Study Of 9, 10-phenanthrenequinone, Poly(Fluorene) And Optoelectronic Properties Of Related Materials

We have described the PQ and Benzil properties. 9,10-phenanthrenequinone also known as phenanthrene-9,10-dione abbreviated as PQ is closely related to Benzil as both of them areα-diketones. The two molecules show some similarities in their UV-vis absorption spectrum due to theπ→π* and n→π* transitions of the aromatic core and C=O groups present in the two compounds. The dissimilarity of the photoluminescence spectrum of PQ and Benzil is due to the more flexible structure of benzil or more rigid structure of PQ. The photoluminescence spectrum of benzil is wider than PQ likely due to slow relaxation of the excited state. The cyclic voltammetry of the two molecules shows that both are good acceptor of electrons and show reversible two-electron reduction process. 9,10-phenanthrenequinone shows better reduction process (lower reduction potential) as compared to the benzil, which is attributed to the presence of an extra ring, formed by linking the 4a and 5a positions. The better reduction process of PQ is attributed to the more conjugation (an extra ring) adjacent to the 9 and 10-positions of the C=O group that provides stability to the reduced species (mono or diradical anions). In addition PQ also shows higher thermal stability as compared to Benzil due to the presence of Phenanthrene unit. The molecular structure of PQ and Benzil is characterized using ¹H NMR, ¹³C NMR, ¹H-¹H COSY, HMBC, HMQC, and FTIR spectroscopic techniques.N-type organic semi-conductors are used in OLEDs as electron transport layer (ETL) or hole blocking layer (HBL). They are also used in photovoltaic devices (PVs) as electron acceptor layer (EAL) for use in bi-layer or as blends in hetero-junction solar cells. N-type organic semi-conductors are also used as ligands to make iridium complexes for applications in OLEDs. In the 3rd chapter, we have synthesized a series of n-type semiconductors using PQ and Benzil as starting materials. The materials are well characterized using NMR. We have compared the optical, electrochemical properties with a famous electron transport material known as Alq₃ to reveal similar or dissimilar properties. We have found that the electrochemical properties of 9 out of 12 compounds show similar and better electrochemical behavior with Alq₃ (reversible two electron reduction process). We have found that some of the n-type materials synthesized from PQ show UV-vis and PL emission properties very similar to Alq₃. All these molecules contain pyrazine nucleus. All the molecules are n-type semiconductors. All the compounds show similar absorption with Alq₃ but few of them show similar emission in terms of emission wavelength. Except H-6 all of them show good electro-reduction reversibility in comparison to Alq₃. All the compounds in PQ series show lower LUMO levels compared to Alq₃. Hm-2, Hm-5 and Hm-6 in the Benz-Series show lower LUMO compared to Alq₃. These lower LUMO levels are highly beneficial for electron transport layer or hole blocking layer in OLEDs and as good electron acceptor materials in solar cells. Suzuki coupling reaction is widely used in the construction of conjugated polymers: however, there is still no report describing the mechanism and coupling of 9,10-phenanthrenequinone (PQ) building blocks via Suzuki reaction because PQ is sensitive to bases and light. In the 4th chapter is reported the efficient Suzuki coupling of PQ with 9,10-dialkylfluorene with Na₂CO₃ as basic species and high molecular weight PQ-Alt-Dialkyl-Fluorene conjugated copolymer obtained. Based on the characterization data and well-accepted literature, we proposed a step-by-step mechanistic explanation for the formation of the PQ containing alternating conjugated copolymer. This chapter describes the synthesis, characterization, basic conditions for polymerization, mechanisms for monomers and polymer formation optical and electro-chemical properties of a 9,10-phenanthrenequinone (PQ)-containing alternating conjugated copolymer, named poly(9,10-phenanthrenequinone-2,7-diyl-alt-9,9-di-n-hexylfluorene-2,7-diyl), abbreviated as PPQF. The copolymer has good solubility in common organic solvents such as CH₂Cl₂, CHCl₃ and THF. The polymer structure was determined using ¹H NMR, FT-IR, GPC and elemental analysis. The polymer possesses a low-energy n→π* electronic state caused by the C=O groups of the PQ repeating units, exhibits interesting and improved electrochemical reduction activity as compared to PDHF (poly(9,9-di-n-hexylfluorene-2,7-diyl)) and molecular PQ. PPQF has no fluorescence in solution but shows interesting transitions from no fluorescence to strong fluorescence after it undergoes electrochemical reduction. The polymer PPQF may find use as starting material for a range of applications and can also be used to prepare other polymers due to the presence of PQ repeating units. Organophosphorus compounds are the organic compounds that contain phosphorus as an integral part of the molecule have been widely used in industry, organic synthesis and optoelectronics. The o-xylylene-α,α'-bis(triphenylphosphinebromide) abbreviated as OXBTPPB is used to convert ortho-quinones (e.g. 9, 10-phenanthrenequinone) to polycyclic aromatic hydrocarbons (PAHs). The 5th chapter describes the synthesis, GC-EIMS, ¹H NMR. ¹³C NMR, mechanistic and thermal properties of OXBTPPB. The EIMS showed characteristic peaks at m/z = 262.4, 183.3, 108.2, 77.1 attributed to the [C₁₈H₁₅P]⁺, [C₁₂H₈P]⁺, [C₆H₅P]⁺, [C₆H₅]⁺ ions respectively. The ¹H NMR, ¹³C NMR of OXBTPPB showed well resolved peaks and all the hydrogens and carbons are well-characterized, using a combined study of ¹H NMR, ¹³C NMR, ¹H-¹H COSY, HMBC, and HMQC experiments. The mechanism for the formation of OXBTPPB is proposed. TGA analysis shows high thermal stability (onset decomposition T_d is 323.6℃) of OXBTPPB.Anthracene (AN) and Dibenz[a,c]anthracene (D[a,c]A) are important semiconductors. The 6th chapter describes the ultrasound assisted synthesis of D[a,c]A (starting from 9,10-phenanthrenequinone), proposed mechanistic aspects of the bis-Wittig reaction for D[a,c]A. In addition, the GC-EIMS, NMR spectroscopy, FTIR spectroscopy, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), optical and electrochemical properties of AN and D[a,c]A are compared. Both compounds show weak blue fluorescence in the THF solution and higher fluorescence in the solid-state. TGA and DSC experiments determined that D[a,c]A have excellent thermal stability in comparison to AN, which indicates that D[a,c]A should be more suitable as active layers to make stable devices. Quantum chemical calculations for the frontier molecular orbital properties reveal that the HOMO and LUMO are mainly localized in the anthracene part of D[a,c]A similar to AN. The D[a,c]A shows wider optical band gap (3.41 eV) as compared to AN (3.24 eV) measured in THF solution. A simple OLED for AN and D[a,c]A, show that the D[a,c]A show similar luminance at lower turn on voltage and blue shifted bluelight. Exciplex were formed at high driving voltage and D[a, c]A showed the potential application as the white OLED by using single material.