Comparative study of the photophysical and crystallographic properties of 4-(9H-pyreno[4,5-d]imidazol-10-yl)phenol and its alkylated derivatives

The photophysical and crystallographic properties of a para-hydroxphenyl-substituted pyrenoimidazole and its decylated analogues were investigated. The fluorescence of these compounds is sensitive to environmental acidity and basicity.

Synthesis and photophysical studies on 2‑styryl phenanthro[9,10‑d]oxazole derivatives

A new series of 2‑styryl phenanthro[9,10‑d]oxazoles was readily accessible from the condensation reaction of 9,10‑phenanthroquinone with cinnamaldehydes in the presence of lactic acid. All these styryl dyes were isolated in good yields and characterized by various analytical and spectroscopic techniques. One of the dyes containing NO₂ group (3d) was structurally characterized by single crystal X-ray analysis. These dyes displayed emission in blue to green region with larger Stokes shift values characteristic to the nature of substituents. In addition, positive solvatochromic trend was observed by increasing the solvent polarity suggestive of a more stabilized polar excited state. Moreover, the addition of trifluoroacetic acid leads to a prominent blue-shift in visible and emission color changes owing to the protonation of the nitrogen atom of oxazole moiety. Among the all, the oxazole derivative having NMe₂ group (3b) exhibits good response to acidic pH in the range of 3.0 to 5.6 with a good linearity upon decreasing the pH from 8.0 to 2.16. The absorption studies were further supported by density functional theory calculations.

Indigo-Based Acceptor Type Small Molecules: Synthesis, Electrochemical and Optoelectronic Characterizations

In this paper, we report design and synthesis of novel low bandgap small molecules, indigo-benzimidazole (Tyr-3) and indigo-schiff base (Tyr-4) type acceptors. In these structures, tert-butoxycarbonyl (t-BOC) group has been attached to indigo nitrogen atom in order to increase the solubility. UV-vis absorption spectra of Tyr-3 and Tyr-4 dyes exhibit wide absorption bands ranging from 350 to 600 nm, indicating the relatively low bandgap giving around 2.07 eV for each. Excitation of both Tyr-3 and Tyr-4 dyes at 485 nm displays characteristic emission features of indigo moiety and also intramolecular charge transfer complex (ICT) related with their subunits. Besides increasing fluorescence quantum yields as compared to model compound, biexponential decay times for fluorescence life times were also obtained for Tyr-3 and Tyr-4 dyes. Their appropriate energy levels along with low HOMO levels are desired for light harvesting acceptors for organic solar cells when blended with poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',1',3'-benzothiadiazole] (PCDTBT) as donor polymer. Photovoltaic behavior of the synthesized dyes were examined in bulk heterojunction concept and achieved photovoltaic conversion efficiencies were discussed.

Optoelectronic performance comparison of new thiophene linked benzimidazole conjugates with diverse substitution patterns

In an approach to develop efficient organic optoelectronic devices to be used in light-driven systems, a series of three thiophene linked benzimidazole conjugates were synthesized and characterized. The combination of two thiophene rings to a benzimidazole core decorated with different functional groups (such as OCH₃, N(CH₃)₂, CF₃) resulted in donor-acceptor type molecular scaffold. The effect of the electronic behavior of the substituents on the optical, electrochemical, morphological and electron/hole transporting properties of the dyes were systematically investigated. DTBI2 dye exhibited distinct absorption properties among the other studied dyes because N,N-dimethylamino group initiated intramolecular charge transfer (ICT) process in the studied solvents. In solid state, the dyes exhibit peaks extending up to 600nm. Depending on the solvent polarities, dyes show significant wavelength changes on their fluorescence emission spectra in the excited states. Morphological parameters of the thin films spin-coated from CHCl₃ solution were investigated by using AFM instrument; furthermore photovoltaic responses are reported, even though photovoltaic performances of the fabricated solar cells with different configurations are quite low.

Fused Methoxynaphthyl Phenanthrimidazole Semiconductors as Functional Layer in High Efficient OLEDs

Efficient hole transport materials based on novel fused methoxynaphthyl phenanthrimidazole core structure were synthesised and characterized. Their device performances in phosphorescent organic light emitting diodes were investigated. The high thermal stability in combination with the reversible oxidation process made promising candidates as hole-transporting materials for organic light-emitting devices. Highly efficient Alq3-based organic light emitting devices have been developed using phenanthrimidazoles as functional layers between NPB [4,4-bis(N-(1-naphthyl)-N-phenylamino)biphenyl] and Alq3 [tris(8-hydroxyquinoline)aluminium] layers. Using the device of ITO/NPB/4/Alq3/LiF/Al, a maximum luminous efficiency of 5.99 cd A(-1) was obtained with a maximum brightness of 40,623 cd m(-2) and a power efficiency of 5.25 lm W(-1).

