Fluorophore(s) Appended Fullerene Dyads and Triads for Probing Photoinduced Energy Transfer: Syntheses, Electronic Structure, and Fluorescence Studies

Abstract

Fullerene, C(60) was functionalized to possess one or two fluorophore entities. The fluorophore-fullerene dyads thus synthesized contain either a naphthalene, pyrene, or fluorene entity while the triads contain either a pyrene or fluorene entity in addition to a naphthalene entity. The redox behavior of these dyads and triads were probed by cyclic voltammetric technique, while the geometry and electronic structures were deduced from ab initio B3LYP/3-21G(*) method. Steady-state emission studies revealed the occurrence of energy transfer from the singlet excited fluorophore to the fullerene entity in the case of the dyads while the occurrence of step-by-step sequential energy transfer is envisioned in the case of the triads. A better 'antenna-effect' owing to the extended range of excitation wavelength to induce energy transfer to the appended fullerene has been achieved in the case of the triads.

Photoinduced electron transfer in fullerene triads bearing pyrene and fluorene

“…The quenching of the fluorophore emission and the appearance/absence of the fulleropyrrolidine emission in the triads are suggestive of electron transfer in polar DMF occurring competitively with energy transfer. It may be mentioned here that in nonpolar o-dichlorobenzene or toluene, energy transfer from the excited fluorophore to fulleropyrrolidine was predominantly observed [15]. That is, quenching of the fluorophore emission was accompanied by only enhanced emission of fulleropyrrolidine entity.…”

“…The synthesis and characterization of the investigated fullerene derivatives are given elsewhere [15] and the samples were freshly purified prior to electrochemical and spectral measurements. The solvents stored in sure seal bottles were purchased from Aldrich Chemicals (Milwaukee, WI) and were used as received.…”

“…3 shows the steady-state emission spectra of the investigated compounds in DMF excited at 290 nm where the appended fluorophores were predominantly excited. Compound 6, bearing no fluorophore revealed an emission band at 715 nm in DMF, corresponding to the fluorescence Table 1 Electrochemical half-wave redox potentials (E 1/2 vs. Fc/Fc + ) and estimated driving forces for forward and reverse electron transfer in DMF [15]). b The first oxidation for compounds 1 and 3 involves pyrene, while for compounds 2 and 4 involves fluorene moiety.…”

“…Steady-state fluorescence studies revealed the occurrence of energy transfer from the singlet excited fluorophore to the fullerene entity in the case of the dyads while the occurrence of step-by-step sequential energy transfer was envisioned in the case of the triads. A better 'antenna-effect' owing to the extended range of excitation wavelength to induce energy transfer to the appended fullerene was achieved in the case of the triads [15]. Interestingly, the B3LYP/3-21G( * ) calculations revealed the frontier HOMO to be located on the pyrene or fluorene entity, while the LUMO on the fullerene entity for AH 1 -C 60 -AH 2 type triads.…”

“…Recently, we reported the syntheses and preliminary results on photoinduced energy transfer in a series of fluorophore-fullerene type dyads and fluorophore 1 -fullerene- fluorophore 2 type triads (AH 1 -C 60 -AH 2 ) in nonpolar odichlorobenzene [15]. Steady-state fluorescence studies revealed the occurrence of energy transfer from the singlet excited fluorophore to the fullerene entity in the case of the dyads while the occurrence of step-by-step sequential energy transfer was envisioned in the case of the triads.…”