Effect on Charge Transfer and Charge Recombination by Insertion of a Naphthalene‐Based Bridge in Molecular Dyads Based on Borondipyrromethene (Bodipy)

Abstract

The photophysical properties of two related dyads based on a N,N-dimethylaniline donor coupled to a fully-alkylated boron dipyrromethene (Bodipy) acceptor are described. In one dyad, BD1, the donor unit is attached directly to the Bodipy group, whereas in the second dyad, BD2, a naphthalene spacer separates the two units. Cyclic voltammograms recorded for the two dyads in deoxygenated MeCN containing a background electrolyte are consistent with the reversible one-electron oxidation of the N,N-dimethylaniline group and the reversible one-electron reduction of the Bodipy nucleus. There is a reasonable driving force (ΔG(CT)) for photoinduced charge transfer from the N,N-dimethylaniline to the Bodipy segment in MeCN. The charge-transfer state is formed for BD1 extremely fast (1.5 ps), but decays over 140 ps to partially restore the ground state. On the other hand, the charge-transfer state for BD2 is formed more slowly, but it decays extremely rapidly. Charge recombination for both dyads leads to a partial triplet formation on the Bodipy group. The naphthalene spacer group is extremely efficient at promoting back electron transfer.

Exciplex Emission from a Boron Dipyrromethene (Bodipy) Dye Equipped with a Dicyanovinyl Appendage

“…Decay of this species occurs with a time constant of approximately 1 ns to form a mixture of the triplet-excited state and the ground state but without clear population of a charge-separated species. Such behavior has been reported previously for Bodipyrelated exciplexes [43] in solvents of medium polarity, and intersystem crossing within exciplexes is well known. [44] The triplet-excited state can be seen after excitation of BOD-DCV with a 4 ns laser pulse at 470 nm (Figure 7), for which the decay profile is monoexponential with a lifetime of approximately 90 ms in the absence of dissolved oxygen.…”

Exploring BODIPY Derivatives as Singlet Oxygen Photosensitizers for PDT

“…However, this hypothesis does not explain the high dependence on 1 O 2 production with the solvent polarity. An alternative explanation for the efficiency of the orthogonal BODIPY dimers as PSs for 1 O 2 production is the triplet‐state population taking place from ICT states generated by charge recombination (ICT transition) in the singlet excited state (16‐108). Nevertheless, the dependence of 1 O 2 generation of halogen‐free orthogonal BODIPY dimers on solvent polarity is in good agreement with a spin–orbit charge‐transfer intersystem crossing (SOCT‐ISC) mechanism (12,109), which basically operates in orthogonal donor–acceptor dyads.…”

Recent advances in artificial photosynthetic systems at Newcastle University

“…During those studies, it was found that the bridging unit plays a key role in the transfer rates, in particular in the recombination to the ground state. Using a bodipy dye as donor and a simple amine as acceptor, charge transfer rates with or without a naphthalene bridging unit were measured; however, the energy levels of donor and acceptor did not display an optimal match and no direct effect could be observed [14]. It was found that a bridging unit with a strong coupling between donor and acceptor promotes a rapid recombination.…”