A. K. Bauri

Photophysical investigations on effective and selective complexation of a designed monoporhyrin with C60 and C70 in solution

The present paper reports spectroscopic and theoretical insights on ground state complexation of a designed monoporphyrin, 1, with C60 and C70 in toluene. The central interest of the present investigations is the selectivity in binding constant (K) of the fullerene-1 complexes in solution. The ground state interaction between fullerenes and 1 is first evidenced from UV-Vis measurements. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 1 in presence of both C60 and C70. Average K values, viz., K(av), for the complexes of C60 and C70 with 1 are determined to be 1620 and 30330 dm(3) mol(-1), respectively. The magnitude of K(av) suggests that 1 preferentially binds C70 in comparison to C60. Time resolved emission measurements establish that C70-1 complex is stabilized much more in comparison to C60-1 system in terms of charge separation process. Ab initio calculations in vacuo substantiate the strong binding between C70 and 1 in terms of heat of formation values of the respective complex, and at the same time, determine the orientation of bound guest (here C70) with the molecular plane of 1.

Absorption spectrophotometric, fluorescence and quantum chemical investigations on non-covalent interaction between PC70BM and designed diporphyrin in solution

Present work reports the photophysical insights on supramolecular interaction of a C₇₀ derivative, namely, [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₀BM), with two designed diporphyrin molecules having dithiophene (1) and carbazole (2) spacer in toluene and benzonitrile. Both absorption spectrophotometric and steady state fluorescence investigations reveal efficient complexation of PC₇₀BM with 1 and 2 in both toluene and benzonitrile. The magnitude of average value of binding constant, viz., Kav, for the complexes of PC₇₀BM with 1 and 2 in toluene (benzonitrile) are estimated to be 2.185 × 10(3)dm(3)mol(-1) (3.215 × 10(3)dm(3)mol(-1)) and 10.180 × 10(3)dm(3)mol(-1) (25.405 × 10(3)dm(3)mol(-1)), respectively. Selectivity in binding for the complexation process of PC₇₀BM with 1 and 2 is estimated to be ∼4.6 and ∼7.90 as observed in toluene and benzonitrile, respectively. The complexation between PC₇₀BM and diporphyrin is well accounted by a theoretical model which takes into account the electronic subsystems of both acceptor and donor. Ab initio calculations in vacuo establish that size selective orientation pattern of PC₇₀BM towards the cavity of diporphyrin dictates the magnitude of binding and electronic structure of the PC₇₀BM/diporphyrin complexes.

Role of charge transfer interaction and the chemical physics behind effective fulleropyrrolidine/porphyrin non-covalent interaction in solution

The present paper reports the photophysical insights on supramolecular interaction of a monoporphyrin derivative, namely, 1, with C60 pyrrolidine tris-acid ethyl ester (PyC60) in toluene and benzonitrile. The ground state interaction between PyC60 and 1 is facilitated through charge transfer interaction. Both UV-Vis and steady state measurements elicit almost similar magnitude of binding constant for the PyC60/1 complex in toluene and benzonitrile, viz., 6825 and 6540 dm(3 )mol(-1), respectively. Life time measurement evokes that rate of charge separation is fast in benzonitrile. Both hybrid-DFT and DFT calculations provide very good support in favor of electronic charge-separation in PyC60/1 system in vacuo.

Study of non-covalent interaction between a designed monoporphyrin and fullerenes (C60 and C70) in absence and presence of silver nanoparticles

The present article reports on supramolecular interaction between fullerenes (C(60) and C(70)) and a designed monoporphyrin, e.g., 5,15-di(para-methoxyphenyl)zincporphyrin (1), in absence and presence of silver nanoparticles (AgNp) having diameter of ~3-7 nm in toluene. While UV-Vis studies establish the ground state electronic interaction between fullerenes and 1 in absence and presence of AgNp, steady state fluorescence experiment enables us to determine the value of binding constant (K) for the fullerene-1 complexes in solution. Steady state fluorescence measurement reveals that reduction in the K value takes place for both C(60)-1 (K=1560 dm(3) mol(-1)) and C(70)-1 systems (K=14,970 dm(3) mol(-1)) in presence of AgNp, i.e., K C(60)(-1)=1445 dm(3) mol(-1) and Kc(60-)(1)=14,550 dm(3) mol(-1). SEM measurements establish formation of surface holes in fullerene-1-AgNp structure. Both SEM and dynamic light scattering measurement demonstrates that the electrostatic attraction between porphyrin-based supramolecules and AgNp is very much responsible behind the formation of larger aggregates. Quantum chemical calculations evoke the single projection geometric structures of the fullerene-1 complexes in vacuo and well interpret the alignment of the C(60) and C(70) molecule with the flat -belt region of 1.

