We investigated the validity of noninteracting molecular chain theories for fully polymerized polydiacetylene crystals by measuring the two photon absorption spectrum of poly[4,6-dodecadiyn-1,10-diol-bis(n-butoxycarbonylmethylurethane)] chains isolated in their monomer matrix and comparing the results to those obtained previously from polydiacetylene single crystals. Data were taken over 800-940 nm using Z-scan and the measurements were found to be consistent with previously measured results in polydiacetylene single crystal poly[bis(p-toluene sulfonate) of 2,4-hexadiyne-1,6-diol], indicating the validity of the isolated molecule theoretical approach. We also report a low photo-induced polymerization threshold

Berréhar, Jeanne

Pauchard, Thomas

Polyakov, Sergey

Schott, Michel

Stegeman, George

English

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University of Central Florida STARS Faculty Bibliography 2000s Faculty Bibliography 1-1-2003 Two photon absorption and photo-induced polymerization in partially polymerized crystals of polydiacetylene poly 4,6-dodecadiyn-1,10-diol-bis(n-butoxycarbonylmethylurethane) Sergey Polyakov University of Central Florida Thomas Pauchard University of Central Florida George Stegeman University of Central Florida Jeanne Berréhar Michel Schott Find similar works at: https://stars.library.ucf.edu/facultybib2000 University of Central Florida Libraries http://library.ucf.edu This Article is brought to you for free and open access by the Faculty Bibliography at STARS. It has been accepted for inclusion in Faculty Bibliography 2000s by an authorized administrator of STARS. For more information, please contact STARS@ucf.edu. Recommended Citation Polyakov, Sergey; Pauchard, Thomas; Stegeman, George; Berréhar, Jeanne; and Schott, Michel, "Two photon absorption and photo-induced polymerization in partially polymerized crystals of polydiacetylene poly 4,6-dodecadiyn-1,10-diol-bis(n-butoxycarbonylmethylurethane)" (2003). Faculty Bibliography 2000s. 3969. https://stars.library.ucf.edu/facultybib2000/3969 J. Chem. Phys. 118, 4341 (2003); https://doi.org/10.1063/1.1556751 118, 4341© 2003 American Institute of Physics.Two photon absorption and photo-induced polymerization in partiallypolymerized crystals of polydiacetylenepoly[4,6-dodecadiyn-1, 10-diol-bis(n-butoxycarbonylmethylurethane)]Cite as: J. Chem. Phys. 118, 4341 (2003); https://doi.org/10.1063/1.1556751Submitted: 16 October 2002 . Accepted: 08 January 2003 . Published Online: 20 February 2003Sergey Polyakov, Thomas Pauchard, George Stegeman, Jeanne Berréhar, and Michel SchottARTICLES YOU MAY BE INTERESTED INAll-optical multiphoton absorption figures of merit: Polydiacetylene poly (bis para-toluenesulfonate) of Applied Physics Letters 84, 5362 (2004); https://doi.org/10.1063/1.1767276Two photon absorption and photo-induced polymerization in partiallypolymerized crystals of polydiacetylene poly4,6-dodecadiyn-1,10-diol-bisn-butoxycarbonylmethylurethaneSergey Polyakov, Thomas Pauchard,a) and George StegemanCREOL/School of Optics, University of Central Florida, Orlando, Florida 32816-2700Jeanne Berre´har and Michel SchottGroupe de Physique des Solides, UMR 7588 CNRS, Universite´ de Paris 6 & 7, 75251 Paris cedex 05,France~Received 16 October 2002; accepted 8 January 2003!We investigated the validity of noninteracting molecular chain theories for fully polymerizedpolydiacetylene crystals by measuring the two photon absorption spectrum ofpoly@4,6-dodecadiyn-1,10-diol-bis~n-butoxycarbonylmethylurethane!# chains isolated in theirmonomer matrix and comparing the results to those obtained previously from polydiacetylene singlecrystals. Data were taken over 800–940 nm using Z-scan and the measurements were found to beconsistent with previously measured results in polydiacetylene single crystal poly@bis~p-toluenesulfonate! of 2,4-hexadiyne-1,6-diol#, indicating the validity of the isolated molecule theoreticalapproach. We also report a low photo-induced polymerization threshold. © 2003 AmericanInstitute of Physics. @DOI: 10.1063/1.1556751#Polydiacetylenes ~PDAs! are known to have strong elec-tric dipole coupling of the ground state to the one photonallowed state and from this excited state to higher lying twophoton states due to one dimensional delocalization of