new decade and the paradigm shift of every sphere of urban life to virtual platforms, it has become imperative for the global researcher community to channelize efforts into upgradation of the existing display-technology. In this context, discotic liquid crystals (DLCs) are a class of self-assembling organic materials that are recently being explored in fabricating the emissive layers of organic light emitting diodes (OLEDs). With their unique inherent structural and functional properties, they have the potential to challenge the currently prevailing OLED-emitters. Yet the applications of this promising class of materials in OLEDs have not been comprehensively reviewed in literature till now. In this account, we present an overview of the developments in the field of luminescent DLC-based emitters, supported by their associated photophysical phenomena and their performance parameters as emitters in fabricated OLED devices.

Aminoindole and naphthalimide based charge transfer fluorescent probes for pH sensing and live cell imaging.

Fluorescent probes are essential for imaging of cancer cells and for tracking organelles inside cells. We have synthesized three molecular rotors AIN, AINP and F-AINP based on 1-aminoindole (AI) as an electron donor and naphthalimide as an electron acceptor. All compounds showed charge transfer (CT) character, aggregation induced emission (AIE) and emission responsiveness towards temperature variation and solvent viscosity. AINP was most sensitive towards viscosity among all molecules with a viscosity sensitivity of ∼0.37. AIN, AINP and F-AINP showed negative temperature coefficients in chloroform with internal sensitivities of -0.04% °C-1, -0.08% °C-1 and -0.1% °C-1, respectively. Furthermore, all the rotors were sensitive towards the pH of the solvent environment as revealed by acid titration and base back-titration and served as colorimetric pH sensors with intriguing photophysical characteristics. Additionally, AINP and F-AINP were used to image the live cancer cell line A549 and the fibroblast cell line L929, and the imaging studies revealed the incorporation of dyes in the cytoplasmic space of the cells except for the nuclei.

Excited state dynamics of BODIPY-based acceptor-donor-acceptor systems: a combined experimental and computational study.

Donor-bridge-acceptor systems based on boron dipyrromethene (BODIPY) are attractive candidates for bio-imagining and sensing applications because of their sensitivity to temperature, micro-viscosity and solvent polarity. The optimization of the properties of such molecular sensors requires a detailed knowledge of the relation between the structure and the photophysical behavior in different environments. In this work we have investigated the excited-state dynamics of three acceptor-donor-acceptor molecules based on benzodithiophene and BODIPY in solvents of different polarities using a combination of ultrafast spectroscopy and DFT-based electronic structure calculations. Transient absorption spectra show that upon photoexcitation an initial excited species with an induced absorption band in the near-infrared regime is formed independent of the solvent polarity. The subsequent photophysical processes strongly depend on the solvent polarity. In non-polar toluene this initial excited state undergoes a structural relaxation leading to a delocalized state with partial charge transfer character, while in the more polar tetrahydrofuran a fully charge separated state is formed. The results clearly show how factors such as donor-acceptor distance and restricted rotational motion by steric hindrance can be used to tune the excited state photophysics to optimize such systems for specific applications.

Structure-property relationships in multi-stimuli responsive BODIPY-biphenyl-benzodithiophene TICT rigidochromic rotors exhibiting (pseudo-)Stokes shifts up to 221 nm.

Structure-property relationships of donor-π-acceptor (D-π-A) type molecular dyad (pp-AD) and triads (pp-ADA and Me-pp-ADA) based on benzodithiophene and BODIPY with biphenyl spacers have been reported. Rotors pp-AD and pp-ADA showed efficient twisted intramolecular charge transfer (TICT) with near infrared (NIR) emissions at ∼712 nm and ∼725 nm with (pseudo-)Stokes shifts of ∼208 nm and ∼221 nm, respectively, and prominent solvatochromism. A structurally similar triad, Me-pp-ADA, with tetramethyl substituents on the BODIPY core instead was TICT inactive and exhibited excitation energy transfer with a transfer efficiency of ∼88% as revealed using steady state emission and transient absorption measurements. Rotors pp-AD and pp-ADA showed NIR emission with an enhancement in intensity with the addition of water in THF solution as well as a pronounced change in emission intensity with temperature and viscosity variations, which justify their utility as temperature and viscosity sensors. Furthermore, the linear correlation of lifetime with fluorescence intensity ratios of the donor and acceptor justifies the rigidochromic behaviour of these rotors.

