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Fluorescent gelNanostructurePerylene tetracarboxy diimidePolystyrenePoly (dimethyl siloxane)

(PTCDI) or perylene imide (PI) phase separate into discrete crystals in polymer lms, we

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1. Introduction

Dispersing functional small molecules in polymermatri-ces is a common approach to fabricating organic-based

http://dx.doi.org/10.1016/j.eurpolymj.2014.11.0220014-3057/ 2015 Published by Elsevier Ltd.

ecommons.org/licenses/by-nc-nd/3.0/).

Corresponding author.E-mail address: Sundar@Carleton.ca (P.R. Sundararajan).

European Polymer Journal 65 (2015) 414

Contents lists available at ScienceDirect

European Poly

journal homepage: www.else

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GYThis is an open access article under the CC BY-NC-ND license (http://creativReferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.3. Composite gels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.4. Morphology of the composite gels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.5. UVVis and fluorescence spectra of the composite gels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Appendix A. Supplementary material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Phase separation

Contents

1. Introduction . . . . . . . . . . . . . . . . .2. Experimental . . . . . . . . . . . . . . . .3. Results and discussion . . . . . . . . .

3.1. Morphology of the compos3.2. Optical properties of the cnd that functionalizing the perylene imide with a polymer or oligomer segment that iscompatible with the host polymer matrix results in highly uniform dispersion of the smallmolecule, with the inherent photophysical properties of the perylene segment unaffected.We demonstrate this approach with oligostyrenePTCDIoligostyrene dispersed inpolystyrene, PDMSPI and PDMSPTCDIPDMS in PDMS in solution cast lms and intwo-component gels from organic solvents. Fluorescent gels of polystyrene and PDMS(without crosslinks or functionalization) were obtained via this route.

2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-NDlicense (http://creativecommons.org/licenses/by-nc-nd/3.0/).

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7ms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7ite films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Keywords:

tional molecule as part of the polymer chain have been examined, although such methodslimit the exibility in materials choice. While perylene or perylene tetracarboxy diimiderticle history:eceived 20 October 2014eceived in revised form 13 November 2014ccepted 16 November 2014

Solution coating of functional small molecules in polymer lms is a convenient approach tofabricating exible optoelectronic and photo-functional devices. Uniform dispersion of thesmall molecule in the polymer and inhibition of aggregation are requirements for therobust functioning of the devices. Alternate approaches such as incorporating the func-ent of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada

i c l e i n f o a b s t r a c tolymer compatibilized self-assembling perylene derivatives

lianne Dahan, Pudupadi R. Sundararajan epartmPFeature Articlemer Journal

vier .com/locate /europol j

exible devices, the earliest examples being the repro-graphic photoreceptors and polymer-dispersed liquidcrystal displays [16]. Solution coating of functional multi-layers using such compositions are preferred for exibledevices. The relative concentration of the functionalmolecule often has to be as high as 50 wt% in the polymer.For example, Santerre et al. [7] reported the properties ofOLED devices based on N,N0-diphenyl-N,N0-bis(3-methyl-phenyl)-[1,10-biphenyl]-4,40-diamine (TPD) dispersed inpolymers with high Tg. The best performance was obtainedwith a TPD concentration of 75%. Detailed studies havebeen reported on the morphologies resulting from phaseseparation of three different charge transport moleculesin polycarbonates and polystyrene [811]. Molecular dis-persion of the small molecule is essential and any phaseseparation and crystallization would lead to degradationof the device performance. Smith et al. [12] have shownthat crystallization of TPD was the cause of delaminationof an OLED device. Scharfe [13] discussed the effect of suchcrystallization on charge trapping in photoreceptors. Theleaching of the transport molecule would be more preva-lent in copiers and printers using liquid developers.

As an alternate to dispersing the functional small mole-cule in polymer matrices, Limburg et al. [14] and Ong et al.

Perylene and its derivatives have been investigated overthe past few decades for their applications in optoelec-tronic and photovoltaic devices [22,23]. The classic crystal-lographic investigations by Hdicke and Gracer [24]related the effect of substituents on the p-overlap andthe color. The self-assembly facilitated by the p-interactioncan be modulated by substitutions at the imide nitrogen aswell as the bay positions [2527]. Linear and dove-tailsubstitutions have been used to create nano-ber mor-phologies [28,29]. Supramolecular association betweenmelamine functionalized perylene tetracarboxylic diimide(PTCDI) and cyanuric acid via hydrogen bonding resultedin nano-ribbon and nano-rope morphologies [30]. Theapplications of perylene imides and diimides in solar celland organic electronics have been summarized in recentreviews [31,32].

When perylene (or PTCDI) by itself was dispersed in apolymer matrix, the small molecule formed discrete crys-tals of a few microns as shown in Fig. 1, irrespective ofthe solvent used for casting the lms. We discussed theself-assembly of PTCDI substituted with oligostyrene onboth imide nitrogens (PSPTCDIPS, Scheme 1a) in solution[33] as well as in the gel state [34]. In another study, wesubstituted poly (dimethyl siloxane) (PDMS) on both imide

(b) PTwas u

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GY[15] designed arylamine based polymers and copolymersby incorporating the photoactive molecules as part of thechain to prevent phase separation. Design and properties ofseveral such polymers with arylamine functionality in themain chain or side chain have been studied [1618]. Conju-gated polymers for solar cell applications have also beenexamined [19,20]. All-polymer bulk hetero-junction solarcells using blends of polymers bearing donor and acceptormoieties have been reported by Jenekhe et al. [21]. Theadvantage of using a functionalmolecule dispersion in a hostpolymer is that either can be changed at will, whereas a spe-cic polymer with the functional segment cannot.

