Studies of selected organic nonlinear optical and light-emitting materials

In this dissertation, the nonlinear optical and light emitting properties of a selected class of organic materials have been studied in detail. Novel organic molecular salts, 4-dimethylaminostyryl-N-methylpyridinium methanesulfonate (DASMS) and 4-diethylaminostyryl-N-methylpyridinium p-toluenesulfonate (DEST), were synthesized. A few selected stilbazolium derivatives, 3-methyl-4-methoxy-4′-nitrostilbene (MMONS), 4-dimethylaminostyryl-N-methylpyridinium p-toluenesulfonate (DAST), and DASMS were grown into excellent optical quality single-crystal thin-films, on which detailed polarized UV-Vis spectroscopy and X-ray diffraction studies were carried out. The crystallographic parameters of p-nitro-benzobromide (NBB) are reported for the first time. The values of the tensor elements of second-order susceptibility of MMONS at the fundamental wavelength of 1064 nm were measured to be d₃₃ = 195 ± 10 pm/V and d₂₄ = 75 ± 5 pm/V by detailed polarization selective second-harmonic generation measurements. Both type I and type II phase-matched propagation directions were identified in the MMONS single-crystal. The electro-optic effects in MMONS and DASMS single-crystal thin-films were studied using field-induced birefringence method. Measured r-coefficients of MMONS are r₃₃ = 55ρ5 pm/V and r₂₃ = 21ρ2 pm/V at 1064 nm. The electro-optic coefficients of DASMS single-crystal thin-films were measured over a broad range of wavelengths (from 632.8 nm to 820 nm). The largest r-coefficients of DASMS were observed at 740 nm to be r₁₁ = 552ρ60 pm/V and r₁₂ = 184ρ20 pm/V. Compact free-space and fiber-coupled DAST electro-optic thin-film devices with both transmission and reflection geometries were demonstrated for the first time. DEST and 4-(4-hydroxystyryl)-N-methylpyridinium p-toluenesulfonate (HSMPT) were shown to have 20% and 30% spectrally narrowed laser-like emission conversion efficiencies without external mirrors despite their small photoluminescence efficiencies. With 55 ps excitation pulses, DEST emits at 617 nm with 10 nm linewidth and HSMPT emits at 530 nm with 14 nm linewidth. The performance was found superior to most of the commercially available dyes, e.g. R6G, coumarin, DCM, etc. Finally, the enhanced photoluminescence of a novel dithienylbenzo[c]thiophene oligomer due to photo-bleaching was studied in detail. Significant enhancement of photoluminescence, from 9% to 92%, was observed in the material after photo-bleaching occurred. The origin of this bleaching was established by UV-visible and FTIR spectroscopic analyses to be photo-oxidation. Spectral-narrowing was observed in solid films of the bleached oligomer for excitation with 1 nJ, 200 fs pulses at 400 nm.