Color-Tunable Thermally Activated Delayed Fluorescence in Oxadiazole-Based Acrylic Copolymers: Photophysical Properties and Applications in Ratiometric Oxygen Sensing

Abstract

Polymer-based emitters are a promising route to the production of low-cost, scalable solution-processable luminescent materials. Here we describe a series of acrylic oxadiazole-based donor–acceptor monomers with tunable emission from blue to orange, with quantum yields as high as 96%. By introducing structural constraints that limit donor–acceptor orbital overlap, thermally activated delayed fluorescence (TADF) was observed in these materials. Polymerization by Cu(0) reversible deactivation radical polymerization (RDRP) gave high-molecular-weight copolymers (M n > 20 kDa) with dispersities ranging from 1.10 to 1.45, using a room-temperature procedure with Cu wire as a catalyst. One of these materials, which had phenothiazine as donor moiety, exhibited conformationally dependent dual emission, giving a mixture of prompt fluorescence and delayed fluorescence peaks, whose relative ratios varied based on the amount of O2 present during measurement. We demonstrate that this material can combine prompt and delayed fluorescence to act as a single-component, all-organic, ratiometric oxygen sensor without external calibrant. Application to ratiometric oxygen sensing is demonstrated both using a polymer thin film and via incorporation of this material into water-soluble polymer dots (Pdots), with a ratiometric response to O2 throughout the range of partial pressures relevant to biological environments.

Using the Mechanical Bond to Tune the Performance of a Thermally Activated Delayed Fluorescence Emitter**

“…In the ground state geometry,time dependent-DFT (TD-DFT) calculations of 1 identified two triplet states below the S 1 energy level, both of which exhibit am ixed 3 CT and acceptor-based 3 LE character (Table 2). For 1&2 and 1&2 2 the acceptor-based 3 LE appears slightly above the S 1 state.T his presence of a 3 LE state is common for high performance TADF emitters [11a] and consistent with the structured luminescence spectra (Figure 3).…”

Stimuli-Responsive Thermally Activated Delayed Fluorescence in Polymer Nanoparticles and Thin Films: Applications in Chemical Sensing and Imaging

“…Polymers exhibiting TADF were recently developed in our laboratory that act as ratiometric sensors for oxygen, based on the dual-emissive nature of a TADF chromophore. A series of TADF dopants were prepared using an oxadiazole acceptor paired with either phenoxazine (POZ, 15), phenothiazine (PTZ, 16), dimethylacridan (DMAC, 17), or N-methylphenazine (MPAZ, 18) donors to achieve emission ranging from blue to orange ( Figures 3A,B) (Tonge et al, 2020). These materials were doped into a carbazole-based host using copper(0) reversible deactivation radical polymerization (Cu(0)-RDRP), giving molecular weights of ∼20 kDa with dispersities from 1.10 to 1.45 (Anastasaki et al, 2016;Sauv et al, 2018;.…”

“…When used as emitters in OLEDs, internal quantum efficiencies up to 100% can be achieved due to their ability to harvest both singlet and triplet excitons (Jankus et al, 2014;Wu et al, 2016). Concurrently, the incorporation of TADF materials into polymer nanostructures led to a range of emerging applications as sensors and imaging probes (Kochmann et al, 2013;Xiong et al, 2014;Gan et al, 2017;Li et al, 2017;Steinegger et al, 2017;Zhu et al, 2018;Tsuchiya et al, 2019;Tonge et al, 2020). TADF emitters can be incorporated into polymer nanostructures either as small molecules dispersed in a polymeric matrix or covalently incorporated into the polymer itself.…”

Through‐Space Charge‐Transfer Polynorbornenes with Fixed and Controllable Spatial Alignment of Donor and Acceptor for High‐Efficiency Blue Thermally Activated Delayed Fluorescence

“…Charge-transfer (CT) interactions between electron donors (D) and acceptors (A) are the basis of many functions of p-conjugated molecules and polymers, [1][2][3][4][5][6][7] Recently,thermally activated delayed fluorescence (TADF) polymers [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] with CT emission have attracted much attention because they can convert triplet excitons to singlet ones through reverse intersystem crossing (rISC) process to realize 100 %i nternal quantum efficiency (IQE), [28][29][30][31][32][33][34][35][36][37][38][39][40][41] providing ap romising approach for developing solution-processed OLEDs without use of precious metal complexes.…”