Spontaneous in situ thermal growth of oriented acentric nanocrystals of [(E)-N,N-dimethylamino-N′-methylstilbazolium][p-toluenesulfonate] embedded in a PMMA film on ITO generating stable SHG

Abstract

A poly(methyl methacrylate) (PMMA) composite film containing 4 wt% of the strongly second order NLOdeposited on an ITO substrate shows by a two step process (electric poling followed by controlled thermal annealing) a nonlinear optical coefficient d 33 higher than the one obtained on a glass substrate.This higher value is the result of a polar order induced on the dye-doped polymeric film at the ITO-film interface, indicating that the polarity of the ITO surface is relevant in controlling the orientation process.By exploiting such induced polar order, oriented dipolar acentric nanocrystals of DAST can be grown in situ by solely and careful annealing, thus avoiding the detrimental effects often induced by the presence of a strong electric field. This leads not only to a spontaneous one step process of self-orientation but also to a better second order NLO response. In addition, different thermal pretreatments of ITO itself can induce different SHG responses from the DAST/PMMA films, the highest response being observed by preheating the ITO substrate at 370 C for 24 hours.

Tunable Chiral Second-Order Nonlinear Optical Chromophores Based on Helquat Dications

“…Electronic Spectroscopy. All of the new Hq salts [1][2][3][4][5][6][7][8][9][10][11][12][13][14][TfO] 2 appear strongly colored due to an intense absorption in the near-UV/visible region. This feature is attributable to intramolecular charge-transfer (ICT), as confirmed by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations (see below).…”

“…Following many years of basic research, a notable development regarding organic materials was the commercialization of the salt (E)-4ʹ-(dimethylamino)-N-methyl-4-stilbazolium tosylate (DAST). [9][10][11][12][13][14] Crystals of DAST can be used to generate terahertz (THz) frequencies by nonlinear mixing of two laser beams. THz radiation has many uses, e.g.…”

“…Figure 1) 28,29,31 in MeOH at room temperature with pyrrolidine as catalyst. They were all isolated as their bistriflate salts and characterized by 1 H/ 13 C NMR spectroscopy (see the Supporting Information, Figures S1-S14), elemental analyses and +electrospray mass spectrometry. [6][TfO] 2 were characterized structurally by singlecrystal X-ray diffraction, and views of these compounds are shown in Figure 2.…”

“…UV-vis absorption spectra of the Hq salts [10][TfO] 2 (gold), [13][TfO] 2 (red), [17][TfO] 2 (blue) and [18][TfO] 2 (green) in MeCN at 293 K; note the red-shifts of the visible band as the π-conjugated system extends on moving from 10 to 13 or from 17 to 18, and the relative constancy of the absorption in the 350-400 nm region. [10][11][12][13][14][TfO] 2 , obtained from (4.32 × 10 -9 M cm 2 )A where A is the numerically integrated area under the absorption peak; for [4][5][6][7][8][9][TfO] 2 , obtained from (4.60 × 10 -9 M cm 2 )ε max × fw 1/2 where ε max is the maximal molar extinction coefficient and fw 1/2 is the full width at half height (in wavenumbers). d Calculated from eq 1. e Calculated from f int Δµ 12 by using f int = 1.33. f Calculated from eq 2; for [4][5][6][7][8][9][TfO] 2 , the total values are given in brackets.…”

“…g Obtained from HRS measurements with a 800 nm Ti 3+ :sapphire laser and MeCN solutions at 293 K. h Derived from β 800 by application of the two-state model. 36 35 to determine resonant β values for [1][2][3][4][5][6][7][8][9][10][11][12][13][14][TfO] in MeCN, and β 0 values have been estimated by using the two-state model. 36,37 The results are listed in M06, 44 or CAM-B3LYP.…”