Pyrazole and Triazole Fused Perylene Bisimides: Synthesis and Photophysical Properties

ABSTRACT We studied the intersystem crossing (ISC) of neutral, monoanion, and dianion of a series of phenyl, pyrazole, and triazole fused perylene bisimides (PBI) derivatives. The neutral compounds exhibit high fluorescence quantum yields ( Φ F = 66.5%−91.9%) and low singlet oxygen quantum yields ( Φ Δ < 7.8%), with no triplet state signals detected via femtosecond transient absorption (fs‐TA) or nanosecond transient absorption (ns‐TA) spectral measurements. Time‐resolved electron paramagnetic resonance (TREPR) revealed an e,e,e,a,a,a electron spin polarization (ESP) for the T 1 state of these PBIs. Calculations of spin‐orbit coupling matrix elements (SOCMEs) and g ‐tensor anisotropy both confirm the weak spin‐orbit coupling (SOC) of the molecules, accounting for their low ISC efficiency. Pulse electron paramagnetic resonance (pulse EPR) measurements of radical anions showed that PBI derivatives lacking pyrazole/triazole moieties have much longer transverse relaxation times ( T m = 2.5−2.6 µs) than the other compounds. Additionally, ns‐TA spectra confirmed ISC in PBI dianions, which possess long‐lived triplet states (213−558 µs). These species can be used as super strong reductants in photocatalytic redox organic reactions.