Fourier analysis of the femtosecond hyper-Rayleigh scattering signal from ionic fluorescent hemicyanine dyes

Abstract

A series of five fluorescent and ionic dimethylamino stilbazolium homologues with increasing conjugation length (from ethenyl to decapentaenyl) is investigated by high-frequency, amplitude-modulated femtosecond hyper-Rayleigh scattering at 1300 nm. A hyperpolarizability value that is not overestimated by the presence of a multiphoton fluorescence contribution is obtained from the Fourier analysis of the hyper-Rayleigh scattering signal. The demodulation curve (decrease of Fourier amplitude versus modulation frequency) is characterized by both the hyperpolarizability value and the fluorescence decay parameters. The fluorescence decay parameters are accurately determined independently by single-photon counting. A detailed analysis of the fluorescence decay parameters from the hyper-Rayleigh scattering demodulation curve and of their relation to the fluorescence decay parameters obtained from single-photon counting experiments is presented. The inherent hyperpolarizability value for these chromophores shows a maximum of (2045 Ϯ 35) ϫ 10 Ϫ30 esu or (760 Ϯ 13) ϫ 10 Ϫ50 C 3 m 3 J Ϫ2 for the hexatrienyl conjugation length. A comparison with theoretical calculations suggests the importance of trans-cis isomerization in the excited state.

Quadratic Optical Nonlinearities of N‐Methyl and N‐Aryl Pyridinium Salts

“…1 Hyper-Rayleigh Scattering: The apparatus and experimental procedures used for the fs HRS studies with high-frequency demodulation of multi-photon fluorescence were exactly as described previously. [14,17] All measurements were carried out in acetonitrile and the reference compounds were Disperse Red 1 (b 1300 = 86 10 ±30 esu in acetonitrile; from the value of 54 10 ±30 esu in chloroform, corrected for local field factors at optical frequencies) or crystal violet (b 800 = 500 10 ±30 esu in acetonitrile; from the value of 340 10 ±30 esu in methanol, corrected for local field factors at optical frequencies). Dilute solutions (10 ±5 ±10 ±6 M ±1 ) were used to ensure a linear dependence of I 2x /I 2 x on concentration, precluding the need for Lambert±Beer correction factors.…”

“…Because they show multi-photon fluorescence, [1±16]PF 6 were studied via femtosecond (fs) HRS with a 1300 nm laser, incorporating high-frequency fluorescence demodulation. [14,17] Owing to their favourable visible absorption profiles, and in order to obtain further data for comparison purposes, the b values of [5±12]PF 6 were also measured with an 800 nm fs laser. [18] Using an 800 nm fundamental also has the advantage of avoiding any possibility of fluorescence contributions at 400 nm.…”

“…However, the 650 nm HRS signals of the high-energy-absorbing salts [1]PF 6 , [13]PF 6 , and [14]PF 6 , were unfortunately too weak to allow determinations of b. The close proximity of their ICT absorption maxima to 400 nm also precludes meaningful 800 nm HRS results for these salts.…”

“…The N-(2,4-dinitrophenyl) (2, cations in [11]PF 6 and [15]PF 6 were synthesized similarly by S N Ar reactions with 2,4-dinitrochlorobenzene. Further reactions of [11]Cl and [15]Cl with aniline afforded the N-phenyl cations in [10]PF 6 and [14]PF 6 . The precursor to [10±12]PF 6 , trans-4-(4-dimethylaminophenyl-4-buta-1,3-dienyl)pyridine, was synthesized via standard Wittig±Horner chemistry.…”

Preparation, properties and structures of 1-methyl-4-{2-[4-(dimethylamino)phenyl]ethenyl}pyridinium crystals with various counter anions

“…In this connection, anion exchange of DAST is worth investigating to find crystals with larger NLO properties. On the other hand, b can be enhanced by elongation of a pconjugation system of the cation part [14,15]. Even in this case, again anion exchange is important to obtain noncentrosymmetric crystal structures.…”