Red/NIR Thermally Activated Delayed Fluorescence from Aza‐BODIPYs

Abstract

The search for long-lived red andN IR fluorescent dyes is challenging and hitherto scarcely reported. Herein, the viability of aza-BODIPY skeleton as ap romising system for achieving thermala ctivated delayed fluorescent (TADF) probes emitting in this target region is demonstrated fort he first time. The synthetic versatility of this scaffold allows the design of energy and charget ransferc assettes modulating the stereoelectronic propertieso ft he energyd onors, the spacer moieties and the linkage positions. Delayed emission from these architectures is recorded in the red spectral region(695-735 nm) with lifetimes longer than 100 msi n aerated solutionsa tr oom temperature. The computationalaided photophysical study under mild andh ard irradiation regimes disclose the interplayb etween molecular structure and photonic performance to develop long-lived fluorescence red emitters through thermally activated reverse intersystemc rossing. The efficienta nd long-lasting NIR emission of the newlys ynthesized aza-BODIPY systems provides a basis to develop advanced opticalm aterials with exciting and appealing photonic response.

Thermally Activated Delayed Fluorescence Material: An Emerging Class of Metal‐Free Luminophores for Biomedical Applications

“…Generally, two types of luminescence mechanisms are represented in TADF: the prompt fluorescence (PF) and the delayed fluorescence (DF), which could be triggered by photoexcitation or electroexcitation. [ 41 , 42 , 43 , 44 ] In light‐emitting devices such as OLEDs, the TADF emitters are electronic excitation ( Figure 3 a ), where 25% singlet and 75% triplet excitons are generated via hole and electron injection. Assuming non‐radiative decay and phosphorescence emission are ignored, the triplet excitons could retransform into singlet excitons by RISC process, and both the initial and back‐formed singlet excitons could realize PF and DF emission.…”

The role of excited-state character, structural relaxation, and symmetry breaking in enabling delayed fluorescence activity in push–pull chromophores

“…We note that in the meantime alternative strategies in the design of red TADF emitters have led to high PLQY extending into the near infrared range. [44][45][46][47][48][49][50][51] Nonetheless, identifying the root cause of the vast drop in PLQY between Cz-AQ and Cz-BDT presents a useful challenge to inform future molecular design and to provide insight into the intricate photophysics of TADF emitters.…”

Triplet Photosensitizers and Their Applications in Triplet–Triplet Annihilation Upconversion

“…It should be pointed out that, for electron donor–acceptor dyad types of TADF molecules, the ε values are usually small, due to the poor spatial overlap of the HOMO and LUMO. ,− This is clearly a disadvantage of using TADF molecules as triplet PSs in TTA-UC. Moreover, TADF molecules showing strong absorption in the green or red light range are rare. − Song et al have investigated the application of a novel monochromophore heavy-atom-free TADF PS in TTA-UC, and a large anti-Stokes shift (207 nm) from red to blue (Figure , compound 18 ) was achieved . The TADF fluorescein derivative 18 has a very small Δ E ST (28.3 meV), which avoids energy loss and has a long triplet-state lifetime (22.11 μs).…”