Organic phosphors with bright triplet excitons for efficient X-ray-excited luminescence

Abstract

Materials that exhibit X-ray excited luminescence have great potential in radiation detection, security inspection, biomedical applications, and X-ray astronomy [1][2][3][4] . However, such materials are almost exclusively limited to inorganic crystals, which are typically prepared under high temperatures 5 . Herein, we report a design principle of purely organic phosphors to boost X-ray excited luminescence with sufficient utilization of triplet excitons. Our experimental data reveal that proportion of emission from bright triplet excitons is significantly improved upon X-ray irradiation, compared with UV excitation. These organic phosphors have a detection limit of 33 nGy/s, which is 167 times lower than the standard dosage for X-ray medical examinations. We further demonstrated their potential application in X-ray radiography, which can be conveniently recorded using a digital camera. These findings illustrate a fundamental principle to design efficient X-ray excited purely organic phosphors, propelling the development of radioluminescence related applications.X-ray-responsive materials generally display large X-ray attenuation coefficients because of high atomic number elements, which have aroused intense research interest owing to their wide applications in bioimaging, radiotherapy, and non-destructive defect detection of industrial products [6][7][8][9][10] . Such X-ray-responsive materials include non-emissive radiocontrast agents (e.g., iohexol and iopromide) and scintillators that can convert high energy X-ray beam into low-energy visible photons 2,11,12 . To date, almost all reported X-ray-sensitive materials are limited to inorganic phosphors or organometallic materials containing heavy metals 13 . Purely organic materials, also termed as metal-free organic phosphors, have congenital advantages as scintillator candidates, including abundant resources, flexibility, mild preparation conditions, and environmental friendliness. However, weak X-ray absorption and low exciton utilization hinder the development of purely organic scintillators 12 , leaving it a formidable challenge. Purely organic phosphors are mainly made up of light atoms, such as C, H, N, etc., resulting in weak absorbance of X-ray (attenuation coefficient μ ∝Z , Equation S1). Besides, there only exists fluorescence from singlet excitons upon irradiation owing to weak spin-orbit coupling (SOC). In principle, almost all triplet excitons,

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

“…Namely, the ultralong RTP in aromatic hydrocarbon materials is extremely rare, ( Clapp, 1939 ; Bilen et al, 1978 ), because of the forbidden intersystem crossing (ISC) process between singlet and triplet excited states. 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.…”

One-axis Two-wing Guest-Host Strategy for Constructing Ultralong-lifetime Near-infrared Organic Phosphorescence Materials for Bioimaging

“…Moreover, organic matter often has advantages of low toxicity and good biocompatibility. [1][2][3][4][5][6][7][8][9][10] Therefore, constructing organic RTP materials would bene t tissue imaging, tumor diagnosis, and drug tracking. [10][11][12][13][14][15] To date, most phosphorescent materials have poor biological tissue permeability because the wavelengths of their emission spectra are short (less than 580 nm).…”

Modulating Tri‐Mode Emission for Single‐Component White Organic Afterglow

“…Recent years have witnessed intensive studies and rapid development of alarge variety of organic afterglow materials with luminescent lifetimes over 0.1 sf or various fascinating applications,r anging from light-emitting diodes,b iological imaging,i nformation storage,s ensing,a nd security protection. [1][2][3][4][5][6][7][8][9] Principally,t og enerate observable afterglow emission, the incorporation of heteroatoms to promote the spinorbital coupling (SOC) between excited singlet and triplet states for the enhanced intersystem crossing (ISC) and stabilization of the lowest triplet excited state (T 1 *) in pursuit of long-lived excitons for ultralong room-temperature phos-phorescence (OURTP) are essential [10][11][12][13][14][15] (Figure 1a). However,l ow-lying T 1 *w ill lead to bathochromic shift of the emission spectrum, so that most organic afterglow bands are in ar ange of 500-600 nm for yellow emission.…”