Fig. 1. OM of solvent cast lms of (a) perylene/polystyrene (5/95 wt%),polycarbonate (5/95) and (e) perylene/PMMA (2/98). Tetrachloroethylenenitrogens (Di-PDMS) (Scheme 1b) or on one (Mono-PDMS)(Scheme 1c) and reported on the differences in the mor-phology of the mono and di-substituted PTCDI in solution[35,36] and gels [37]. Both PSPTCDIPS and Di-PDMS arenon-ionic Gemini surfactants. We believed that by attach-ing an oligomeric or polymeric chain which is compatiblewith the host polymer, the mixing of such compatibilizedPTCDI would be better, and a uniformly dispersedcomposite lm could be obtained. For example, with oligo-styrene attached to PTCDI, we expect that a good dispersionin polystyrene (Scheme 1d) could be achieved. In the pres-ent work, we dispersed PSPTCDIPS in the corresponding

CDI/polystyrene (5/95), (c) perylene/polycarbonate (2/98), (d) perylene/sed for (e) and chloroform for the others.

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GYpolymer, polystyrene (PS), in an attempt to make compos-ite polymer lms. We also prepared gels of PSPTCDIPSrecently, with trans-decalin [34]. Since this solvent hasbeen used in the past for gelation involving polystyrene,we prepared two-component composite gels with differentconcentration of PSPTCDIPS in polystyrene. In our previ-ous work, we used propylamine for gelation of Mono- andDi-PDMS [37]. This solvent was also used for gelation withPDMS without having to crosslink or functionalize thepolymer [38]. In the present work, we prepared PTCDIdispersed gels of PDMS with different concentrations ofMono- or Di-PDMS. The optical properties of the self-assembled polymer-compatibilized PTCDI remained thesame upon dispersion in the corresponding polymer matrices.

2. Experimental

The syntheses of Mono-PDMS and Di-PDMS have beendescribed in our previous publications [35,36]. PSPTCDIPS was synthesized as described by Islam and Sundararajan[33]. Poly (dimethylsiloxane) (Mw = 182,600;Mn = 106,000,CASRN 9016-00-6), polystyrene (Mw = 239,700 and

Scheme 1. (a) PolystyrenePTCDIpolystyrene Gemini surfactant, (b) PDMSPTCPDMS, (d) polystyrene and (e) PDMS.Mn = 119,600) and all the solvents (propylamine, chloro-benzene, THF, or chloroform of laboratory grade) were pur-chased from Aldrich Chemical Company. Solvent cast lmswere prepared by dissolving appropriate mixtures ofPSPTCDIPS and PS in chlorobenzene, THF, or chloroform.Relative concentrations of 1, 5 or 10 wt% of PSPTCDIPS inPS were used. Films were coated on a glass substrate usingan electrically driven lm coater and were dried at avery low rate of the solvent evaporation at ambient condi-tions for 24 h and then under vacuum for 24 h. The nalthickness of the lms was about 20 lm.

Gelation studies on PSPTCDIPS (a Gemini surfactant)were discussed in our previous publication [34]. In thepresent work, PS/PSPTCDIPS composite gels were pre-pared with 210 wt% of PSPTCDIPS in PS. A total soluteconcentration of 0.8 mM was dissolved in trans-decalinat temperatures ranging from 78 to 82 C with constantstirring. This resulted in a red solution. Closed vials wereused to avoid the evaporation of the solvent. The gels wereprepared by slow cooling the solution and as a quick test,gelation was conrmed by tube inversion, i.e., no owingsolvent.

DIPDMS Gemini surfactant, (c) inverse macromolecular surfactant PDI

We reported the gelation with PDMS before, withoutany crosslinks or functionalization [38], as well as the gela-tion ofMono-PDMS and Di-PDMS [37]. In the present study,a solute concentration of 0.1 M (18.26 g/L) in propylaminewas used, with 2%, 5%, or 10 wt% Mono-PDMS and 5%,10 wt% Di-PDMS in PDMS. Solutions were prepared withconstant stirring at temperatures ranging from 65 to75 C. Gels were then prepared by slow cooling to roomtemperature by turning off the hot plate. Gels were pre-pared in closed vials to avoid the evaporation of the solvent.Gelation was tested by tube inversion with no owingsolvent.

The optical micrographs (OM) were recorded using aZeiss Axioplan polarized optical microscope in transmis-sion mode. Northern Eclipse (version 6.0 and 8.0) imageprocessing software was used to record the images. Scan-ning electron microscopy (SEM) images were obtainedusing a VEGAII XMU (TESCAN, Czech Republic) scanningelectron microscope. Dry samples were sputter coatedwith 80:20 Au/Pd target using a Hummer VIII SputteringSystem (Anatech Ltd., Alexandria, VA). Thermal analysiswas performed using a TA Instruments 2010 differentialscanning calorimeter at 10 C/min heating rate. The instru-ment was calibrated for temperature and energy with

indium and tin as certied reference materials. DSC tracesfor lms were recorded with about 8 mg of the samplesunder the ow of nitrogen. UVvisible absorption spectrawere recorded using a Varian CARY 3 UVVis spectropho-tometer. The data were processed with CARY WinUV Soft-ware version 3.00. The uorescent emission data werecollected using a Varian CARY Fluorescence spectropho-tometer at the excitation wavelengths (kex) of 460 nmand 417 nm with a bandwidth of 5 nm for excitation and5 nm for emission. Data collection and processing weredone by Eclipse WinFLR Software (version 1.1).

