Charge Shift/Recombination and Triplet Formation in a Molecular Dyad based on a Borondipyrromethene (Bodipy) and an Expanded Acridinium Cation

Abstract

A molecular monocationic dyad comprising a borondipyrromethene (Bodipy) and an expanded planar acridinium cation was prepared. The dyad, when excited in solution by an ultrashort laser pulse, generates a charge‐shift state, where a positive charge is transferred to the Bodipy from the acridinium subunit. The process takes less than 1 ps in MeCN and around 8 ps in 1,2‐dichloroethane. The charge‐shift state collapses, in part, back to the ground state but it also leads to partial triplet formation; the discrimination between rates for the forward and reverse processes is circa 7.

BODIPY‐Pyrene and Perylene Dyads as Heavy‐Atom‐Free Singlet Oxygen Sensitizers

“…This has been previously demonstrated with methylpyridinium and acridinium ion-based BODIPY dyads. 16 Finally, the fact that in BPyrD5 triplet state formation was not observed may be associated with the molecular geometry in this dyad. It has been noted in previous works that an orthogonal arrangement of the subunits in multichromophoric systems provides efficient ISC, e.g., in donor-orthogonal-acceptor conjugated polymers [36] and OLED emitters exhibiting thermallyactivated delayed fluorescence.…”

“…2), [14] have been shown to form triplet excited states of BODIPY without directly relying on the heavy atom effect. Similarly, BODIPY dyads containing quinone, [15] methylpyridinium or acridinium ion [16] (structures 3 and 4, Fig. 2) subunits as electron donors and BODIPY dimers [17] demonstrated such properties.…”

Heavy-atom-free BODIPY photosensitizers with intersystem crossing mediated by intramolecular photoinduced electron transfer

“…Tkachenko and co-workers described dyad 53 incorporating hexalkyl-substituted BODIPY and an expanded acridinium cation as electron donor and acceptor subunits, respectively, separated by a phenylethynyl spacer (Figure 11). 69 Excitation of 53 in acetonitrile leads to a CT state in which a positive charge is localized on the BODIPY and a negative on the acridinium subunit. Although this state recombines on the picosecond timescale predominantly back to the ground state, formation of the BODIPY triplet state with 15% yield was noted.…”

Control of triplet state generation in heavy atom-free BODIPY–anthracene dyads by media polarity and structural factors

“…25 For instance, recently reported BODIPY dyads bearing an extended acridinium cation as an electron donor showed a triplet excited state yield of up to 15%. 26 It is still unclear which factors govern ISC efficiency in CT states. To further advance applications of heavy atom-free PeT sensitizers, insights into their photophysical characteristics and guidelines for the design of new material systems are required.…”