Poly(etherimide)s and poly(esterimide)s containing azobenzene units: Characterization and study of photoinduced optical anisotropy

In this paper novel processable, photoresponsible aromatic polymers with imide rings and covalently boned azobenzene units are presented. Prepolymerization strategy based on polycondensation of two diamines with azobenzene group, that is, 2,4-diamino-4′-cyanoazobenzne and 2,4-diamino-4′-nitroazobenzene and two dianhydrides, was utilized for preparation of the new photochromic polyimides. The obtained polymers differ in the chemical structure of polymer backbone and the kind of substituents on azobenzene moieties. Polymers were characterized and evaluated by FT-IR, ¹H NMR, X-ray, UV-vis, DSC, and TGA methods. The synthesized azopolymers exhibited glass transition temperatures in the range of 140-170 °C, thermal stability with initial decomposition temperatures (T_d) in the range of 266-290 °C, and excellent solubilities in common organic solvents, providing optical-quality films. The light-induced optical anisotropy was studied in obtained polymers by photoinduced birefringence measurements. The birefringence was generated by the femtosecond pulses at 400 nm via a linear absorption of the trans-azobenzene. A large light-induced birefringence (Δn = 0.02) was achieved in poly(esterimide)s contrary to poly(etherimide)s. The birefringence exhibited a very stable behavior after switching off the writing light indicating a permanent storage capacity.     

Synthesis and nonlinear optical properties of polyurethanes containing nitro-substituted 1,3,4-oxadiazole chromophores

NLO active nitro-substituted oxadiazole chromophores were prepared and condensed with tolylene-2,4-diisocyanate (TDI) and 4,4′-methylenedi(phenyl isocyanate) (MDI) to yield a series of polyurethanes. The resulting polyurethanes exhibited an excellent solubility in many common organic solvents, suggesting that these polyurethanes offer good processability. Molecular structural characterization of these polyurethanes was achieved by FT-IR, UV–vis, ¹H NMR and analytical technique. The weight-average molecular weights of polyurethanes determined by gel permeation chromatography (GPC) were in range of 21,000–23,000 (M_w/M_n = 1.87–2.00). Thermal behavior of polyurethanes was investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The glass transition temperatures of the polyurethanes were in the range of 155–170 °C. The second harmonic generation (SHG) coefficients (d₃₃) of the poled polyurethanes were in the range of 38.93–48.64 pm/V at 532 nm. High thermal endurance of poled dipoles was observed for all the polyurethanes. Further, it was found that all the developed polyurethanes were stable up to 140 °C, signifying the acceptability for nonlinear optical devices.     

Spiro‐Bridged Ladder‐Type Oligo(para‐phenylene)s: Fine Tuning Solid State Structure and Optical Properties

A set of ladder‐type quaterphenyls with an incremental number of spiro‐bifluorene units in the bridge positions as well as an in‐plane bent quaterphenyl carrying all bridges on one and the same side of the ribbon are synthesized and characterized. While spiro‐bifluorene substituents lead to bathochromically shifted maxima in the UV–vis absorption spectra, this effect can be compensated by in‐plane bending. The influence of different deposition techniques on the solid state structure is analyzed by X‐ray diffraction of single crystals obtained by crystallization from solution as well as sublimation. An increasing number of spiro‐bifluorene substituents are found to aid thin‐film formation.     

Synthesis and characterization of novel polyarylates bearing NLO moieties

A series of thermally stable second‐order nonlinear optical polyarylates containing azo side‐chain groups have been obtained by interfacial polycondensation. Theoretical calculations of the static hyperpolarizabilities, first‐ and second‐order hyperpolarizability, were carried out. The structures of the obtained monomers and polymers were confirmed by infrared, ¹H NMR and ultraviolet spectroscopies. Thermal and optical properties of the obtained polymers were evaluated. The investigations show that some of the new polymers obtained in this study may find use in optical applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2195–2201, 2006     

Epoxy resin cured with diamine bearing azobenzene group

The epoxy resin: N,N-diglycidyl-4-glycidyloxyaniline (DGOA) is cured with the new diamine-chromophore: 2,4-diamino-4′-methylazobenzene (DMAB). The spectral characterization of infrared spectroscopy (FTIR), ¹H NMR spectroscopy and of elemental analysis (EA), confirm the chromophore structure. The curing kinetics of aminophenol epoxy resin/2,4-diamino-4′-methylazobenzene system is studied in isothermal experiments by means of differential scanning calorimetry (DSC). The structural changes occurring during the cure reaction are investigated by Fourier transform infrared spectroscopy (FTIR). Thermal stability characterized by the temperature of 5 and 10% weight loss and residue at 1000 °C of the cured product is studied by thermogravimetric analysis (TGA). Amorphous character of the cured material is determined using X-ray spectroscopy. The preliminary investigations of optical grating recording are carried out.     

