Persistent room temperature phosphorescence films based on star-shaped organic emitters

Abstract

Developing pure organic materials with ultralong lifetimes in neat film is attractive but challenging. Here, we report a series of metal-free star-shaped organic luminogens (CzO, CzS and CzSe) based on...

Conformational isomeric thermally activated delayed fluorescence (TADF) emitters: mechanism, applications, and perspectives

“…105–108 However, achieving efficient pure organic RTP materials is not straightforward due to the less efficient ISC process from singlet to triplet excited states and rapid nonradiative decay loss of triplet excitons. 109,110 To address these issues, strategies such as (i) introducing heavy atoms, 111–115 heteroatoms, 116–118 and aromatic carbonyl 119–121 and (ii) crystal engineering, 122,123 guest doped in host, 124–127 and H-aggregation 128 have been proposed. Conformational isomerism may endow D–A typed emitters in different forms with TADF and RTP properties, respectively, which can facilitate the development of multi-functional smart materials.…”

“…[105][106][107][108] However, achieving efficient pure organic RTP materials is not straightforward due to the less efficient ISC process from singlet to triplet excited states and rapid nonradiative decay loss of triplet excitons. 109,110 To address these issues, strategies such as (i) introducing heavy atoms, [111][112][113][114][115] heteroatoms, [116][117][118] and aromatic carbonyl [119][120][121] and (ii) crystal engineering, 122,123 guest doped in host, [124][125][126][127] and H-aggregation 128 (25)(26)(27)(28)(29)(30)(31)(32) to investigate the interplay of TADF and RTP for the first time by changing the steric alkyl groups on the PTZ unit. 129 Compared with the TADF characteristics of unsubstituted 25 and 30, introducing a methyl group at the 2-position of the PTZ unit results in 26 and 31 mainly exhibiting RTP phenomenon, which can be ascribed to the restricted rotation of the C-N bond.…”

Theoretical insights into the room temperature phosphorescence properties in star-shaped carbazole-based molecules

“…2. To generate efficient RTP molecules, groups with lone pairs 25 were used as n-units and carbazolyl moieties are chosen as the p-unit in the previously described RTP materials. 50 The intermolecular electronic couplings and interactions associated with the n-unit are crucial for the RTP process.…”

“…[21][22][23][24] Shu et al experimentally reported star-shaped carbazole-based molecules (CzO, CzS and CzSe) with hetero atoms of chalcogen (O, S, Se) atoms. 25 These benzene-cored star-shaped molecules are substituted with bromine, which is a heavy halogen at the ortho position of the benzene rings present in the carbazolyl moieties used to study RTP properties. 26 The introduction of a heavy halogen atom (Br) increases the electron-absorbing capacity and stabilizes the triplet state.…”

Suppression of nonradiative transitions of triplet excitonsviaa fused/non-fused strategy for realizing efficient room-temperature phosphorescence

“…[1][2][3][4][5][6][7][8][9][10][11][12] Unlike most phosphors based on organometallic complexes containing noble metals, most of the metal-free phosphors are inefficient due to the slow intersystem crossing (ISC) process and serious non-radiative relaxation of triplet excitons. [13][14][15] To achieve efficient RTP, two basic prerequisites should be followed: one is to facilitate ISC from singlet to triplet excited states by the introduction of heavy atoms (Br and I), [16][17][18][19][20] heteroatoms (N, O, S, P, and so on) 15,[21][22][23][24] or aromatic carbonyl groups; [25][26][27][28] another is to reduce the nonradiative transitions of triplet excitons, which can be achieved by crystallization engineering. [29][30][31][32][33] Especially for RTP materials with a rotatable and twisted skeleton, excellent RTP performance can be achieved in crystals or cocrystals.…”