Pd(II) Phthalocyanine-Sensitized Triplet−Triplet Annihilation from Rubrene

Abstract

Upconverted yellow singlet fluorescence from rubrene (5,6,11,12-tetraphenylnapthacene) was generated from selective excitation (lambdaex = 725 nm) of the red light absorbing triplet sensitizer palladium(II) octabutoxyphthalocyanine, PdPc(OBu)8, in vacuum degassed toluene solutions using a Nd:YAG/OPO laser system in concert with gated iCCD detection. The data are consistent with upconversion proceeding from triplet-triplet annihilation (TTA) of rubrene acceptor molecules. The TTA process was confirmed by the quadratic dependence of the upconverted delayed fluorescence intensity with respect to incident light, measured by integrating the corresponding kinetic traces as a function of the incident excitation power. In vacuum degassed toluene solutions, the red-to-yellow upconversion process is stable under continuous long wavelength irradiation and is readily visualized by the naked eye even at modest laser fluence (0.6 mJ/pulse). In aerated solutions, however, selective excitation of the phthalocyanine sensitizer leads to rapid decomposition of rubrene into its corresponding endoperoxide as evidenced by UV-vis (in toluene), 1H NMR (in d6-benzene), and MALDI-TOF mass spectrometry, consistent with the established reactivity of rubrene with singlet dioxygen. The upconversion process in this triplet sensitizer/acceptor-annihilator combination was preliminarily investigated in solid polymer films composed of a 50:50 mixture of an ethyleneoxide/epichlorohydrin copolymer, P(EO/EP). Films that were prepared under an argon atmosphere and maintained under this inert environment successfully achieve the anticipated quadratic incident power dependence, whereas air exposure causes the film to deviate somewhat from this dependence. To the best of our knowledge, the current study represents the first example of photon upconversion using a phthalocyanine triplet sensitizer, furthering the notion that anti-Stokes light-producing sensitized TTA appears to be a general phenomenon as long as proper energy criteria are met.

Near‐Infrared Optogenetic Genome Engineering Based on Photon‐Upconversion Hydrogels

“…t p % 3.5 msf or palladium(II) 1,4,8,11,15,18,22,25-octabutoxyphthalocyanine). [10] Thermal equilibrium among the excited states in Os-(peptpy) 2 2+ was confirmed by measuring its temperaturedependent photoluminescence (PL) spectra ( Figure 3b . By decreasing the temperature from 40 8 8CtoÀ50 8 8C, the peak at 835 nm remained, while the peak around 760 nm became weaker.B yf urther decreasing the temperature to À196 8 8C, the peak around 760 nm almost disappeared (Supporting Information, Figure S3).…”

Green to Blue Annihilated Upconversion from a Simple Iridium(III) Sensitizer with Carboxylic Group

“…Moreover, the single DPA in deaerated DMF is also excited by the same laser and no blue emission is obtained as well (shown in Figure S3 in supporting information) under the identical experimental condition, which indicate the observed blue emission of Ir-COOH/DPA system in this work was all from the triplet-triplet annihilation upconversion step, rather than from the direct excitation of DPA. [18,21,[46][47][48] The inset picture of Figure 3 is the photograph of Ir-COOH/DPA (8 mM/2.8 mM) in deaerated DMF under 532 nm laser irradiation (60 mW/cm 2 ), we could find green to blue upconversion from Ir-COOH/DPA is obviously visible under the naked eyes, which directively proves that Ir-COOH is an efficient triplet sensitizer for TTA upconversion.…”

“…[11][12][13] According to the revealed mechanism, [14][15][16] TTA-upconversion undergoes a series of multiple quantum processes: (i) the sensitizer first absorbs one photon to the excited singlet state and goes across its triplet excited state by intersystem crossing (ISC); (ii) then, the triplet-triplet energy transfer (TTET) occurs from the sensitizer to the acceptor, and then two triplet acceptors undergo the triplet-triplet annihilation (TTA) with the result that photon-upconversion is produced. Due to strong spin-orbital effect of transition metal center, [14] transition metal complexes are identified as a class of competent phosphorescent dyes, and have been widely designed and synthesized as the triplet sensitizers in TTA upconversion, including platinum, [14,[17][18][19] palladium, [20][21][22][23] ruthenium, [14,[24][25][26] rhenium, [14,27] zinc, [28] etc.In the past decades, due to their high quantum efficiencies, large Stokes' shifts, excellent anti-photobleaching abilities and tunable emission colors, cyclometalated iridium(III) complexes have attracted much attention and been used in wide areas, such as organic light-emitting diodes (OLEDs), [29] bioimaging, [30] electrochemiluminescence (ECL), [31,32] etc. However, due to the weak absorption in visible light regions, the applications of iridium(III) complexes in the emerging TTA upconversion technology have been intensely limited.…”

Transition-Metal Complexes for Triplet–Triplet Annihilation-Based Energy Upconversion

“…It is worth noting that the anthryl fluorescence was observed with incident irradiance as low as 0.6 mW cm À2 (λ ex ¼ 547 nm) [33]. In 2008, upconverted yellow fluorescence from rubrene was observed with selective excitation (λ ex ¼ 725 nm) of the red-light-absorbing triplet sensitizer PdPc(OBu) 8 (Pd-4, Pc(OBu) 8 ¼ octabutoxyphthalocyanine) in deaerated toluene [34]. The energy level of triplet sensitizer is 1.24 eV and that of rubrene is 1.14 eV, which met the requirements of TTET process.…”