Effect of concentration on the photophysics of solution of [6,6]-phenyl C61 butyric acid methyl ester (PCBM) in chloroform

Abstract

The present paper describes a detailed study of the concentration-dependent photophysics of [6,6]-phenyl C61 butyric acid methyl ester (PCBM) in chloroform solution with the help of steady-state and time-domain fluorescence measurements. The absorption pattern of PCBM shows strong absorption band in the UV region and a weak band in the visible range. The absorption profile remains unaffected by the concentration, denying any possibility of ground-state complex formation. Corresponding to this absorption profile, PCBM shows dual-structured blue (anti-Kasha emission; ∼435 nm) and red (normal emission; ∼650 nm) emission bands. The blue emission band is the charge transfer band and its intensity first increases and then decreases with concentration. The emission intensity of the red band, corresponding to emission from the monomer unit, decreases with increasing concentration. While at higher concentrations of PCBM, a new emission band around 715 nm emerges, whose intensity increases with concentration showing the possibility of being excimer emission of PCBM. The monomeric unit shows a fluorescence decay time of 3.0 ns, and the excimer decay time obtained is around 1.4 ns, while the charge transfer band shows multi-exponential fluorescence decay profile. © 2023