Sc3N@ I h -C80 based donor-acceptor conjugate: role of thiophene spacer in promoting ultrafast excited state charge separation

Abstract

Light induced charge separation in a newly synthesized triphenylamine-thiophene-Sc₃N@I _h -C₈₀ donor-acceptor conjugate and its C₆₀ analog, triphenylamine-thiophene-C₆₀ conjugate is reported, and the significance of the thiophene spacer in promoting electron transfer events is unraveled.

Fig. 1. Structure of the newly synthesized triphenylamine–thiophene-Sc₃N@I_h-C₈₀ endohedral fullerene conjugate, (3a) and its C₆₀ analog derivative (3b).

Scheme 1. Reagents and conditions: (a) hydroxylamine hydrochloride, pyridine; (b) NCS; pyridine (c) Et₃N, Sc₃N@I_h-C₈₀ or C₆₀, r.t.

Fig. 2. (a) Absorption and (b) fluorescence spectra of 10⁻⁶ M solutions of 2 (red), 3a (black) and 3b (blue) in CH₂Cl₂.

Fig. 3. (a) Cyclic voltammograms of 3b (black) and 3a (blue) in o-DCB : acetonitrile (4 : 1) (b) energy level diagram showing the different photochemical events occurring for 3a and 3b due to TPA excitation. Energies of different states were evaluated from spectral and electrochemical studies. Solid arrows indicate major photo-processes, dashed arrow indicates minor photo-processes. CS = charge separation, CR = charge recombination.

Fig. 4. Fs-TA spectra at the indicated delay times of (a) 2 (λ_ex = 390 nm), (b) 3a (λ_ex = 500 nm), and (c) 3b (λ_ex = 390 nm) in o-DCB. The DAS are shown in the right hand panels.