Discrete Dimeric Anthracene Stackings in Solids with Enhanced Excimer Fluorescence

Abstract

Polyaromatic compounds are significant members of leading candidates for organic semiconductors and optical materials. However, a thorny problem of polyaromatic materials is that their good emissive abilities in solutions are seriously weakened in solids due to strong π−π interactions between aromatics. As a typical case, the intermolecular π−π interaction tends to form excimers for polyaromatic system, which were always considered to quench fluorescence and decrease luminous efficiency in the past decades. Herein, anthracene is modified by meta-substituted bromobenzene to facilitate the formation of discrete dimeric stack in solids, leading to the enhanced anthracene excimer fluorescence. Particularly, instead of excimer quenching fluorescence, the more anthracene dimers in solids, the higher fluorescence efficiency, namely, excimer-induced enhanced solid-state emission. This work not only provides a meta-substituted strategy for molecular design to form excimer in solids but also demonstrates that high-efficiency solid-state emission can be achieved by excimer species.

Solid‐State TICT‐Emissive Cruciform: Aggregation‐Enhanced Emission, Deep‐Red to Near‐Infrared Piezochromism and Imaging In Vivo

“…However, the corresponding intensity of this PL peak gradually weakened up to 1% w/w, and the LE‐emissive peak completely disappeared from the PL spectrum, similar to the results observed for the DFPA crystals (Figure d). The blend films comprising 0.1‰, 1‰, and 1% w/w DFPA revealed PL lifetimes of 5.3, 7.2, and 8.0 ns (Figure b), respectively, demonstrating enhanced intermolecular interactions . Thus, we speculated that the quenching of the LE emission was due to intermolecular interactions.…”

One Stimulus In Situ Induces Two Sequential Luminescence Switchings in the Same Solvent‐Fuming Process: Anthracene Excimer as the Intermediate

“…9‐(4‐(2,2‐Diphenylvinyl)phenyl)anthracene (tPE‐AN) composed of anthracene (AN) core and one‐sided substituent (2‐( p ‐tolyl)ethene‐1,1‐diyl)dibenzene (tPE) was designed for dimer formation with antiparallel π–π stacking by a molecular design in our previous works (Scheme S1 and Figure S1, Supporting Information): substituent asymmetrically orientates on the one side of anthracene plane in single‐molecule conformation which is appropriate for dimer formation with antiparallel overlap of π–π stacking . The pristine tPE‐AN powder precipitated from the mixed dichloromethane (DCM) and methanol emits the bright green light under UV irradiation, in sharp contrast to blue emission of tPE‐AN in dilute solutions.…”

“…In crystal G, along with a ‐axis of unit cell, AN units are stacked in the staggered forms of π–π dimer (Figure d and Figures S9–S12, Supporting Information). The geometry optimization of dimer tends to be a “compressed” excited state with the shortened π–π distance and the increased π–π overlap, in favor of the suppression of nonradiative quenching (Figure S13a, Supporting Information) 6c,e. Natural transition orbitals (NTOs) denote the coexistence between locally excited and CT states in excimer excited state of dimer, featured with the typical characteristic of hybridized local and CT state (Figure S13b, Supporting Information) .…”

“…However, the other designed molecule composed of the same units (AN and tPE), 9‐(1,2,2‐triphenylvinyl)anthracene (TBE‐AN), shows the monomer‐like fluorescence instead of excimer fluorescence in solid (Figures S19 and S20, Supporting Information). The comparison between tPE‐AN and TBE‐AN verifies the effective molecular design strategy ( Figure ): the substituent asymmetrically orientates on the one side of anthracene plane in single‐molecule conformation, which is thus appropriate for dimer formation with antiparallel overlap of π–π stacking …”

“…In contrast with tPE‐AN, 2‐(anthracen‐9‐yl)thianthrene (2‐TA‐AN) materials with AN excimer fluorescence previously reported by our group6d were not affected at all by both grinding and fuming (Figures S37 and S38, Supporting Information), although 2‐TA‐AN material has a high solubility of about 110 mg mL −1 in DCM solvent. A possible reason is that the discrete AN dimers in 2‐TA‐AN crystal had much stronger π–π interactions between AN moieties than those in crystal G of tPE‐AN, which is demonstrated by the larger interaction energy of 2‐TA‐AN dimer (470 meV) than that of tPE‐AN dimer (360 meV) at ground state through theoretical calculation.…”