Synthesis and nonlinear optical properties of soluble fluorinated polyimides containing hetarylazo chromophores with large hyperpolarizability

The novel fluorinated polyimides with side-chain nonlinear optical (NLO) chromophores were synthesized from hydroxyl polyimides, followed by the Mitsunobu reaction with NLO chromophores. Molecular structural characterization for the resulting polymers was achieved by ¹H NMR, FT-IR, UV-Vis spectra, elemental analysis and gel permeation chromatography (GPC). The polymers exhibit excellent solubility in common organic solvents, good film-forming properties, high glass transition temperature (T_g) in the range from 193 to 200 °C and thermal stability up to 290 °C. The polyimides P1 and P2 containing hetarylazo chromophores with large hyperpolarizability possess a high electro-optic (EO) coefficient (r₃₃), which is larger than that of the polyimide P3 attached DR1. Excellent temporal stability and low optical losses in the range of 1.9-2.1 dB/cm at 1.55 μm were observed for these polymers. Such new NLO fluorinated polyimides are distinguished by an excellent combination of NLO activity, temporal stability, and optical loss.     

新型有机非线性光学材料的制备及性能研究

合成了一种新型含呋喃共轭桥的有机二阶非线性光学生色团分子,用IR、1H-NMR和元素分析表征了其结构。热失重分析(TGA)结果表明,化合物的热分解温度为272℃。利用溶致变色法对材料的超极化率μβ值进行了测量,在1 064 nm激光波长下,材料的μgβ值达24 898×10-48esu。将材料作为客体掺杂于聚砜(PSU)中,用旋涂成膜法制成薄膜,对薄膜进行电晕极化后用二次谐波法(SHG)测量其二阶非线性光学系数d33,在激光基频波长为1 064 nm时,测得d33=70 pm/V。     

Natural and non-natural antenna chromophores in the DNA photolyase from Thermus thermophilus

X-ray crystallographic and functional analysis of the class I DNA photolyase from Thermus thermophilus revealed the binding of flavin mononucleotide (FMN) as an antenna chromophore. The binding mode of FMN closely coincides with the binding of a deazaflavin-like chromophore in the related class I DNA photolyase from Anacystis nidulans. Compared to the R46E mutant, which lacks a conserved arginine in the binding site for the antenna chromophore, the FMN-comprising holophotolyase exhibits an eightfold higher activity at 450 nm. The facile incorporation of the flavin cofactors 8-hydroxy-deazariboflavin and 8-iodo-8-demethyl-riboflavin into the binding site for the antenna chromophore paves the way for wavelength-tuning of the activity spectra of DNA photolyases by using synthetic flavins.     

Enhanced Two‐Photon Absorption of Organic Chromophores: Theoretical and Experimental Assessments

Functional organic materials with enhanced two‐photon absorption lead to new technologies in the fields of chemistry, biology, and photonics. In this article we review experimental and theoretical methodologies allowing detailed investigation and analysis of two‐photon absorption properties of organic chromophores. This includes femtosecond two‐photon excited fluorescence experimental setups and quantum‐chemical methodologies based on time‐dependent density functional theory. We thoroughly analyze physical phenomena and trends leading to large two‐photon absorption responses of a few series of model chromophores focusing on the effects of symmetric and asymmetric donor/acceptor substitution and branching.     

Selective Triplet–Singlet Förster-Resonance Energy Transfer for Bright Red Afterglow Emission

Förster-resonance energy transfer (FRET_T-S) from the lowest excited triplet state (T₁) of a donating sensitizer to a fluorescence acceptor can be used to obtain bright room-temperature afterglow emission at long wavelengths. However, the energy transfer from the lowest excited singlet state of the donor to the acceptor is an undesirable deactivation pathway that prevents FRET_T-S. Herein, heteroatoms in chromophores are shown to allow selective and efficient FRET_T-S for enhanced triplet emission for bright room-temperature afterglow emission at long wavelengths. Different transition characteristics between the lowest singlet excited state and triplet states in heteroatom-containing chromophores accelerate triplet generation, enabling near-zero fluorescence yields. Out-of-plane vibrations of the heteroatoms in aromatic fused rings greatly enhance the radiative rate from T₁ by a factor of 88 relative to non-heteroatom-containing fused chromophore. The compatibility of the near-zero fluorescence and the enhanced triplet emission in a heteroatom-containing fused chromophore enable selective and efficient FRET_T-S pathways, resulting in room-temperature red afterglow emission with a yield of 17%. The bright emission at long-wavelengths allows distinguishable, multiple spectral signals in ambient white light.