The arylvinylpyrimidine scaffold: a tunable platform for luminescent and optical materials

The incorporation of electron-withdrawing pyrimidine rings within π-extended systems allows access to a wide variety of fluorescent push-pull molecules that display emission properties highly sensitive to external stimuli. A suitable design of these compounds leads to interesting materials for a variety of optoelectronic applications. In this context, a vast number of arylvinylpyrimidine-based chromophores have been extensively studied during the last two decades. Along with the main synthetic pathways, this review summarizes the photophysical features of these active compounds having great potential and their most important applications as sensors and luminescence materials.

Unsymmetrically β-Functionalized π-Extended Porphyrins: Synthesis, Spectral, Electrochemical Redox Properties, and Their Utilization as Efficient Two-Photon Absorbers

Two new series of unsymmetrically β-functionalized porphyrins, MTPP(NO₂)MA (1M), (MA = methyl acrylate) and MTPP(NO₂)MB (2M) (MB = mono-benzo) (where M = 2H, Co(II), Ni(II), Cu(II) and Zn(II)), were synthesized and characterized by various spectroscopic techniques. The saddle shape conformation of ZnTPP(NO₂)MAPy and ZnTPP(NO₂)MB was confirmed by single-crystal X-ray analysis. Density functional theory (DFT) calculation revealed that NiTPP(NO₂)MB has a severe nonplanar geometry possessing a high magnitude of ΔC_β = ±0.727 Å and Δ24 = ±0.422 Å values among all other porphyrins. Synthesized β-substituted porphyrins exhibited red-shifted B- and Q-bands corresponding to their parent molecule due to the electron-withdrawing peripheral substituents. Notable redshift (Δλ_max = 50-60 nm) in electronic spectral features and with weak-intensity emission spectral features were observed for the free-base porphyrins and Zn(II) complexes compared to H₂TPP and ZnTPP, respectively. The first-ring reduction potential of MTPP(NO₂)MA (1M) exhibited 0.21-0.5 V anodic shift, whereas 0.18-0.23 V anodic shift was observed in the first-ring oxidation potential compared to the corresponding MTPPs due to the presence of electron-withdrawing β-substituents at the periphery of the macrocycle. Interestingly, NiTPP(NO₂)MA (1Ni) has shown an additional Ni^II/Ni^III oxidation potential observed at 2.05 V along with two ring-centered oxidations. The first-ring reduction and oxidation potentials of MTPP(NO₂)MB (2M) have shown 0.39-0.46 and 0.19-0.27 V anodic shifts with respect to their corresponding MTPPs. The nonlinear optical (NLO) properties of all of the porphyrins were investigated, and the extracted nonlinear optical parameters revealed intense reverse-saturable absorption (RSA) behavior and the self-focusing behavior with positive nonlinear refractive index in the range of (0.19-1.75) × 10^-17 m²/W. Zn(II) complexes exhibited the highest two-photon absorption coefficient (β) and cross section (σ_TPA) of ∼95 × 10^-12 m/W and 19.66 × 10⁴ GM, respectively, among all of the metal complexes.

A series of asymmetric and symmetric porphyrin derivatives: one-pot synthesis, nonlinear optical and optical limiting properties

In this work, a series of asymmetric and symmetric porphyrin derivatives (structure types: A4, A3B1, trans-A2B2, cis-A2B2, A1B3, and B4) have been synthesized via a one-pot method and characterized to identify their structures and properties.

Branching effect on the linear and nonlinear optical properties of styrylpyrimidines

The branching effect on the photophysical properties of styrylpyrimidines is studied experimentally and theoretically.

Unsymmetrical nonplanar 'push-pull' β-octasubstituted porphyrins: facile synthesis, structural, photophysical and electrochemical redox properties

