polythiophenes ( pts ) 
 are the most widely studied conjugated polymers 
 in organic electronics and are currently employed in field - effect 
 transistors , light - emitting diodes , and organic photovoltaics . unsubstituted 
 pt is highly crystalline and thus insoluble , hampering its processability ; 
 however , 3-hexyl substitution overcomes these limitations . the synthesis 
 of poly(3-hexylthiophene ) ( p3ht ) has been studied extensively over 
 the last few decades . grignard metathesis ( grim ) polymerization is 
 a particularly powerful approach and allows for the large - scale preparation 
 of highly regioregular p3ht at noncryogenic reaction temperatures . in order to enhance and fully exploit the properties of pts , 
 facile 
 chemical modification of pts is necessary . in particular , the tailoring 
 of pt properties has largely focused on the addition of alkyl or functional 
 side chains to the 3- and/or 4-positions in order to expand their 
 structure  property relationships for improved utility in optoelectronic 
 devices . for example , ueda and co - workers reported regioregular pts with 
 phenyl and pyridyl side chains , which have resulted in decreased band - gaps 
 as a result of extended -conjugation . ludwigs and co - workers reported that head - to - tail pts having an 
 alkylthiophene side chain display a 30% increase in open circuit voltage 
 ( voc ) in solar cells , which was attributed 
 to a lowered highest occupied molecular orbital ( homo ) . our group has reported pentafluorophenoxy - containing 
 analogues of regioregular p3ht , which behave as surfactants at the 
 bulk heterojunction interfaces . it was found that the addition of 
 only a small amount of these materials yielded a 30% increase in power 
 conversion efficiency ( pce ) as compared to a p3ht : pcbm standard . in addition to solar cells , functionalized pts 
 play a pivotal role in designing chemoresistive sensors when used 
 to wrap carbon nanotubes ( cnts ) . using this scheme , customized , receptor - functionalized 
 pts were used to create selective detection schemes for chemical warfare 
 agents and were able to distinguish between 
 structural isomers of xylene . methods 
 to prepare functionalized pts generally integrate the side - chains 
 or functional groups at the monomer stage . a clear advantage of this 
 approach is that 100% of the thiophene repeating units can be reliably 
 functionalized . however , this method is not universally applicable , 
 and in particular , grim polymerization conditions are not compatible 
 with many functional groups . as a result , postpolymerization modification can offer an alternative , efficient strategy 
 to functionalize pts . for example , current methods to modify pts via 
 postpolymerization modification include the grim polymerization of 
 protected terminal alkyne or alkyl bromide 
 thiophene monomers , which can be modified 
 after polymerization through cu - mediated huisgen 1,3-dipolar cycloaddition or nucleophilic substitution , respectively . these approaches allow 
 for the installation of functional groups which could not be employed 
 in a grim polymerization ; however , these examples still entailed preparation 
 of specialized monomers . a more attractive approach is the direct 
 modification of commercially 
 available regioregular p3ht . previously , holdcroft and co - workers 
 have achieved efficient , direct modification of the 4-position of 
 p3ht through electrophilic bromination with n - bromosuccinimide 
 ( nbs ) . the brominated p3ht ( br  p3ht ) 
 then served as a cross - coupling substrate to introduce functionality 
 to the 4-position of p3ht via suzuki others have extended these 
 cross - coupling strategies to introduce fullerene derivatives , pyrene , perylene bisimide , and copolymers . herein , we expand the 
 utility of br  p3ht and demonstrate that near - quantitative lithiumhalogen 
 exchange occurs at the 4-position and can be quenched with a variety 
 of electrophiles to yield new 4-position functionalized p3hts ( scheme 1 ) . chemicals were purchased 
 from aldrich , alfa aesar , and tci america without further purification 
 unless noted otherwise . methanol - d4  100%  
 ( d , 99.95% ) in ampules were purchased from cambridge isotope laboratories , 
 inc . anhydrous 
 tetrahydrofuran ( thf ) was obtained from sigma - aldrich dry solvent 
 kegs and kept in a schlenk flask with molecular sieves ( 3  ) . difluorobenzocyclooctyne ( 20 ) was synthesized by the 
 literature procedure with the use of tetrabutylammonium fluoride ( tbaf ) , 
 instead of csf . all h and f nmr spectra were collected on a bruker avance-400 and data 
 are reported in ppm . h nmr spectroscopy is referenced 
 to solvent peaks , and f nmr spectroscopy is referenced 
 to trifluorotoluene (  = 62.72 ppm ) . the multiplicity 
