Tuning Intramolecular Förster Resonance Energy Transfer and Activating Intramolecular Singlet Fission

Abstract

The synergy of panchromatic absorption throughout most of the visible range of the solar spectrum and intramolecular singlet fission (SF) has been realized in a series of conjugates featuring different light-harvesting subphthalocyanines (SubPcs) and an energy accepting pentacene dimer (Pnc ). At the focal point was a modular SubPc approach, which was based on decorating the SubPc core with different peripheral substituents to tailor and fine-tune their optical properties. Transient absorption measurements assisted in corroborating that the SubPcs act as energy-transfer antennas by means of unidirectional and quantitative intramolecular Förster resonance energy transfer (FRET) to the Pnc , where an intramolecular SF affords triplet quantum yields reaching unity.

Controlling Intramolecular Förster Resonance Energy Transfer and Singlet Fission in a Subporphyrazine–Pentacene Conjugate by Solvent Polarity

“…A comparison of the extinction coefficients in the respective solvents is given in the Supporting Information in Figures S23-S24. A comparison of panchromatic absorption presented by the conjugates C and ZnPzPnc 2 , from previous works [35,36] conveys the advantage of SubPzs as energy donor. Namely, broad absorptions and high extinction coefficients in the 400 to 600 nm lead to an overall increase in absorption by roughly 85 % relative to B, which is superior to both SubPc (65 %) and ZnPz (51 %) as donors.…”

“…For B , a kinetic model including three‐species was applied for all solvents, as previously developed [35, 36] . In short, the initially populated singlet excited state 1 (S 1 S 0 ) B with maxima at 451, 510, and 1383 nm and GSB between 550 and 750 nm, transforms rapidly into the singlet correlated triplet pair state 1 (T 1 T 1 ) B , with maxima at 472, 506, 858, and 972 nm and GSB between 550 and 750 nm (in all solvents).…”

“…In other words, our findings confirm that the nature for the triplet excited state population is SF. A closer look at the fingerprints at 860, 970, and 1400 nm reveals that the correlated triplet pair 1 (T 1 T 1 ) is formed via an intermediate state that carries both singlet excited state and charge transfer (CT) character CT (S 1 S 0 ) B [35, 36] . In the last step, 1 (T 1 T 1 ) B decays and leads to direct recovery of the ground state (S 0 S 0 ) within a couple of nanoseconds.…”

“…A closer look at the fingerprints at 860, 970, and 1400 nm reveals that the correlated triplet pair 1 (T 1 T 1 ) is formed via an intermediate state that carries both singlet excited state and charge transfer (CT) character CT (S 1 S 0 ) B . [35,36] In the last step, 1 (T 1 T 1 ) B decays and leads to direct recovery of the ground state (S 0 S 0 ) within a couple of nanoseconds. This is facilitated by strong coupling between the two pentacenes (both triplet as excited states), which activates geminate triplet-triplet annihilation ( Figures S27, S29, S31 and S35).…”

Kontrolle des intramolekularen Förster‐Resonanzenergietransfers und der Singulettspaltung in einem Subporphyrazin‐Pentacen‐Konjugat mittels Lösungsmittelpolarität

“…ZnPzPnc 2 . SubPc und ZnPz dienten als Energieantennen und Donoren, die ihre Energien im angeregten Zustand über einen intramolekularen Förster‐Resonanzenergietransfer (i‐FRET) auf ein Pentacen‐dimer (Pnc 2 ) vermittelten [35, 36] . Durch komplementäre Absorptionen, insbesondere über den sichtbaren Bereich, fördert i‐FRET die Gesamteffizienz von intramolekularem SF (i‐SF).…”