Previously we have reported a series of perylene dimide (PDI) dimers as efficient solution-processible small molecule acceptors. In this paper we present a new solution-processible PDI trimer with triphenylamine as the romatic bridge. This trimer was synthesized by Suzuki coupling reaction and fully characterized with 1H-NMR, 13C-NMR, TOF-MS, and elementary analysis. It exhibits a broad absorption band in the wavelength range from 450 to 650 nm with a peak round 533 nm and a maximum extinction coefficient of 9.61 × 104 M-1 cm-1. Its lowest unoccupied and highest occupied molecular orbit (LUMO and HOMO) energies are −3.75 and −5.60 eV. When blend with the commercial P3HT, it gives an open-circuit voltage (Voc) of 0.73 V, a short-circuit current-density (Jsc) of 0.60 mA/cm2, a fill-factor (FF) of 51.0% and an efficiency of 0.22%. When utilizing the conjugated polymer of PBDTTT-C-T as the donor and 5% DIO as the additive, the best conventional cell yields 1.82% efficiency with a Voc of 0.99 V, a Jsc of 3.44 mA/cm2, and an FF of 53.0%.
Organic materials with large two-photon absorption are desired for numerous photonics applications, such as optical limiting,upconversion lasing, three-dimensional data storage,and photodynamic therapy. Stilbazolium derivatives are interesting two-photon absorbers for these applications. In this work,the nonlinear transmissivities of trans -4-[4-(dimethylamino)styryl ]-1-methylpyridinium iodide (DASPI),trans -4-(4-aminostyryl)-1-methylpyridinium iodide (ASPI),trans -4-[2-(1-methylpyrryl)vinyl ]-1-methylpyridinium iodide (MPVPI),trans -4-(2-pyrrylvinyl)-1-methylpyridinium iodide (PVPI),and trans -4-styryl-1-methylpyridinium iodide (SPI)at 800,850,900,950 and 1000 nm have been studied respectively using 21 ps laser pulses. The two-photon induced fluorescence of these compounds at 872,900,and 940 nm has also been investigated.All of these compounds exhibit two-photon absorption and two-photon induced up-converted fluorescence in the near-IR wavelengths,and the two-photon absorption cross section and
two-photon induced fluorescence intensity vary with the wavelength and with the chemical structure changes. These preliminary results suggest that it is possible to increase the two-photon absorption cross-sections by proper structure modifications
Strong three-photon absorption (3PA) and the frequency up- conversion fluorescence induced by 3PA in two novel stilbazolium-like dyes containing triple conjugated bridge have been observed, pumped with 35 ps laser at 1064 nm. The maximum fluorescence peaks are located in the 550, 610 and 700 nm respectively. The emission intensity dependence for the visible emissions on the 1064 nm excitation obeys the cubic law. A local emission (LE) of the donor moiety, excited intramolecular charge transfer state (ICT) and twisted intramolecular charge transfer state (TICT) are response for the multiple fluorescence emissions. The nonlinear transmitted intensity dependence on the laser incident intensity has been demonstrated as a main result referred to three-photon absorption in a 1-cm-path sample quartz cell with solute dissolved in dimethyl sulfoxide (DMSO) at 1064 nm, from which the calculated nonlinear absorption coefficient inferred from three-photon absorption fitted curve are (alpha) 3 equals 4.3 and 3.2 X 10-21 cm3/W2 and the corresponding molecular three-photon absorption cross sections are (sigma) 3 equals 1.9 and 1.6 X 10-76 cm6(DOT)s2, respectively. The optical limiting performances induced by 3 PA have been also performed and discussed for both dyes in DMSO.
