Excitation Energy Transfer and Exchange‐Mediated Quartet State Formation in Porphyrin‐Trityl Systems

Abstract

Photogenerated multi‐spin systems hold great promise for a range of technological applications in various fields, including molecular spintronics and artificial photosynthesis. However, the further development of these applications, via targeted design of materials with specific magnetic properties, currently still suffers from a lack of understanding of the factors influencing the underlying excited state dynamics and mechanisms on a molecular level. In particular, systematic studies, making use of different techniques to obtain complementary information, are largely missing. This work investigates the photophysics and magnetic properties of a series of three covalently‐linked porphyrin‐trityl compounds, bridged by a phenyl spacer. By combining the results from femtosecond transient absorption and electron paramagnetic resonance spectroscopies, we determine the efficiencies of the competing excited state reaction pathways and characterise the magnetic properties of the individual spin states, formed by the interaction between the chromophore triplet and the stable radical. The differences observed for the three investigated compounds are rationalised in the context of available theoretical models and the implications of the results of this study for the design of a molecular system with an improved intersystem crossing efficiency are discussed.

Accessing the triplet state of perylenediimide by radical-enhanced intersystem crossing

“…This and a previous study 37 suggest that excitation energy transfer is often the main factor limiting the yield of EISC in strongly-coupled photogenerated multi-spin systems. Consequently, regarding the design of novel chromophore–radical systems with high triplet yields, we believe that it will be essential to reflect on strategies to limit EET as a possible deactivation pathway.…”

“…When carefully analyzing the recovery of the ground state bleach, it is possible to determine the triplet/EISC yield from the fsTA data of the different PDI–TEMPO systems 37 as illustrated in Fig. S7 in the ESI † using PDI 0sg –TEMPO as an example.…”

“…However, guidelines for a rational design of such chromophore–radical systems still remain to be established. 37 Apart from the magnitude of the exchange interaction between chromophore triplet and radical ( J TR ), the excited state energies may also play an important role and may limit the overall yield of EISC, e.g. by favoring other excited state decay pathways.…”

Coherent manipulation and quantum phase interference in a fullerene-based electron triplet molecular qutrit

“…Photoexcitation has been used to generate S > 1/2 systems for a long history, with many examples showing quantum entanglement or long coherence times 19,[33][34][35][36] . Recent researches have demonstrated that a photogenerated radical pair can be utilized to perform quantum teleportation in a donor-acceptor stable radical system 37 .…”

Improved, Odorless Access to Benzo[1,2-d;4,5-d′]- bis[1,3]dithioles and Tert-butyl Arylsulfides via C-S Cross Coupling

“…Furthermore, such triaryl methyl (TAM)-radicals are used as sensors for local oxygen concentrations within EPR-imaging [ 11 , 12 ], as pH-probes [ 13 ], viscosimetry [ 14 ], and as polarizing agents for dynamic nuclear polarization (DNP) [ 15 , 16 ]. Additionally, TAM radicals incorporating benzo[1,2-d;4,5-d′]bis[1,3]dithiol moieties were recently taken into account for the design of magnetic materials and information transfer [ 17 , 18 ]. The synthesis of all of the thioketals shown in Figure 1 regularly involves 1,2,4,5-tetrakis( tert -butylthio)benzene 5 as the starting material [ 4 ], since the 1,2,4,5-tetrathiobenzene required for ketal formation easily undergoes oxidative degradation rendering its isolation cumbersome [ 19 ].…”