Synthesis and Two-Photon Absorption Property Characterizations of Small Dendritic Chromophores Containing Functionalized Quinoxaliniod Heterocycles

Multi-photon properties of branched chromophores derived from indenoquinoxaline and oxadiazole heterocyclic units

Two chromophoric congeners derived from indenoquinoxaline and oxadiazole are designed, synthesized and characterized for their multi-photon properties in the femtosecond time domain. These two model structures are experimentally found to exhibit strong and widely distributed two- and three-photon activities within the spectral range of 680-1500 nm and the larger congener manifests maximum two- and three-photon absorption cross-section values of 2120 GM (at 750 nm) and ∼85 × 10^-80 cm⁶ s² (at 1280 nm), respectively. Both two- and three-photon absorption-based optical power-limiting performance of a representative model compound are also evaluated and demonstrated.

Ultrafast broadband nonlinear optical properties and excited-state dynamics of two bis-chalcone derivatives

The development of organic nonlinear optical (NLO) chromophores is vital for various fields such as two-photon biomedical imaging, optical limiting, etc. In this work, two bis-chalcone molecules 1,4-bis[3-(2,4-dimethoxyphenyl)-2-acryloyl]benzene (C1) and 4,4′-bis[3-(2,4-bimethoxy phenyl)-2-acryloyl]biphenyl (C2) were synthesized and characterized. The excited-state dynamics of these two chromophores were studied using femtosecond transient absorption (TA) measurements. And their broadband nonlinear absorption properties and optical limiting (OL) response were investigated by femtosecond open-aperture Z-scan and intensity-dependent transmittance measurements in the wavelength range from 515 nm to 800 nm, respectively. The TA results demonstrate that C2 has strong excited-state absorption behavior and longer lifetime. In addition, the nonlinear absorption response of C2 was found to be superior to that of C1 in the visible range after 500 nm, which is attributed to a two-photon-absorption induced excited-state absorption mechanism. These results indicate that the nonlinear optical response and excited-state dynamics in bis-chalcone compounds could be enhanced via intramolecular charge-transfer.

The introduction of a benzene ring largely affects the excited-state absorption spectra and dynamics of these chromophores.

High-Performance Organic Dyes with Electron-Deficient Quinoxalinoid Heterocycles for Dye-Sensitized Solar Cells under One Sun and Indoor Light

A series of Y-shaped sensitizers incorporating quinoxaline or quinoxalinoid moieties were prepared and applied in dye-sensitized solar cells (DSSCs). By the introduction of quinoxalinoid functionalities, the absorption extinction coefficients could be enhanced. The molecular structures were modified by introducing an extra acceptor group (A) between a donor (D) and a π-bridge (D-A-π-A) and also by incorporating electron-donating substituents at various positions of the quinoxalinoid moiety. Some of the dyes and mixtures thereof were found to exhibit good light-harvesting efficiencies under both sunlight and indoor light, with efficiencies up to 7.92 % under one sun (AM 1.5G). When operated under indoor light, the efficiency could be boosted to 27.76, 28.74, and 30.45 % under 600, 1000, 2500 lux illumination, respectively. The best performance could be ascribed partly to an improved dye coverage on the TiO₂ surface.

Regioselective ortho-functionalization of bromofluorenecarbaldehydes using TMPMgCl·LiCl

A highly regioselective functionalization of 7-bromofluorene-2-carbaldehydes, potent organic chromophores, in position C3 using a mild ortho-metallation strategy (DoM) with TMPMgCl·LiCl has been developed.

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.

Controllable preparation and properties of active functional hybrid materials with different chromophores

POSS-based active functional hybrid materials were controllably prepared and their optical properties were influenced by molecular structure.

Four new two-photon polymerization initiators with varying donor and conjugated bridge: synthesis and two-photon activity

A specific series of dumbbell-shaped bis-carbazoles or bis-phenothiazines dyes (1, 2, 3 and 4) constructed with styrene or biphenylethyne as the π-bridge have been synthesized and characterized. Detailed spectral properties including linear absorption, one and two-photon fluorescence properties were investigated. The results show that extending conjugated chain and introducing donors have substantial effect on their photophysical properties. Among them, two-photon absorption cross sections (σ) of the four dyes in DMF determined by the Z-scan technique are successively increased from 1 to 4 with enhancing electron-donating ability and extending conjugated chain, but electron-donating ability has larger contribution to the σ values than extending conjugated chain based on the comparison of small molecules (D-π-D). Two-photon initiation polymerization (TPIP) microfabrication experiments have been carried out using compound 4 as an initiator under irradiation of 200 fs, 76 MHz femtosecond laser at 760 nm. The results confirm that the four dyes can be effectively used as organic two-photon photopolymerization initiators.