3. Results and discussion

3.1. Morphology of the composite lms

While perylene, without any substitution, would formcrystals, attaching short chains to perylene mono- or dii-mide leads to vesicular, nano-web or nanowiremorphologywhen precipitated from solution or during gelation. Fig. 1shows the opticalmicrographs (OM) of lms cast from chlo-roform or TCE solutions of polystyrene, polycarbonate orPMMA with low concentrations of perylene or PTCDI. Evenin the presence of the polymers, large, discrete crystals of

(5 wtd (h)

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GYFig. 2. OM images of PS/PSPTCDIPS lms (top: 1 wt% PSPTCDIPS) andTHF. Spin cast lms with PS/PSPTCDIPS (95/5 wt%) in (g) chloroform an% PSPTCDIPS) cast from (a,d) chlorobenzene, (b,e) chloroform and (c, f)THF are also shown.

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GYthe small molecules are seen in all these cases. Fig. 2 showsthe OM of lms of PSPTCDIPS in polystyrene, cast fromthree different solvents. Spherical domains, with almostuniform size are seen with lms cast from chlorobenzeneand chloroform. Especially with a 5 wt% concentration inchloroform (Fig. 2(e)), dense spheres with uniform size areseen. Such close packed morphology ensures that percola-tion threshold has been reached andwould facilitate chargehopping. The lms made with THF, however, do not showdiscrete domains (see Optical Properties below). The lengthof the oligostyrene chain attached to PTCDI in this case isonly about 12 units. The molecular weight of the polysty-rene matrix is over 100,000. With the oligostyrene attach-ment, single crystals of perylene is not seen in thepolystyrene matrix. We have shown previously thatdrop-cast lms of PSPTCDIPS show vesicular and fusedvesicular morphologies [33]. Such spherical morphology ismaintained when this Gemini surfactant is dispersed inpolystyrene. Fig. 2(g) and (h) shows spin cast lms withchloroform and THF. A highly uniform spherical morphol-ogy is seen in these lms. With the oligostyrene segmentdispersed in the polystyrene matrix, the domain formationis due to the self-assembly of PTCDI. Thus it is a supramolec-ular solution.

Fig. 3 shows the SEM images of lms with 5 wt%PSPTCDIPS in polystyrene. No domains similar to thosein Fig. 2(a), (b), (d) and (e) are seen in Fig. 3(a) and (b)which would indicate that the domains seen in Fig. 2 are

Fig. 3. SEM images of lms with 5 wt% PSPTCDIPS (ac) and 10 wt% PSPchlorobenzene, (e) chloroform.sub-surface. We have reported such a phenomenon beforein the case of a functionalized phthalocyanine dispersed inpolycarbonate or PMMA [39], as well as biscarbamates dis-persed in polycarbonate [40]. In another study [41], wedescribed a polymer dispersed self-assembling small mol-ecule system, in which a homologous series of carbamates,with a hydrogen-bonding moiety and alkyl side chains,was dispersed in polycarbonate. These self-assemblingmolecules formed colloidal size domains in the polymer,which involved a hierarchy of three levels of assembly.When a lm is cast from solution, the self-assembly ofthese small molecules is so rapid that they form domainsin the bulk of the polymer during solvent evaporationand do not diffuse to the surface of the polymer lm. Dueto the sub-surface assembly, no domains are seen in theSEM images, although their presence is seen in the trans-mission OM. Fig. 3(c) shows that with THF, sphericaldomains of less than a micron are seen on the surface aswell. The SEM images of lms with a higher concentrationof 10 wt% PSPTCDIPS (Fig. 3(d) and (e)) show domainson the surface as well, with those in Fig. 3(e) being of nano-meter size. The highly monodisperse size of these domainsshow that spontaneous nucleation occurs due to self-assembly in the polymer matrix. Fig. 4 shows the photo-graphs of the polystyrene lms with 1, 5 and 10 wt% PTCDI.Consistent with the OM observations, the lm is transpar-ent with 1 and 5 wt%, becoming opaque with higherconcentration.