Spectroscopic and theoretical insights on effective and selective non-covalent binding between fullerenes (C60 and C70) and a designed diporphyrin in solution

The present work reports the photophysical insights behind effective non-covalent interaction between a designed diporphyrin (1) and fullerenes C60 and C70 in toluene. Ground state electronic interaction between fullerenes and 1 is evidenced from UV-Vis measurements in which it is observed that the intensity of the Soret absorption band of 1 is decreased considerably in presence of both C60 and C70. Steady state fluorescence studies reveal efficient quenching of the fluorescence intensity of 1 in presence of fullerenes. Evaluation of binding constants for the fullerene/1 systems evoke that 1 may be employed as an efficient molecular tweezers for C70 in toluene as selectivity in binding is determined to be ∼9.4. Time resolved emission studies establish relatively long-lived charge separated state for the C70/1 system in comparison to C60/1. Molecular mechanics calculations by force field method in vacuo interpret well regarding stability difference between C60 and C70 complexes of 1 and give formidable support in favor of side-on orientation motif of C70 towards the plane of 1 during non-covalent complexation process.

Chemical physics behind formation of efficient charge-separated state for complexation between PC70BM and designed diporphyrin in solution.

The present work reports supramolecular interaction of [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) with two designed diporphyrin molecules having dithiophene (1) and carbazole (2) spacer in solvent having varying polarity. Studies on complex formation reveal relatively higher binding constant for PC70BM/2 complex in all the solvent studied. Solvent dependence of charge separation and charge recombination processes in PC70BM/diporphyrin non-covalent complexes has been well established in present work. Donor-acceptor geometry and stabilization of the singlet excited state of the diporphyrin during charge recombination are considered to be the possible reasons for this behavior.

Photophysical insights on effect of gold nanoparticles over fullerene–porphyrin interaction in solution

The present article reports the role of gold nanoparticles, i.e., AuNp (having diameter ∼2-4nm), in non-covalent interaction between fullerenes (C60 and C70) and a monoporphyrin (1) in toluene. Both UV-vis and fluorescence measurements reveal considerable reduction in the average value of binding constant (Kav) for the C70-1 system (KC70-1(av)=19,300 dm3 mol(-1)) in presence of AuNp, i.e., KC70-1-AuNp(av)=13,515 dm3 mol(-1) although no such phenomenon is observed in case of C60-1 system, viz., KC60-1(av)=1445 dm3 mol(-1) and KC60-1-AuNp(av)=1210 dm3 mol(-1). DLS study reveals sizeable amount of increase in the particle size of C70-1-AuNp nanocomposite, i.e., ∼105 nm, compared to C60-1-AgNp system, e.g., ∼5.5 nm which gives very good support in favor of decrease in the value of Kav for the former system. SEM study reveals that nanoparticles are dispersed in larger extent in case of C70-1-AuNp system. Time-resolved fluorescence study envisages that deactivation of the excited singlet state of 1 by C70 takes place at a faster rate in comparison to C60 in presence of gold nanoparticles.

Photophysical investigations on determination of molecular structure and binding strength of supramolecular complexation between fulleropyrrolidine and a designed bisporphyrin in solution.

The present article reports, for the first time, the photophysical aspects of non-covalent interaction of a fullerene derivative, namely, C60 pyrrolidine tris-acid ethyl ester (PyC60) with a designed bisporphyrin (1) (having carbazole spacer unit) in toluene. Absorption spectrophotometric studies reveal that decrease in the absorption intensity of the Soret absorption band of 1 takes in presence of PyC60 in the solvent studied. Steady state fluorescence studies reveal efficient quenching of fluorescence intensity of 1 in presence of PyC60. Static quenching model explores a binding constant (KS) value of 2,910 dm(3) mol(-1) in toluene. Time resolved emission study establishes static quenching mechanism for the investigated supramolecule in non-polar solvent. Molecular mechanics calculations in vacuo evoke the single projection structure of the PyC60-1 complex and interpret the geometrical arrangement of both PyC60 and 1 during non-covalent complexation.

Spectroscopic and theoretical insights on supramolecular complexation of C60 and C70 with a designed bisporphyrin

The present paper reports the synthesis of a designed bisporphyrin (1), and its supramolecular complexes with C(60) and C(70) in toluene medium. Ground state non-covalent interaction between fullerenes and 1 is evidenced from absorption spectrophotometric study in which it is observed that the intensity of the Soret absorption band of 1 decreases considerably in presence of both C(60) and C(70). Jobs plot of continuous variation method establishes 1:1 stoichiometry for fullerene/1 complexes. Steady state fluorescence studies reveal efficient quenching of fluorescence of 1 in presence of fullerenes. The Stern-Volmer diffusion constant for the supramolecular complexes of 1 with C(60) and C(70) is determined to be 1450 and 12,485 dm(3) mol(-1). The binding constants of the C(60)/1 and C(70)/1 complexes are estimated to be 12,500 and 17,200 dm(3) mol(-1), respectively. Time-resolved emission studies establish relatively long-lived charge separated state for the C(70)/1 complex. Transient absorption spectral analysis reveals formation of radical anion species, i.e., C(60)(-) and C(70)(-) Molecular mechanics calculations at force field model in vacuo evoke the stereoscopic structures of the fullerene/1 complexes and interpret the stability difference between C(60) and C(70) complexes of 1 in terms of heat of formation values.

Crystal structure of a photobiologically active brominated angular pyran­ocoumarin: bromo-hy­droxy-seselin

The title compound, is a brominated product of seselin [8,8-dimethyl-2H,8H-pyrano[2,3-f]chromen-2-one], a photo biologically active compound.