Synthesis and Characterization of Amorphous Lawsone Polymer Dots for Fluorescent Applications.

In this work, a two-step hydrothermal/solvothermal process was developed to generate highly fluorescent lawsone polymer dots (LPDs) utilizing an inexpensive and abundant starting material, 2-hydroxy-1,4-napththoquinone (lawsone). This hydrothermal/solvothermal process produces LPDs that have excitation independent emission with well-defined electronic transitions. This two-step protocol provides a straightforward approach to remove unwanted small molecular fluorescence, which has plagued carbon dot systems, without the need for advanced chromatographic purification methods or steps.

Spectroscopic investigation of the electronic and excited state properties of para-substituted tetraphenyl porphyrins and their electrochemically generated ions.

Porphyrins play pivotal roles in many crucial biological processes including photosynthesis. However, there is still a knowledge gap in understanding electronic and excited state implications associated with functionalization of the porphyrin ring system. These effects can have electrochemical and spectroscopic signatures that reveal the complex nature of these somewhat minor substitutions, beyond simple inductive or electronic effect correlations.

Near-IR Intramolecular Charge Transfer in Strongly Interacting Diphenothiazene-TCBD and Diphenothiazene-DCNQ Push-Pull Triads.

Three types of phenothiazines dimers (PTZ-PTZ, 1-3), covalently linked with one or two acetylene linkers, were synthesized by copper-mediated Eglinton and Pd-catalyzed Sonogashira coupling reactions in excellent yields. The dimers 1-3 were further engaged in [2+2] cycloaddition-retroelectrocyclization reactions with strong electron acceptors, tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) to yield tetracyanobutadiene (TCBD, 1 a-3 a), and dicyanoquinodimethane (DCNQ, 1 b-3 b) functionalized donor-acceptor (D-A) conjugates, respectively. The conjugates were examined by a series of spectral, computational, and electrochemical studies.

Nickel(II) Bisporphyrin-Fused Pentacenes Exhibiting Abnormal High Stability.

A series of largely π-extended multichromophoric molecules including cross-conjugated, half cross-conjugated, conjugation-interrupted and linearly conjugated systems were synthesized and characterized. These multichromophoric molecular systems revealed interesting structural-property relationships. Bisporphyrin-fused pentacenes Pen-1 b and Pen-2 a showed rich redox chemistry with 7 and 8 observable redox states, respectively.

Preparation, Photophysical and Electrochemical Evaluation of an Azaborondipyrromethene/Zinc Porphyrin/Graphene Supramolecular Nanoensemble.

The preparation of an entirely supramolecular, multichromophoric azaborondipyrromethene (ABDP)/zinc tetraphenylporphyrin (ZnTPP)/exfoliated graphene (GR) nanoensemble was accomplished. The ABDP derivative bears glycol chains for enhancing solubility and a pyridine functionality for allowing coordination with ZnTPP. The ABDP/ZnTPP/GR nanoensemble was characterized in terms of morphology and composition by using complementary microscopy imaging, thermogravimetric analysis, Raman as well as steady-state and time-resolved absorption and emission spectroscopy.

Strong Ground- and Excited-State Charge Transfer in C -Symmetric Truxene-Derived Phenothiazine-Tetracyanobutadine and Expanded Conjugates.

The C -symmetric star-shaped phenothiazene-substituted truxene 1 was reacted with the electron acceptors tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). The cycloaddition-retroelectrocyclization reaction yields the conjugates 2 and 3. A combination of spectral, electrochemical, and photophysical investigations of 2 and 3 reveals that the functionalization of the triple bond has a pronounced effect on their ground and excited-state interactions.

C-Symmetric Positional Isomers of BODIPY Substituted Triazines: Synthesis and Excited State Properties.

A series of meso- O-aryl functionalized BODIPY trimers positioned along the C-symmetric axis of triazine ring have newly been synthesized to probe the ground and excited state intramolecular type interactions between the BODIPY entities within the trimer. The developed synthetic strategy resulted in BODIPY trimers in good yields. The electron rich, meso- O-aryl functionalized BODIPYs revealed larger HOMO-LUMO gap and higher Stokes shift and fluorescence lifetimes compared to the traditional BODIPY derivatives having an aryl group attached at the meso position.

