| With the development of lasers and synthesization of novelnonlinear optical materials, people begin to study on nonlinear optics,especially multi-photon process. Two-photon technic has achieved agreat progress in recent decades. The great developments largelypromoted nonlinear optics in the following directions: templatefluorescence and up-converted lasing ( UCL ) , optical limiting,two-photon fluorescence microscopy, three-dimensional optical datastorage and two-photon absorption micro-fabrication. For two-photonpumped UCL application, the large two photon emitting cross sectionand high chromophore density (c) are required, namely thefluorescence intensity of UCL is proportion to the value ηδc. The resource of this work is fs laser. The sample is 1,4-di (4'-N,N-diphenylaminostyryl) benzene (DPA-DSB) and 2,5,2',5'-tetra (4'-N,N-diphenylaminostyryl)biphenyl(DPA-TSB), we studied the two-photonabsorption characteristic of the sample, summarized the relation of thestructural and characteristic. We measured two-photon absorptioncross sections, for explore new material. The content of this paper is:1. linearity optics characters of the sampleThe absorption and emission spectra of two oligomers and thedetails were tabulated in Table 1. Both compounds showed the similaroptical absorption (λabs = 410 nm for DPA-DSB and 417 nm forDPA-TSB) and emission(λexm = 466 nm for DPA-DSB and 477 nm for DPA-TSB) insolutions, but significant different in solid fluorescent emissionproperties. Firstly, the emission spectrum of DPA-TSB in film showedrelatively smaller shift (peak-peak difference of 33 nm) compared toits diluted solution, while the spectra shift of DPA-DSB crystal wasabout 61 nm. Secondly, DPA-TSB exhibited bright greenlight-emission with a high solid-state PL efficiency of about 39 %,which is significantly higher than the efficiency of DPA-DSB (16 %)in solid states.2. measurement of fluorescence quantum effciencyFor obtain the two-photon absorption cross sections, we mustmeasure fluorescence quantum efficiency.3. Two-photon absorption character and two-photon absorptioncross sections of the sampleThe peak position of the two-photon excitation spectrum ofDPA-TSB was at 745 nm, which was very similar to its monomerDPA-DSB (743 nm). Meanwhile, as same to single photon excitation(SPE) spectra, the two photon excitation (TPE) peak position of thedimmer were 12 nm red shift to that of the monomer, which indicatedthat the main transition dipoles didn't change in TPEF from singlephoton excited fluorescence (SPEF). According to the results oftheoretical simulation and NMR experiment, there were 12 both planarand twisting conformations of DPA-DSB moieties in a DPA-TSBmolecule. But both TPE and SPE peak of DPA-TSB were red shift tothe monomer, it was unambiguous evidence that the biphenyl centercan effectively implemented as a conduit for charge transfer betweenlinear subunits. The peak cross section was up to 3288 GM at thewavelength almost twice of the one-photon peak, which wasapproximately four times to that of its monomer (940 GM). Thislarge value of δ mainly resulted from the three-dimensionaltetra-donor substituted biphenyl chromophores in the correspondingoligomer system.4. The two-photon absorption characters of the solid state sampleMeanwhile, being benefit from its high efficiency both in solutionand in solid state, the two-photon emitting cross section (ηδ) ofDPA-TSB was located at relatively high level: δηsolution=2006GM, and especially δηsolid = 1282 GM. Such value of δηsolidhad a remarkable enhancement compared to that of DPA-DSB (about150 GM in solid state). Considering the fluorescence intensity of UCLis proportion to the value ηδc, the new dimer, with high efficiencyin solid state and good TPA characteristics, has exhibited greatpotentials for actual application in solid-state two-photon emittingfluorescence. Actually, as the spin-coating DPA-TSB film excited byan 800 nm laser, the green fluorescence is bright enough to be seen bynaked eye.
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