pelectrons along the polymerization backbone.1,2 This resultsin large nonresonant third order nonlinearities forl.1 mm.1 There is a long history of theoretical work ex-plaining these large nonlinearities in terms of the electronicstates of single, isolated polymer molecules dating back tothe 1970s.1,3–12 Many experimental studies of nonlinearproperties have been performed on single crystal PDAs, oron oriented or amorphous films,13–20 indeed, for nonlinearapplications the density of active species, i.e., the polymerchains, should be maximized.21–23 Such measurements, how-ever, may be compared to theory only if interchain interac-tions in the solid are only a small perturbation of the singlechain properties. Recent theoretical calculations24–27 dealwith the effect of interchain interactions on the properties ofconjugated polymer crystals, and predict relatively large ef-fects on energy spacings, and the optical observation of newstates. Since the modeling for the third order susceptibility,x (3), has yet to advance to the same level of sophisticationthat has occurred for the second order susceptibility, x (2), anexperimental study of the effect of chain interactions on x (3)in the crystalline phase would, therefore, be useful. Experi-mental results relevant to this question are presented here.Some PDAs are soluble, but the conformation and electronicstructure of the isolated PDA chain in solution are very dif-ferent from those in the crystal and such studies cannot beused to test the influence of interchain interactions. Here westudy monomer DA crystals containing small polymer con-centrations. A concentration of 5 to 8% in weight is smallenough for most chains to have no nearest neighbor chaininteractions, but still large enough to make measurementspossible.Materials in the PDA family differ primarily from oneanother in the organic side groups which link the PDA back-bone chains, and the electronic states, the vibrational modes,etc. which play a large role in the optical properties are foundto be only weakly dependent on these side groups. Hence allPDAs are expected to have comparable linear and nonlinearproperties. Two photon absorption in particular has beenstudied extensively in polydiacetylenes.17–20,28–31 However,some of these measurements were made in solution or amor-phous thin films where it is known that different conforma-tional forms of many conjugated polymers can exist makingthe situation complex.17,29,30 To date, the most detailed twophoton absorption measurements have been performed onthe single crystal conjugated polymer poly@bis~p-toluene sul-fonate! of 2,4-hexadiyne-1,6-diol# ~PTS!.19,20,28,31 Specifi-cally, the strongest two photon state is excited with photonsof wavelength 920 nm and the two photon absorption spec-trum has vibrational side-bands down to about 700 nm.19,20Recently polymerized chains of PDAs dilutely dispersedin a 3BCMU monomer single crystal matrix were producedby controlled gamma-ray polymerization and characterizedas discussed in Ref. 32. This particular PDA has the advan-tage that there is minimal stress induced when it is partiallypolymerized from the monomer crystal, since the room-temperature lattice parameter of the poly@4,6-dodecadiyn-1,10-diol-bis~n-butoxycarbonylmethylurethane!# ~3BCMU!monomer in the chain growth direction is almost exactlyequal to the equilibrium repeat distance of the PDA chain.33In such a diluted polymer PDA the interchain interactions areweak.34 A number of features of such dilute polydiacetylenesa!Current address: Royal Institute of Technology ~KTH!, Stockholm, Swe-den; Electronic mail: george@creol.ucf.eduJOURNAL OF CHEMICAL PHYSICS VOLUME 118, NUMBER 10 8 MARCH 200343410021-9606/2003/118(10)/4341/4/$20.00 © 2003 American Institute of Physicsincluding the linear absorption, pump-probe triplet and sin-glet exciton generation and relaxation have already beenmeasured.2,35 Since the monomer has optical transitions thatoccur at higher photon energies than those in the polymer,i.e., in the UV spectral region, it is possible to study the twophoton spectrum of aligned individual chains in a transparentdielectric medium. Such an investigation allows a directcomparison of the two photon response of single crystal ~oramorphous! PDA with that of an ‘‘isolated’’ but oriented ~bythe crystal