Molecular Engineering of Efficient Light Harvesting Organic Antennas for Multitasking Organo EuIII Complexes: Design, Synthesis, and Photophysical Investigations

Abstract

This thesis work mainly going to describe about the designing and synthesis of the ancillary ligands (antenna) for the Eu(III) based complexes and to investigate their application in red/white LEDs, sensors (temperature and vapoluminescence sensor) and bioimaging. Chapter 1 represents a general introduction of lanthanides and its unique spectral properties and it application in various fields. The importance of Eu(III) complexes, antenna effect of Dibenzoylmetahne DBM/ 2-Theonyl trifluoro acetone (TTA) and ancillary ligand, the lanthanides (specially Eu(III)) application in Red/white LED, temperature sensor vapoluminescence and bioimaging were systematically discussed. In addition, the recent progress of Eu(III) complexes for light emitting diodes (LEDs) and sensors were also being discussed. The main objective and significance of the present work of the thesis were documented. Chapter 2 describes the tailor-made molecular siblings induced single component bright white light emissive EuIII luminogens in EuIII systems. Such characteristics not been observed for analogue Eucomplex. It therefore demonstrates a proof-of-concept of applying molecular sibling as a choice of antenna for Eu-complexation and could modulate the complex emission. This research opens a path to discover new single component white light emissive luminogens through molecular siblings (proper choice of connectivity). This describes about both the phenanthroline (Phen) based ligands shown blue emission under 365nm UV lamp, whereas the corresponding complexes were shown red emission with tremendous color purity in solid and thin film. In solution (polar and non-polar), both the isomeric complexes were shown different emissive behaviour (red/white). Ligand to metal energy transfer mechanism was summarized thorough experimental and theoretical analysis. Glowing red LEDs were fabricated with different ratio of complex and PMMA with high LER values. Chapter 3 describes design and synthesis of two isomeric ligands for EuIII complexation. The purposelydesigned ancillary ligands show greenish-yellow emission in the solution as well as in solid state. However, the corresponding Eu-complex based mCF3 functionalized showed single component white light emission with balanced color purity, in contrast, the pCF3 functionalized Eu-complex showed pure red emission. The systematic solvatochromism study reveals that the Eu(TTA)3-TPA-DPA-mCF3 show multi-color /tunable emission with variable CIE color coordinates, in contrast Eu(TTA)3-TPA-DPA-pCF3 shows pure red emission. The mechanism suggests that the partial and complete energy transfer from ligand to Eu(III) ion is responsible and supported by theoretical as well as experimental study. Both the complexes have applied as a potential phosphor for red/white LEDs fabrication and particularly Eu(TTA)3-TPA-DPA-mCF3 is applied for white LEDs fabrication in conjugation with blue LED. The white LED produced superior white emission (CIE = 0.35, 0.34) with CRI = 86 %) and correlated color temperature (CCT) = 4645K, whereas near UV conjugated white LED showed CRI of 78 %. The red fabricated LED can be applied for visual detection of acid and bases vapors (act as electronic noses) from the environment due to emission swapping characteristics. Dual emission behavior of complex lead to study the thermometric property in higher temperature ranges Chapter 4 describe two efficient molecular EuIII based red-emitting complexes for SSL.The synthesized complexes harvest narrow-band red emission (FWHM ∼6 nm), which is extremely superficial to the human eyes, and lead to excellent chromatic saturation of the red spectral window. Significant efforts have been devoted to understand the energy transfer mechanism theoretically (by DFT) and experimentally. The highly bright full red color emissive LEDs were created by coupling red Eu(III) complexes as red phosphor with a near-UV LED chip (395 nm) operated at 20 mA forward bias, and the hybrid white LED spectra (yellow dye + Eu-complex) to show a pure white light emission with a low CCT (3704 K), high CRI (93), and CIE values of x = 0.33; y = 0.33. In addition, using Eu(TTA)-TPA-DPA-Ph as red components and TPA-DPA-Ph as the green component, hybrid white LEDs are created. The two-component hybrid white LED spectrum, which demonstrates pure white light emission with a low CCT (4499 K), a high CRI (87), and CIE values of x = 0.33; y = 0.36. All the synthesized red phosphors are found to be excellent for solidstate lighting applications Chapter 5 describes a series of unique EuIII complexes with the new class of ancillary neutral ligands named