Multidimensional Structure Conformation of Persulfurated Benzene for Highly Efficient Phosphorescence

Abstract

It is a challenge to acquire, realize and comprehend highly emissive phosphorescent molecules. Herein, we report that, using persulfurated benzene compounds as models, phosphorescence can be strongly enhanced through the modification of molecular conformation and crystal growth conditions. By varying the peripheral groups in these compounds, we were able to control their molecular conformation and crystal growth mode, leading to one-(1D), two-(2D) and three-dimensional (3D) crystal morphologies. Two kinds of typical molecular conformations were separately obtained in these crystals through substituent group control or solvent effect. Importantly, a symmetrical 3,3-conformer exhibits that planar central benzene ring prefers a 3D-type crystal growth mode, demonstrating high 2 phosphorescence efficiency. Such outcome is attributed to strong crystal protection effect of 3D crystal and bright global minimum (GM) boat-like T1 state of the symmetrical 3,3-conformer.The conformation studies further reveal small deformation of the inner benzene ring in both singlet and triplet states. The GM boat-like T1 state is indicated by theoretical calculations, which is far away from the conical intersection (CI) point between the S0 and T1 potential energy surface. Meanwhile, the small energy gap between S1 and T1 states and the considerable spinorbit coupling matrix elements allow an efficient population of the T1 state. Combined with the crystal protection and conformation effect, the 3,3-conformer crystal shows high phosphorescence efficiency. The unsymmetrical 2,4-conformer conformation with the twisted central benzene ring leads to 1D or 2D crystal growth mode, which has weak crystal protection effect. In addition, the unsymmetrical conformation has a dark GM T1 state that is very close to the T1-S0 CI point, implying an efficient nonradiative T1-S0 quenching. Thus, weak phosphorescence was observed from the unsymmetrical conformation. This study provides an insight for the development of highly emissive phosphorescent materials.

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

“…10,52,56–60 Several persulfurated aromatic compounds with bright green phosphorescence (phosphorescence quantum yield ( Φ P ) up to 100%) in crystal states were first reported by Ceroni et al 61,62 Later on, hexasulfurated, pentasulfurated and tetrasulfurated benzene-cored star-shaped molecules have been designed, synthesized and studied as highly efficient RTP materials. 52,63–67 However, most of them only exhibited rather short phosphorescence lifetime ( τ P < 1 ms). 52,64–67 By combining carbazolyl groups with chalcogen atoms, He and co-workers prepared organic phosphorescent crystals containing O, S, Se and Te atoms with ultralong τ P up to 753 ms. 68 Unfortunately, no persistent RTP films based on these RTP materials have been successfully fabricated.…”

“…52,63–67 However, most of them only exhibited rather short phosphorescence lifetime ( τ P < 1 ms). 52,64–67 By combining carbazolyl groups with chalcogen atoms, He and co-workers prepared organic phosphorescent crystals containing O, S, Se and Te atoms with ultralong τ P up to 753 ms. 68 Unfortunately, no persistent RTP films based on these RTP materials have been successfully fabricated. Here, we design and synthesize three benzene-cored star-shaped materials containing both O, S and Se atoms and carbazolyl moieties (CzO, CzS and CzSe), which not only exhibit persistent RTP in crystal states, but also in doped and neat film states.…”

Modulating Room-Temperature Phosphorescence through the Synergistic Effect of Heavy-Atom Effect and Halogen Bonding

“…To achieve high-efficiency RTP emission, two key points need to be addressed: (1) sufficient generated triplet excitons through the ISC process and (2) stable radiative transition of triplet excitons. − Based on the above issues, some design principles have been developed, such as n−π* transition, , incorporation of heavy atoms or aromatic carbonyl , for promoting the ISC process, as well as crystallization, − H-aggregation, , host–guest doping, − and organic/inorganic frameworks , for stabilizing triplet excitons. Especially, the introduction of heavy atoms can achieve high-efficiency RTP due to heavy-atom effect (HAE). − However, excessive HAE can also be harmful to the phosphorescence lifetime to some extent because of the intrinsic competition between phosphorescence lifetime (τ p ) and quantum yields (Φ p ). − Thus, it still remains a big challenge to develop RTP materials with both high Φ p and long τ p .…”

Long-Lived Organic Room-Temperature Phosphorescence from Amorphous Polymer Systems

“…On the basis of this process, a set of rational strategies to generate and stabilize the excited triplet excitons under ambient conditions for realizing efficient RTP have been proposed. For example, introducing heavy atoms (e.g., bromine and iodine) and heteroatoms with lone-pair electrons (e.g., nitrogen, sulfur, and oxygen) can effectively facilitate the ISC transition. , Creating a rigid environment through crystal engineering, host–guest doping, polymerization, and supramolecular assembly would reduce the triplet nonradiative decay rate ( k nr ), which is beneficial to improving the phosphorescence quantum yield ( Φ p ) and lifetime ( τ P ). Among them, a polymeric enhancement strategy for RTP emission based on multiple inter/intramolecular interactions arouses increasing concern, and a series of research advancements have been achieved in recent years.…”