Ramesh Maragani

Synthesis, optical and electrochemical properties of new ferrocenyl substituted triphenylamine based donor–acceptor dyes for dye sensitized solar cells

Two new ferrocenyl substituted triphenylamine based donor–acceptor dyes D1 and D2 were synthesized and used as sensitizers for dye sensitized solar cells (DSSCs). The DSSC based on D2 shows a higher power conversion efficiency of 4.96% as compared to dye D1 (PCE = 3.65%). The higher value of PCE was attributed to the increase in the light harvesting property of dye D2 because of its extended absorption profile up to the near infrared region and a higher value of dye loading on the photoanode surface. The observed value of a higher PCE has also been confirmed by electrochemical impedance data and dark current.

Reversible mechanochromism in dipyridylamine-substituted unsymmetrical benzothiadiazoles

We report the design and synthesis of push–pull benzothiadiazoles (BTDs) of type D1–π–A–π–D2 and D1–π–A–D2. These BTDs show strong charge transfer interaction. BTD 3 shows reversible mechanochromism with color contrast between yellow (crystalline state) and orange (amorphous state). Photophysical and computational studies reveal that the planar orientation of the pyridyl and BTD unit in 2 results in no change in solid state emission whereas non-planar orientation of the dipyridylamine and BTD unit in 3 results in efficient mechanochromism.

C 3 symmetric ferrocenyl triazines: synthesis, structure, and properties

A series of C3 symmetric ferrocenyl-substituted 1,3,5-triazines has been designed and synthesized by the Sonogashira cross-coupling reaction. The photophysical and electrochemical properties of these triazines show substantial donor–acceptor interaction. The single crystal X-ray structure of triazine 3 is reported, which shows a planar structure. The supramolecular structure of 3 exhibits intermolecular π–π interaction, which leads to the formation of 2D layered structures.

Aryl-substituted symmetrical and unsymmetrical benzothiadiazoles

A set of benzothiadiazoles (BTD) of the type D–π–A–π–D and D1–π–A–π–D2 were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. Their photophysical and electrochemical properties were studied. The substitution of anthracene on BTD improves its thermal stability, and lowers the HOMO–LUMO gap, which results in a red shift of the electronic absorption. The experimental optical gap values show good agreement with the calculated HOMO–LUMO gap.

Ferrocenyl end capped molecular rods: synthesis, structure, and properties

A series of ferrocenyl phenylethynyl rods 1–11 were designed, and synthesized by a Pd catalysed Sonogashira cross-coupling, and oxidative homo-coupling reactions. The ferrocenyl moieties in the rods 1–11 are attached at the para/meta position of phenylethynyl unit or at the acetylenic unit. The effect of enhancing the conjugation, and connectivity (meta/para) on the photonic and electrochemical properties were explored. The para linkage, and butadiynyl linkage lower the band gap in the rods. The meta linked ferrocenyl phenylethynyl rods 2, 4, and 10 show good HOMO–LUMO separation compared to para linked rods 1, 3, 9. The single crystal X-ray structures of rods 2, 4, 10, 14 and 19 are reported. The ferrocene units in rods 2, 4, and 10 are in a trans configuration with respect to the phenyl ring.

Heteroatom-connected ferrocenyl substituted naphthalimides

A family of heteroatom (oxygen, sulphur and nitrogen) connected ferrocenyl naphthalimides 3a–3f were designed and synthesized by the nucleophilic aromatic substitution and Buchwald coupling reactions. The effects of the heteroatom and ferrocenyl group on the photonic and electrochemical properties of the ferrocenyl naphthalimides were explored. The electronic absorption spectra of the ferrocenyl naphthalimides 3a–3f show a red shifted absorption as compared to 4-bromonaphthalimide 2. The nitrogen atom connected FcNMIs (3e and 3f) show a considerable red shift, whereas oxygen and sulphur connected FcNMIs (3a–3d) show a moderate red shift. The computational calculations show good agreement with the experimental results. The ferrocenyl naphthalimide containing a nitrogen atom (3e and 3f) show high thermal stability compared to the oxygen and sulphur containing dyes 3a–3d. The single crystal X-ray structures of 3a and 3c are reported and these crystal structures form 2-D network.

Star shaped ferrocenyl substituted triphenylamines

This manuscript reports design and synthesis of star shaped ferrocenyl substituted triphenylamine conjugates (Fc-TPA) 3a–3c by the Pd-catalyzed Sonogshira cross-coupling reaction. Their photophysical and electrochemical properties were investigated, which are a function of the conjugation length. The time dependent density functional (TD-DFT) studies were performed to understand and support the experimental findings. The LUMO could be significantly stabilized by increasing the conjugation. The thermal stability of Fc-TPA 3a–3c can be improved by increasing the conjugation length. The single crystal X-ray structure of Fc-TPA 3a is reported, which show interesting supramolecular interactions leading to the formation of 2D-network.

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 C2 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 (Jsc) 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 ELUMO 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.

C 3-Symmetric star shaped donor–acceptor truxenes: synthesis and photophysical, electrochemical and computational studies

This manuscript reports the design and synthesis of C3-symmetric star shaped donor and acceptor substituted truxenes 6, 7, 10 and 11 using Pd-catalyzed Sonogashira cross-coupling and [2+2] cycloaddition–retroelectrocyclization reactions. Their photophysical, electrochemical and computational studies were explored, which indicate strong donor–acceptor interactions and effective tuning of the HOMO–LUMO gap. The computational studies reveal that the TCNE and TCNQ substituted truxenes 10 and 11 exhibit lower HOMO–LUMO gaps compared to truxenes 6 and 7. The reaction pathway of [2+2] cycloaddition–retroelectrocyclization was studied using computational calculations, which reveal that the donor substituted truxene 7 is favourable for cycloaddition–retroelectrocyclization reactions, whereas acceptor substituted truxene 6 is not favourable.

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.