Heavy-Atom-Free Red-to-Yellow Photon Upconversion in a Thiosquaraine Composite

Abstract

We demonstrate a completely heavy-atom-free red-to-yellow triplet–triplet annihilation (TTA) photon upconversion system using a thionated squaraine sensitizer, both in fluid solution and in a solid-state composite architecture. Previous works have shown that thionation introduces sulfur nonbonding (n) orbitals that invert the native energy ordering of the ππ*­(S1) and nπ*­(S2) singlet transitions on the squaraine core, opening a channel for efficient intersystem crossing in the thiosquaraine without relying on the heavy-atom effect, as expected based on El-Sayed’s rule. Our thiosquaraine [2-(4-(dibutylamino)­phenyl)-4-(4-(dibutyliminio)­cyclohexa-2,5-dien-1-ylidene)-3-thioxocyclobut-1-enethiolate] exhibits an intense red absorption band, no measurable room-temperature fluorescence, and a native triplet lifetime on the order of 20 μs. This triplet is readily quenched (k Q = 1.4 × 109 M–1 s–1) upon sensitizing the triplet excited state of rubrene as a model upconversion emitter. We observe a 0.27 eV anti-Stokes shift, with selective 685 nm excitation of the thiosquaraine resulting in upconverted rubrene fluorescence centered at 570 nm. The system shows an upconversion quantum efficiency of ∼1.5% in deaerated toluene solution. This quantum efficiency is defined based on a maximum 50% quantum efficiency for TTA upconversion. This system exhibits upconversion under filtered (650 nm long-pass) simulated solar illumination and an intensity transition from quadratic to linear optical power dependence at ∼150 W/cm2 under 685 nm laser diode illumination. We also apply this thiosquaraine system to demonstrate red-to-yellow photon upconversion in a solid-state polymer composite, a prerequisite for light-harvesting device integration. In contrast with traditional TTA upconversion photosensitizers incorporating cost-prohibitive precious metals or photolabile arylhalide groups, we present an easily tunable squaraine dye that serves as a promising red-absorbing heavy-atom-free upconversion sensitizer for increased scalability and photostability.

Triplet–triplet annihilation based near infrared to visible molecular photon upconversion

“…38 and 39. Copyrights 2016, American Chemical Society and 2017 The Royal Society of Chemistry. thiosquaraine 47 and BODIPY 15 as TTA-UC sensitizer for showing TTA-UC from 4700 to o500 nm, can give suitable solution to develop non-toxic bio-nanovehicles for bio-applications. The squaraine dyes are well known for their biomedical applications due to their low toxicities.…”

“…The squaraine dyes are well known for their biomedical applications due to their low toxicities. 47 19 The high F UC of S 0 -to-T 1 sensitized NIR to Vis TTA-UC systems are highly suitable for NIR stimulated photocatalytic synthesis and solution integrated solar cells. 39,40 Further efforts in this direction are desired to realize aerobic photocatalysis employing these systems as dispersed catalytic phase in organogels and aerobic solid-state NIR to Vis TTA-UC for solar cell integration.…”

Renewable Energy Powered Membrane Technology: Electrical Energy Storage Options for a Photovoltaic-Powered Brackish Water Desalination System

“…Solar irradiance data with 1-s resolution were collected via an irradiance sensor (meteocontrol; SI-12-TC, Germany) at the KIT Solar Park-a 1-MW PV system located on the KIT campus in Karlsruhe, Germany (latitude: 40 • 00 33.73", longitude: 82 • 4 15.98" E)and used as the input for the SAS. The SI data were converted into a current-voltage (I-V) curve via the built-in Sandia formula [60], while the module temperature was provided via an external temperature sensor. There were two different settings for the SAS for the experiments conducted using i) batteries and ii) SCs (as well as the battery-less reference directly coupled with the pump).…”

Elongation of Triplet Lifetime Caused by Intramolecular Energy Hopping in Diphenylanthracene Dyads Oriented to Undergo Efficient Triplet–Triplet Annihilation Upconversion

“…Triplet-triplet annihilation (TTA)-upconversion (UC), 1,2 a photophysical phenomenon in which long-wavelength light is converted to short-wavelength light of various wavelengths, [3][4][5][6] is a promising approach to the efficient use of the sunlight. 7,8 The system comprised of platinum 2,3,7,8,12,13,17,18octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA) as a respective energy donor (D) and energy acceptor (A), is a representative of those undergoing TTA-UC.…”