We have synthesized a novel class of imidazole-based excited-state intramolecular proton-transfer (ESIPT) materials, i.e., hydroxy-substituted tetraphenylimidazole (HPI) and its derivative HPI-Ac, which formed large single crystals exhibiting intense blue fluorescence and amplified spontaneous emission (ASE). Transparent, clear, and well-defined fluorescent single crystals of HPI-Ac as large as 20 mm x 25 mm x 5 mm were easily grown from its dilute solution. From the X-ray crystallographic analysis and semiempirical molecular orbital calculation, it was deduced that the four phenyl groups substituted into the imidazole ring of HPI and HPI-Ac allowed the crystals free from concentration quenching of fluorescence by limiting the excessive tight-stacking responsible for intermolecular vibrational coupling and relevant nonradiative relaxation. Fluorescence spectral narrowing and efficient ASE were observed in the HPI-Ac single crystal even at low excitation levels attributed to the intrinsic four-level ESIPT photocycle.
Multiarmed nonlinear optical (NLO) molecules containing triphenylamine as a core and 4-(2-ethylhexylsulfonyl)benzene-(1E)-2-vinyl group or 4-{2-[4-(2-ethylhexylsulfonyl)phenyl]-(1E)-vinyl}benzene-(1E)-2-vinyl group as arms were synthesized (STEH series and SSEH series, respectively). Because triphenylamine linked to the sulfonylated stilbenic arms provided effective push-pull NLO structure and strong 2-D charge transfer, they were capable of both two-photon absorption (TPA) and photorefraction. Effective TPA cross sections of these molecules were as high as 0.94 × 10 -46 cm 4 ‚s and significantly enhanced as the number of arms and conjugation length increased. One-and two-armed STEH molecules (STEH1 and STEH2) showed moderate two-beam coupling gain coefficients (13.4 cm -1 at 45 V/µm and 17.4 cm -1 at 55 V/µm, respectively) and distinct diffraction efficiency (0.45% at 40 V/µm and 0.55% at 55 V/µm). On the other hand, the centrosymmetric three-armed STEH molecule exhibited no photorefraction at all. It is importantly claimed that the multiarmed bifunctional molecules of this work are easily fabricated into optically clear amorphous films by themselves, which is a key advantage toward potential applications such as solid-state optical limiting devices and two-photon excited photorefractive materials.
Erratum: The cubic susceptibility dispersion of Alkoxynitrostilbene (MONS) and Dialkylaminonitrostilbene (DANS) side chain substituted polymers: Comparison with the twolevel model [J. Chem. Phys. 9 4, 6851 (1991)] J. The cubic susceptibility dispersion of Alkoxynitrostilbene (MONS) and Dialkylaminonitrostilbene (DANS) side chain substituted polymers: Comparison with the twolevel modelThe one-and two-photon optical absorption spectra as well as the frequency dependent third-harmonic generation response of a side-chain polymer containing 4-dialkylamino-4Ј-nitro-stilbene ͑DANS͒ as its side group have been measured over a wide range of frequency. A three-state model, based on an intermediate neglect of differential overlap/multireference double-configuration interaction description of the excited states, provides a coherent picture of the dynamic response of DANS, but fails in reproducing the red shift observed when going from the linear to the nonlinear absorption spectra; including vibronic coupling within the Franck-Condon approximation improves the fit.
A novel scheme for broadband second-harmonic generation was developed with type I quasi phase matching by use of an off-digital nonlinear optical coefficient d(31) . This was achieved by matching of the group velocities of the second harmonic and the fundamental, while the phase velocities were quasi phase matched. The desired group-velocity dispersion could be obtained with LiNbO(3) doped with 5 mol. % of MgO. Efficient second-harmonic generation with a bandwidth of 52 nm was obtained for the fundamental wavelength centered at 1566 nm in MgO-doped periodically poled LiNbO(3) , compared with a bandwidth of 1.3 nm for the conventional scheme using d(33) . Efficient frequency doubling of an ultrafast pulse is expected without group-velocity walk-off or pulse distortion.
Enhanced nonlinear absorption and optical limiting in semiconducting polymer methanofullerene charge transfer films Cha, M.; Sariciftci, N. S.; Heeger, A. J.; Hummelen, J. C.; Wudl, F.
The two photon absorption spectrum has been measured in the 780–1600 nm range for a di-alkyl-amino-nitro-stilbene side-chain polymer. A single two photon peak centered at 920 nm is observed with a peak two photon coefficient of 5.5 cm/GW. Bleaching via two photon absorption at this wavelength is investigated by measuring a refractive index change after an intensive exposure.
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