Benzo and Naphthopyrans (chromenes) have been extensively studied since the discovery of photochromic reaction of 2H-1-benzopyrans in 1966 by Becker and Michl. Researchers have investigated chromenes for their use in sunglass lenses and also other potential applications such as optical memories and optical switches. Femto/picosecond and nano/microsecond experiments were released on two 6,6a-dihydrochromeno(3,4-b)chromene derivatives. After disappearance of the singlet state S1 formed from each compound, photoproducts with short lifetime (2.2 to 21 ?s) obtained were attributed to the open forms. Keywords: 6,6a-dihydrochromeno(3,4-b)chromene, photochromic, nano/microsecond domain, femto/picosecond domain, wavelength, lifetime. 

Buntinx, Guy

GNANGA, Honoré

MAGGIANI, Alain

MEBALE, Aimé-Jhustelin ABOGO

NDONG, Roger ONDO

ONDO, Jean Aubin

SAMAT, André

English

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Chemical and Process Engineering Research                                                                                     www.iiste.org ISSN 2224-7467 (Paper) ISSN 2225-0913 (Online) Vol.8, 2013  1   Spectrokinetic studies of two 6,6a-dihydrochromeno(3,4-b) chromene derivatives  Aimé-Jhustelin ABOGO MEBALE,1* Alain MAGGIANI,2 Roger ONDO NDONG,1 Guy Buntinx,3  Jean Aubin ONDO,1 Honoré GNANGA,1   André SAMAT.2 1Laboratoire Pluridisciplinaire des Sciences (LAPLUS), Ecole Normale Supérieure  BP 17009 Libreville, Gabon. 2CINaM, CNRS UMR 7325, Aix-Marseille Université Faculté des Sciences de Luminy, 163 Avenue de Luminy, Case 901 F-13288 Marseille Cedex 9 France. 3Laboratoire de Spectrochimie Infrarouge et Raman, UMR-CNRS 8516 Université des Sciences et Technologies de Lille Cité Scientifique, 59650 Villeneuve d’Ascq. * E-mail of the corresponding author: abogo.mebale@yahoo.fr  Abstract Benzo and Naphthopyrans (chromenes) have been extensively studied since the discovery of photochromic reaction of 2H-1-benzopyrans in 1966 by Becker and Michl. Researchers have investigated chromenes for their use in sunglass lenses and also other potential applications such as optical memories and optical switches. Femto/picosecond and nano/microsecond experiments were released on two 6,6a-dihydrochromeno(3,4-b)chromene derivatives. After disappearance of the singlet state S1 formed from each compound, photoproducts with short lifetime (2.2 to 21 µs) obtained were attributed to the open forms. Keywords: 6,6a-dihydrochromeno(3,4-b)chromene, photochromic, nano/microsecond domain, femto/picosecond domain, wavelength, lifetime.   1. Introduction Chromenes (benzopyrans) are compounds with excellent pharmacological (Cassidi et al, 1992) and photochromic (Guglielmetti et al, 1999) properties. Since the industrial marketing of the first photochromic lenses (Crano et al, 1992), the studies moving towards the development of new systems of photochromic compounds (Maggiani et al, 2005). Many studies showed that the bichromenes can develop a persistent staining after UV irradiation (Berthet et al, 2004; Samat et al, 2004). On the over hand, the photochromic properties observed can be consider as the sum of those of each chromene unit (Berthet et al, 2004; Samat et al, 2004).  This paper presents the study of the photochemical behavior of two compounds derived from 6.6a-dihydrochromeno(3,4-b)chromene to elucidate the process of ring opening who occurs (Delbaere et al, 1998).   2. Results and discussion 2.1 Description of the spectra.  