The structures of 3,5-bis[4-(diethylamino)benzylidene]-1-methyl-4-piperidone, C(28)H(37)N(3)O, (I), and 3,5-bis[4-(diethylamino)cinnamylidene]-1-methyl-4-piperidone, C(32)H(41)N(3)O, (II), have been characterized. Because of conjugation between donor and acceptor parts, the central heterocycles (including the carbonyl group) in (I) and (II) are flattened and exhibit a 'sofa' conformation, with a deviation of the N atom from the planar fragment. The dihedral angles between the planar part of the heterocycle and the two almost flat fragments that include a phenyl ring and bridging atoms are 23.2 (1) and 11.2 (1) degrees in (I), and 11.8 (1) and 8.7 (2) degrees in (II). One- and two-photon absorption of light and the fluorescence of (I) and (II) have also been characterized.

We report on two-photon absorption and two-photon excited fluorescence of a selected group of new derivatives of cyclohexanone and piperidone with regard to their molecular structure. The molecular cross-section of the two-photon absorption of these compounds, as high as 3000 × 10-50 cm4 s/photon at nanosecond pumping, makes then promising nonlinear materials for optical limiting in the near-infrared region. They also exhibit an intense two-photon exciting fluorescence. Similar compounds have previously demonstrated strong anticancer effect. Both features combined in a single compound thus open the way for more efficient treatment of cancer, when biochemical destruction of malignant cells is accompanied by their two-photon fluorescent imaging.

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A detailed study was conducted for two-photon absorption of a selected group of new derivatives of cyclohexanone/piperidone with regard to their molecular structure and the feasibility of using these derivatives as nonlinear optical absorbers for optical limiting. Derivatives of cyclohexanone/piperidone have a cross-section of two-photon absorption of the order of 3000 x 10 -50 cm 4 s/photon and compare well against known two-photon absorbers. This makes them promising nonlinear optical absorbers and optical limiters. Their important feature is that the energy is absorbed in the infrared region, where the protection is needed for remote IR sensors and night-vision systems. It is also important that the energy of the dissipated infrared radiation is converted mostly into fluorescence but not into heat that can damage optical limiter.

The dynamics of organic compounds 2-cyclo-octylamino-5-nitropyridine (COANP), (S)-2-N--(methylbenzylamino)-5-nitropyridine (MBANP), 2-(N-prolinol)-5-nitropyridine (PNP), and N-(4-nitrophenyl)-(L)-prolinol (NPP) were studied by dielectric relaxation spectroscopy in the frequency range of 10 Hz-2 MHz and differential scanning calorimetry (DSC). The dielectric and DSC studies showed that COANP, MBANP and PNP underwent glass transition. However, NPP crystallized so rapidly upon cooling that the glass state could not be observed. It was found that the crystalline process of COANP did not slow the structure relaxation of COANP glass. The relaxation times fitted well to the empirical Vogel-Fulcher equation = exp[Ea/kb(T-TVF)]. The activation energies Ea and the Vogel-Fulcher temperature TVF were 54.5 meV and 239 K for COANP, 86.2 meV and 249 K for MBANP and 84.9 meV and 245 K for PNP, respectively. The crystalline temperatures of COANP and MBANP were given as 300 K and 330 K, respectively. An anomalous behaviour of the dielectric permittivity of PNP glass was observed.