Sequential energy transfer followed by electron transfer in a BODIPY-bisstyrylBODIPY bound to C triad via a 'two-point' binding strategy.

Excitation transfer from BODIPY* to bisstyrylBODIPY followed by electron transfer to C leading to a charge separated state of appreciable lifetime in a supramolecularly assembled triad is demonstrated, as a mimic of the photosynthetic 'antenna-reaction centre'.

β-Functionalized Push-Pull opp-Dibenzoporphyrins as Sensitizers for Dye-Sensitized Solar Cells.

A novel class of β-functionalized push-pull zinc opp-dibenzoporphyrins were designed, synthesized, and utilized as sensitizers for dye-sensitized solar cells. Spectral, electrochemical, and computational studies were systematically performed to evaluate their spectral coverage, redox behavior, and electronic structures. These porphyrins displayed much broader spectral coverage and more facile oxidation upon extension of the π conjugation.

Competitive Energy and Electron Transfer in β-Functionalized Free-Base Porphyrin-Zinc Porphyrin Dimer Axially Coordinated to C : Synthesis, Supramolecular Formation and Excited-State Processes.

Simultaneous occurrence of energy and electron transfer events involving different acceptor sites in a newly assembled supramolecular triad comprised of covalently linked free-base porphyrin-zinc porphyrin dyad, H P-ZnP axially coordinated to electron acceptor fullerene, has been successfully demonstrated. The dyad was connected through the β-pyrrole positions of the porphyrin macrocycle instead of the traditionally used meso-positions for better electronic communication. Interestingly, the β-pyrrole functionalization modulated the optical properties to such an extent that it was possible to almost exclusively excite the zinc porphyrin entity in the supramolecular triad.

Investigation of the push-pull effects on β-functionalized benzoporphyrins bearing an ethynylphenyl bridge.

A series of β-pyrrole functionalized push-pull porphyrins with amine push groups linked via an ethynylphenyl spacer, and cyclic imide or carboxylic esters as pull groups have been newly synthesized and characterized. The β-pyrrole functionalized ethynylphenyl spacer extends the conjugation of the porphyrin π-system, as reflected by their red-shifted absorbance and fluorescence spectra. The computed structures revealed no steric hindrance between the porphyrin π-system and the β-substituents.

Ultrafast Charge-Separation in Triphenylamine-BODIPY-Derived Triads Carrying Centrally Positioned, Highly Electron-Deficient, Dicyanoquinodimethane or Tetracyanobutadiene Electron-Acceptors.

A series of new triphenylamine (TPA)-substituted BODIPYs 1-3 have been designed and synthesized through the Pd-catalysed Sonogashira cross-coupling and [2+2] cycloaddition-retroelectrocyclization reactions in good yields. This procedure yielded highly electron-deficient tetracyanobutadiene (TCBD) or dicyanoquinodimethane (DCNQ) electron-acceptor units centrally located at the TPA-BODIPY system. As a consequence, significant perturbation of the photonic and electronic properties was observed.

Directly Attached Bisdonor-BF Chelated Azadipyrromethene-Fullerene Tetrads for Promoting Ground and Excited State Charge Transfer.

The efficiency and mechanism of electron- and energy-transfer events occurring in both natural and synthetic donor-acceptor systems depend on their distance, relative orientation, and the nature of the surrounding media. Fundamental knowledge gained from model studies is key to building efficient energy harvesting and optoelectronic devices. Faster charge separation and slower charge recombination in donor-acceptor systems is often sought out.

Multichromophoric Perylenediimide-Silicon Phthalocyanine-C System as an Artificial Photosynthetic Analogue.

Sequential photoinduced energy transfer followed by electron transfer and the formation of charge-separated states, which are primary events of natural photosynthesis, have been demonstrated in a newly synthesized multichromophoric covalently linked triad, PDI-SiPc-C . The triad comprises a perylenediimide (PDI), which primarily fulfils antenna and electron-acceptor functionalities, silicon phthalocyanine (SiPc) as an electron donor, and fulleropyrrolidine (C ) as a second electron acceptor. The multi-step convergent synthetic procedure developed here produced good yields of the triad and control dyads, PDI-SiPc and SiPc-C .