Synthesis and photonics of polyfunctional conjugated polyenes

Methods for the synthesis of various types of polyfunctional conjugated polyenes based on aminals of unsaturated -amino aldehydes are surveyed. The influence of the interaction of chromophores on the photophysical properties of polyene bis(amino)-substituted ketones and polymethine salts based on them as well as on the properties of absorption and fluorescence spectra of the cation-anionic polymethine dyes are considered.     

Surface Conductivity of DR1-Functionalized Organic-Inorganic Sol-Gel Materials

In recent years, in looking for an important photorefractive application, several studies on electro-optic and photoconductive sol-gel responses have been done. A very important effort has been addressed to establish the appropriate induced-orientation procedure, in order to get the highest electro-optic coefficient. In this way a very high coefficient of 48 pm/V at 831 nm in sol-gel has been already found. Similarly, the importance of the non-linear chromophore concentration into the material electro-optic behavior has been studied. However, the influence of the orientation procedure and the chromophore concentration over the photoconductive response has not been performed. In this work we study the vacuum-surface-charge-transport under and without illumination after poling times of 10, 30 and 120 min on DR1-functionalized sol-gel thin films of 1.3 m in thickness with a suitable concentration of DR1. We include the measures before poling for other chromophore concentrations. We found the largest density of photocurrent at 633 nm for a poling time of 30 min. We also measured the order parameter in order to follow the Corona induced orientation evolution as function of time for each case. The saturation found into this parameter and into the photoconduction show the existence of an optimal poling time.     

Nonlinear optical constants of polymers from molecular hyperpolarizabilities of donor–acceptor molecules

A mathematical analysis previously developed to solve the quadratic tensor equations that relate molecular hyperpolarizability and bulk medium nonlinear optical constants is applied to donor–acceptor polyene molecules. The focus is on mutual polarization of spatially organized collections of molecules, e.g., chromophore side chains in an optical polymer. The performance of the electrostatic model is first confirmed by comparison with MOPAC calculations of composite molecules containing a pair of chromophores, and then applied to linear polymer chains as well as lattices in two and three dimensions. An optimal chromophore packing density is determined to maximize the macroscopic susceptibilities of polymer materials of the type studied. This is lower than the density allowed by the structure of the polymer, because of the mutual depolarization of chromophores at high packing densities. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Electronic excitations of the green fluorescent protein chromophore in its protonation states: SAC/SAC-CI study

Two ground-state protonation forms causing different absorption peaks of the green fluorescent protein chromophore were investigated by the quantum mechanical SAC/SAC-CI method with regard to the excitation energy, fluorescence energy, and ground-state stability. The environmental effect was taken into account by a continuum spherical cavity model. The first excited state, HOMO-LUMO excitation, has the largest transition moment and thus is thought to be the source of the absorption. The neutral and anionic forms were assigned to the protonation states for the experimental A- and B-forms, respectively. The present results support the previous experimental observations.     

兼具大的二阶光学非线性与良好透明性的有机生色团的分子设计进展

从采用特殊的共轭桥、寻求给受体强度的最佳组合及设计双（多）重电荷转移 分子三方面，综述了近几年来在兼具较大分子一阶超极化率与良好透光范围的有机 二阶非性光学生色团的研究进展。     

Controlling Light-Induced Proton Transfer from the GFP Chromophore

Green Fluorescent Protein (GFP) is known to undergo excited-state proton transfer (ESPT). Formation of a short H-bond favors ultrafast ESPT in GFP-like proteins, such as the GFP S65T/H148D mutant, but the detailed mechanism and its quantum nature remain to be resolved. Here we study in vacuo, light-induced proton transfer from the GFP chromophore in hydrogen-bonded complexes with two anionic proton acceptors, I⁻ and deprotonated trichloroacetic acid (TCA⁻). We address the role of the strong H-bond and the quantum mechanical proton-density distribution in the excited state, which determines the proton-transfer probability. Our study shows that chemical modifications to the molecular network drastically change the proton-transfer probability and it can become strongly wavelength dependent. The proton-transfer branching ratio is found to be 60 % for the TCA complex and 10 % for the iodide complex, being highly dependent on the photon energy in the latter case. Using high-level ab initio calculations, we show that light-induced proton transfer takes place in S₁, revealing intrinsic photoacid properties of the isolated GFP chromophore in strongly bound H-bonded complexes. ESPT is found to be very sensitive to the topography of the highly anharmonic potential in S₁, depending on the quantum-density distribution upon vibrational excitation. We also show that the S₁ potential-energy surface, and hence excited-state proton transfer, can be controlled by altering the chromophore microenvironment.     

