Supramolecular interaction of PCBM with porphyrins in solution: Photophysical insights

Subrata Nayak; Shalmali Bhattacharya; Pialee Roy; Viki Bhakta; Sumanta Bhattacharya

doi:10.1016/j.saa.2023.123476

Supramolecular interaction of PCBM with porphyrins in solution: Photophysical insights

Spectrochim Acta A Mol Biomol Spectrosc. 2024 Jan 15:305:123476. doi: 10.1016/j.saa.2023.123476. Epub 2023 Oct 5.

Authors

Subrata Nayak¹, Shalmali Bhattacharya², Pialee Roy³, Viki Bhakta⁴, Sumanta Bhattacharya⁵

Affiliations

¹ Physical Research Laboratory-2, Chemistry Department, The University of Burdwan, Golapbag, Purba Bardhaman, West Bengal 713 104, India.
² Department of Computer Science & Engineering, Academy of Technology, Adisaptagram, Hooghly 712 502, India.
³ Department of Chemistry, Guskara Mahavidyalaya, Guskara, West Bengal 713 128, India.
⁴ Department of Chemistry, Rajabazar Science College, University of Calcutta, 92, Acharya Prafulla Chandra Road, Kolkata, West Bengal 700009, India.
⁵ Physical Research Laboratory-2, Chemistry Department, The University of Burdwan, Golapbag, Purba Bardhaman, West Bengal 713 104, India. Electronic address: sbhattacharya@chem.buruniv.ac.in.

PMID: 37827003
DOI: 10.1016/j.saa.2023.123476

Abstract

This work reports the self-assembly between [6,6]-phenyl C₇₁ butyric acid methyl ester (PCBM) and 2,3,7,8,12,13,17,18-octaethyl-21H,23H porphyrin (1)(and/2,3,7,8,12,13,17,18-octaethyl-21H,23H porphyrin Zn(II) (2) in toluene. Ground state intermolecular interaction is evidenced from absorption spectrophotometric measurements. New absorption bands are observed in the visible region which may be identified due to charge transfer (CT). Several important physicochemical factors are enumerated for PCBM-1 and PCBM-2 systems. Fluorescence investigations elicit complex formation of PCBM with porphyrins (with both 1 and 2) and reveal considerable magnitude of binding constant (K) for PCBM-2 system, i.e., K_PCBM-2 = 80,435 dm³⋅mol^-1 compared to PCBM-1 system, i.e., K_PC_M-1 = 12,600 dm^3·mol^-1 as well as highly ratio of selectivity in binding (K_PCBM-2/K_PCBM-1 ∼ 6.4). Time resolved fluorescence experiments reveal that photoexcited decay from the excited singlet state of porphyrins (i.e., 1* and 2*) by PCBM is statically controlled compared to dynamic path. Magnitude of solvent reorganization energy indicates possibility of faster charge recombination in case of PCBM-2 system. Both ¹H and ¹³C NMR measurements provide substantial support behind complexation of PCBM with porphyrins (both 1 and 2) in solution. Ab initio calculations in vacuo support the trend in K for PCBM-1 and PCBM-2 systems and establish the proper orientation of PCBM towards 1 (and/ 2) during complexation. Transient absorption measurements establish two different mode of energy transfer pathway from porphyrin to PCBM in toluene.

Keywords: Ab initio calculations; PCBM; Photophysical insights; Porphyrins; Supramolecular interaction; Transient absorption studies.