TCDIPS (d,e) using (a) chlorobenzene, (b) chloroform and (c) THF, (d)

The sub-surface self-assembly of the small molecules inthe polymer matrix has another advantage. Typically, thecharge transport layer (CTL) of a photoreceptor containsthe charge transportmolecule (CTM) such as TBD, to a load-ing of about 50%. Such a high loading of CTM essentiallyleads to a metastable composite. Abrasion due to brush-cleaning of the photoreceptor after each copy/print cycle,leaching due to the use of liquid developer etc., result inthe loss of the charge transport molecule (CTM) which

However, with THF the decrease is linear, with the Tg reduc-

Fig. 4. Transparency of the PS/PSPTCDIPS lms. L to R: 1, 5

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GYwould change the composition of the active layer and henceits performance. Over-coating the CTL with abrasion-resis-tant layers (such as siloxane) has been adopted as a route toreduce the loss of the CTM [42]. Sundararajan et al. [43]showed that introducing cyclodextrins in the CTL to formpolycarbonate/cyclodextrin rotaxanes reduced the abra-sion signicantly. The use of a self-assembling moleculesuch as PSPTCDIPS obviates the need for such add-oncoatings, since the active molecule is assembled sub-sur-face in the polymer matrix. An optimum concentration isneeded as well for such sub-surface morphology sincebeyond a certain concentration of the small molecule,domains are formed on the surface as well, as seen inFig. 3(d) and (e). In spite of the domains seen on the surfaceof the lms, note that these are highly monodisperse in size(nanometers) in the case of lms cast from chloroform(Fig. 3(e)).

To address the question of whether a compatible oligo-mer is indeed required as a side chain to form such uniformdomains described above, we dispersed Mono-PDMS andFig. 5. The variation of glass transition temperature of polystyrene withvarious concentrations of PSPTCDIPS using three different solvents.ing by 14 C, to 90 C with 5 wt% of PSPTCDIPS. The dif-ferences in the morphology and the thermal propertybetween the lms made with the three solvents do notrelate to the solubility parameter. However, it should benoted that the viscosity of THF is 0.48 cP, while that of chlo-robenzene and chloroform are 0.75 and 0.56 cP, respec-tively. The effect of the viscosity of the solvent on theresulting morphology during self-assembly was discussedbefore in our work on phthalocyanine aggregation in poly-carbonate and PMMA matrices [39].

3.2. Optical properties of the composite lms

In our previous studies [37] on the self-assembly ofPSPTCDIPS in solution, the monomeric form of this com-pound in chloroform showed three distinct peaks at 456,489 and 526 nm in the UVVis spectra, corresponding tothe S02, S01 and S00 transitions respectively. TheUVVis spectra in Fig. 6 shows that PSPTCDIPS in thelm with PS cast from chloroform is in aggregate form,with peaks at 498 and 532 nm, which are red-shifted1 withrespect to the solution spectrum. The lms from chloroben-zene also showed a red shit to 494 nm and 528 nm. Inaddition, less intense peaks are seen in both Fig. 6(a) andDi-PDMS in polystyrene. As the PDMS segment and poly-styrene are not miscible, the morphology shown in Fig. S1(Supplementary data) was obtained. The dagger-like mor-phology in the OM shown in Fig. S1a is due to the fusionof the vesicles of Mono-PDMS is the polystyrene matrix,as seen in the SEM image in Fig. S1b.

As expected, the glass transition temperature (Tg) ofpolystyrene was depressed as seen in Fig. 5. Although theTg was reduced from 104 C to about 80 C with 10 wt% ofPSPTCDIPS with the three solvents, the rate is different.With the lms made with chlorobenzene and chloroform,the Tg is reduced only by about 4 C with 5 wt% PSPTCDIPS and the decrease is more pronounced thereafter.

and 10 wt% PTCDI in polystyrene, cast from chloroform.(b) at 564 and 589 nm with chlorobenzene and at 568 and590 nm with chloroform, which could be assigned to theaggregated state of PSPTCDIPS. However, when THF wasused as the solvent, the UVVis spectrum (Fig. 6(c)) showedthe monomeric form of PSPTCDIPS. The lm drop castfrom THF showed a major peak at 526 nm correspondingto the S00 vibronic transition, a second peak at 491 nm cor-responding to the S01 vibronic transition, and a hump at

1 For interpretation of color in Fig. 6, the reader is referred to the webversion of this article.

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GY461 nm corresponding to the S02 vibronic transition. Theabsorption spectra for the lms cast with chlorobenzeneand chloroform are broader which would indicate strongeraggregation than that cast with THF. As discussed above,there is a signicant difference in the morphologies of thelms cast from the two chlorinated solvents and THF. Thelatter did not show discrete domains in Fig. 2.

3.3. Composite gels

A recent review by Ajayaghosh et al. [44] summarizedthe various p-system gels and their possible applications.As wementioned in our recent publication, there have beena fewstudies onperylenediimide andphthalocyaninebasedgels [26,4549]. The poor integrity and mechanical proper-ties of these gels limit their applications. Incorporating themin polymer matrices and fabricating two-component gelsmight be a route to overcome these limitations. Such gelsinwhich the twocomponents eitherdonot haveany specicinteractions ormutually complex are known [5054]. In thepresent work, both polystyrene and PDMS are known toform gels. We recently discussed the thermo-reversiblegelation of PSPTCDIPS,mono-PDMS andDi-PDMS.Hence,

Fig. 6. UVVis absorption spectra of lms drop cast from diffewe prepared the composite gels, in which the PTCDI bearsthe compatible polymer segment inwhich it is incorporated.Note that in contrast to theworkof others, the three gelatorsdo not have C@OandNAH type hydrogenbonding groups intheir structure.

