C3-Symmetric Positional Isomers of BODIPY Substituted Triazines: Synthesis and Excited State Properties.

A series of meso- O-aryl functionalized BODIPY trimers positioned along the C3-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. The optical absorption, steady-state fluorescence, and electrochemical studies revealed weak, if any, intramolecular type interactions among the BODIPY entities within the trimer and the central triazine unit to be both photo- and redox-salient. The possibility of singlet-singlet energy migration among the BODIPY entities was investigated using time-resolved emission and femtosecond transient absorption studies. Excitation of a BODIPY entity in the trimers led to successful formation of 1BODIPY*, which populated the 3BODIPY* via intersystem crossing. Among the three trimers, although very weak, only trimer 8 revealed excitation transfer to some extent. The present findings suggest that the meso- O-aryl functionalized BODIPYs due to their superior fluorescence properties are better probes to build light energy harvesting supramolecular oligomeric systems and for other applications such as sensing and imaging.

(D-π-A)2-π-D-A type ferrocenyl bisthiazole linked triphenylamine based molecular systems for DSSC: synthesis, experimental and theoretical performance studies.

We have designed and synthesized ferrocenyl (donor) bisthiazole linked triphenylamine (donor) based donor-π-acceptor-π-donor-acceptor (D-π-A)2-π-D-A type dyes D1 and D2 by using Pd-catalyzed Sonogashira cross-coupling and Knoevenagel condensation reactions. Their photophysical, electrochemical and computational studies reveal strong donor-acceptor interaction. Dye sensitized solar cells (DSSCs) based on D1 and D2 exhibit power conversion efficiencies (PCE) of 6.33% and 5.03%, respectively. The higher PCE value of the D1 based DSSC is attributed to its enhanced short-circuit current (Jsc) and open-circuit current (Voc) and fill factor (FF) values because of the strong binding of the anchoring cyanoacrylic acid with the TiO2 surface as compared to the dicyanovinyl unit in D2. Time dependent density functional theory (TD-DFT) calculations at B3LYP level on dyes D1 and D2 were performed, which reveal that both dyes show HOMO-1 → LUMO as a major transition. Computational photovoltaic calculations also reveal that dye D1 has better electron injection (ΔGinject) from ELUMO to the conduction band (CB) of TiO2 as compared to dye D2, which is in good agreement with experimental results.

Thermoresponsive swelling of photoacoustic single-chain nanoparticles.

NIR-fluorescent LCST-type single-chain nanoparticles (SCNPs) change their photophysical behaviour upon heating, caused by depletion of water from the swollen SCNP interiors. This thermoresponsive effect leads to a fluctuating photoacoustic (PA) signal which can be used as a contrast mechanism for PA imaging.

Charge Carrier Mobility Improvement in Diketopyrrolopyrrole Block-Copolymers by Shear Coating.

Shear coating is a promising deposition method for upscaling device fabrication and enabling high throughput, and is furthermore suitable for translating to roll-to-roll processing. Although common polymer semiconductors (PSCs) are solution processible, they are still prone to mechanical failure upon stretching, limiting applications in e.g., electronic skin and health monitoring. Progress made towards mechanically compliant PSCs, e.g., the incorporation of soft segments into the polymer backbone, could not only allow such applications, but also benefit advanced fabrication methods, like roll-to-roll printing on flexible substrates, to produce the targeted devices. Tri-block copolymers (TBCs), consisting of an inner rigid semiconducting poly-diketo-pyrrolopyrrole-thienothiophene (PDPP-TT) block flanked by two soft elastomeric poly(dimethylsiloxane) (PDMS) chains, maintain good charge transport properties, while being mechanically soft and flexible. Potentially aiming at the fabrication of TBC-based wearable electronics by means of cost-efficient and scalable deposition methods (e.g., blade-coating), a tolerance of the electrical performance of the TBCs to the shear speed was investigated. Herein, we demonstrate that such TBCs can be deposited at high shear speeds (film formation up to a speed of 10 mm s-1). While such high speeds result in increased film thickness, no degradation of the electrical performance was observed, as was frequently reported for polymer-based OFETs. Instead, high shear speeds even led to a small improvement in the electrical performance: mobility increased from 0.06 cm2 V-1 s-1 at 0.5 mm s-1 to 0.16 cm2 V-1 s-1 at 7 mm s-1 for the TBC with 24 wt% PDMS, and for the TBC containing 37 wt% PDMS from 0.05 cm2 V-1 s-1 at 0.5 mm s-1 to 0.13 cm2 V-1 s-1 at 7 mm s-1. Interestingly, the improvement of mobility is not accompanied by any significant changes in morphology.

Cs -Symmetric Triphenylamine-Linked Bisthiazole-Based Metal-Free Donor-Acceptor Organic Dye for Efficient ZnO Nanoparticles-Based Dye-Sensitized Solar Cells: Synthesis, Theoretical Studies, and Photovoltaic Properties.

