Wavelength dependence of first molecular hyperpolarizability of a dendrimer in solution

Abstract

The frequency dependence of the first molecular hyperpolarizability of a dendrimer incorporated with thiophene-stilbene based charge-transfer chromophores is investigated by using a nanosecond 1907 nm laser and a number of wavelengths ranging from 1160 to 1760 nm emitted from an optical parametric amplifier pumped by a 1 kHz 130 fs Ti:sapphire laser. The measured hyperpolarizabilities are compared with those calculated from the charge-transfer absorption spectrum involving a Kramers-Kronig transformation scheme. The Kramers-Kronig transformation analysis provides a satisfactory account of the dispersion of the first molecular hyperpolarizability over the entire excitation wavelength range measured. The Kramers-Kronig technique extends the Oudar-Chemla two-level model previously proposed for the first molecular hyperpolarizability and it can be used in the nonresonance as well as the resonance region where the Oudar-Chemla model fails. The Kramers-Kronig transformation scheme allows a consistent intrinsic hyperpolarizability beta(0) to be obtained from the measured beta(HRS) using different excitation wavelengths for the dendrimer. The comparison of beta(0) for the dendrimer, which contains three chromophores, with that of corresponding monomer chromophore suggests that the chromophores inside the dendrimer are independent. This gives the evidence of the site isolation effect of the dendrimer and substantiates the larger macroscopic optical nonlinearity recently obtained for the dendrimer.

Synthesis, linear & non linear optical (NLO) properties of some indoline based chromophores

“…Lastly, there is a significant difference in the observed molecular response for compound 7 when values obtained in chloroform at 1300 nm (b 0 , 90 Â 10 À30 esu) are compared to those obtained at 800 nm (b 0 , 815 Â 10 À30 esu). The dependence of the molecular hyperpolarizability on wavelength is a known phenomenon [34]. The low static hyperpolarizability value found for 7 at 1300 nm reflects the fact that the magnitude of b 0 decreases the closer the two photon absorption wavelength (viz.…”

Observing Second‐Order Nonlinear Optical Properties by Symmetry Breaking in Centrosymmetric Furan‐Containing Oligoaryl Cyclophandienes

“…To obtain b from the HRS measurement, the external reference method was adopted and used a reliable standard b HRS value to serve as an external reference. [24] Since disperse red-1 (DR1) has been shown to follow the Oudar-Chemlas two-level model (TLM) [25] at off-resonance region and has a b value of 22.7 10 À30 esu at 1907 nm, the b value of DR1 at 1320 nm was used as the reference standard (37.1 10 À30 esu). Each compound was measured by using chloroform or cyclohexane as the solvent, and the concentration was in the range of 10 À6 -10 À8 m. In the dilute concentration limit, the HRS intensity (I 2w ) is proportional to the square of the intensity of the fundamental beam and is related to molecular parameters as shown in Equation (1) …”

“…[24] A fundamental laser source with a wavelength at 1320 nm was generated by an OPA pumped by a kHz Ti:sapphire regenerative amplifier system (Spectra Physics OPA-800 and Hurricane). The intensity was controlled by a half-wave plate followed by one polarizer such that no intensity change due to damaged sample was observed.…”

Synthesis, thermal and light absorption properties of push-pull azochromophores substituted with dendronizing phenyl and perfluorophenyl fragments

“…The more interesting ones are molecular glasses based on dendrimers of chromophores and on the reversible self-assembly of chromophores [10]. The chromophore molecule modification by dendritic substituents [11][12][13][14] or simultaneously both phenyl and perfluorophenyl moieties [15,16] improve material properties. These dendritic substituents increase solubility and macroscopic nonlinearity [4,9,[11][12][13][14]17] via stabilization of chromophore alignment in amorphous phase.…”

“…The chromophore molecule modification by dendritic substituents [11][12][13][14] or simultaneously both phenyl and perfluorophenyl moieties [15,16] improve material properties. These dendritic substituents increase solubility and macroscopic nonlinearity [4,9,[11][12][13][14]17] via stabilization of chromophore alignment in amorphous phase. Fluoroaromatic parts being together with aromatic moieties increase glass transition temperature and thermal stability [4,9], because of the self-assembly in stacks owing to arene-perfluoroarene (Ar-Ar F ) π-π interactions [15,[18][19][20][21][22], and that can lead to increased electro-optical coefficients [18][19][20].…”