 is reported as follows : s = singlet , d = doublet , t = triplet , m = 
 multiplet or unresolved , br = broad , bs = broad singlet , and bm = 
 broad multiplet . coupling elemental analyses were carried out by robertson microlit laboratories , 
 ledgewood , nj ( usa ) . the solutions were prepared 
 in dichloromethane or chloroform with concentrations between 10 m and 10 m. thin films were prepared 
 on glass by spin - coating 3500 rpm for 30 s from a solution of functionalized 
 p3ht in chlorobenzene ( 1 mg / ml , f p3ht is not completely soluble 
 in this concentration , and undissolved polymers are removed by filtration ) . fluorescence measurements were performed at room temperature with 
 a horiba jobin yvon spex fluorolog-3 fluorimeter ( model fl-321 , 
 450 w xenon lamp ) using right - angle conformation . infrared ( ir ) spectra 
 were measured on a thermo scientific nicolet 6700 fourier transform 
 infrared spectrometer using the attenuated total reflectance ( atr ) 
 mode on a germanium crystal . thf gel permeation chromatography ( gpc ) 
 was performed ( 0.5 mg / ml ) on an agilent 1260 infinity system , calibrated 
 with polystyrene standards . cyclic voltammetry was carried out with 
 an autolab pgstat 10 potentiostat ( eco chemie ) on a three electrode 
 system : polymer film on indium tin oxide ( ito)-coated glass ( 1.2 cm 
  1.2 cm ) as a working electrode , pt wire as a counter electrode , 
 and ag / agcl as a reference electrode . polymer films on ito - coated 
 glass were prepared by spin - coating a solution of pt in chloroform 
 ( 2 mg / ml , f p3ht was sonicated to dissolve it for about 1 h ) 
 with 2000 rpm for 30 s. the film was dried and annealed at 70 c 
 for 15 min . the area of 1.2 cm  0.7 cm was immersed in the electrolyte 
 ( 0.1 m tetrabutylammonium hexafluorophosphate in anhydrous acetonitrile ) 
 during measurement . briefly , to a stirring solution of commercial p3ht ( 300 mg , 1.80 
 mmol in terms of repeat unit ) in chloroform ( 20 ml ) , nbs ( 386 mg , 
 2.16 mmol ) was added portionwise . the temperature was elevated to 50 c 
 for 2 h , then the mixture was cooled and poured into a saturated nahco3 solution ( 50 ml ) . the precipitate was isolated by filtration and dried 
 overnight under vacuum at room temperature , resulting in a yellow 
 solid ( 441.6 mg , 1.80 mmol in terms of repeat unit , 99% yield based 
 on 100% bromination ) . to a stirring solution 
 of br p3ht ( 30 mg , 0.122 mmol in terms of repeat units ) in 
 thf ( 6 ml ) at 78 c , was added n - buli 
 ( 0.612 mmol , 5 equiv , 1.6 m in hexane , 0.38 ml ) dropwise . after 15 
 min of stirring , an electrophile ( 1.22 mmol , 10 equiv ) was added to 
 the mixture . the temperature 
 was increased to room temperature , and the resulting mixture was stirred 
 for 4 h. methanol ( 50 ml ) was added and stirring continued until precipitate 
 was generated . the precipitated solution was filtered , and the polymer 
 was dried overnight under vacuum at 50 c . to a 
 stirring solution of br  p3ht ( 30 mg , 0.122 mmol in terms of 
 repeat units ) in thf ( 6 ml ) at 78 c , was added n - buli ( 0.612 mmol , 5 equiv , 1.6 m in hexane , 0.38 ml ) dropwise . after 20 min of stirring , n - fluorobenzenesulfonimide 
 ( 1.22 mmol , 10 equiv , 0.386 mg ) dissolved in thf ( 2 ml ) was added . the mixture was stirred for 2 h , at which point the temperature was 
 increased to room temperature and the solution was further stirred 
 for 20 h. methanol ( 50 ml ) was added to precipitate the polymer . p3ht 
 ( 16 ) was collected by filtration , washed with methanol 
 and acetone , and dried under vacuum at 50 c overnight . the procedure 
 is the same as the general procedure until the quenching step ( 4 h 
 stirring at room temperature ) . this reaction is quenched by glacial 
 acetic acid ( 1.22 mmol , 10 equiv , 0.068 ml ) or hydrochloric acid ( 1.22 
 mmol , 10 equiv , 3 m , 0.4 ml ) , and then the mixture was stirred for 
 3060 min . methanol ( 50 ml ) was added and stirring continued 
 until precipitate was generated . the precipitated solution was filtered , 
 and the polymer was dried overnight under vacuum at 50 c . because 
 of insolubility after precipitation , the crude mixture prior to methanol - induced 
 precipitation was used for the next click reaction . to the 
 mixture of 17 containing acetic acid were added 
 phenyl propargyl ether ( 12 equiv , 0.094 ml ) , dipea ( 50 equiv , 0.54 
 ml ) , and cui ( 14 mg , 10 mol % of the acetylene ) . the mixture was heated 
 at 50 c and stirred for 42 h. methanol was added to precipitate 
 the polymer , and the polymer was collected by centrifugation ( 11k 
 rcf , 10 min ) , washed with acetone : ethyl 
 acetate ( 1:1 ) , and dried under vacuum at 50 c overnight . the mixture 
 of 17 containing hcl was neutralized with 
