resumo
Europium (t-Eu) and gadolinium (t-Gd) beta-diketonate complexes with photoactive t-bpete ligand, [Ln-(btfa)(3)(t-bpete)(MeOH)] (Ln = Eu, Gd), where btfa(-) and t-bpete are 4,4,4-trifluoro-1-phenyl-1,3-butanedionate and trans-1,2bis(4-pyridyl)ethylene, respectively, were synthesized, characterized by vibrational, absorption (reflectance) and photoluminescence spectroscopies and their crystal structure was determined using single-crystal X-ray diffraction. B3LYP calculations were performed to support the interpretation and rationalization of the experimental results. The complexes, under UV irradiation, do not display the typical photodegradation of the beta-diketonate ligands exhibiting, in turn, an unprecedented photostability during, at least, 10 h. During UV-A exposure (>330 nm), the emission intensities of both complexes increase drastically (similar to 20 times), whereas for t-Eu the emission quantum yield is enhanced at least 30 fold A mechanism based on a photoclick trans-to-cis isomerization of both t- and c-bpete moieties was proposed to explain the abnormal photostability of these compounds, either in solid state or in solution. The experimental and computational results are consistent with a photostationary state involving the trans-to-cis isomerization of the bpete ligand under continuous UV -A exposure, which thus diverts the incident radiation from other deleterious photochemical or photophysical processes that cause the typical photobleaching behavior of chelate lanthanide complexes. This shielding mechanism could be extended to other ligands permitting the design of new lanthanide-based photostable systems under UV exposure for applications in lighting, sensing, and displays.
palavras-chave
ORGANIC-INORGANIC HYBRIDS; TRANSFER EXCITED-STATES; TO-CIS ISOMERIZATION; LUMINESCENT MATERIALS; CONICAL INTERSECTIONS; ENERGY-TRANSFER; EUROPIUM; LIGAND; PHOTOISOMERIZATION; EU(III)
categoria
Chemistry; Materials Science
autores
Lima, PP; Nolasco, MM; Paz, FAA; Ferreira, RAS; Longo, RL; Malta, OL; Carlos, LD
nossos autores
Filipe Alexandre Almeida Paz
Investigador Principal
Luís Carlos
Professor Catedrático
Maria Rute de Amorim e Sá Ferreira André
Professor Catedrático
Mariela Martins Nolasco
Investigador Auxiliar
Patrícia Pereira Lima
Bolseiro de pós-DoutoramentoGrupos
G1 - Materiais Porosos e Nanossistemas
G2 - Materiais Fotónicos, Eletrónicos e Magnéticos
G6 - Materiais Virtuais e Inteligência Artificial
Projectos
agradecimentos
The authors are grateful to Fundacao para a Ciencia e a Tecnologia (FCT, Portugal), COMPETE and FEDER programs (Pest-C/CTM/LA0011/2011, PTDC/CTM/101324/2008, PTDC/CTMNAN/112168/2009), CNPq, CAPES, PRONEX-FACEPE-CNPq (APQ-0859-1.06/08) and inct-INAMI (Brazil) for financial support. LDC thanks Nanobiotec-CAPES network and PPL (SFRH/BPD/34365/2006) and MMN (SFRH/BPD/32103/2006) FCT for the grants. We are grateful to FCT for the financial support towards the purchase of the single-crystal diffractometer.