Regioisomeric BODIPY Benzodithiophene Dyads and Triads with Tunable Red Emission as Ratiometric Temperature and Viscosity Sensors.

Regioisomeric acceptor-donor (AD) molecular rotors (p-AD, m-AD and m-ADA) were synthesized and characterized, wherein dyads p-AD and m-AD, and triad m-ADA contained 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) and benzodithiophene (BDT) as electron-acceptor and electron-donor, respectively. In all the compounds, the donor and acceptor moieties are electronically decoupled by a phenyl spacer, either through a para coupling or through a meta coupling. The dyad counterparts p-AD and m-AD showed distinct photophysical characteristics in which dyad p-AD showed TICT band at ca. 654 nm characterized by a Stokes shift of ca. 150 nm and prominent solvatochromism. However, meta regioisomeric triad m-ADA showed well-defined aggregation in solution. Notably, because of the temperature-tunable and solvent-viscosity-dependent emission, efficient ratiometric temperature sensing with positive and negative temperature coefficients and viscosity sensing was observed for all compounds. Interestingly, the fluorescence of dyad m-AD (in 10/90 v/v THF/water) revealed a near-white light emission with CIE chromaticity coordinates (x, y) of (0.32, 0.29). Furthermore, the fluorescence emission of p-AD in THF at 0 °C also showed a near-white light emission with chromaticity coordinates (x, y) of (0.34, 0.27). Such multifunctional rotors with readily tunable emission in the red region and prominent temperature- and viscosity-sensing abilities are promising for sensing and bioimaging applications.

Dual emissive bodipy-benzodithiophene-bodipy TICT triad with a remarkable Stokes shift of 194 nm.

An acceptor-donor-acceptor (A-D-A) triad based on a BODIPY acceptor and a benzodithiophene donor exhibited dual fluorescence and pronounced fluorescence solvatochromism because of twisted intramolecular charge transfer (TICT) state formation. Furthermore, it showed a Stokes shift of ∼194 nm which is the highest known for any BODIPY compound with a readily tunable fluorescence and a high charge carrier mobility of 4.46 × 10-4 cm2 V-1 s-1.

Chlorophyll J-aggregates: from bioinspired dye stacks to nanotubes, liquid crystals, and biosupramolecular electronics.

Among the natural light-harvesting (LH) systems, those of green sulfur and nonsulfur photosynthetic bacteria are exceptional because they lack the support of a protein matrix. Instead, these so-called chlorosomes are based solely on "pigments". These are self-assembled bacteriochlorophyll c, d, and e derivatives, which consist of a chlorophyll skeleton bearing a 3(1)-hydroxy functional group. Chemists consider the latter as an essential structural unit to direct the formation of light-harvesting self-assembled dye aggregates with J-type excitonic coupling. The intriguing properties of chlorosomal J-type aggregates, particularly narrow red-shifted absorption bands, compared with monomers and their ability to delocalize and migrate excitons, have inspired intense research activities toward synthetic analogues in this field. The ultimate goal of this research field is the development of (opto-)electronic devices based on the architectural principle of chlorosomal LH systems. In this regard, the challenge is to develop small, functional building blocks with appropriate substituents that are preprogrammed to self-assemble across different length scales and to emulate functions of natural LH systems or to realize entirely new functions beyond those found in nature. In this Account, we highlight our achievements in the past decade with semisynthetic zinc chlorins (ZnChls) as model compounds of bacteriochlorophylls obtained from the naturally most abundant chlorin precursor: chlorophyll a. To begin, we explore how supramolecular strategies involving π-stacking, hydrogen bonding, and metal-oxygen coordination can be used to design ZnChl-based molecular stack, tube, and liquid crystalline assemblies conducive to charge and energy transport. Our design principle is based on the bioinspired functionalization of the 3(1)-position of ZnChl with a hydroxy or methoxy group; the former gives rise to tubular assemblies, whereas the latter induces stack assemblies. Functionalization of the 17(2)-position with esterified hydrophilic or hydrophobic chains, dendron-wedge substituents, and chromophores having complementary optical properties such as naphthalene bisimides (NBIs) is used to modulate the self-assembly of ZnChl dyes. The resulting assemblies exhibit enhanced charge transport and energy transfer abilities. We have used UV/vis, circular dichroism (CD), fluorescence spectroscopy, and dynamic light scattering (DLS) for the characterization of these assemblies in solution. In addition, we have studied assembly morphologies by atomic force microscopy (AFM), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), and cryogenic-TEM. Crystallographic techniques such as powder X-ray and solid-state NMR have been used to explain the precise long- and short-range packing of dyes in these assemblies. Finally, functional properties such as charge and energy transport have been explored by pulse radiolysis time-resolved microwave conductivity (PR-TRMC), conductive AFM, and time-resolved fluorescence spectroscopy. The design principles discussed in this Account are important steps toward the utilization of these materials in biosupramolecular electronics and photonics in the future.

