Spectroscopic and Theoretical Insights into the Origin of Fullerene−Calix[4]pyrrole Interaction

Abstract

The present paper reports, for the first time, supramolecular interaction of meso-octamethyl calix[4]pyrrole (1) with fullerenes C(60) and C(70) in solutions having varying polarity (e.g., toluene, 1,2-dichlorobenzene and benzonitrile and chloroform). The interaction is facilitated through charge transfer (CT) transition as evidenced from well-defined CT absorption bands in the visible region of absorption spectroscopy. Utilizing the CT transition energy for the complexes of 1 with various electron acceptors, we have determined the ionization potential of 1. Estimation of degrees of CT, oscillator, and transition dipole strengths suggest that the complexes are almost of neutral character in ground state. Higher magnitude of electronic coupling element value for the C(70)-1 complex compared to C(60)-1 indicates strong binding between C(70) and 1. Binding constants (K) of the fullerene-1 complexes have been determined from UV-vis investigations, which indicate high selectivity of 1 toward C(70). Extraordinary large K value of the C(70)-1 complex in chloroform medium (K approximately 1.43 x 10(6) dm(3) x mol(-1)) establishes that a polar environment facilitates such interaction. Both proton NMR and liquid IR studies provide very good support in favor of strong binding between C(70) and 1. (13)C NMR study proves that C(70) binds 1 with its equatorial belt, which substantiates the role of pi-pi interaction behind such strong interaction (i.e., high K value). Semiempirical theoretical calculations at the third parametric level (PM3) explore the stability difference between C(60)- and C(70)-1 complexes. PM3 calculations also reveal that approach of C(70) toward 1 is directed in side-on manner rather than in a conventional end-on alignment.

Macrocyclic Hosts for Fullerenes: Extreme Changes in Binding Abilities with Small Structural Variations.

“…These values make p -xylmac12 one of the most efficient receptors for C 60 reported to date. With regards to C 70 , naphmac14 and p -xylmac14 show log K a = 6.1 ± 0.2 and 5.9 ± 0.3, respectively, in PhCl at 298 K. These are two of the very few examples of hosts capable of associating C 70 with micromolar affinity. , From the general point of view of the design of hosts for fullerenes, our results show that relatively small structural variations in the receptor lead to large changes in binding affinities, and in, some cases, even stoichiometry. For example, while m -xylmac14 forms 1:1 complexes with C 70 with a respectable binding constant of log K a = 5.4 ± 0.3, the smaller member m -xylmac10 forms associates of both 1:1 and 2:1 stoichiometries, with log K 1:1 = 4.4 ± 0.4 and log K 2:1 8.3 ± 0.5.…”

Photophysical and Theoretical Insights on Fullerene/Zincphthalocyanine Supramolecular Interaction in Solution

“…The values of both k CS and Φ CS are estimated to be higher for fullerene/ 1 complexes in DCB compared to toluene. From this very interesting observation, we may surmise that polar solvent facilitates electrostatic interaction between fullerenes and 1 , which in turn is very much responsible for getting a fruitful CT phenomenon in this particular solvent. Therefore, it would be highly beneficial if quantum chemical calculations may invoke some light on the geometrical arrangement of both the fullerenes and 1 molecules in fullerene/ 1 systems.…”