Stilbazolium derivatives are very attractive nonlinear optical (NLO) materials for photonics and biophotonics applications due to their low linear absorption at low incident intensities in most of the visible spectral range and potentially very strong nonlinear absorption at high intensities. In this work, we investigated the nonlinear absorption of five stilbazolium derivatives, trans-4-[2-(pyrryl)vinyl]-1-methylpyridinium iodide (PVPI), trans-4-[2-(1-ferrocenyl)vinyl]-1-methylpyridinium iodide (FcVPI), trans-4-[2-(1-ferrocenyl)styryl]-1-methylpyridinium iodide (FcSPI), trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (DASPI) and trans-4-(4-aminostyryl)-1-methylpyridinium iodide (ASPI) using 6 ns and 40 ps laser pulses at 532 nm. These compounds exhibit different nonlinear absorption behavior for nanosecond and picosecond laser pulses. In the nanosecond time regime, they all show reverse saturable absorption, with PVPI exhibiting the best result. With 90% linear transmission in a 2-mm cell, the transmittance of a chloroform solution of PVPI drops to 5% when the incident fluence is increased to 7 J/cm2. The nonlinear absorption behavior of these compounds is influenced dramatically by the nature of the electron donating group, with reverse saturable absorption decreasing in the order of PVPI>FcVPI>FcSPI>ASPI>DASPI. In contrast, for picosecond laser pulses, only PVPI exhibit slight reverse saturable absorption, while DASPI, FcVPI and FcSPI show saturable absorption, and ASPI shows no nonlinear absorption. The different nonlinear absorption for ns and ps laser pulses may be due to the relative contributions from triplet excited state absorption and singlet excited state absorption.
The optical nonlinearity of (TBA)2Ni(dmit)2 (TBA = tert-n-butanyl-amonimium, dmit = 1,3-dithiol-2-thione-4,5-dithiolate) at high incident irradiance was investigated using Z-scan technique with 1064 nm picosecond laser pulses. This molecule shows a strong absorption band ranging from 900 to 1600 nm. Under excitation by 1064nm laser pulses, this molecule exhibits typical saturable-absorption (SA) due to this transition, and shows a negative third-order contribution to nonlinear refraction (NLR). This result indicates that it shows a third-order self-defocusing. In addition, a positive fifth-order contribution to NLR, and the influences of aggregation and high excited-state absorption on nonlinear absorption were also observed in this molecule.
We have studied the solvent effects on the molecular first hyperpolarizabilities of the R-4-(N-methyl-pyridinio)- stilbazolium iodide dyes determined by solvatochromism and those of p-nitroaniline and 1-anilinonaphthalene-8-sulfonic acid determined by using HRS techniques, and observed that they are in a linear correlation with the modified reaction field function, a[L((epsilon) )r-bL(n2)] + gETN, with high correlation coefficient ((gamma) >=0.950) in nonselected solvents, in which all of the points are divided into two groups and can be fitted to form two lines which intersect at one point for each compound. From the ordinate of the intersection, the intrinsic molecular first hyperpolarizabilities for each compound in pure solid state can be estimated, according to the hypothesis of the equal energy levels of the polarized surrounding molecules (solute or solvent) to influence on the solute molecule both in solid state and in some solution systems. Therefore we developed a simple experimental method for determining the intrinsic first hyperpolarizabilities of the stilbazolium- like dyes, which excludes the solvent effects.
Stilbazolium-like dyes, which contain different heterocyclic groups as electron donors and an N-methylpyridinium iodide group as an electron acceptor, are very interesting optical limiting materials. These materials exhibit low linear absorption, but potentially very strong nonlinear absorption at high intensities. In this paper, the results from investigations of the third-order susceptibilities and nonlinear refractive indices of a stilbazolium-like dye, trans-4-[2-(pyrryl)vinyl]-1-methylpyridinium iodide (PVPI), in different solvents using degenerate four wave mixing (DFWM) and Z-scan techniques with 6.8 ns laser pulses at 532 nm are reported. The molecular second-order hyperpolarizability of PVPI increases from 1.6x10-31 esu in methanol to 3.4x10-29 esu in chloroform, a factor of 212. The third-order nonlinearity of this compound is dominated by nonlinear absorption, which leads to strong optical limiting of nanosecond laser pulses. The strength of the optical limiting is dramatically influenced by the solvent used, with limiting decreasing in the order chloroform>dichloromethane, 1,2- dichloroethane>methanol, acetonitrile. While both nonlinear absorption and nonlinear scattering contribute to the optical limiting, nonlinear absorption is the dominant mechanism.
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