Synthesis of regioisomerically pure 1,7-dibromoperylene-3,4,9,10-tetracarboxylic acid derivatives.

The perylene derivative 1,7-dibromoperylene-3,4,9,10-tetracarboxylic tetrabutylester has been obtained in regioisomerically pure form, by employing a highly efficient, scalable, and robust synthesis starting from commercially available perylene-3,4,9,10-tetracarboxylic bisanhydride. Subsequently, this compound is utilized for the synthesis of extremely valuable and versatile regioisomerically pure intermediates, namely, 1,7-dibromoperylene-3,4,9,10-tetracarboxylic dibutylester monoanhydride, 1,7-dibromoperylene-3,4,9,10-tetracarboxylic bisanhydride, and 1,7-dibromoperylene monoimid monoanhydride. These compounds possess at least one anhydride functionality in addition to the 1,7 bromo substituents and thus allow for a virtually limitless attachment of substituents both at the "peri" and the "bay" positions. The intermediate 1,7-dibromoperylene monoimide monoanhydride is of special interest as it provides access to unsymmetrically imide-substituted 1,7-dibromoperylene derivatives, which are not accessible by previously known procedures. Finally, substitution of the 1,7 bromine atoms in the bay area by phenoxy groups, which is a generally applied reaction for 1,7-dibromoperylene bisimides, was proven to be equally effective for a 1,7-dibromoperylene tetraester and a 1,7-dibromoperylene diester monoimid.

Molecular rotors of naphthalimide and benzodithiophene as effective solvent polarity probes, temperature sensors, and for g-C3 N4 sensitization.

Acceptor-donor-acceptor (A-D-A) molecular rotors have drawn substantial attention for their applications in monitoring temperature variations within cellular microenvironments, biomimetic photocatalysis, and bioimaging. In this study, we have synthesized two novel rotor molecules, NBN1 and NBN2, by incorporating benzodithiophene (BDT) as the donor core and naphthalic anhydride/naphthalimide (NA/NI) moieties as acceptors using Pd-catalyzed Stille coupling reactions. These molecules exhibited distinct charge transfer (CT) behavior in both their absorption and emission spectra and displayed prominent emission solvatochromism. Notably, NBN1 exhibited better CT properties among the two molecules. Moreover, these A-D-A molecular rotors demonstrated remarkable sensitivities of their emission spectra toward solvent polarities and temperatures. Rotors NBN1 and NBN2 showed positive temperature coefficients with internal temperature sensitivities of 0.34% °C-1 and 0.13% °C-1 in chloroform, respectively, and thus hold significant promise for detecting temperature variations in cellular microenvironment. Furthermore, we have modeled these molecules with graphitic carbon nitride (g-C3 N4 ) to form composite systems and performed theoretical calculations to obtain valuable insights into their charge transfer behavior. Theoretical results suggested that these molecules have the potential to efficiently sensitize and modulate the band gap of g-C3 N4 and show potential for diverse photocatalytic applications.

