Highly Efficient Triplet–Triplet Annihilation Upconversion with a Thermally Activated Delayed Fluorescence Molecule as Triplet Photosensitizer

Abstract

Thermally activated delayed fluorescence (TADF) molecules have great potential for practical applications as triplet photosensitizers, owing to their long triplet lifetimes, almost negligible energy loss in intersystem crossing, and excellent lightharvesting ability. Recently, several triplet−triplet annihilation (TTA) upconversion systems using the TADF photosensitizer have been reported. To provide comprehensive dynamic information for designing an optimized system in the future, more experiments with the new TADF photosensitizers are necessary. Herein, we conducted a new TTA upconversion system with a recently developed TADF molecule, DMACPDO, as the triplet photosensitizer and 9,10-diphenylanthracene (DPA) as the annihilator. The overall upconversion yield was determined to be relatively high, e.g., 22.3% in toluene, 21.9% in benzene, and 8.1% in chlorobenzene. By examining elementary photophysical and photochemical processes with time-resolved transient absorption and fluorescence emission spectroscopy, we revealed the influence of solvent polarity and viscosity on each step. Our conclusion highlights the elusive solvent effect in TTA upconversion application of the TADF photosensitizer.

Isoacridone dyes with parallel reactivity from both singlet and triplet excited states for biphotonic catalysis and upconversion

“…26,27 In this context, the metal-free dyes investigated herein represent an attractive alternative. Despite important progress in the past few years with quantum yields for upconversion to the UV of up to ∼20%, 31,32,35,60,99,105,106,[109][110][111][112][113][114] the eld of purely organic (metal-free) sensitizers with photoactive triplet excited states seems still underdeveloped.…”

“…With these F UC values, the observed upconversion serves as a promising starting point for a new class of purely organic UCsystems, which currently show UC-quantum yields typically below 5% 61,84,99,100,103,[106][107][108][109][110][111][112][113] to supplement purely organic UCsystems which mostly rely on BODIPY dyes 50,60,61,108 or donoracceptor cyanoarenes. 95,99,100 Furthermore, the developed isoacridones represent a modular and tunable addition to the available range of organic sensitizers suitable for the TTA-UC.…”