Analysis were performed on the compounds A and B represented in the figure 1 (Abogo Mebale et al, 2006; Abogo Mebale et al, 2012). Their absorption spectra in the ultraviolet and visible (UV-Visible) showed similar maximum wavelength (λmax) : 352 nm for A and 348 nm for B (Figure 2). Chemical and Process Engineering Research                                                                                     www.iiste.org ISSN 2224-7467 (Paper) ISSN 2225-0913 (Online) Vol.8, 2013  2      In femto/picosecond domain, the spectra obtained after photo-irradiation show a strong absorption band centered at 530-560 nm and a negative signal (bleaching signal) to 400 nm (Figure 3).  After excitation in the nano/microsecond domain, the spectra show intense bleaching signal (Figure 4) whose shape corresponds to the electronic absorption spectra of compounds A and B.  2.2 Interpretation of results.  In femto/picosecond experiments, absorption bands and bleaching signals disappear with the same kinetics. This is due to the excited singlet state S1 (Aubard et al, 2000; Birks, 1973). After the disappearance of S1, new chemical species with wide spectrum absorption, very low intensity and stable in the 100-1500 ps are observed. The maximum wavelength of the spectrum, better seen in the nano/microsecond experiment, is at 420 nm for the compound C and 400 nm for compound D respectively formed from the excitation of A and B (Table 1).  The kinetics of disappearance of C (2.2 to 4 µs) and D (4.1 to 21µs) is insensitive to the presence of oxygen (O2). These compounds do not correspond to the triplet state T1 (Birks, 1973; Turro, 1978). In addition, tests using hexane show that the absorbance is independent of the polarity of the solvent. There is linear variation of the intensity of the absorption spectrum with the intensity of the excitation whatever the solvent used. Species C and D are not the radicals cations (Lomoth et al, 1998; Stirk et al, 1992). The rapid disappearance of C and D is accompanied by the almost total decline, with the same kinetic, of the bleaching signal restoring almost compounds A and B respectively. C and D are the products of the isomerization reaction of the closed form following the photo-excitation (Aubard et al, 2000). The maximum wavelength of C is higher than that of A and D higher than that of B: C and D correspond to the chemical structure of the intermediate open form OF1 or the final open form OF2 (Figure 5). The important difference of thermal stability of the compounds C and D shows a dual ring opening occurs directly after the photon excitation. The stability of D is due to the presence of the phenyl group which stabilizes the system by conjugation. Compounds C and D should correspond to the open form OF2.  After 100 µs, a residual spectrum and a light bleaching signal is still after disappearance of C and D in each case. The presence of these signals indicates that a minority of molecules are not returned to the initial state. This residual spectrum could correspond to another open form more stable than the previous one. Compound B leads to a residual spectrum of significant amplitude (23 to 26%), which is clearly distinguishable from that of the compound D. Her maximum wavelength is on the blue. This molecule is therefore more conjugated than D.  3. Experimental section  3.1 Nano/microsecond domain   Experiments were performed using as excitation source the third harmonic (355 nm, 8 ns, 1 mJ) of a Nd: Yag laser (Thales Laser DIVA) and as a source of white light lamp xenon, an optical configuration in cross Bonneau et al, 1997). The light transmitted by the sample is dispersed by a monochromator and detected by a photomultiplier (Applied Photophysics Model 504) coupled to a digital oscilloscope (Tektronix TDS 540). It is therefore a single-channel detection. Each measurement provides, for a wavelength selected by the monochromator, the time variation of the transient absorbance (∆OD). From these kinetics, spectra can be