Here we report the synthesis and physical characterization of four substituted phenylenevinylene molecules, 1-4, which serve as short chain model oligomers of poly(1,4-phenylenevinylene). Quantum mechanical calculations on alkoxy substituted stilbene derivatives 1 and 2 reveal a direct correlation between the torsional angles and the substituent pattern. HOMO and LUMO energy levels were calculated for all four compounds and showed that the introduction of alkoxy substituents reduce the energy gaps between the ground and first excited singlet states of these molecules. In addition, absorption spectra, fluorescence life-times and quantum yield data of the four compounds are presented.
The effect of extending the conjugation length, the deployment of various substituents and configurational locking of the
polyene backbone on the second-order nonlinear optical (NLO) response of a series of indoline based compounds has
been investigated. The compounds were examined using Hyper-Rayleigh scattering (HRS) and relative second-harmonic
generation (SHG) techniques with a femtosecond operating system with a 1300 nm fundamental wavelength. All of the
compounds were found to have high molecular hyperpolarizabilities with β values of up to 1230 × 10<sup>-30</sup> esu. At the
macroscopic level-for poled polymer thin films-a strong second-order NLO signal has been detected and d<sub>33</sub> values of
up to 217 pm/V are found-a response of some ten times greater than that found for the well known azo dye Disperse
The molecular linear and second-order nonlinear optical (NLO) properties of a series of donor (D)-π-acceptor (A)
merocyanine molecules have been studied in three solvents, dimethylformamide (DMF), tetrahydrofuran (THF), and
chloroform (CHCl<sub>3</sub>). All the compounds have a cyanodicyanomethylidenedihydrofuran electron acceptor system with either a pyridinylidene or quinolinylidene donor group. In high polarity solvents the molecules with a quinolinylidene donor have
larger first hyperpolarizabilities than those with a pyridinylidene donor, while the opposite is true in low polarity solvents.
The molecules under investigation have an aromatizable donor unit, which leads to a high degree of charge separation in the
ground-state; as a result they have a strong tendency to aggregate. To minimize these interactions arene-rich bulky groups
have been introduced in a number of these compounds.
Optical and photostability measurements have been made on nonlinear optical films containing amorphous
polycarbonate and an organic chromophore that has a high 2nd order nonlinear optical figure of merit. We show that the
decrease in the photodegradation quantum efficiency with increasing optical intensity can be modelled in terms of
oxygen depletion by oxygen-mediated chomophore photodegradation. The addition of a known singlet oxygen quencher,
beta carotene, leads to a 1100% decrease in the photodegradation quantum efficiency.
Photostability measurements have been made on host-guest films containing amorphous polycarbonate and an
organic chromophore with a high 2<sup>nd</sup> order nonlinear optical figure of merit. We find that the rate of photodegradation
strongly depends on the oxygen partial pressure. At very low oxygen partial pressures (1.4×10<sup>-5</sup> bar) the average number
of photons required to photodegrade a chromophore is as high as 1×10<sup>9</sup> at 655 nm. Encapsulation leads to an initial rapid
decrease in the photodegradation rate due to the trapped oxygen and a gradual photodegradation where 2×10<sup>9</sup> photons
are required to photodegrade a chromophore. There is an anomalous increase and then decrease in the
photoluminescence intensity during ultraviolet irradiation.