Substitution Effect on Luminescence of 5H‐Indeno[1,2‐b]pyridin‐5‐one Based Isomers

Abstract

A series of novel fluorescent isomers were designed by using 5H‐indeno[1,2‐b]pyridin‐5‐one (IP) as electron acceptor and triphenylamine (TPA) as electron donor, and were synthesized through Suzuki coupling reactions. The substitution position of TPA on IP was adjusted to form 6‐(4‐(diphenylamino)phenyl)‐5H‐indeno[1,2‐b]pyridin‐5‐one (IP‐6‐TPA), IP‐7‐TPA, IP‐8‐TPA, and IP‐9‐TPA. The photophysical, thermal, and electrochemical properties of these isomers were systematically studied through experimental and theoretical methods. It was observed that the substitution position of TPA on IP results in different molecular conformation and finally determine the luminescent behavior of these isomers. The 6‐ and 9‐substituted isomers IP‐6‐TPA and IP‐9‐TPA with larger torsion angles exhibited thermally activated delayed fluorescence (TADF) feature with long fluorescence lifetimes of microsecond range, while another two isomers IP‐7‐TPA and IP‐8‐TPA are only normal fluorescent molecules. Relatively higher photoluminescence quantum yields were detected for IP‐6‐TPA (0.70) and IP‐8‐TPA (0.69), while IP‐7‐TPA is poor emissive (0.23). These isomers were used as doped emitters to fabricate organic light‐emitting diodes (OLEDs), among which IP‐6‐TPA realized the best performance with a maximum external quantum efficiency of 9.0% and a current efficiency of 24.2 cd A−1.

Synthetic progress of organic thermally activated delayed fluorescence emitters via C–H activation and functionalization

“…Interestingly, they observed that the positional isomers with the donor linked at the 7 or 8 position exhibited normal fluorescence behavior, whereas isomers (IP-6-TPA and IP-9-TPA) at the 6-or 9-position with a more twisted conformation displayed TADF characteristics (Scheme 49c). 249 Free radical-induced transformations of CÀH bonds have been adopted in the synthesis of an MR-TADF emitter. In 2020, Duan's group revealed the synthetic method involving free radicals for the construction of a bathochromic-shift B/Nbased MR-ATDF emitter, AZA-BN (Scheme 50).…”

“…Interestingly, they observed that the positional isomers with the donor linked at the 7 or 8 position exhibited normal fluorescence behavior, whereas isomers (IP-6-TPA and IP-9-TPA) at the 6- or 9-position with a more twisted conformation displayed TADF characteristics (Scheme 49c). 249…”