Ultrafast Intersystem Crossing in Selenium-Annulated Perylene Bisimide

Abstract

An intersystem crossing (ISC), the non-radiative transition between two electronic states with different spin multiplicities, is ubiquitous and imperative in molecular photochemistry. The manifestation of a triplet manifold in π-conjugated chromophoric materials has a crucial role in enhancing the efficiency of photofunctional devices. Herein, we explore the triplet-state population in a series of chalcogen-annulated perylene bisimides (O-PBI, S-PBI, and Se-PBI), where the selenium-annulated PBI (Se-PBI) exhibits a near-quantitative triplet quantum yield ( = 94 ± 1%). Annulation of Se in the PBI core results in a drastic decrease in the fluorescence quantum yield ( = 1.5 ± 0.2%) compared to the bare PBI ( = 97.0 ± 1%), indicating the possibility of an efficient non-radiative decay pathway in the Se-PBI motif. Femtosecond and nanosecond transient absorption measurements unambiguously confirmed the ultrafast triplet population in Se-PBI with an ISC rate constant of = 2.39 × 1010 s–1 and the triplet-state decay to the ground state with a time constant of 3.78 μs. A theoretically calculated spin–orbit coupling constant (V SOC) of 122.4 cm–1 employing the SA-CASSCF/NEVPT2 method has rationalized the excited-state dynamics of Se-PBI. By virtue of the poor SOC between the singlet and triplet states, we observed a partial triplet population in S-PBI, whereas ISC is negligible in O-PBI. We demonstrate an increase in the spin–orbit coupling constant ( ≪ < ) and rate constant of ISC ( ≪ < ) across the series of chalcogen-annulated PBIs (O-PBI, S-PBI, and Se-PBI). The heavier chalcogenide PBI (Se-PBI) thus adds to the array of potential organic photoactive materials for the design of efficient solar energy conversion devices.

bay-Dissymmetrical hetero- and Aza-Benzannulated PeryleneDiimides as new n-type semiconductors

“…This more important quenching of the fluorescence suggests the possibility of an intersystem crossing induced by the introduction of heavy atoms, already reported for S and Se functionalized PDIs. 40 CV was then performed in dichloromethane with 0.1 M n -Bu 4 NPF 6 as a supporting electrolyte and the Fc + /Fc couple as a reference to determine the electronic properties of these dyes (Fig. S5, ESI†).…”

Application of the Heavy-Atom Effect for (Sub)microsecond Thermally Activated Delayed Fluorescence and an All-Organic Light-Emitting Device with Low-Efficiency Roll-off

“…Although this approach can potentially enhance ISC, our previous investigations showed that the selective acceleration of rISC can be achieved by a controlled incorporation of bromine atoms into the structure of TADF emitters . Analysis of the literature also evidenced that the various modifications of TADF emitters with HAs can significantly improve their photophysical kinetic properties. − …”

Interchromophoric Twist: Gateway to Long-Lived Excitons

“…In our lab, we use a wide range of techniques from organic synthesis, crystal engineering, spectroscopy and computational chemistry to identify distinct chromophoric systems and architectures exhibiting exciting and emergent photophysical properties. [4][5][6][7][8][9][10] In this article, we will focus on a particular intermolecular packing feature-the interchromophoric twist, whose photophysical relevance and importance we are still exploring, and in course, will also touch upon the recent experimental and theoretical reports we have communicated along this line. We first elaborate on the importance of the rotation angle as a tool to fine-tune the interchromophoric interactions and serve as a potentially new design guideline for efficient singlet fission (SF), a current, hot topic of research to better harness solar energy through photon energy conversion.…”