Persistent Solid‐State Phosphorescence and Delayed Fluorescence at Room Temperature by a Twisted Hydrocarbon

Abstract

The dehydrating cyclotrimerization of 1-tetralone in the presence of titanium tetrachloride at high temperatures leads to homotruxene,anonplanar arene in whicht he twist angles between its three outer benzene rings and the central benzenea re stabilized by ethylene bridges.T his non-planar configuration allows for pronounced spin-orbit coupling and ah igh triplet energy,l eading to room-temperature phosphorescence in air with al ifetime of 0.38 sa nd aquantum yield of 5.6 %, clearly visible to the human eye after switching off the excitation. Triplet-triplet annihilation is found to simultaneously lead to asubstantial delayed fluorescence,unprecedented from apure hydrocarbon at ambient conditions,with alifetime of 0.11 s.Although the phosphorescence and, to al esser extent, delayed fluorescence (DF) of polycyclic aromatic hydrocarbons in host matrices has been studied in the middle of the last century at low as well as at room temperature, [1][2][3][4][5][6] this class of materials is notably absent from the recent surge of interest in room-temperature phosphorescence (RTP) and DF by single-component crystalline organic materials. [7,8] Recent metal-free RTPa nd DF materials either contain heavy atoms,s uch as bromine,t of acilitate singlet-triplet intersystem crossing (ISC), or polarizing heteroatoms,such as oxygen or nitrogen, that induce charge-transfer states. [7] Simple prototypical examples are dibromo-biphenyl 1, [9] benzophenone 2, [9] and carbazolylbenzoate 3 [10] with RTP quantum yields F in the crystalline state of 14 %(1), 16 %(2), and 2.1 %(3)and RTPlifetimes t of 0.81 ms (1), 0.31 ms (2), and 0.8 s(3). These data illustrate the obvious:while there is, of course,n ol inear correlation between yield and lifetime, ah igh F is much harder to achieve if phosphorescence is persistent (3)than if lifetimes are in or below the millisecond range (1, 2), where it can more easily compete with non-radiative deactivation. Short-lived RTPwith F near unity has been obtained with Ir and Pt complexes [11] and with abenzene bearing six arylthio substituents. [12] Innovative approaches for the improvement of RTPv ia intermolecular interactions are crystallization-induced phosphorescence, [9] halogen bonding in co-crystals, [13] aggregation-induced ISC, [14] complexationinduced RTPi ns olution, [15] and emission from H-aggregates. [16] In general, electronic transitions between non-coplanar (orthogonal or tilted) orbitals are necessary to allow for spinorbit coupling (SOC), [17,18] but the vast majority of polycyclic aromatic compounds do not present this kind of geometry. However,ahydrocarbon whose persistent solid-state RTP was noted early is tetraphenylmethane 4. [19] Its peculiar threedimensional structure of four-fold symmetry [20] distinguishes 4 from most polycyclic arenes,w hich generally show no persistent RTPi nt he pure crystalline state.V ery weak longlived RTPint he crystal has also been reported [3] forthe two C 3 -symmetric species triphenylene 5 [21] and sym-triphenylbenzene 6 (which is non-planar). This...

Organic luminescent materials: The concentration on aggregates from aggregation‐induced emission

“…Thus, more and more scientists have devoted themselves into the research of it in recent years. [82][83][84][85][86][87][88][89][90][91] Especially, Ruren Xu and coworkers proposed "Towards a new discipline of condensed matter chemistry" in 2018. [82,83] It is believed that after constant exploration, the molecular structure-packing property relationship could be revealed clearly and the adjustment of luminescence property in aggregation state could be easily realized from the source of molecular design.…”

Dual-Responsive Thermally Activated Delayed Fluorescence of Spiropyran Derivatives

“…Consequently, the delayed emission was assigned to TADF of SP1. 25,[58][59][60][61] After irradiating it with 365 nm light for about 1 s, the peak at 588 nm Page 8 of 24 CCS Chemistry This article presented here has been accepted for publication in CCS Chemistry and is posted at the © 2021 Chinese Chemical Society.…”

Theoretical Insight Into the Ultralong Room-Temperature Phosphorescence of Nonplanar Aromatic Hydrocarbon

“…To overcome this issue, the heavy atoms (eg., Br and I) ( Cai et al, 2018 ; Wang et al, 2021b ) and carbonyl groups ( Zhao et al, 2016 ; Jia et al, 2020 ) were incorporated into organic molecules to promote ISC process for achieving ultralong RTP, in combination with the suppression of the nonradiative quenching through rigid environment, ( Wu et al, 2020 ; Zheng et al, 2020 ; Zhou et al, 2020 ; Chen et al, 2021 ; Xie et al, 2021 ), such as crystal engineering and host-guest system. Very recently, Bechtold et al reported that the nonplanar aromatic hydrocarbon, named as 5,6,11,12,17,18-hexahydrobenzo [2,1-p]chrysene (HD), ( Salla et al, 2019 ), can show an ultralong RTP, which was attributed to the pronounced SOC induced by non-planar configuration. However, the enhanced SOC also reduces the RTP lifetime.…”

“…The 5′-phenyl-1,1’:3′,1″-terphenyl (PT) has a faint RTP in crystal, while HD shows an efficient RTP with a lifetime of 380 m by introducing saturated ethylene bridges between the central benzene and outer benzene rings of PT. ( Li et al, 2015 ; Salla et al, 2019 ). Therefore, PT and HD molecules are good prototype to expound the dependence of ultralong RTP on the nonplanar conformation.…”