Metal-free FRET macrocycles of perylenediimide and aza-BODIPY for multifunctional sensing.

Two multichromophoric FRET macrocycles M1 [1+1] and M2 [2+2] with red emission (λem ∼ 721 nm) composed of perylenediimide (PDI) as the energy donor and aza-BODIPY (ABDP) as the energy acceptor were synthesized by click reaction in a metal-free fashion. M1 and M2 exhibited distinct reversible ratiometric temperature responsive emission with temperature sensitivities of 0.09-0.14% °C-1 and owing to the redox active chromophores, they showed solution phase redox responsive reversible colour changes.

Correction: Multi-stimuli programmable FRET based RGB absorbing antennae towards ratiometric temperature, pH and multiple metal ion sensing.

[This corrects the article DOI: 10.1039/D1SC05112A.].

Efficient charge transport in semisynthetic zinc chlorin dye assemblies.

We have studied the charge transport properties of self-assembled structures of semisynthetic zinc chlorins (ZnChls) in the solid state by pulsed radiolysis time-resolved microwave conductivity measurements. These materials can form either a two-dimensional (2D) brickwork-type slipped stack arrangement or a one-dimensional (1D) tubular assemblies, depending on the exact molecular structure of the ZnChls. We have observed efficient charge transport with mobilities as high as 0.07 cm(2) V(-1) s(-1) for tubular assemblies of 3(1)-hydroxy ZnChls and up to 0.28 cm(2) V(-1) s(-1) for 2D stacked assemblies of 3(1)-methoxy ZnChls at room temperature. The efficient charge transporting capabilities of these organized assemblies opens the way to supramolecular electronics based on biological systems.

Zinc chlorins for artificial light-harvesting self-assemble into antiparallel stacks forming a microcrystalline solid-state material.

We introduce a concept to solve the structure of a microcrystalline material in the solid-state at natural abundance without access to distance constraints, using magic angle spinning (MAS) NMR spectroscopy in conjunction with X-ray powder diffraction and DFT calculations. The method is applied to a novel class of materials that form (semi)conductive 1D wires for supramolecular electronics and artificial light-harvesting. The zinc chlorins 3-devinyl-3(1)-hydroxymethyl-13(2)-demethoxycarbonylpheophorbide a (3',5'-bis-dodecyloxy)benzyl ester zinc complex 1 and 3-devinyl-3(1)-methoxymethyl-13(2)-demethoxycarbonylpheophorbide a (3',5'-bis-dodecyloxy)benzyl ester zinc complex 2, self-assemble into extended excitonically coupled chromophore stacks. (1)H-(13)C heteronuclear dipolar correlation MAS NMR experiments provided the (1)H resonance assignment of the chlorin rings that allowed accurate probing of ring currents related to the stacking of macrocycles. DFT ring-current shift calculations revealed that both chlorins self-assemble in antiparallel pi-stacks in planar layers in the solid-state. Concomitantly, X-ray powder diffraction measurements for chlorin 2 at 80 degrees C revealed a 3D lattice for the mesoscale packing that matches molecular mechanics optimized aggregate models. For chlorin 2 the stacks alternate with a periodicity of 0.68 nm and a 3D unit cell with an approximate volume of 6.28 nm(3) containing 4 molecules, which is consistent with space group P2(1)22(1).

Biosupramolecular nanowires from chlorophyll dyes with exceptional charge-transport properties.

Conductive tubes: Self-assembled nanotubes of a bacteriochlorophyll derivative are reminiscent of natural chlorosomal light-harvesting assemblies. After deposition on a substrate that consists of a non-conductive silicon oxide surface (see picture, brown) and contacting the chlorin nanowires to a conductive polymer (yellow), they show exceptional charge-transport properties.

Columnar mesophases based on zinc chlorophyll derivatives functionalized with peripheral dendron wedges.