Quantification of the push-pull character of the isophorone chromophore as a measure of molecular hyperpolarizability for NLO applications

The push-pull character of a series of para-phenyl substituted isophorone chromophores has been quantified by the ¹³C chemical shift difference of the three conjugated partial CC double bonds and the quotient of the occupations of both the bonding and anti-bonding orbitals of these CC double bonds as well. The correlations of the two push-pull quantifying parameters, and to the corresponding bond lengths, strongly recommend /π_CC as the general parameter to estimate charge alternation and as a very useful indication of the molecular hyperpolarizabilities for NLO application of the compounds studied.     

Electronic Substitution Effect on the Ground and Excited State Properties of Indole Chromophore: A Computational Study**

Indole, being the main chromophore of amino acid tryptophan and several other biologically relevant molecules like serotonin, melatonin, has prompted considerable theoretical and experimental interest. The current work focuses on the investigation of substitution effect on the ground and excited electronic states of indole using computational quantum chemistry. Having three close-lying excited electronic states, the vibronic coupling effect becomes extremely important yet challenging for the photophysics and photochemistry of indole. Here, we have evaluated the performance of time-dependent density functional theory against available experimental and ab initio results from the literature. The electronic effects on the excited states of indole and indole derivatives e. g. tryptophan, serotonin and melatonin are reported. A bathochromic shift has been observed in the absorption spectrum for the L_a state. The absorption wavelength increases in the order of indole<tryptophan <serotonin <melatonin. While the contribution of the in-plane small adjacent groups increases the electron density of the indole ring, the out-of-plane long substituent groups have minor effect. The absorption spectra calculated including the vibronic coupling are in good agreement with experiments. These results can be used to estimate the error in photophysical observables of indole derivatives calculated considering indole as a prototypical system.     

Polycyclic aromatic hydrocarbon-substituted push–pull chromophores: an investigation of optoelectronic and nonlinear optical properties using experimental and theoretical approaches

A series of new push–pull chromophores were synthesized in moderate to very high yields (65%–97%) by treating TCNE and TCNQ with alkynes substituted by electron-rich diethylaniline and polycyclic aromatic hydrocarbons. Some of the chromophores exhibit strong intramolecular charge-transfer bands in the near-IR region with λ_max values between 695 and 749 nm. With the help of experimental and theoretical analysis, it is concluded that the trend in λ _max values is affected by PAH substituents sterically, not electronically. Steric constraints led to the increased dihedral angles, reducing conjugation efficiencies. The absorption properties of push-pull compounds have been investigated in solvents possessing different polarities. All chromophores exhibited positive solvatochromism. As an additional proof of efficient charge-transfer in push–pull chromophores, quinoid character (dr) values were predicted using calculated bond lengths. Remarkably, substantial dr values (0.045–0.049) were predicted for donor diethylaniline rings in all compounds. The effects of various polycyclic aromatic hydrocarbons on optical and nonlinear optical properties were also studied by computational methods. Several parameters, such as band gaps, Mulliken electronegativity, chemical hardness and softness, dipole moments, average polarizability, first hyperpolarizability, were predicted for chromophores at the B3LYP/6-31++G(d,p) level of theory. The predicted first hyperpolarizability β_(tot) values vary between 198 to 538 × 10^–30 esu for the reported push–pull chromophores in this study. The highest predicted β_(tot) value in this study is 537.842 × 10^–30 esu, 8150 times larger than the predicted β_(tot) value of benchmark NLO material urea, suggests possible utilization of these chromophores in NLO devices. The charge-transfer character of the synthesized structures was further confirmed by HOMO-LUMO depictions and electrostatic potential maps.     

Preparation and Optical Properties of Novel 3-Alkoxycarbonyl Aza- and Diazacoumarins

A series of 14 new 3-alkoxycarbonyl 6-aza-, 7-aza-, and 6,8-diaza-coumarins was prepared using various strategies involving either a Knoevenagel or a Pechmann condensation reaction. The coumarin nucleus displays different reactive functional groups allowing straightforward derivatization. The optical properties of the new azacoumarins were measured in methanol.