Propriedades fotofísicas de complexos heterolépticos de Ir(III) e heterobimetálico Ir(III) – Eu(III) emissores no deep-red para aplicação em concentradores solares luminescentes
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2022-04-04
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Universidade Estadual Paulista (Unesp)
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A Energia solar é uma das fontes de energia renováveis que mais se destaca devido à sua disponibilidade em função do intenso fluxo de irradiância solar sobre a Terra. Sua conversão em eletricidade é feita por dispositivos fotovoltaicos (PV), sendo a célula mais utilizada a de silício cristalino (PV c-Si), com energia do band gap de 1,12 eV (1107 nm), ou seja, apresenta maior Eficiência Quântica Externa (EQE) na região do infravermelho próximo (NIR). No entanto, a PV c-Si tem conversão máxima de energia teórica (PCE) de apenas 32% do espectro solar AM1.5G. Esse problema pode ser minimizado com o incremento de um dispositivo acoplado à célula capaz de absorver a radiação solar indente e converter essa energia por down-shifting para região espectral ótima da célula PV, os chamados Concentradores Solares Luminescentes (LSCs). Neste trabalho foram investigadas as propriedades fotofísicas do estado emissor híbrido 3LC– 1,3MLCT de duas novas séries de complexos heterolépticos luminescentes de Ir(III): [Ir(C^N)2bqdc], C^N = ppy, phq e bzq; e [Ir(C^N)2tptz], C^N = ppy, phq e btpy, que foram sintetizados e caracterizados. Por meio das técnicas espectroscópicas de IV-FTIR, Espectrometria de Massas MALDI-TOF e 1H-RMN foram elucidadas as estruturas dos complexos. Estudos fotofísicos indicam intensas bandas de absorção (225-600 nm) e excitação (250-600 nm), resultados de processos eletrônicos eficientes das transições singletos e tripletos LC e MLCT. Por meio do estudo fotoluminescente foi possível relatar complexos de Ir(III) com emissões alargadas no deep-red, bons rendimentos quânticos () e longos tempos de vida () de decaimento do estado excitado. Os resultados experimentais e cálculos teóricos por TD-DFT sugerem que a série [Ir(C^N)2bqdc] exibe um nível emissor com maior contribuição 3MLCT, já para a série do [Ir(C^N)2tptz] o nível emissor com maior contribuição é o 3LC. Também foram estudados os processos de transferência de energia via intercomplexos 3LC 1,3MLCTIr(III) →5D0 Eu(III) de um novo complexo heterobimetálico Ir(pb)-Eu(III), por meio do decaimento do estado excitado, investigou-se a influência do acoplamento spin-orbital (SOC), perturbado pelo Eu(III), no nível emissor 3LC 1,3MLCT da componente do Ir(III). Este complexo teve sua estequiometria sugerida por Análise Elementar e pelos estudos fotofísicos propomos a coordenação do Eu(III) no sítio do carboxilato. Por meio dos estudos de fotoluminescência verificou-se dois processos de emissão: o primeiro proveniente do nível 3LC 1,3MLCT do Ir(III) e o segundo do nível 5D0 do Eu(III). A emissão proveniente do Eu(III) não se dá via efeito antena do nível emissor híbrido da componente de Ir(III) para o Eu(III), mas via tripleto do ligante em ponte bqdc. As propriedades fotofísicas dos complexos heterolépticos de Ir(III) foram testadas quando dispersos em filmes de PMMA variando-se a concentração em 0,10%; 0,25%; 0,50%; 0,75% e 1,0% (m/m). Filmes homogêneos de PMMA:Ir(III) foram obtidos com excelentes propriedades fotofísicas como fortes absorções no UV-Vis, ampla região de excitação no UV-Vis, altos rendimentos quânticos, e emissões alargadas no deep-red (550–800 nm). Assim, concluímos que os filmes PMMA:Ir(III) apresentaram interessantes propriedades para a aplicação como um Concentrador Solar Luminescente.