Mixed substitution at the β-position of porphyrins influences their photophysical and electrochemical redox properties. Two new series of asymmetrically mixed β-octasubstituted porphyrins viz. MTPP(Ph)2Br5X (X = NO2 or Br and M = 2H, Co(ii), Ni(ii), Cu(ii), and Zn(ii)) have been synthesized and characterized by various spectroscopic techniques. The single crystal X-ray structure of H2TPP(NO2)(Ph)2Br5 showed a nonplanar saddle shape conformation of the macrocyclic core. Furthermore, the fully optimized geometries confirmed the saddle shape conformation of H2TPP(Ph)2Br5X (X = NO2 or Br). Electronic spectra revealed a significant bathochromic shift by appending both electron donor and acceptor substituents at the β-position of the meso-tetraphenylporphyrin skeleton, which reflects the following order H2TPP < H2TPP(NO2) < H2TPP(NO2)(Ph)2 < H2TPP(Ph)2Br6 < H2TPP(NO2)(Ph)2Br5. H2TPP(Ph)2Br5X (X = NO2 or Br) exhibited a significant bathochromic shift (Δλmax = 53-61 nm) in the Soret band and (Δλmax = 90-95 nm) in the longest wavelength Qx(0,0) band as compared to H2TPP. Nonplanar conformations and electron withdrawing β-substituents induce higher protonation and deprotonation constants for H2TPP(NO2)(Ph)2Br5 and H2TPP(Ph)2Br6 as compared to precursor porphyrins viz. H2TPP, H2TPP(NO2) and H2TPP(NO2)(Ph)2. The electronic spectral properties and redox potentials of MTPP(Ph)2Br5X (X = NO2 or Br and M = 2H, Co, Ni, Cu and Zn) are affected by β-substituents at the periphery of the porphyrin core. Redox tunability was achieved by appending push-pull substituents at the β-position of the MTPP (M = 2H, CoII, NiII, CuII, and ZnII) skeleton of the macrocycle. CuTPP(Ph)2Br6 and CuTPP(NO2)(Ph)2Br5 exhibited a dramatically reduced HOMO-LUMO gap with a difference of 0.55 V and 0.62 V, respectively as compared to CuTPP due to the push-pull effect of β-substituents and nonplanarity of the porphyrin core.

An insight into the communication between β-olefin/phenyl olefin-mediated acceptors and porphyrin π-system: a way to establish porphyrin based chemodosimeters and chemosensors

Porphyrins bearing electron acceptors attached to β-carbon through olefin or phenyl–olefin bridges act as chemodosimeters for CN⁻ as well as chemosensors for F⁻, CN⁻ and OAc⁻ ions depends on acceptor strength and position.

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the function of optical power limiting. All known mechanisms of optical limiting have been analyzed and discussed for the different types of materials.

TiO2–multi-walled carbon nanotube nanocomposites: hydrothermal synthesis and temporally-dependent optical properties

MWCNTs/TiO2 nanocomposites have been prepared by a hydrothermal method and characterized by various spectroscopic techniques, and an enhanced optical nonlinearity was observed for M1.00 due to a combination of mechanisms.

Series of Carbazole-Pyrimidine Conjugates: Syntheses and Electronic, Photophysical, and Electrochemical Properties

A series of carbazole-pyrimidine conjugates 1-17 were synthesized by Pd-catalyzed cross-coupling, oxidation, and nucleophilic aromatic substitution reactions. In 1-17, the carbazole moieties are connected at the 4,6-positions of the pyrimidine ring either directly or via ethynylene or vinylene spacers, and various electron-donating or electron-withdrawing substituents are introduced at the 2-position of the pyrimidine ring. The effects of structural variations on the electronic, photophysical, and electrochemical properties of 1-17 were comprehensively investigated. Compounds 1-17 exhibit intramolecular charge-transfer (ICT) states, which essentially lead to moderate-to-strong fluorescence emission with large Stokes shifts depending on the solvent polarity. These compounds tend to show significant changes in optical and fluorescence properties upon addition of trifluoroacetic acid. The electron-accepting ability of these compounds can be tuned by both substituents on the pyrimidine moiety and spacers. The ethynylene spacer lowers both the HOMO and LUMO levels, while the vinylene spacer elevates the HOMO level and lowers the LUMO level. The X-ray crystal structures of 3, 6, 11, and 14 are also disclosed.

Synthesis, spectroscopic, electrochemical redox, solvatochromism and anion binding properties of β-tetra- and -octaphenylethynyl substituted meso-tetraphenylporphyrins

β-Phenylethynyl (PE) porphyrins exhibited unique photophysical properties and solvatochromic behavior due to ICT from the porphyrin core to PE moieties. Further, Zn(ii) porphyrins were utilized for anion sensing.

Porphyrin chemodosimeters: synthesis, electrochemical redox properties and selective ‘naked-eye’ detection of cyanide ions

β-Dicyanovinyl substituted porphyrins have been synthesized and utilized as chemodosimeters for ratiometric and colorimetric sensing of cyanide ions in CH₃CN and H₂O/CH₃CN mixture.