Synthesis, electronic, and electro-optical properties of emissive solvatochromic phenothiazinyl merocyanine dyes.

Phenothiazinyl merocyanine dyes with variable substitution patterns on the peripheral benzene ring were synthesized in good yields by Knoevenagel condensation of the corresponding phenothiazinyl aldehydes and N-methylrhodanine or indan-1,3-dione. The electronic properties were investigated by cyclic voltammetry, absorption, electro-optical absorption, and emission spectroscopy. All these merocyanines reveal reversible redox behavior that stems from the phenothiazinyl-centered oxidation to give stable radical cations. The redox potentials strongly correlate with Hammett σ(p) parameters. All merocyanines reveal large Stokes shifts. They also display a pronounced emissive solvatochromism, which is caused by large dipole moment changes upon excitation from the ground to the excited state. These findings are supported by solvatochromism studies and time-dependent DFT computations.

Second-order nonlinear optical activity of dipolar chromophores based on pyrrole-hydrazono donor moieties.

A series of highly efficient and thermally stable second-order nonlinear optical (NLO) dipolar donor-auxiliary donor-acceptor chromophores have been synthesised in which a hydrazono group and a pyrrole ring act as donor and auxiliary donor components, respectively, in combination with different aromatic and heteroaromatic acceptors. The new dyes have been systematically investigated by NMR spectroscopy, absorption spectroscopy, NLO measurements and thermal stability studies. NLO properties have been studied in detail by electro-optical absorption (EOA) and hyper-Rayleigh scattering (HRS) measurements in 1,4-dioxane and DMSO, respectively. The results originating from the two different methods have been compared and analysed in detail. We found that the NLO properties measured by the EOA and HRS methods correlate with each other and converge to reveal the dye with the acceptor 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran as the most efficient system. The unprecedented combination of a strong donor hydrazono group and the auxiliary donor effects of pi-excessive heteroaromatic rings afforded NLO chromophores with very high values (mu(g)beta0(EOA) up to 2038 x 10(-48) esu and beta(HRS) up to 3980 x 10(-30) esu at 1.5 microm).

Three-branched dendritic dipolar nonlinear optical chromophores, more than three times a single-strand chromophore?

To elucidate the dependence of the nonlinear optical (NLO) response on the conformation of triply branched derivatives, a new series of D-pi-A dendrimers has been synthesized. A combined approach of experiments (UV-vis and EOA measurements) and computational predictions (semiempirical and ab initio) was applied both on the dendrimers and on the corresponding single-strand chromophores. It has been shown that depending on the surrounding media the NLO activity of a flexible dendrimer can be very different. Two limiting cases are proposed: (i) the dendrimer resembles a solution of the corresponding single-strand chromophores with about 3-fold concentration, where the hyperpolarizability is the sum of the effect of three noninteracting single-strand subunits ("independent chromophores" limit); (ii) the dendrimers show nearly parallel or helical alignments of the single-strand subunits. Because of this change of conformation the NLO activity can be enhanced up to nine times the value of the "independent chromophores" limit and, thus, are more than a single strand chromophore. Conformers of dendrimers with interacting single-strand chromophores have been identified experimentally in nonpolar solutions by the EOA spectroscopy and possible structures have been revealed by numerical calculations, which could moreover show the tendency of the effects on the hyperpolarizability due to structural changes of the flexible dendritic architecture. Implications for future research developments are given to implement the "more than three times" concept.

CD and ACD spectroscopy on anisotropic samples: chirality of oriented molecules and anisotropic phases--a critical analysis.

Chiral anisotropic phases exhibit an elliptical birefringence and dichroism instead of the circular effects of isotropic dissymmetric and the linear effects of achiral anisotropic phases. Therefore, techniques to determine chiral effects of chiral anisotropic phases yield not always results of chirality measurements, namely, pseudoscalar quantities. From definitions for a chirality measurement with non-oriented and oriented macroscopic anisotropic phases procedures are derived by which the pseudoscalar contribution included in the elliptical birefringence and dichroism can be obtained. Within this description the CD of chiral microcrystallites, isotropically distributed in pressed KBr plates or in Nujol, is a chirality measurement. With an excess of anisotropic distributed material in pressed KBr plates or, in general, with oriented macroscopic anisotropic phases, the ACD is no longer a pseudoscalar. An achiral information is included in the ACD which is not an artifact obtained by the mixing of "circular and linear effects" via nonideal optical elements in a CD spectrometer.

Chirotopical properties of cisoid enones from circular dichroism (CD) and anisotropic circular dichroism (ACD) spectroscopy.

Substituted cisoid 4-en-6-one steroids with isotropically distributed and partially oriented molecules were analyzed by circular dichroism (CD) and anisotropic circular dichroism (ACD) spectroscopy, respectively. CD and ACD data supplement their respective phenomenological information. For a series of C3-substituted enones 1 to 7, the difference of CD (Delta epsilon) and ACD (Delta epsilon(A)) values, that is, Delta epsilon -Delta epsilon(A), vary in the n-* transition region in the same direction, independently of the nature and position (3 alpha or 3 beta) of the substituent. For 7-bromo-substituted enones 5 and 6 the sign of the n-pi* CD band is opposite to that predicted by the enone helicity rule. The ACD data indicate that this behavior is a consequence of the effect of vibronic coupling caused by the 7-bromo substituent. In contrast to the results obtained for the series of C7-unsubstituted compounds 1 to 4, the intensity of the CD bands for 5 and 6 is determined by the vibrational progressions of a different symmetry. Therefore, the helicity rule must fail in both cases because the rule can only be applied to those vibrational transitions for which the rule was developed. The sign of the coordinates Delta epsilon(*)(II), estimated from the ACD data, yields additional stereochemical information that cannot be obtained from the CD data alone. The CD and ACD spectra in the region of the pi-pi* transition vary for enones 1 to 4 in a different fashion and indicate dependence upon spatial orientation (3 alpha or 3 beta) of substituents. This dependence may lead to the possibility of extracting additional stereochemical information from the ACD spectra. Furthermore, the experimental findings indicate that the second CD band located at about 220 nm belongs to a forbidden transition and not to an allowed pi-pi* transition.