Two‐Component Molecular Materials of 2,5‐Diphenyloxazole Exhibiting Tunable Ultraviolet/Blue Polarized Emission, Pump‐enhanced Luminescence, and Mechanochromic Response

Abstract

The development of π‐conjugated molecular systems with high‐efficiency generation of UV and blue light plays an important role in the fields of light‐emitting diodes, fluorescent imaging, and information storage. Herein, supramolecular construction of solid‐state UV/blue luminescent materials are assembled using 2,5‐diphenyloxazole (DPO) with four typical co‐assembled building blocks (1,4‐diiodotetrafluorobenzene, 4‐bromotetrafluorobenzene carboxylic acid, pentafluorophenol, and octafluoronaphthalene). Compared with the pristine DPO sample, the as‐prepared two‐component molecular materials feature ease of crystallization, high crystallinity, enhanced thermal stability and tunable luminescence properties (such as emissive wavelength, color, fluorescence lifetime, and photoluminescence quantum yield) as well as multicolor polarized emission in the UV/blue region. Moreover, pump‐enhanced luminescence and reversible mechanochromic fluorescence (MCF) properties can also be obtained for these molecular solids, which are absent for the pristine DPO sample. Therefore, this work provides a procedure for the facile self‐assembly of ordered two‐component molecular materials with tunable UV/blue luminescence properties, which have potential application in the areas of light‐emitting displays, polarized emission, frequency doubling, and luminescent sensors.

Rational Design of Charge-Transfer Interactions in Halogen-Bonded Co-crystals toward Versatile Solid-State Optoelectronics

“…The above phenomenon observed in the BFC system, to the best of our knowledge, is surprising and limited reported, since co-crystallization alter the original molecular packing structure and is regarded as an advanced strategy to tune the optical properties of solid materials as proposed recently. [9][10] Interestingly, incorporating the similar co-formers into cocrystal systems leads to different intermolecular interactions, molecular self-assembly behaviors, crystal morphologies and molecular stacking structures, as well as distinct photophysical properties. We think that the board, structureless and redshifted PL from BICs with longer PL lifetime (1.66 ns) may be attributed to the CT interactions from donor (D) Bpe to acceptor (A) IFB, which does not appear in BFCs, resulting in a white-light emission simply made up of those from single component crystals.…”

Organic Cocrystals: Beyond Electrical Conductivities and Field‐Effect Transistors (FETs)

“…[1] When 1,3,5-trifluoro-2,4,6-triiodobenzene (IFB) and 1,4-diiodotetrafluorobenzene (F4DIB) are selected as acceptors,asegregated stacking form with charge-transfer interactions or am ixed stacking form without charge-transfer interactions are obtained ( Figure 4, DD' and DB'). [21,67] Compared with the single-component DPO crystals,t he resulting DPO-based co-crystals exhibit tunable optical properties and multi-color polarized emission within the UV/blue region, and also present reversible mechanochromic fluorescence (MCF) properties.T hese new properties make DPO-based co-crystals candidates for applications in solid UV/blue opto-electronics.Non-or poor fluorescent 3ring-N-heterocyclic hydrocarbons ( Figure 4, VB',W B ',X B ', SB',TB',UB, and TP') [68][69][70][71] and fluoranthene ( Figure 4, KD', KK',KP',and KN') [72] in the solid-state can be endowed with different emissions,s uch as pink, orange,o range yellow, green, or blue light after being co-crystalized with haloperfluorobenzenes.T he emitting colors of (naphthylvinyl)pyridine can also be adjusted via co-crystallizing with HFB or 4bromo-2,3,5,6-tetrafluorobenzoic acid (Figure 4, EB' and EI'). [21,67] Compared with the single-component DPO crystals,t he resulting DPO-based co-crystals exhibit tunable optical properties and multi-color polarized emission within the UV/blue region, and also present reversible mechanochromic fluorescence (MCF) properties.T hese new properties make DPO-based co-crystals candidates for applications in solid UV/blue opto-electronics.Non-or poor fluorescent 3ring-N-heterocyclic hydrocarbons ( Figure 4, VB',W B ',X B ', SB',TB',UB, and TP') [68][69][70][71] and fluoranthene ( Figure 4, KD', KK',KP',and KN') [72] in the solid-state can be endowed with different emissions,s uch as pink, orange,o range yellow, green, or blue light after being co-crystalized with haloperfluorobenzenes.T he emitting colors of (naphthylvinyl)pyridine can also be adjusted via co-crystallizing with HFB or 4bromo-2,3,5,6-tetrafluorobenzoic acid (Figure 4, EB' and EI').…”

“…[13] Organic cocrystals were discovered by Wçhler in 1844, [14] but did not begin to attract much attention till 1973 when the cocrystals (charge-transfer complexes) formed from tetrathiafulvalene /7,7,8,8-tetracyanoquinodimethane (TTF-TCNQ) [15] presented high conductivity over aw ide range of temperature,which aroused great research interest in organic optoelectronics. Especially,v ery recently,organic cocrystals,which are regarded as an efficient way to prepare multifunctional and high performance optoelectronic materials,h ave attracted increasing attention owing to their unexpected and versatile chemicophysical properties and charming applications,s uch as high electrical conductivity, [15] photoconductivity, [18] photovoltaics properties, [19] nonlinear optics (NLO), [3,20,21] optical waveguide, [1, 22a] ambipolar charge carrier transportation, [23,24] tunable luminescent features, [3,4,25,26] ferroelectrics, [27,28] stimuli-responsiveness, [10,29] light-driven actuators, [10] liquid crystal materials, [30] and pharmaceutics. insulators, semiconductors,a nd superconductors) and magnetic properties.I n2 004, the first case of ambipolar charge-transport behavior under low temperature based on organic cocrystal bis(ethylenedithiolo)tetrathiafulvalene(BEDT-TTF)-TCNQ was reported, [17] and the door to the charge-carrier-transport area of organic cocrystals was opened.…”

Positional isomers of cyanostilbene: two-component molecular assembly and multiple-stimuli responsive luminescence

“…In this regard, multi-component solid-state materials (such as co-crystals)2425, in which the molecular organization assembled from photoactive molecules and co-assembled units based on molecular recognition, can serve as ideal systems for the tailoring of supramolecular interactions (such as halogen/hydrogen bonds and π–π interactions)2627 by external perturbations. The dynamic assembly and disassembly of multi-component molecular materials induced by environmental stimuli potentially offers the combined advantages of both supramolecular chemical reaction and changes in molecular arrangement, which can result in controllable and switchable luminescence28; however examples of such multi-component molecular materials with stimuli-responsive properties remain rather rare29.…”