Dual Emission from Precious Metal‐Free Luminophores Consisting of C, H, O, Si, and S/P at Room Temperature

Abstract

Fluorescence-phosphorescence dual-emissive compoundsa re valuablet ools for ratiometric luminescence sensing.H erein, it is reported that 2,5-bis(phenylsulfonyl)-and 2,5-bis[bis(4-methoxyphenyl)phosphinyl]-1,4disiloxybenzenes exhibit dual emission with emission peaks that were easily identified without performing timegated measurement. The disiloxybenzenes in powder simultaneously fluoresced and phosphoresced at 358-374 and 457-470 nm, respectively,u nder vacuum.T he intensity ratios of the phosphorescence/fluorescence maxima of the disiloxybenzenes in powder and in at hin film of poly-(methyl methacrylate) weres ensitive to temperature and molecular oxygen, respectively.T he plots of the relative intensity versust emperature or partial pressureofm olecular oxygen were well fitted with calibration curvesd efined by an exponential approximation with excellent correlation coefficients R 2 (0.9708-0.9921), demonstrating the high potential of the disiloxybenzenes as precious metalfree probes applicable to ratiometric luminescence sensing.Organicl uminophores that exhibit dual emission of fluorescence and phosphorescence at room temperature are versatile materials because they are applicable in bio-imaging, data security protection,w hite-light emission, and ratiometric luminescences ensing of molecular oxygen, temperature, and solvent viscosity. [1,2] To attain the dual emission at RT,au nique molecular design is essential, which balances the rates of fluorescence and intersystem crossing( ISC) and suppresses RTcaused nonradiatived ecayso ft he excited triplet states (T n ). The conventionala pproach to realize dual emission involves design of (co)polymersc onsisting of fluorescent organic chromophores andp hosphorescent precious metal complexes. [3] Dual-emissive metal complexeswerealso developed with careful design of ligands and choice of am etal ion. [4] Precious metals accelerateboth ISC and phosphorescence at RT.However,t hey are limited resources and thus expensive.P recious metal complexes also exhibit cytotoxicity,w hich is an undesirable characteristic, especially in applications involving imaging and sensing in biological environments. The molecular design of metal complexes is less flexible than that of metal-free organic luminophores. Therefore, fluorescent-phosphorescent dual-emissive small molecules, free of precious metals are greatly desired.The pioneering examples of precious metal-free luminophores exhibiting the dual emissiona tR Tare poly(lactic acid)tethered boron difluoride dibenzoylmethane derivatives developed by Fraser and co-workers. [5] Owing to the growing interest in the design and development of precious metal-free organic phosphors, [6] the number of metal-free small molecules that simultaneously fluoresce and phosphorescea tR Ti si ncreasing. However, almost all of such dual-emissive luminophores reported so far exhibit intense fluorescencew ith faint phosphorescence whose emission peak cannotb ed etected by using steady-state luminescence measurements. [7] In other words, there a...

Dual emission in purely organic materials for optoelectronic applications

“…The authors proposed that the easily detectable emission maxima of PF and RTP could enable accurate ratiometric luminescence sensing of temperature and molecular oxygen using a simple steady-state set-up. 99 RTP can readily occur in compounds with a simple molecular architecture if supported by molecular packing and/or ISC-enhancing groups. Alternatively, a D-A structure with wellchosen molecular fragments allows minimization of both S 1 -T 1 and S 1 -T n gaps, which was shown to facilitate spin-orbit coupling regardless of the molecular packing.…”

Metal‐Free Organic Luminophores that Exhibit Dual Fluorescence and Phosphorescence Emission at Room Temperature

“…In addition, the applications of the dual‐emissive compounds, which include quantitative imaging of tumour hypoxia, in vivo camera wound imaging, RGB‐channel‐based camera imaging, ratiometric sensing of oxygen and temperature, emission‐lifetime‐based data encryption and decryption, white‐light‐emission, and OLED, are also presented. Meanwhile, several dual‐emissive compounds that cannot be classified into the categories exist, that include (pinacolatoboryl)arenes, [63] boron cluster, [64] 1‐benzyl‐4,4′‐bipyridinium, [65] 2,5‐disiloxy‐1,4‐bis(diarylphosphinyl)benzene, [45] difluorotetrakis(arylthiol)benzene, [66] brominated fluorenes, [67] naphthalimides, [68] norbornane‐annulated arenes, [69] tetrakis(aryloxy)phthalonitriles, [2c] N ‐alkyl‐ and N ‐benzoylcarbazoles, [70] N , N ′‐di(1‐naphthyl)‐ N , N ′‐di‐phenyl‐(1,1‐biphenyl)‐4,4‐diamine, [71] polyimides, [72] N ‐(4‐trifluoromethylphenyl)‐4‐bromophthalimide, [73] di(phenothiazinyl)naphthalene, [3b] di(phenothiazinyl)dibenzothiophenes, [74] and three‐component crystals consisting of 5,5′‐(ethyne‐1,2‐diyl)‐bis(2‐pyridin‐3‐yl‐isoindoline‐1,3‐dione), tris(pentafluorophenyl)borane, and simple benzenes [75] . We hope that this article will contribute to the advancement of fluorescence–phosphorescence dual‐emissive materials and their applications.…”

“…Crystals of 1,4-dibenzoyl-2,5-disiloxybenzenes reportedly exhibited green phosphorescence in excellent quantum yields ranging from 0.46 to 0.64 with a long lifetime of 76.0 to 98.3 ms. [44] Replacing the benzoyl groups of phosphorescent benzenes by arylsulfonyl groups renders the resulting compounds dual-emissive. [45] For example, the crystalline powder of 2,5-bis(t-butyldiphenylsiloxy)-1,4-bis(phenylsulfonyl)benzene (20) under vacuum simultaneously fluoresced at 375 nm (τ F = 1.6 ns) and phosphoresced at 469 nm (τ P = 194 ms) with an Φ total of 0.37 and I P /I F of 0.4 (Figure 8). When the luminescence spectra were measured at various temperatures ranging from À 60 to 40°C, the plots of I P /I F were well fitted with a calibration curve, defined by an exponential approximation with an excellent correlation coefficient (R 2 = 0.9921).…”

“…Crystals of 1,4‐dibenzoyl‐2,5‐disiloxybenzenes reportedly exhibited green phosphorescence in excellent quantum yields ranging from 0.46 to 0.64 with a long lifetime of 76.0 to 98.3 ms [44] . Replacing the benzoyl groups of phosphorescent benzenes by arylsulfonyl groups renders the resulting compounds dual‐emissive [45] . For example, the crystalline powder of 2,5‐bis( t ‐butyldiphenylsiloxy)‐1,4‐bis(phenylsulfonyl)benzene ( 20 ) under vacuum simultaneously fluoresced at 375 nm ( τ F =1.6 ns) and phosphoresced at 469 nm ( τ P =194 ms) with an Φ total of 0.37 and I P / I F of 0.4 (Figure 8).…”

Taking Advantage of Ortho- and Peri-Substitution to Design Original 9-Membered P,O,Si-Heterocycles

“…Such unexpected red-shifted solid-state emission can have two main origins: specific aggregate formation or triplet emission (phosphorescence). 13,14 Time-resolved fluorescence measurements allowed to rule out the possibility of phosphorescence as all compounds display emission lifetime in the range of the ns, typical of fluorescent materials (see Figure S21-24). The study of the packing in the crystals did not allow to clarify the presence of specific interactions that would favour these observations, as some of these compounds form -dimers but other don't.…”