The dissolution and gelation onset temperatures of thedifferent composite gels are given in Table 1. The tableshows the effect of concentration of the oligomer-function-alized perylene in the corresponding polymer on the tem-peratures of dissolution and the onset of gelation. Forexample with the PS/PSPTCDIPS composite gels thatwere formed with trans-decalin at 5% PSPTCDIPS, a redsolution was obtained at 82 C. When the solution wasslow cooled, a deep red-colored, opaque and immobilegel began to form at 57 C. However, when the concentra-tion of PSPTCDIPS increases to 10 wt% PSPTCDIPS thegelation onset of gelation drops to 50 C.

3.4. Morphology of the composite gels

We previously discussed that the morphology of PDMSgels (without crosslinks or functionalization) consistedof interconnected spherical domains, the Mono-PDMS gel

rent solvents at different PSPTCDIPS concentrations.

forms vesicular morphology and the Di-PDMS gel formsnano-bers. Fig. 7 shows the morphology of the compositegels with PDMS/Mono-PDMS and PDMS/Di-PDMS.Fig. 7(a)(c) shows that the spherical/vesicular individualmorphologies of PDMS and Mono-PDMS are maintainedin the composite gels. Both the Mono-PDMS and the Di-PDMS self-assemble in the PDMS matrix, forming uni-formly distributed spheres for Mono-PDMS and bers forDi-PDMS. The spheres in the background of the gel blendsare due to the PDMS which has also been known to gel inpropylamine [38]. Note that the distribution of theMono-PDMS spheres and Di-PDMS bers are fairly uniformin the polymer matrix, considering that the relativeconcentration of the Mono- or Di-PDMS is no more than10 wt% in the polymer. Fig 7(g) and (i) shows the photo-

gels, and so does polystyrene. The morphology of the com-posite gel consists of inter-meshed bers of polystyreneand PSPTCDIPS, as seen in Fig. 8(c). These bers arefew hundred microns long and also fold along their lengthto resemble an eaves trough, as seen in the higher magni-cation images in Fig. 8(d) and (e). This behavior was dis-cussed in our previous work [34]. Fig. 8(g) shows theuorescent polystyrene gel, with PSPTCDIPS in it.

3.5. UVVis and uorescence spectra of the composite gels

The absorption and uorescence spectra of the PS gelswith 2%, 5% and 10% PSPTCDIPS are shown in Fig. 9(a)and (b). The absorption spectrum of the gel with 2%PSPTCDIPS showspeaks at 500 and535 nmwith intensity

Table 1The dissolution temperatures and onset of gelation of the different composite gels.

Composite gel Solvent %wt Concentration of oligomerfunctionalized PTCDI (%)

Dissolution temperature (C) Onset of gelation (C)

PS/PSPTCDIPS Trans-decalin 2 78 53PS/PSPTCDIPS Trans-decalin 5 82 57PS/PSPTCDIPS Trans-decalin 10 79 50PDMS/Mono-PDMS Propylamine 2 65 55PDMS/Mono-PDMS Propylamine 5 68 59PDMS/Mono-PDMS Propylamine 10 66 58PDMS/Di-PDMS Propylamine 5 65 55PDMS/Di-PDMS Propylamine 10 63 53

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GYgraph of the uorescent PDMS gel, with Mono or Di-PDMSincorporated.

The morphology in the case of PS/PSPTCDIPS withtrans-decalin gel is shown in Fig. 8. As we discussed before,PSPTCDIPS forms brillar morphology in trans-decalinFig. 7. OM images of gels of PDMS with (a) 2%, (b) 5%, (c) 10% Mono-PDMS anPDMS + 5 wt% MonoPDMS gel, (g) emission color (kEx: 470 nm), (h) PDMS + 5 wtreferences to color in this gure legend, the reader is referred to the web versioratio I00/I01 of 0.97. There is a slight red shift of the of theS00 peak, in the absorption spectrum with increasing con-centration of PSPTCDIPS to 5% (503 nm, 546 nm) and10% (504 nm, 548 nm) and the S00 peak increases in inten-sity signicantly. Such a change in the relative intensity ofd (d) 5%, (e) 10% Di-PDMS. Photographs are shown for the following: (f)% DiPDMS gel, (i) emission color (kEx: 497 nm). (For interpretation of then of this article.)

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GYthe S00 peak with concentration was seen with the gels ofPSPTCDIPS by itself [34]. Fig 9(b) shows quenching ofthe uorescence with increasing PSPTCDIPS concentra-tion. This would indicate a higher order aggregation processwith higher concentration.

The absorption spectra (not shown here) of the PDMS/5% Mono-PDMS gels showed peaks at 470, 495 and ashoulder at 545 nm. This is nearly identical to the spectraof pure Mono-PDMS gels in propylamine. The quenchingof uorescence intensity indicated stacking of the peryleneunits in the gel state.

Fig. 8. OM of polystyrene gels with (a) 5% and (b) 10% PSPTCDIPS; (ce) SEM im(g) show the color of the gel and the emission color (kEx: 503 nm), respectively. (Fis referred to the web version of this article.)

Fig. 9. (a) UVVis and (b) uorescence spectra4. Conclusions

We have shown that dispersing oligomer functionalizedperylene imides in the corresponding polymers gives riseto organized domains, without any change in the opticalproperties. While perylene or perylene diimide by itselfwill form single-crystal-like morphology when dispersedin polymers, the oligomer attached to the imide nitrogen(s)acts as a compatibilizer. Typically, concentration of 50 wt%or more of the photo-conducting molecule (such as TPD) inthe polymer matrix is required for efcient charge

ages of polystyrene gels with (c) 2%, (d) 5%, (e) 10% PSPTCDIPS. (f) andor interpretation of the references to color in this gure legend, the reader

of PS with 2%, 5%, or 10% PSPTCDIPS.

shown in Fig. 1(c)(e).

