No abstract

By analyzing the effect of benzene-fused position on a compound's optical properties, an excellent benzocoumarin-based two-photon fluorescent probe for H2O2 detection was fabricated.

Investigation of the clear structure−property relationship and microscopic mechanism of thermally activated delayed fluorescence (TADF) emitters with high emission quantum yield is a direction worthy of continuous efforts. The instructive theoretical principle of TADF material design is critical and challenging. Here, we carried out theoretical calculation on two experimental Cu(I) complexes with the same 7,8-bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate (dppnc) but different N^N ligands [dmbpy = 6,6′-dimethyl-2,2′-bipyridine (1) or dmp = 2,9dimethyl-1,10-phenanthroline (2)] to briefly elaborate the structure−TADF performance relationship and luminescence mechanism. It was found that enhanced rigidity by the fused benzene ring between two pyridyl units in complex 2 leads to (i) higher allowedness of S 1 → S 0 , (ii) more effective reverse intersystem crossing (RISC), and (iii) better relative stability of the T 1 state, which could be responsible for its excellent TADF behavior. Thus, a strategy of extending π conjugation in the N^N ligand could be deduced to further enhance the quantum yield. We validated it and have succeeded in designing analogue complex 4 by extending π conjugation with an electron-withdrawing pyrazinyl. Benefiting from the smaller energy gap (ΔE ST ) and plunged reorganization energy between the S 1 and T 1 states, the rate of RISC in complex 4 (1.05 × 10 8 s −1 ) increased 2 orders of magnitude relative to that of 2 (5.80 × 10 6 s −1 ), showing more superiority of the TADF behavior through a better balance of RISC, fluorescence, and phosphorescence decay. Meanwhile, the thermally activated temperature of 4 is only 165 K, implying that there is a low-energy barrier. All of these indicate that the designed complex 4 may be a potential TADF candidate.