Thiabendazole (TBZ, N1 position functionalized with benzyl and N-alkylated carbazole (CBZ) pendants moiety) and DBM/TTA as anionic ligands. All the freshly synthesized TBZ-based Eu-complexes exhibited enormously outstanding narrow-band red emission due to ED transition (5D0→7F2), in solid, solution, and thin-film with high quantum yield. Theoretical analysis (TD-DFT) and experimental study (phosphoresce spectra) designate that the energy transfer (ET) from ligand to Eu(III) ion is comprehensive. The Eu(III) complexes are potentially applied for red LEDs and hybrid white LEDs fabrication. LEDs were made up by spreading Eu(III) over UV LED/blue LED chips conjugated with yellow dye with proper concentration. The fabricated red LEDs showed high luminous efficiency of radiation (LER) values and blue LED-based hybrid white LEDs showed superior performance with high color rendering index CRI (83%), CIE (x = 0.37, y = 0.34) close to NTSC standard. The Eu-complexes showed outstanding alterable on-off-on luminescence performance with the contact of acid-base vapors. Pure red emission of complexes gives rise to anti-counterfeiting applications. Thanks to an excellent spectroscopic exploration of the Eucomplexes (pure red emission), they are acting as a key model in the cytotoxicity study (less toxic) and bioimaging applications and perform a great job as cytoplasmic staining reagent due to intense red emission. Chapter 6 describes the new design strategy of Organo-EuIII based narrowband red-emitting phosphors which validate their energetic character in an unexpected performance in smart Red/white LEDs, sensing, and biomedical fields. In this chapter, a series of unique EuIII complexes have been synthesized with coumarin integrated with a new class of Phen/ TBZ based ancillary ligands and DBM/ TTA as an anionic ligand. All the Eu-complexes demonstrated outstanding red emission due to ED transition (5D0→7F2), in solid, solution, and thin film with high quantum yield (QY). Both theoretical analysis (TD-DFT) and experimental findings (phosphorescence emission at 77 K) describe that the energy transfer (ET) from the ligand’s triplet level to the Eu(III) ion is completely occurring. The Eu(III) complexes can potentially be used to fabricate the intense red LEDs and hybrid white LEDs. All the fabricated Red LEDs revealed high luminous efficiency of radiation (LER) values. The fabricated blue LED-based hybrid white LEDs displayed remarkable performance with low CCT (5634 K), high color rendering index CRI (88), and CIE values (x = 0.33; y = 0.342) for Eu(TTA)3Phen-UMB-C2. Furthermore, with the interaction of acid-base vapors, these Eu-complexes displayed good alterable on-off-on luminescence performance. A thorough investigation was conducted to evaluate the cell viability. The cells were viable at the concentration levels and employed in fluorescence imaging as potential biomarkers. Chapter 7 briefly describes new molecular design of two butterfly-shaped organic light harvesters (ancillary ligands L1, L2) to produce binuclear EuIII complexes (C1 and C2) and characterized by using various spectroscopy methods. The ligand with a simple benzene ring (L1) at the core showed bluish-green emission, in contrast, CF3 substituted ligand (L2) showed pure white light emission. Notably, under 390 nm excitation both the complexes showed sharp red emission in solid owing to (5D0→7F2) ED transition of Eu(III) ion at 612 nm (FWHM 3-4) with color purity 95-96%. The photophysical characteristics were investigated for both ligands and complexes. The europium complexes in the solid and liquid phases show intense red emissions due to the ED transitions of the Eu(III) ion. The solvatochromism investigation accounted for both the Eu(III) complexes in the non-polar solvent to polar solvent yielded a pure red emission. The synthesized butterfly-shaped organic chromophores and TTA as supportive ligands coordinated with Eu(III) ions can effectively assist energy transmission to the Eu(III) ion. Therefore, the ligand (L2) and two complexes (C1, C2) were devoted as a phosphor for red LEDs fabrication (1:10 (LER = 387/263). L2 acts as a single integrant white light-emissive phosphor and emits white light (CIE= 0.32, 0.37) by conjugating with the NUV chip. Chapter 8 deals the summary and conclusion as well as future perspective of the work. The present thesis works deals with rational design and synthesis of new and novel class of ancillary ligand and their corresponding EuIII complexes for white LEDs and sensor (temperature and vapoluminescence) and bioimaging applications. In addition, Eu molecular complexes also been explored for single component white light emitter based white LEDs. The observations and the conclusions derived from the present investigations are summarized in this chapter.