E. Dahan, P.R. Sundararajan / European Polymer Journal 65 (2015) 414 13

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GYAppendix A. Supplementary material

Supplementary data associated with this article can befound, in the online version, at http://dx.doi.org/10.1016/j.eurpolymj.2014.11.022.

References

[1] Borsenberger PM, Weiss DS. Organic photoreceptors forxerography. New York: Marcel Decker Inc.; 1998.

[2] Stolka M, Yanus JF, Pai DM. Hole transport in solid solutions of adiamine in polycarbonate. J Phys Chem 1984;88:470714.

[3] Borsenberger PM. Hole transport in tri-para-tolylamine-dopedbisphenol-A-polycarbonate. J Appl Phys 1990;68:626373.

[4] Lin LB, Jenekhe SA, Borsenberger PM. High electron mobility inbipolar composites of organic molecules. Appl Phys Lett1996;69:34957.

[5] Zmija J, Klosowicz SJ, Raszewski Z. Polymer-dispersed liquid-crystaldisplays: properties and applications. Opto-Electron Rev1993;4:1304.

[6] Zmija J, Klosowicz SJ, Raszewski Z. Polymer-dispersed liquid-crystaldisplays: principles, preparation, properties and applications. ProcSPIE, Liquid Solid State Cryst: Phys Technol Appl 1993;1845:1628.

[7] Santerre F, Bedja I, Dodelet JP, Sun Y, Lu J, Hay AS, et al. Hole transportmolecules in high Tg polymers: their effect on the performance oforganic light-emitting diodes. Chem Mater 2001;13:173945.

[8] Khan F, Sundararajan PR. Inuence of polycarbonate exibility onthe annealing-induced phase separation of the hole transportmolecule TPD in a model charge transport composite. J Phys ChemB 2004;108:11726.

[9] Khan F, Hor AM, Sundararajan PR. Morphological reasoning for theenhanced charge carrier mobility of a hole transport molecule inpolystyrene. Pure Appl Chem 2004;76:146778.

[10] Khan F, Hor AM, Sundararajan PR. Morphological aspects andthermal behavior of tri-p-tolylamine (TTA) based model chargetransport. However, both self-assembly and percolationthreshold were achieved with less than 10 wt% of the oli-gomer functionalized PTCDI in the corresponding poly-mers, while maintaining the transparency of thecomposite lm. The concept of photoconductors with con-trolled aggregation was discussed by Dulmage et al. [55]almost 36 years ago. In this paper we have shown thatpolymer-compatibilized PTCDI enables creation of suchuniform morphology of self-assembled PTCDI segments.It is also seen that the self-assembled structures developin the bulk of the polymer matrix, and are not seen onthe surface. This would be an advantage for exible poly-mer based devices. Although nano-wires and similar self-assembled morphologies have been reported with dove-tail or hydrophilic/hydrophobic asymmetric substitutions,the work described here involves compatibilization withcommon, commodity polymers as matrices. The compositegels discussed here show that the oligomer functionalizedphotoactive molecules in the polymer based gels retaintheir optical (aggregation) behavior and these could beeventually candidates for uidic photoactive applications.With the gels also, we used common polymers: polysty-rene with a Tg of 100 C and PDMS with a Tg of 100 C.

Acknowledgements

Financial support from the Natural Sciences and Engi-neering Research Council of Canada is gratefully acknowl-edged. We thank Dr. M.R. Islam of our group for the OMtransport composites: a comparison with TPD. Synth Met2005;150:199211.

[11] KhanF,KhannaS,HorA, Sundararajan PR. The role ofmolecular volumeand the shape of the hole transport molecule in the morphology ofmodel charge transport composites. Can J Chem 2010;88:24759.

[12] Smith PF, Gerroir P, Xie S, Hor AM, Popovic Z. Degradation of organicelectroluminescent devices. Evidence for the occurrence ofspherulitic crystallization in the hole transport layer. Langmuir1998;14:594650.

[13] Scharfe M. Electrophotography principles and optimization. NewYork: John Wiley & Sons; 1984.

[14] Frechet JMJ, Gauthier S, Limburg WW, Loutfy RO, Murti DK, SpiewakJW. Polyarylamine compounds and systems utilizing polyarylaminecompounds. US Patent 4,801,517; 1989.

[15] Ong BS, Keoshkerian B, Baranyi G, Murti DK. Photoconductiveimaging members with diaryl biarylamine copolymer chargetransport layers. US Patent 4, 959, 288; 1990.

[16] Liu Y, Liu MS, Li XC, Jen AKY. Synthesis and characterization of anovel light-emitting polymer containing highly efcient hole-transporting aromatic diamine. Chem Mater 1998;10:33014.

[17] Schmitz C, Thelakkat M, Schmidt HW. A combinatorial study of thedependence of organic LED characteristics on layer thickness. AdvMater 1999;11:8216.

