Tridib Sarma

Dinaphthoporphycenes: synthesis and nonlinear optical studies.

Naphthobipyrrole-derived porphycenes are synthesized for the first time via McMurry coupling of the β-alkylated 2,9-diformylnaphthobipyrrole derivatives, which in turn were prepared easily from 2,3-naphthalene bishydrazine in four steps. Insertion of nickel into the porphycene core results in transformation of the rectangular N4-core into a square type geometry owing to the fusion of naphthalene moiety onto the bipyrrole entities. These porphycenes show large, intensity dependent three-photon absorption.

Ultrafast excited state dynamics and dispersion studies of nonlinear optical properties in dinaphthoporphycenes

Ultrafast excited state dynamics of dinaphthoporphycenes were investigated using femtosecond and picosecond degenerate pump-probe techniques at 600 nm and 800 nm, respectively. Femtosecond pump-probe data indicated photo-induced absorption at 600 nm resulting from two-photon/single photon excitation, whereas picosecond pump-probe data demonstrated photo-bleaching which was a consequence of three-photon absorption. The fastest lifetimes (100–120 fs) observed are attributed to the intramolecular vibrational relaxation, the slower ones (1–3 ps) to internal conversion, and the slowest components (7–10 ps) to non-radiative decay back to ground state. Z-scan studies in the 560–600 nm range were also carried out.

Conformational and spectroscopic properties of π-extended, bipyrrole-fused rubyrin and sapphyrin derivatives.

Two new expanded porphyrins, naphthorubyrin and naphthosapphyrin, were synthesized. The π-extended rubyrin was isolated and structurally characterized in its monoprotonated form. The sapphyrin congener undergoes pyrrole inversion as a function of the protonation state. These conformational effects are reflected in the spectroscopic features, including the excited singlet state lifetimes.

Naphthobipyrrole-derived sapphyrins: rational synthesis, characterization, nonlinear optical properties, and excited-state dynamics.

Two new free-base β-octa and hexaalkyl naphthobipyrrole-derived sapphyrins are reported along with various salts thereof. One of them has substituents at all of its β positions, whereas the pyrrole unit opposite to the bipyrrolic moiety is unsubstituted in the other. The effect of bipyrrole fusion on the structure of sapphyrins was explored. Interestingly, an unprecedented sandwiched supramolecular aqua-bridged free-base sapphyrin dimer was also characterized in the solid state. Further, the effect of anions on the third-order nonlinear optical properties of these sapphyrins were explored in the salt form, along with their detailed excited-state dynamics by both degenerate and nondegenerate pump-probe studies.

β,β′-Bipyrrole Fusion-Driven cis-Bimetallic Complexation in Isomeric Porphyrin

An unprecedented cis-bimetallic complex of dinaphthoporphycene (DNP), namely [Pd2(μ-DNP)(μ-OAc)2], is reported. The most striking feature of this complex is that two palladiums coordinate to the macrocycle on the same side and are closely held together (Pd-Pd: 2.67 Å) by two bridging acetate ligands exhibiting significant metal-metal bonding interaction (bond order 0.18 evaluated by NBO analysis). Interestingly, replacing acetate with acetylacetonate (acac) could stabilize an unusual mono-palladium complex of DNP, where Pd coordinates unsymmetrically to two ring Ns above the macrocyclic plane, as well as coordinating with two Os of the acac ligand. Remarkably, the rigid DNP core displays enhanced complexation induced aromaticity (as per NICS and HOMA analysis), despite undergoing severe core deformation during complexation with metal ion(s) as noticed from their solid-state structures.

Effect of β − β ′

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fusion on metal ion complexation of porphycene

\end{document} fused π-extended porphycene, namely dinaphthoporphycene was carried out successfully with copper(II) and its solid state structure shows a square-type planar N4-coordination core. The photophysical and electrochemical properties of this complex, along with the nickel(II) complex were also investigated. Further, electronic paramagnetic resonance (EPR) analysis of this complex is also reported. Square type coordination for metalloporphycene was observed. Square type coordination for metalloporphycene was observed.

Multiphoton Absorption Studies in Porphycenes Using Picosecond and Femtosecond Pulses

We present our results obtained from the Z‐scan measurements in porphycenes performed using ∼2 picosecond (ps) and ∼40 femtosecond (fs), 800 nm pulses with a repetition rate of 1 kHz delivered by amplified Ti:sapphire laser systems. Open aperture Z‐scan data demonstrated interesting multi‐photon absorption properties for these molecules. In the ps regime these compounds exhibited two‐photon absorption (2PA) at lower peak intensities whereas three‐photon absorption (3PA) was dominant mechanism observed at higher peak intensities. In the fs regime saturable absorption was the mechanism detected. Closed aperture data was collected to evaluate the nonlinear refractive indices of these molecules in both the time domains. The magnitude of n2 was ∼10−17 cm2/W in the fs regime and ∼10−15 cm2/W in the ps regime.

Ultrafast dynamics of Naphthosapphyrins: Degenerate and Non-degenerate Pump-Probe Studies

We present ultrafast excited state dynamics of free base as well as salts of Naphthosapphyrins using degenerate and non-degenerate pump probe and Z-scan techniques. The dynamics have been explained using a Jablonski diagram.