lattice! polymer chain, which in turn is a test ofwhether the single chain theories should provide a good ap-proximation for solid state polymers. Here we report both onthese studies, and the difficulties encountered due to lightinduced polymerization of the sample.We performed standard open aperture Z-scan experi-ments36 at room temperature using 140 fs long, mode-lockedpulses from a Ti:sapphire laser operating at 76 MHz, tunableover the wavelength range 800 to 940 nm. Based on theprevious PTS results, this range covers the expected twophoton resonance peak.19,20 The light was collected by Sidetectors. Special care was taken to collect all the light at theoutput to insure the detected power drop is due to intensitydependent absorption.The samples were fabricated at GPS at Jussieu in Paris,using techniques developed there.32 The pure monomer crys-tals were clear and colorless and acquired a pink and then redtinge on progressive polymerization. Two samples, 98 mmthick with a polymer concentration of 8.561%, and 168 mmwith a 6.861% polymer concentration, were used in the ex-periments. Polymer concentrations were determined bymeasuring the one-photon absorption spectra for lightpolarization perpendicular to the chain direction, using thepreviously determined calibration.35 Polymer chain lengthis expected to be over 2000 monomer units, based on themolar weight studies of 3BCMU37 and 4BCMU32 ~stands fordiacetylene poly@5,7-dodecadyine-1,12-diol-bis ~n-butoxy-carbonylmethylurethane!#!. Both samples had sufficient sur-face quality to obtain useful open aperture Z-scans.The linear absorption spectrum of both samples for lightpolarization perpendicular to the b-crystalline axis was mea-sured and is shown in Fig. 1. Both spectra exhibit the samefeatures, a strong exciton peak at about 630 nm and vibra-tional side-bands to shorter wavelengths. Also shown forcomparison is the absorption spectrum of a poly-PTS singlecrystal.38 The gross features of the crystal spectrum associ-ated with the exciton feature are similar to the dilutesamples, although there are some differences in details.Initial Z-scan experiments near the expected two photonabsorption peak around 900 nm indicated that above rela-tively small pulse energies, an irreversible change occurredin the optical properties of the samples. This became theprincipal limitation for this experiment. After damage, theZ-scan spectrum showed a large decrease in throughputwhen the maximum intensity was incident on the sample.This indicates a localized damage of the crystal. We foundthat the damage depends only on the input energy per pulseand not on the average power. Also, it was shown that thepolarization of the incident light had to coincide with thedirection of polymerization. These features indicate that theorigin of the photo-damage was due to photo-induced poly-merization of the monomer which increased the concentra-tion of the polydiacetylene in the monomer crystal. This inturn led to a deeper minimum in the open aperture Z-scan. Inretrospect these results are not surprising since photo-induced polymerization is well-known to frequently occur inPDAs.1,39 The wavelength dependence of the pulse energy atthe 76 MHz repetition rate at which damage first occurs, asevidenced by changes in the Z-scan, is shown in Fig. 2.Such a low pulse energy damage threshold, 0.1 nJ,which is well below the maximum available laser pulse en-ergy, made the Z-scan experiments very difficult. Working atlower pulse energies meant that the open aperture nonlineartransmission dips were shallow, making it difficult to obtainan accurate measurement of the two photon absorption coef-ficient a2 where Da5a2I ~and I is the intensity!. The maxi-mum ‘‘dip’’ observed under condition that no optical damageoccurs was approximately 15%.Some typical results obtained for the coefficient a2 nearthe expected two photon absorption peak and taken at pulseenergies low enough to avoid damage are shown in Fig. 3.Notice the large uncertainties at low pulse energies due to thesmall multiphoton absorption minimum in the Z-scan, andthe associated uncertainty in its measurement. The measuredvalues are consistent between the two samples whose conju-gated polymer concentrations were equal to within 10%. Thedifference between the coefficients measured for the two dif-ferent concentrations is well within the uncertainties associ-ated with the measurements. Note that experiments were alsoFIG. 