[18] Liu Y, Ma H, Jen AKY. Synthesis and characterization of a bipolarlight-emitting copolymer consisting of tetraphenyldiaminobiphenyland bis-quinoline units. Chem Mater 1999;11:279.

[19] Chen JT, Hsu CS. Conjugated polymer nanostructures for organicsolar cell applications. Polym Chem 2011;2(12):270722.

[20] Cheng YJ, Yang SH, Hsu CS. Synthesis of conjugated polymers fororganic solar cell applications. Chem Rev 2009;109(11):5868923.

[21] Earmme T, Hwang YJ, Subramaniyan S, Jenekhe SA. All-polymer bulkheterojuction solar cells with 4.8% efciency achieved by solutionprocessing from a Co-solvent. Adv Mater 2014;26:60805.

[22] Law KY. Organic photoconductive materials: recent trends anddevelopments. Chem Rev 1993;93:44986.

[23] Schmidt-Mende L, Fechtenktter A, Mllen K, Moons E, Friend RH,MacKenzie JD. Self-organized discotic liquid crystals for high-efciency organic photovoltaics. Science 2001;293:111922.

[24] (a) Graser F, Hdicke E. Crystal structure and color of perylene-3, 4:9, 10-bis (dicarboximide) pigments. Liebigs Ann Chem1980;12:19942011;(b) Hdicke E, Graser F. Structures of eleven perylene-3,4:9,10-bis(dicarboximide) pigments. Acta Crystallogr Sect C1986;42:18995;(c) Klebe G, Graser F, Hdicke E, Berndt J. Crystallochromy as a solid-state effect: correlation of molecular conformation, crystal packingand colour in perylene-3,4:9,10-bis(dicarboximide) pigments. ActaCrystallogr Sect B 1989;45:6977.

[25] Wrthner F, Hanke B, Lysetska M, Lambright G, Harms GS. Gelationof a highly uorescent urea-functionalized perylene bisimide dye.Org Lett 2005;7:96770.

[26] Li XQ, Stepanenko V, Chen Z, Prins P, Siebbeles LD, Wurthner F.Functional organogels from highly efcient organogelator basedon perylene bisimide semiconductor. Chem Commun 2006;37:38713.

[27] Wrthner F. Perylene bisimide dyes as versatile building blocks forfunctional supramolecular architectures. Chem Commun2004:156479.

[28] Balakrishnan K, Datar A, Oitker R, Chen H, Zuo J, Zang L. Nanobeltself-assembly from an organic n-type semiconductor: propoxyethyl-PTCDI. J Am Chem Soc 2005;127:104967.

[29] Balakrishnan K, Datar A, Naddo T, Huang J, Oitker R, Yen M, et al.Effect of side-chain substituents on self-assembly of perylenediimide molecules: morphology control. J Am Chem Soc2006;128:73908.

[30] Yagai S, Monma Y, Kawauchi N, Karatsu T, Kitamura A.Supramolecular nanoribbons and nanoropes generated fromhydrogen-bonded supramolecular polymers containing perylenebisimide chromophores. Org Lett 2007;9:113740.

[31] Chen L, Henrike W. Perylene imides for organic photovoltaics:yesterday, today, and tomorrow. Adv Mater 2012;24:61336.

[32] Huang C, Barlow S, Marder SR. Perylene-3,4,9,10-tetracarboxylicacid diimides: synthesis, physical properties, and use in organicelectronics. J Org Chem 2011;76:2386407.

[33] Islam M, Sundararajan PR. Nano-scale self-assembly impeded byCH p interaction in block selective solvents in the case ofoligostyreneperylene diimideoligostyrene (CoilRodCoil)molecule. Eur Polym J 2013;49:204251.

[34] Dahan E, Sundararajan PR. Solvent-dependent nanostructures of gelsof a Gemini surfactant based on perylene diimide spacer andoligostyrene tails. Eur Polym J 2014;61:11323.

[35] Yao D, Bender TP, Gerroir PJ, Sundararajan PR. Self-assembledvesicular nanostructures of perylene end-cappedpoly(dimethylsiloxane). Macromolecules 2005;38:69728.

[36] Yao D, Tuteja B, Sundararajan PR. Pigment-mediated nanowebmorphology of poly(dimethylsiloxane)-substituted perylenebisimides. Macromolecules 2006;39:77868.

[37] Dahan E, Sundararajan PR. Thermo-reversible gelation of rod-coiland coil-rod-coil molecules based on poly (dimethyl siloxane) andperylene imides and self-sorting of the homologous pair. Soft Matter2014;10:533749.

[38] Dahan E, Sundararajan PR. Thermoreversible physical gels ofpoly(dimethylsiloxane) without cross-links or functionalization.Langmuir 2013;29(27):84528.

[39] Islam MR, Sundararajan PR. Tubular or subsurface morphology ofoctabutoxyphthalocyanine upon self-assembly in polymermatrices: effect of the casting solvent. Chem Eur J

(d) Saha A, Roy B, Garai A, Nandi AK. Two-componentthermoreversible hydrogels of melamine and gallic acid. Langmuir2009;25:8457.

[51] Dasgupta D, Srinivasan S, Rochas C, Ajayaghosh A, Guenet JM. Hybridthermoreversible gels from covalent polymers and organogels.Langmuir 2009;25:85938.

[52] Lopez D, Guenet JM. Encapsulation of laments of a self-assemblingbicopper complex in polymer nanowires. Eur Phys J Part B1999;B12:40511.