The use of Solar Energy is, among all renewable energy sources, the most desired for its abundant availability due to the intense flux of solar irradiance on Earth. Its conversation into electricity happens in photovoltaic devices (PV), and crystalline silicon (PV c-Si) is the most used semiconductor for this purpose, with energy band gap of 1.12 eV (1107 nm), i.e. higher External Quantum Efficiency (EQE) is observed in the near infrared region (NIR). Nonetheless, it is predicted that the c-Si PV has a maximum energy conversion (PCE) of only 32 % of the AM1.5G solar spectrum. This drawback can be minimized by using a coupled device to the solar cell, which is capable of absorb the incident radiation and via down-shifting process, convert it into the optimal spectral range of the PV, the so-called Luminescent Solar Concentrators (LSCs). In this work, we investigated the photophysical properties of the hybrid emitting level 3LC–1,3MLCT of two novel series of luminescent heteroleptic Ir(III) complexes: [Ir(C^N)2bqdc], C^N = ppy, phq, and bzq; and [Ir(C^N)2tptz], C^N = ppy, phq, and btpy, that were synthesized and characterized. Structural elucidation was performed by spectroscopy techniques IV-FTIR, MALDI-TOF, and 1H-NMR. Photophysical studies indicated intense absorption (225-600 nm) and excitation (250-600 nm) bands, which is a result of highly efficient electronic processes associated to singlet and triplet LC and MLCT transitions. Based on photoluminescence studies, it is possible to report here Ir(III) complexes with wide emission bands in the deep-red region, with good quantum yields (), and high excited state lifetime values (). Experimental and TD-DFT theoretical results suggest that the [Ir(C^N)2bqdc] series exhibits a higher contribution of the 3MLCT state in the emitting level, while the 3LC state is the major contributor for the [Ir(C^N)2tptz] series. Additionally, the 3LC 1,3MLCTIr(III) → 5D0Eu(III) intercomplex energy transfer process was studied for a novel Ir(pb)-Eu(III) heterobimetallic complex, and through excited state decay rates it was investigated the influence of the spin-orbital coupling (SOC) disturbed by the Eu(III) in the 3LC 1,3MLCT emitting level of the Ir(III) component. This complex had its stoichiometry suggested by Elemental Analyses, and by photophysical studies it was inferred the coordination of Eu(III) via carboxylate group. By photoluminescence studies, it was verified two emitting processes: the first from the 3LC 1,3MLCT level of the Ir(III) component, and the second from the 5D0 of the Eu(III) component. The Eu(III) emission can not be associated to the antenna effect via hybrid emitting level o the Ir(III) component, but it is attributed to the direct excitation via the bridge ligand, bqdc. Yet, the photophysical properties of the heteroleptic Ir(III) complexes were tested when they were dispersed in PMMA films, and varying the concentration in mass at 0.10%; 0.25%; 0.50%; 0.75%, and 1.0% (m/m). Homogeneous PMMA:Ir(III) films were obtained with excellent photophysical properties, for example, high UV-Vis absorptions, a wide excitation range from UV to visible, high quantum yields, and wide deep-red emission (550-800 nm). Therefore, we conclude that these PMMA:Ir(III) films gather interesting optical properties to be applied as Luminescent Solar Concentrators.
The use of Solar Energy is, among all renewable energy sources, the most desired for its abundant availability due to the intense flux of solar irradiance on Earth. Its conversation into electricity happens in photovoltaic devices (PV), and crystalline silicon (PV c-Si) is the most used semiconductor for this purpose, with energy band gap of 1.12 eV (1107 nm), i.e. higher External Quantum Efficiency (EQE) is observed in the near infrared region (NIR). Nonetheless, it is predicted that the c-Si PV has a maximum energy conversion (PCE) of only 32 % of the AM1.5G solar spectrum. This drawback can be minimized by using a coupled device to the solar cell, which is capable of absorb the incident radiation and via down-shifting process, convert it into the optimal spectral range of the PV, the so-called Luminescent Solar Concentrators (LSCs). In this work, we investigated the photophysical properties of the hybrid emitting level 3LC–1,3MLCT of two novel series of luminescent heteroleptic Ir(III) complexes: [Ir(C^N)2bqdc], C^N = ppy, phq, and bzq; and [Ir(C^N)2tptz], C^N = ppy, phq, and btpy, that were synthesized and characterized. Structural elucidation was performed by spectroscopy techniques IV-FTIR, MALDI-TOF, and 1H-NMR. Photophysical studies indicated intense absorption (225-600 nm) and excitation (250-600 nm) bands, which is a result of highly efficient electronic processes associated to singlet and triplet LC and MLCT transitions. Based on photoluminescence studies, it is possible to report here Ir(III) complexes with wide emission bands in the deep-red region, with good quantum yields (), and high excited state lifetime values (). Experimental and TD-DFT theoretical results suggest that the [Ir(C^N)2bqdc] series exhibits a higher contribution of the 3MLCT state in the emitting level, while the 3LC state is the major contributor for the [Ir(C^N)2tptz] series. Additionally, the 3LC 1,3MLCTIr(III) → 5D0Eu(III) intercomplex energy transfer process was studied for a novel Ir(pb)-Eu(III) heterobimetallic complex, and through excited state decay rates it was investigated the influence of the spin-orbital coupling (SOC) disturbed by the Eu(III) in the 3LC 1,3MLCT emitting level of the Ir(III) component. This complex had its stoichiometry suggested by Elemental Analyses, and by photophysical studies it was inferred the coordination of Eu(III) via carboxylate group. By photoluminescence studies, it was verified two emitting processes: the first from the 3LC 1,3MLCT level of the Ir(III) component, and the second from the 5D0 of the Eu(III) component. The Eu(III) emission can not be associated to the antenna effect via hybrid emitting level o the Ir(III) component, but it is attributed to the direct excitation via the bridge ligand, bqdc. Yet, the photophysical properties of the heteroleptic Ir(III) complexes were tested when they were dispersed in PMMA films, and varying the concentration in mass at 0.10%; 0.25%; 0.50%; 0.75%, and 1.0% (m/m). Homogeneous PMMA:Ir(III) films were obtained with excellent photophysical properties, for example, high UV-Vis absorptions, a wide excitation range from UV to visible, high quantum yields, and wide deep-red emission (550-800 nm). Therefore, we conclude that these PMMA:Ir(III) films gather interesting optical properties to be applied as Luminescent Solar Concentrators.
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Palavras-chave
Irídio(III), Lantanídeos(III), Acoplamento spin-orbital (SOC), Estado híbrido 3LC-1,3MLCT, Filmes de PMMA, Células fotovoltaicas (PV), Iridium(III), Lanthanides(III), Spin-orbital coupling (SOC), Hybrid state 3LC-1,3MLCT, Pmma films, Photovoltaic cells (PV)