reconstructed at selected times. The spectral investigation covers the region 300-650 nm. The time domain extends from 0.1 to 100 µs. The samples were placed in a quartz cell of 4 ml (section 1 cm x 1 cm) sealed with a device for degassing. Solutions were studied firstly under an inert atmosphere after degassing with N2 during 15 min, secondly under an atmosphere of O2. The sample concentration (10-4 mol.L-1) was adjusted so as to have an optical density of 1.0 at the wavelength 355 nm. Chemical and Process Engineering Research                                                                                     www.iiste.org ISSN 2224-7467 (Paper) ISSN 2225-0913 (Online) Vol.8, 2013  3   3.2 Femto/picosecond domain  Experiments were performed using a laser Ti: Sa oscillator (Coherent MIRA 900D + regenerative amplifier BM Industries alpha 1000) operating at 1 kHz (Buntinx et al, 1996). The excitation of pump (383 nm , 80 fs, 5 µJ) corresponds to the second harmonic of the system. A pulse characterized by a continuum of spectrally white light, covering the area from 390 to 700 nm (about 80 fs), generated by focusing a portion of the laser pulse in a window of CaF2 is used as a probe. This is time-delayed relative to the excitation pulse using a delay optical line (Microcontrol Model MT160-250PP) with the precision ±1 µm. The polarizations of the pump pulses and probe are adjusted to 54°5 from each other. The overall time resolution of the experiment (full width at half-height of the cross-correlation signal pump-probe) is estimated at about 300 fs. The probe pulse is split into two parallel beams from both in the sample (Salin, 1998; Bonneau et al, 1997). The lights transmitted on the two channels are simultaneously analyzed by a multi channel detector (CCD camera Princeton Instrument LN/CCD-1340/400-EB ) and provides a direct ratio of the variation range of transient absorption (∆OD) generated by the excitation of the pump within the pump-probe selected by the delay line. From the spectra obtained for different possible pump-probe the kinetics may be reconstituted to selected wavelengths. The spectral investigation covers the region 390-700 nm. The time domain extends from 0.3 to 1500 ps. The sample (concentration of 10-3 mol.L-1) is placed in a flow cell (to minimize the photodegradation). The spectra were accumulated during 3 minutes (or 180 000 pump-probe sequences).  4. Conclusion  Spectrokinetic studies released on compounds A and B in the nano/microsecond and femto/picosecond domains showed that 6,6a-dihydrochromeno(3,4-b)chromenes derivatives can undergo a double ring opening after photo-irradiation . The thermal instability of the species C and D is a limiting factor for photochromic applications of these compounds. More investigations should therefore continue to improve on this very important parameter.   References  Abogo Mebale, A.-J., Maggiani, A., Brun, P. (2006). Magn. Reson. Chem., 44, 892. Abogo Mebale, A.-J., Maggini A., Ondo, J.A., Menye Biyogo, R., Samat, A. (2012). Chemistry and Materials Research, Vol 2, N° 7, 83. Alfano., R.R. (1989). The supercontinum laser source, Springer-Verlag Ed., Berlin.      Aubard, J., Maurel, F., Buntinx, G., Poizat, O., Levi, G., Guglielmetti, R., Samat, A. (2000). Mol. Cryst. Liq. Cryst., 345, 3075. Berthet, J., Delbaere, S., Lokshin, V., Samat, A., Micheau, J.C., Vermeersh, G. (2004). Intern. J. Photoenergy, 6, 215. Birks, J.B. (1973). Organic Molecular Photophysics. John Willey & Sons. Bonneau, R., Wirtz, J. (1997). Pure & Appl. Chem., 69, 979. Buntinx, G., Naskrecki, R., Poizat, O. (1996). J. Phys. Chem., 100, 19380. Casssidi, F., Evans, J.M., Hadley, M.S., Haladij, A.H., Leach, P.E., Stemp, G. (1992). J. Nat. Prod., 61, 896. Crano, J.C., Kwack W.S., Wech, C.N. (1992). Applied photochromic polymer systems, Ed. G. Mc Ardle, Blackie, Londres. Delbaere, S., Luccioni-Houze, B., Bochu, C., Téral, Y., Campredon, M., Vermeersh, G. (1998). J. Chem. Soc., Perkin Trans. 