[53] Khan MK, Sundararajan PR. Encapsulation of dye molecules andnanoparticles in hollow organogel bers of a nonchiral polyurethanemodel compound. Chem Eur J 2011;17:118492.

[54] KhanMK, ChanA, Sundararajan PR. Two component gels of immiscibleblends of biscarbamates (polyurethane model compounds) andpoly(e-caprolactone). Soft Matter 2012;8:1014957.

[55] Dulmage WJ, Light WA, Marino SJ, Salzberg CD, Smith DL,Staudenmayer WJ. An aggregate organic photoconductor. I.Chemical composition, preparation, physical structure, and opticalproperties. J Appl Phys 1978;49:554354.

14 E. Dahan, P.R. Sundararajan / European Polymer Journal 65 (2015) 414

MACR

OMOLECU

LARNANOTE

CHNOLO

GY2011;17:6098108.[40] Islam MR, Sundararajan PR. Morphology of a hydrogen-bond

mediated self-assembling small molecule in a polycarbonatematrix. Can J Chem 2008;86:6007.

[41] Tuteja B, Moniruzzaman M, Sundararajan PR. Domains of colloidalsize, mediated by self-assembly of small molecules in a polymermatrix: a three-level hierarchy of assembly. Langmuir2007;23:470911.

[42] Ong BS, Keoshkerian B, Murti DK. Photoresponsive imagingmembers with electron transport overcoatings, US Patent4,835,081; 1989.

[43] Sundararajan PR, Murti DK, Odell PG, Hamer GK. Photoreceptorincluding rotaxanes. US Patent 6, 096,464; 2000.

[44] Babu SS, Praveen VK, Ajayaghosh A. Functional p-gelators and theirapplications. Chem Rev 2014;114:19732129.

[45] Sugiyasu K, Fujita N, Shinkai S. Visible-light-harvesting organogelcomposed of cholesterol-based perylene derivatives. Angew ChemInt Ed 2004;43:122933.

[46] Wurthner F, Hanke B, Lysetska M, Lambright G, Harms GS. Gelationof a highly uorescent urea-functionalized perylene bisimide dye.Org Lett 2005;7:96770.

[47] Wu HX, Xue L, Shi Y, Chen YL, Li XY. Organogels based on J- and H-type aggregates of amphiphilic perylenetetracarboxylic diimides.Langmuir 2011;27:307482.

[48] Diaz DD, Cid JJ, Vazquez P, Torres T. Strength enhancement ofnanostructured organogels through inclusion of phthalocyanine-containing complementary organogelator structures and in situcross-linking by click chemistry. Chem Eur J 2008;14:926173.

[49] Diaz DD, Torres T, Zentel R, Davis R, Brehmer M. Physicochemicalcharacterization of octakis(alkyloxy)-substituted Zn(II)-phthalocyanines non-covalently incorporated into an organogeland their remarkable morphological effect on the nanoscale-bers.Chem Commun 2007:236971.

[50] (a) Lee HY, Nam SR, Hong JI. Microtubule formation using two-component gel system. J Am Chem Soc 2007;129:10401;(b) Hirst AR, Smith DK, Harrington JP. Unique nanoscalemorphologies underpinning organic gel-phase materials. Chem EurJ 2005;11:65529;(c) Hirst AR, Smith DK, Feiters MC, Geurts HPM, Wright AC. Two-component dendritic gels: easily tunable materials. J Am Chem Soc2003;125:90101;Professor Bob Marchessault at University ofMontreal. Sundar was then employed at XeroxResearch Centre of Canada in Mississauga,Ontario for 25 years, as a member of researchstaff, Manager of Materials Characterizationand as Principal Scientist. His work at Xeroxwas focused on morphology of photorecep-tors, simulation of polymer conformations

and chain-folding. He became a professor at the Department of Chemis-try, Carleton University in Ottawa, Canada in 2000 as the NSERC-XeroxIndustrial Research Chair. Sundars current research is on morphology ofpolymer composites, self-assembly, organo- and polymer gelation. He is aFellow of the Chemical Institute of Canada and the winner of theMacromolecular Science and Engineering Award of the Chemical Instituteof Canada and the Materials Chemistry Award of the Canadian MaterialsSociety. He has published over 150 papers and holds 10 patents.of RodCoil and CoilRodCoil MoleculesBased on Perylene Diimide. E.D. was a reci-pient of the Ontario Government Scholarshipfor Science and Technology in 2011 as well aswell as a recipient of the Queen Elizabeth IIGraduate Scholarship in 2012.

Dr. Sundararajan (Sundar) graduated fromthe University of Madras in 1969. He spentpost-doctoral tenures with Professor PaulFlory at Stanford University and withDr. Elianne Dahan graduated from CarletonUniversity with a Doctorate of Philosophy inChemistry in January 2014. Her doctoralresearch was on The Gelation and Morphology

Polymer compatibilized self-assembling perylene derivatives1 Introduction2 Experimental3 Results and discussion3.1 Morphology of the composite films3.2 Optical properties of the composite films3.3 Composite gels3.4 Morphology of the composite gels3.5 UVVis and fluorescence spectra of the composite gels

4 ConclusionsAcknowledgementsAppendix A Supplementary materialReferences