1. Absorption spectra of the dilute polydiacetylene in the monomermatrix ~a! and of the single crystal poly-PTS ~b! ~arbitrary units! for inputpolarization perpendicular to the chain axes.FIG. 2. Pulse energy at which optical damage occurred vs wavelength.4342 J. Chem. Phys., Vol. 118, No. 10, 8 March 2003 Polyakov et al.done with a chopper present which reduced the averagepower by a factor of 8. This clearly made no differenceshowing that thermal effects were not important in thiscase.The measured wavelength variation in the two photonabsorption coefficient is shown in Fig. 4. The dilute samplesshow evidence for an expected peak between 900 and 940nm ~Ref. 19!, although its exact location is uncertain due tolarge experimental error. The average concentration of thetwo dilute samples is 7.5% so that a simple linear rescalingof two-photon absorption data for 100% polymerized PTS19gives a good overlap for on-peak and off-peak values. Theaccuracy of PTS measurement is much higher as 2PA valuesare more than ten times higher and the error bars for PTSmeasurements are not shown to simplify the representation.In particular, the value obtained previously for PTS is ;700cm/GW at 920 nm, when scaled down to 3BCMU concen-tration exhibits reasonable agreement.19,20 Similarly thevalue 441 cm/GW for PTS at 800 nm gives 33.1 cm/GW at800 nm gives, also in reasonable agreement with diluted3BCMU with two-photon absorption of 30 cm/GW.19,20Therefore, the values of the magnitude and spectral distribu-tion of the two photon spectra are in reasonable agreementbetween the PTS crystal and the dilute isolated polymerchains in the 3BCMU monomer matrix. Note that compari-son of the dilute 3BCMU samples with a fully polymerizedpoly-3BCMU crystal is not possible, since 3BCMU cannotbe fully polymerized.40These results indicate that single chain theories of non-linearities in PDAs should give reasonable predictions fornonlinear optical properties in single crystal PDAs and thatany discrepancy between observations on a bulk sample andsingle chain theories should not be explained by chain inter-actions in the solid state.In conclusion, we have investigated the two photon ab-sorption near its predicted peak at about 920 nm in dilutemixtures of diacetylene polymer chains imbedded in a singlecrystal 3BCMU monomer. Photopolymerization induced bythe probe beam used for the Z-scan measurements limitedthe maximum pulse energy that could be used for 140 fspulses. Thus the measurements were performed with pulseenergies of 0.1 nJ and less. This introduced a large uncer-tainty into the coefficient measurement. Despite the largeuncertainties, good agreement was found with PTS polymercrystal values, when the dilute samples were scaled to a100% concentration of polymer content. These measure-ments verify the hypothesis that single crystal values of theimaginary part of the susceptibility x (3) reflect the singlechain polymer values and, therefore, interpolymer chain in-teractions are negligibly small.1 M. Schott and G. Wegner, Nonlinear Optical Properties of Organic Mol-ecules and Crystals, Vol. 2, edited by D. S. Chemla and J. Zyss ~Aca-demic, Orlando, 1987!.2 B. Kraabel, M. Joffre, C. Lapersonne-Meyer, and M. Schott, Phys. Rev. B58, 15 777 ~1998!.3 K. C. Rustagi and J. Ducuing, Opt. Commun. 10, 258 ~1974!.4 G. P. Agrawal, Phys. Rev. B 17, 776 ~1978!.5 R. R. Birge and B. M. Pierce, J. Chem. Phys. 70, 165 ~1979!.6 D. N. Beratan, J. N. Onuchic, and J. W. Perry, J. Phys. Chem. 91, 2696~1987!.7 Z. Soos and S. Ramasesha, J. Chem. Phys. 90, 1067 ~1989!.8 S. N. Dixit, D. Guo, and S. Mazumdar, Phys. 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Phys., Vol. 118, No. 10, 8 March 2003 Polyakov et al.

Two photon absorption and photo-induced polymerization in partially polymerized crystals of polydiacetylene poly 4,6-dodecadiyn-1,10-diol-bis(n-butoxycarbonylmethylurethane)

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Two photon absorption and photo-induced polymerization in partially polymerized crystals of polydiacetylene poly 4,6-dodecadiyn-1,10-diol-bis(n-butoxycarbonylmethylurethane)

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