Abstract
Room-temperature phosphorescent (RTP) materials have been attracting tremendous interest, owing to their unique material characteristics and potential applications for state-of-the-art optoelectronic devices. Recently, we reported the synthesis and fundamental photophysical properties of new RTP materials based on benzil, i.e., fluorinated monobenzil derivative and fluorinated and non-fluorinated bisbenzil derivative analogues [Yamada, S. et al., Beilstein J. Org. Chem. 2020, 16, 1154–1162.]. To deeply understand their RTP properties, we investigated the excited-state dynamics and photostability of the derivatives by means of time-resolved and steady-state photoluminescence spectroscopies. For these derivatives, clear RTP emissions with lifetimes on the microsecond timescale were identified. Among them, the monobenzil derivative was found to be the most efficient RTP material, showing both the longest lifetime and highest amplitude RTP emission. Time-resolved photoluminescence spectra, measured at 77 K, and density functional theory calculations revealed the existence of a second excited triplet state in the vicinity of the first excited singlet state for the monobenzil derivative, indicative of the presence of a fast intersystem crossing pathway. The correlation between the excited state dynamics, emission properties, and conformational flexibility of the three derivatives is discussed.
Highlights
Room-temperature phosphorescent (RTP) materials have drawn intense interest, owing to their potential uses in medical applications, such as bio-imaging, security applications, including security inks for information encryption and anticounterfeiting measures, as well as photosensitizers, in emergency signage, in geochemical dating, in advanced turbo-machinery, for oxygen measurements inside and outside living organisms, and for electronic applications, such as data storage, logic gates and organic light-emitting diodes (OLEDs) [1,2,3,4,5,6,7]
We reported the synthesis of new derivatives based on the benzil framework (Figure 2), as well as their steady-state photophysical properties [31]
The first fluorescence band (flu.(1)) peaked at 340−360 nm, the second fluorescence band (flu.(2)) peaked at approximately 520 nm, and the phosphorescence band peaked at around 560 nm, as previously reported [31], and could be ascribed to an emission from S2 for flu.(1), S1 for flu.(2), and T1 for phos. bands. These bands were typical of the benzil moiety [30,32], but not tolane [33,34,35,36,37]
Summary
Room-temperature phosphorescent (RTP) materials have drawn intense interest, owing to their potential uses in medical applications, such as bio-imaging, security applications, including security inks for information encryption and anticounterfeiting measures, as well as photosensitizers, in emergency signage, in geochemical dating, in advanced turbo-machinery, for oxygen measurements inside and outside living organisms, and for electronic applications, such as data storage, logic gates and organic light-emitting diodes (OLEDs) [1,2,3,4,5,6,7]. Heavy-metal-based inorganic compounds and organometallic materials have proven to be the most efficient RTP material. The efficient heavy metal yield and was investigated for a highly green Materials 2020, x FOR. PEER REVIEW effectemitter leads intoOLEDs the large spin–orbit light [1]. Whichleads results in large the fast rate ofcoupling the spin-flip presence the Ir for atom, metal effect to the spin–orbit (SOC) processes for the Ir from the first excited singlet (S1) of tothe thespin-flip first excited triplet state. 1) (i.e., the singlet intersystem compound, which results in thestate fast rate processes from the(T first excited state crossing (ISC)) and from
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