Accessing blue-room-temperature phosphorescence from pyridine-fused extended coumarins

Modulation of Delayed Fluorescence Guided by Conformational Effect-Mediated Thermally Enhanced Phosphorescence in Phenothiazines–Quinoline–Cl Conjugates

“…In contrast, harvesting triplet excitons via room-temperature phosphorescence (RTP) from the lowest triplet (T1) state to the ground (S0) state has become an attractive alternative approach. Recently, many design principles that rely on intra- and/or intermolecular interactions, − aggregates, , host–guest chemistry, excited-state engineering, halogen effect, ,, heavy chalcogen atom effect, and orthogonal donor–acceptor (D–A), ,,, biaryl, and donor–spacer–acceptor ,,− geometries have been developed. Nevertheless, a handful of reports comprising chemical modification, mechanical force, , conformational switching, intramolecular CT, regioisomeric effect on the excited state, and change of host matrices have recently observed simultaneous TADF and RTP. ,− Despite these achievements, structure–property correlation in simultaneous thermally enhanced phosphorescence (TEP) and its impact on TADF remain unclear due to fast internal conversion and the supersensitive nature of the triplet excitons.…”

Conformational Effect of Catechol-Terephthalonitrile Emitters Leading to Ambient Violet Phosphorescence

“…Furthermore, highest occupied and lowest unoccupied natural transition orbital (HONTO/LUNTO) analysis of the F1 revealed that both S1′ and T1′ show CT character, as the hole and electron wave functions are distributed over the long (fused rings) and short (TPN) axes of the molecular backbone (Figure b). Upon careful investigation of the hole and electron wave functions of T1′, we found a shift in electron density from the O atoms (long axis) toward the carbon and nitrogen atoms of the CN group (short axis), leading to nπ* character of the triplet state, which is effective in realizing efficient RTP . However, the ππ* character of the triplet state can also be realized from transition orbitals along the long axis of the molecular backbone.…”

“…Upon careful investigation of the hole and electron wave functions of T1′, we found a shift in electron density from the O atoms (long axis) toward the carbon and nitrogen atoms of the CN group (short axis), leading to nπ* character of the triplet state, which is effective in realizing efficient RTP. 25 However, the ππ* character of the triplet state can also be realized from transition orbitals along the long axis of the molecular backbone. Also, NTOs of both S1′ and T1′ states are almost similar, which implies a low SOC value between the two states, which hinders direct RISC from T1 to S1.…”

“…Over the past decade, substantial progress has been made in developing organic blue-green and yellow-red RTP emitters with millisecond (ms) lifetimes for data security − and sensors , due to their advantages of structural versatility and facile processability. It has been established that the RTP characteristics of most of the reported twisted geometries heavily rely on the heavy-atom effect, , El-Sayed’s rule, , the energy gap principle, ,,,− El-Sayed analogy, donor–acceptor, donor–spacer–acceptor, and donor–sp 3 linker–acceptor. ,,− In addition, the incorporation of intermolecular interactions, ,, aggregation, ,,,− and rigid single crystals, along with host–guest studies , has also been demonstrated to significantly suppress radiationless decays ( k nr ). Moreover, the insights gained from the past decade of organic RTP research have resulted in green-yellow-red RTP with high triplet lifetimes.…”

Carbazole–Benzonitrile–Norbornadiene Conjugates for Photothermally Reversible Ambient Phosphorescence

“…However, achieving RTP (T1 → S0) is an exasperating task because phosphorescence is a quantum mechanically forbidden process that occurs at a meager rate. Numerous design principles that rely on aggregates, , host guest chemistry, , heavy atom effects, , orthogonal donor–acceptor (D–A), − biaryl, D–spacer–A geometries, − mechanical forces, conformational effects, , and inter/intramolecular charge transfer ,, have been overwhelmingly developed to observe RTP, where a low S1–T1 gap (Δ E ST ) is considered an essential prerequisite. However, achieving blue–violet RTP remains challenging.…”