Shrabanti Banerjee

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.

NMR spectrometric study of molecular complex formation of [60]- and [70]fullerenes with a number of phosphine oxides

Molecular complex formation between [60]- and [70]fullerenes with a series of phosphine oxides, namely, tri-n-octyl phosphine oxide, triphenyl phosphine oxide and tri-n-butyl phosphine oxide has been studied in CCl4 medium by NMR spectrometric method. Both [60]- and [70]fullerenes have been shown to form 1:1 adducts with the above series of phosphine oxides. Formation constants (K) for all the complexes have been determined from the systematic variation of NMR chemical shifts of specific protons of the donors in presence of [60]- and [70]fullerenes. Trends in the values of K suggest that [70]fullerene binds stronger with the phosphine oxides relative to [60]fullerene.

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.