A chlorophyll derivative with a central zinc ion, a methoxy functionality at its 3(1)-position, and functionalized with a second-generation dendron (3,4-3,4,5)12G2-CH(2)OH at its 17(2)-position was synthesized starting from natural chlorophyll a (Chl a). This compound exhibits liquid crystalline (LC) behavior and its mesomorphic properties have been characterized by differential scanning calorimetry (DSC), polarisation optical microscopy (POM), powder X-ray diffraction (XRD), and scanning probe microscopy (SPM). A combination of powder XRD, high resolution scanning tunneling microscopy (STM), and atomic force microscopy (AFM) experiments revealed the formation of nano-segregated well-ordered columnar tubular superstructures consisting of about five molecules in the column stratum. These self-assembled columns are further self-organized into a two-dimensional oblique unit cell lattice. Semiconducting behavior of this compound has been studied by pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) method and charge carrier mobility values of ∼10(-2) cm(2) V(-1) s(-1) are observed. Such organized columnar superstructures constructed from semisynthetic zinc chlorins are reminiscent of the tubular organization of the bacteriochlorophyll dyes in the light-harvesting chlorosomal antennae of green sulphur bacteria.

Multi-stimuli programmable FRET based RGB absorbing antennae towards ratiometric temperature, pH and multiple metal ion sensing.

A red-green-blue (RGB) multichromophoric antenna 1 consisting of energy donors naphthalimides and perylenediimides and a central aza-BODIPY energy acceptor along with two subchromophoric red-blue (RB 6) and green-blue (GB 12) antennae was designed that showed efficient cascade Förster resonance energy transfer (FRET). RGB antenna 1 showed pronounced temperature-dependent emission behaviour where emission intensities in green and red channels could be tuned in opposite directions by temperature giving rise to unique ratiometric sensing with a temperature sensitivity of 0.4% °C. RGB antenna 1 showed reversible absorption modulation selectively in the blue region (RGB ↔ RG) upon acid/base addition giving rise to pH sensing behaviour. Furthermore, RGB antenna 1 was utilized to selectively sense metal ions such as Co2+ and Fe3+ through a FRET turn-off mechanism induced by a redox process at the aza-BODIPY site that resulted in the selective spectral modulation of the red band (i.e., RGB → GB). Model antenna RB 6 showed white light emission with chromaticity coordinates (0.32, 0.33) on acid addition. Antennae 1, 6 and 12 also exhibited solution state electrochromic switching characterized by distinct colour changes upon changing the potential. Finally, antennae 1, 6 and 12 served as reversible fluorescent inks in PMMA/antenna blends whereby the emission colours could be switched or tuned using different stimuli such as acid vapour, temperature and metal ions.

Data Quality Assessment and Multi-Organizational Reporting: Tools to Enhance Network Knowledge.

OBJECTIVE: Multi-organizational research requires a multi-organizational data quality assessment (DQA) process that combines and compares data across participating organizations. We demonstrate how such a DQA approach complements traditional checks of internal reliability and validity by allowing for assessments of data consistency and the evaluation of data patterns in the absence of an external "gold standard." METHODS: We describe the DQA process employed by the Data Coordinating Center (DCC) for Kaiser Permanente's (KP) Center for Effectiveness and Safety Research (CESR). We emphasize the CESR DQA reporting system that compares data summaries from the eight KP organizations in a consistent, standardized manner. RESULTS: We provide examples of multi-organization comparisons from DQA to confirm expectations about different aspects of data quality. These include: 1) comparison of direct data extraction from the electronic health records (EHR) and 2) comparison of non-EHR data from disparate sources. DISCUSSION: The CESR DCC has developed codes and procedures for efficiently implementing and reporting DQA. The CESR DCC approach is to 1) distribute DQA tools to empower data managers at each organization to assess their data quality at any time, 2) summarize and disseminate findings to address data shortfalls or document idiosyncrasies, and 3) engage data managers and end-users in an exchange of knowledge about the quality and its fitness for use. CONCLUSION: The KP CESR DQA model is applicable to networks hoping to improve data quality. The multi-organizational reporting system promotes transparency of DQA, adds to network knowledge about data quality, and informs research.