2, 1153. Guglielmetti, R.J., Crano, J.C. (1999). Organic photochromic and Thermochromic Compounds, Plenum Press, New York, Vol 1, Chap.5. Lomoth, R., Brede, O. (1998). Chemical Physics Letters, Vol 288, Issue 1, 47. Maggiani, A., Garzino, F., Brun, P. (2005). J. Photochem. Photobiol. A: Chem, 171, 173. Salin, F. (1998). How to manipulate and change the characteristics of laser pulses, Ed. C. Ruillère, Vol 6, Berlin. Samat, A., Lokshin, V., Chamontin, K., Lévi, D., Pepe, G., Guglielmetti, R.J. (2001). Tetrahedron, 57, 7349. Stirk, K.S., Orlowski, J.O., Leeck, D.T., Kenttamaa, H.I. (1992). J. Am. Chem. Soc., Vol 114, Issue 22, 8604. Turro, N.J. (1978). Modern Molecular Photochemistry. Benjamin Cummings. Chemical and Process Engineering Research                                                                                     www.iiste.org ISSN 2224-7467 (Paper) ISSN 2225-0913 (Online) Vol.8, 2013  4        Figure 1. Structure of compounds A and B.                                          Spectrum of A                                                          Spectrum of B  Figure 2. Absorption spectra of compounds A and B.  in acetonitrile at 5.10-4 mol.L-1.                                                          Spectrum of A                                                          Spectrum of B  Figure 3. Spectra of compounds A and B in femto/picosecond domain. MeO OOMeO OOA B450 500 550 600 650 700-0.0050.0000.0050.0100.0150.0200.0250.030ch1Ac閠onitriledata5532∆ODnm -1 ps 0.4 ps 0.5 ps 0.6 ps 0.8 ps 1 ps 1.2 ps 1.5 ps 2 ps 3 ps 4 ps 5 ps 7 ps 10 ps 15 ps 20 ps 30 ps 50 ps 100 ps 400 450 500 550 600 650 7000.0000.0020.0040.006 ch8acetonitriledata5785∆ODnm 0.5 ps 0.7 ps 1 ps 1.5 ps 2 ps 3 ps 5 ps 7 ps 10 ps 20 ps 50 ps Chemical and Process Engineering Research                                                                                     www.iiste.org ISSN 2224-7467 (Paper) ISSN 2225-0913 (Online) Vol.8, 2013  5                                                 Spectrum of A                                                          Spectrum of B  Figure 4. Spectra of compounds A and B in nano/microsecond domain.  Table 1. Spectrokinetic results.    Absorption and lifetime of S1  Absorption and lifetime of C and D  bleaching Residual spectrum t >100 µs λmax / nm      t1/2 / ps λmax / nm        t1/2 / µs λmax / nm %  A 542                    6,1 420       acetonitrile : 4                  hexane : 2,2 350, ep 370 acetonitrile: 1,5%            hexane : 2% B 535                     5.8  400      acetonitrile: 21                 hexane: 4,1 350, ep 370 acetonitrile: 23%            hexane : 26%                Figure 5. Photochemical opening of chromenes.   350 400 450 500 550 600-0.25-0.20-0.15-0.10-0.050.00ch1acetonitrileDATA284∆[OD]λ en nm 1 祍 3 祍 5 祍 9 祍 15 祍 85 祍 300 350 400 450 500 550 600 650-0.45-0.36-0.27-0.18-0.090.000.09ch8Ac閠onitriled間 az? N2DATA311∆[OD]λ en nm 1 祍 5 祍 15 祍 40 祍 85 祍 MeO OOR MeO OOR MeO OOROF1 OF2This academic article was published by The International Institute for Science, Technology and Education (IISTE).  The IISTE is a pioneer in the Open Access Publishing service based in the U.S. and Europe.  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Spectrokinetic studies of two 6,6a-dihydrochromeno(3,4-b) chromene derivatives

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Spectrokinetic studies of two 6,6a-dihydrochromeno(3,4-b) chromene derivatives

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