Browsing by Author "Garcia, Luis"

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    New Light-Green Thermally Activated Delayed Fluorescence Polymer Based on Dimethylacridine-Triphenyltriazine Light-Emitting Unit and Tetraphenylsilane Moiety as Non-Conjugated Backbone
    (MDPI, 2023) Hauyon Sepúlveda, Rene Alejandro; Sobarzo Aucal, Patricio Antonio; Medina Martínez, Jean André; Garcia, Luis; Tundidor Camba, Alain; Terraza Inostroza, Claudio Alberto; Fuentealba Patino, Denis Alberto; Pizarro, Nancy; Ortega Alfaro, María C.; Ugalde Saldívar, Víctor M.; Jessop Rivera, Ignacio Andrés; González Henríquez, Carmen
    In the search for solution-processable TADF materials as a light emitting layer for OLED devices, polymers have attracted considerable attention due to their better thermal and morphological properties in the film state with respect to small molecules. In this work, a new polymer (p-TPS-DMAC-TRZ) with thermally activated delayed fluorescence (TADF) light-emitting characteristics was prepared from a conjugation-break unit (TPS) and a well-known TADF core (DAMC-TRZ). This material was designed to preserve the photophysical properties of DAMC-TRZ, while improving other properties, such as thermal stability, promoted by its polymerization with a TPS core. Along with excellent solubility in common organic solvents such as toluene, chloroform and THF, the polymer (Mn = 9500; Mw = 15200) showed high thermal stability (TDT5% = 481 °C), and a Tg value of 265 °C, parameters higher than the reference small molecule DMAC-TRZ (TDT5% = 305 °C; Tg = 91 °C). The photoluminescence maximum of the polymer was centered at 508 nm in the solid state, showing a low redshift compared to DMAC-TRZ (500 nm), while also showing a redshift in solution with solvents of increasing polarity. Time-resolved photoluminescence of p-TPS-DMAC-TRZ at 298 K, showed considerable delayed emission in solid state, with two relatively long lifetimes, 0.290 s (0.14) and 2.06 s (0.50), and a short lifetime of 23.6 ns, while at 77 K, the delayed emission was considerably quenched, and two lifetimes in total were observed, 24.6 ns (0.80) and 180 ns (0.20), which was expected from the slower RISC process at lower temperatures, decreasing the efficiency of the delayed emission and demonstrating that p-TPS-DMAC-TRZ has a TADF emission. This is in agreement with room temperature TRPL measurements in solution, where a decrease in both lifetime and delayed contribution to total photoluminescence was observed when oxygen was present. The PLQY of the mCP blend films with 1% p-TPS-DMAC-DMAC-TRZ as a dopant was determined to be equal to 0.62, while in the pure film, it was equal to 0.29, which is lower than that observed for DMAC-TRZ (0.81). Cyclic voltammetry experiments showed similarities between p-TPS-DMAC-TRZ and DAMC-TRZ with HOMO and LUMO energies of ?5.14 eV and ?2.76 eV, respectively, establishing an electrochemical bandgap value of 2.38 eV. The thin film morphology of p-TPS-DMAC-TRZ and DMAC-TRZ was compared by AFM and FE-SEM, and the results showed that p-TPS-DMAC-TRZ has a smoother surface with fewer defects, such as aggregations. These results show that the design strategy succeeded in improving the thermal and morphological properties in the polymeric material compared to the reference small molecule, while the photophysical properties were mostly maintained, except for the PLQY determined in the pure films. Still, these results show that p-TPS-DMAC-TRZ is a good candidate for use as a light-emitting layer in OLED devices, especially when used as a host-guest mixture in suitable materials such as mCP.
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    Thiophene- and bithiophene-based π-conjugated Schiff base oligomers containing binaphthalene moieties in the backbone. Properties and computational simulations
    (2024) Gonzalez, Alexis F.; Mariman, Andrea P.; Hauyon, Rene A.; Pavez-Lizana, Danitza; Saldias, Cesar; Schott, Eduardo; Zarate, Ximena; Garcia, Luis; Gonzalez-Henriquez, Carmen M.; Jessop, Ignacio A.; Tundidor-Camba, Alain; Sobarzo, Patricio A.; Terraza, Claudio A.
    New pi-conjugated Schiff base oligomers (o-AZdAN1Th and o-AZdAN2Th) based on a binaphthalene core and containing thiophene or bithiophene units in their backbone were synthesized from the reaction between [1,1 '-binaphthalene]-4,4 '-diamine with thiophene-2,5-dicarbaldehyde and [2,2 '-bithiophene]-5,5 '-dicarbaldehyde by a high-temperature polycondensation method. These new materials were slightly soluble in non-protic polar solvents, such as chloroform and dichloromethane. From GPC analysis of the CHCl3-soluble fraction, o-AZdAN1Th was found to be a tetramer, whereas o-AZdAN2Th was a trimer with 1.4 kDa and 1.3 kDa average molecular weight (Mn), respectively. Both samples exhibited high thermal stability with T5% values of 452 degrees C and 456 degrees C and relatively high Tg values of 346 degrees C and 384 degrees C, for o-AZdAN1Th and o-AZdAN2Th, respectively. The samples showed absorptions in the deep-blue (o-AZdAN1Th) and blue (o-AZdAN2Th) regions of the visible spectrum, and emission responses at 387 nm and 447 nm, respectively, with moderate Stokes shifts (77-95 nm). Their optical and electronic properties were similar to those described for thiophene-based materials, with optical bandgap values close to 2.4 eV. HOMO energy values of -5.98 and -5.95 eV and LUMO energy values of -3.87 eV and -3.84 eV were obtained for o-AZdAN1Th and o-AZdAN2Th, respectively. Theoretical DFT and TD-DFT calculations were used to compare the effect of increasing thiophene units along the backbone for the real and also theoretical o-AZdANxTh samples (x = 3 and 4 thiophene units). According to our study, these two new thiophene-based can be proposed for optoelectronic applications.