Turn-off of fluorescence of styryl phenanthrimidazole on doping ZnO nanoparticles with Ce(3+)

ZnO nanoparticles were doped with Ce(3+) by sol-gel synthesis and characterized by high-resolution scanning electron microscopy (HR-SEM), powder X-ray diffraction (XRD) and UV-visible diffuse reflectance (DRS) and photoluminescence (PL) spectroscopies. The dynamics of photoinduced electron injection from styryl phenanthrimidazole to Ce(3+)-doped ZnO nanoparticles has been studied by absorption, fluorescence and lifetime spectroscopic methods. Both the absorption and fluorescence quenching results suggest association between Ce(3+)-doped ZnO and the phenanthrimidazole. The free energy change (ΔGet) for electron injection has been calculated. The critical energy transfer distance between the phenanthrimidazole and Ce(3+)-doped ZnO nanoparticles has been deduced. In contrast to our earlier observation of enhancement of fluorescence of the phenanthrimidazole by ZnO nanoparticles, doping ZnO with Ce(3+) turns off its fluorescence. These findings provide a method to test the presence of Ce(3+) in ZnO nanocrystals.

Synthesis and optical properties of phenanthromidazole derivatives for organic electroluminescent devices

The external quantum efficiency roll-off may be due to triplet–triplet annihilation (TTA) and triplet–polaron annihilation (TPA).

Kamlet-Taft and Catalán solvatochromism of some π-expanded phenanthrimidazole derivatives - DFT analysis

Some π-expanded phenanthrimidazole derivatives have been synthesised and characterised by different spectral techniques. Kamlet-Taft and Catalán solvatochromism of synthesised phenanthrimidazole derivatives have been analysed. Non-linear optical (NLO) and natural bond orbital (NBO) analysis have been made by ab initio method to show intramolecular interactions. The energies of the HOMO and LUMO levels, the molecular electrostatic potential (MEP) energy surface, NBO studies have exploited the existence of intramolecular charge transfer (ICT) within the molecule.

Sensitive and selective PET-based π-expanded phenanthrimidazole luminophore for Zn2+ ion

The novel photoinduced electron transfer (PET) chemosensor, 1-(1-(4-methoxyphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol [MPPN] and its zinc complex were synthesised and characterized by electronic spectral and Frontier molecular orbital energy analysis. MPPN becomes efficient fluorescent chemosensor upon binding with metal ions and shows a strong preference toward Zn(2+) ion. Density Functional theory (DFT) calculations reveal that luminescence of free MPPN originates from its orbital structure in which two π-orbitals (HOMO and HOMO-1) of the imidazole ring are situated between two π-orbitals (HOMO-2 and LUMO) of the naphthyl fragment. Therefore the absorption and emission processes occur between the two π- orbitals (HOMO-2 and LUMO). The two higher energy imidazole orbitals (HOMO and HOMO-1) serve as quenchers for the excited state of the molecule through nonradiative processes. Upon binding with Zn(2+) ion, MPPN becomes a highly luminescent with λemi - 421 nm. The significant enhancement of luminescence upon binding with Zn(2+) ion is attributed to the stabilization of HOMO-2 and HOMO-1 π-orbitals of imidazole ring upon their engagement in new bonds with Zn(2+) ion. The affinity of MPPN to zinc ion is found to be very high [K = 6 × 10(6) M(-1)] when compared with other metals ions. The nonlinear absorption coefficient γ for MPPN is 1.9 × 10(-12) m/W and 3.9 × 10(-11) m/W for MPPN-Zn complex.

Nano rutile TiO2 catalysed synthesis of (E)-4-(2-(1-(4-chlorophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)-N,N-dimethylaniline and its interaction with super paramagnetic nanoparticles

The synthesis of (E)-4-(2-(1-(4-chlorophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)-N,N-dimethylaniline (CPPIVI) has been carried out using TiO₂ (R) as catalyst under solvent free conditions and characterized by NMR spectral studies.

Styryl phenanthrimidazole-fluorescence switched on by core/shell BaTiO3/ZnO and Mn-doped TiO2/ZnO nanospheres and switched off by the core nanoparticles

Photoelectron transfer to core/shell Mn–TiO₂/ZnO and BaTiO₃/ZnO nanospheres. Enhanced absorbance because of binding with nanosemiconductors. Enhanced emission due to charge injection from the excited ligand to CB of ZnO.