Herein, we have designed a metal-free donor-acceptor dye by incorporating an electron deficient bisthiazole moiety as a linker in between the electron donor triphenylamine and cyanoacetic acid acceptor. The bisthiazole-based organic dye D1 was synthesized using the Pd-catalyzed Suzuki cross-coupling and Knoevenagel condensation reactions. On the basis of the optical, electrochemical, and computational studies, dye D1 showed a better electronic interaction between the donor and acceptor moieties. As-synthesized C 2 symmetric triphenylamine-linked bisthiazole-based organic dye D1 has four anchoring groups, which play a significant role for better adsorption on the ZnO surface along with the enhanced kinetics of photoexcited electron injection. Consequently, photovoltaic properties of the organic dye D1 has been carried out by fabricating the ZnO nanoparticles (ZnO NPs)-based solar device. We obtained the maximum incident photon-to-current conversion efficiency of about 56.20%, with a short-circuit photocurrent density (J sc) of 13.60 mA cm-2, which results in a power conversion efficiency (PCE) of 4.94% under AM 1.5 irradiation (100 mW cm-2). The high PCE value is the result of proficient electron injection from E LUMO of dye D1 to the conduction band of ZnO NPs, as suggested by the computational calculations. Electrochemical impedance spectroscopy measurement is carried out to calculate the electron lifetime and also reveals the insight to the reduced charge recombinations at the various active interfaces of the photovoltaic device.

C2-Symmetric ferrocenyl bisthiazoles: synthesis, photophysical, electrochemical and DFT studies.

A series of donor-acceptor ferrocenyl substituted bisthiazoles 3-8 were designed and synthesized by the Pd-catalyzed Suzuki, Heck, and Sonogashira cross-coupling reactions. Their photophysical, electrochemical and computational studies reveal strong donor-acceptor interactions. The photonic and electrochemical studies show that the ferrocenyl bisthiazoles with vinyl linkage ferrocenyl-bisthiazole 4, show better electronic communication compared to rest of the ferrocenyl bisthiazoles. The time dependent density functional theory (TD-DFT) calculation at B3LYP on the ferrocenyl substituted bisthiazoles 3-5 was performed, in which the ferrocenyl-bisthiazole 4 shows strong donor-acceptor interactions compared to the Fc-bisthiazoles 3 and 5. The thermal stability of the ferrocenyl substituted bisthiazoles 3-8 is reported, in which Fc-bisthiazole 8 shows high thermal stability. The single crystal structures of ferrocenyl-bisthiazoles 3 and 5 are reported.

Triarylborane substituted naphthalimide as a fluoride and cyanide ion sensor.

Triarylborane substituted naphthalimide 3 was designed and synthesized by the Sonogashira cross-coupling reaction. The electronic absorption and emission spectra of the triarylborane naphthalimide 3 show red shifted absorption and emission as compared to 4-bromonaphthalimide 2. The sensing behaviour of 3 was studied for different anions. The triarylborane naphthalimide 3 selectively detects F(-) and CN(-) ions in the presence of Cl(-), Br(-), I(-) and NO2(-) ions. The effect of F(-) and CN(-) ions on the structure of 3 was studied by performing DFT calculations. The theoretical calculations show good agreement with the experimental results. The detection limits for F(-) and CN(-) were found to be 2.01 × 10(-10) M and 3.94 × 10(-10) M respectively.

Carbazole-BODIPY conjugates: design, synthesis, structure and properties.

A set of carbazole substituted BODIPYs 2a-2c were designed and synthesized by the Pd-catalysed Sonogashira cross-coupling reaction. The effects of variation in the donor strength of various carbazoles were investigated by photophysical, electrochemical and computational studies. The electronic absorption spectra of BODIPYs 2a and 2c show charge transfer bands, which show red shift in polar solvents. The BODIPYs 2a-2c are highly fluorescent in nonpolar solvents (emission from the localized state) and poorly fluorescent in polar solvents (emission from the charge transfer state). The photophysical and electrochemical studies reveal strong donor-acceptor interaction between carbazole and BODIPY and follows the order 2a > 2c > 2b. The computational calculations show good agreement with the experimental results. The single crystal structures of BODIPYs 2a-2c are reported, which exhibit interesting supramolecular interactions. The packing diagrams of 2a show a zigzag 3D structural arrangement, whereas 2b and 2c show complex 3D structural motifs.

Design and synthesis of donor-acceptor pyrazabole derivatives for multiphoton absorption.

A series of ferrocenyl substituted pyrazaboles were prepared, which have an electron-withdrawing pyrazabole moiety as the central core, with a D-π-A-π-D structural motif (D = donor, A = acceptor) and containing a variety of π bridges. A crystallographic study reveals that the pyrazabole central core was observed in planar geometry. Strong two-photon absorption in the visible region and three-photon absorption in the near IR region were observed in the ferrocenyl substituted pyrazaboles. It was observed that the 2PA absorption cross-section increases with the conjugation length.