 naoh ( aq , 10% ) , and difluorobenzocyclooctyne ( 20 ) ( 1.47 mmol , 12 equiv , 282 mg ) in thf was added . the 
 polymer was precipitated with methanol ( 50 ml ) , collected by filtration , 
 washed with methanol , and dried overnight under vacuum at 50 c . 7,7-difluoro-5-(trimethylsilyl)-7,8,9,10-tetrahydrobenzoannulen-6-yl 
 triflate ( 700 mg , 1.69 mmol ) was dissolved 
 in thf ( 3 ml ) . to this mixture was added tetrabutylammonium fluoride 
 solution ( 1 m in thf , 1.1 equiv , 1.86 ml ) , and the reaction mixture 
 was stirred at room temperature for 10 min . lithium  bromine exchange is an extensively 
 utilized chemical 
 transformation , and most aryl or vinyl bromides react with alkyllithium 
 reagents to form new organolithiates . these aryl- and vinyllithium 
 species are highly reactive intermediates and readily combine with 
 electrophiles . this strategy is widely employed in small - molecule 
 chemistry ; however , its extension to polymer chemistry has been limited , 
 most likely as a result of concerns over polyanion formation . specifically , 
 it is well - accepted that generating a second anion within the same 
 molecule is much more difficult to form than the first . extrapolating this to a polymer chain , the ( n + 1 ) anion should be more difficult to form 
 than the n anion . to explore the limits 
 of lithium  halogen exchange and its utility in polymer systems nmr indicates 
 conversions determined 
 by h nmr integration , and ea indicates conversions determined 
 by elemental analysis . h nmr spectra of the polymers : ( a ) p3ht , ( b ) 1 ( br  p3ht ) , 
 ( c ) 3c , and ( d ) 4 . the sharp peak at 6.98 
 ppm from 4-position proton (  ) enables 
 the estimation of the li br exchange by comparison to the peak 
 at 2.81 ppm from methylene (  ) of the hexyl 
 chain . for detailed integration values and peak locations , please 
 refer to the supporting information . to test the efficiency of polyanion 
 formation from br p3ht 
 ( 1 ) , we subjected 1 to varying amounts of n - butyllithium ( n - buli ) , followed by quenching 
 with excess methanol and examined the conversion back to p3ht ( scheme 2 ) . bromine 
 exchange by comparing the nmr spectrum integration values of the thiophene 
 4-h ( 6.98 ppm , figure 1 ) with the -methylene 
 of the hexyl chain ( 2.81 ppm , figure 1 ) in 
 addition to analyzing the weight percent of bromine as determined 
 by elemental analysis ( ea ) . the results are summarized in table 1 and the nmr spectra are shown in figure 1 , where x and y represent monomers containing hydrogen and bromine at the 4-position , 
 respectively . gratifyingly , our results indicated we were indeed able 
 to achieve near - quantitative lithium  bromine exchange on p3ht . standard small - molecule conditions for lithiumhalogen exchange 
 often employ 1.2 equiv of butyl lithium . using analogous conditions , 
 we found that 73% lithiation was observed ( 3a ) . upon 
 increasing the amount of n - buli ( 3b3d ) , more than 95% lithium the ea data for 3a3d also display 
 analogous trends to the nmr spectra . from table 1 , it is evident that as the amount of n - buli is 
 increased , the recovered yields also increase . this relationship appears 
 to be the result of more efficient precipitation of the polymers from 
 methanol due to the higher salt concentration ( lithium salt ) in the 
 reaction mixture . the salt weakens the solvation of the polymer by 
 interacting with thf and thus facilitate polymer aggregation . the 
 dispersity of 3a3d is increased 
 during the reaction from the corresponding br p3ht starting 
 polymer ( 26 kda , mw / mn = 1.80 ) to 3a ( 15 kda , mw / mn = 3.01 ) , 3b ( 28 kda , mw / mn = 9.43 ) , 3c ( 41 kda , mw / mn = 7.39 ) , and 3d ( 24 
 kda , mw / mn = 13.4 ) . the gpc traces of these polymers ( supporting 
 information ) show that new peaks at higher molecular weight 
 portions ( such as 100 kda and 550 kda ) emerged , suggesting some oligomerization 
 and/or cross - linking . the exact nature of these high molecular weight 
 species has not been determined . considering the above results , we 
 choose to develop a new pt modification methodology using 5 equiv 
 of n - buli . before proceeding with the introduction 
 of electrophiles to the 
 lithiated p3ht , we further investigated the origin of the 4-position 
 proton in our methanol quenching experiments . in light of the high 
 basicity of the multilithium intermediate 2 , a portion 
 of the recovered 4-position proton could originate from undesired 
 proton impurities such as deprotonation of the -methylene on 
 the hexyl chain or the solvent , thf . to assay this , under rigorously 
 dry conditions , br p3ht was combined with 5 equiv of n - buli and quenched with deuterated methanol ( cd3od ) , yielding 4 ( scheme 2 ) . the 
 nmr spectrum of polymer 4 ( figure 1d ) showed 24% recovery of the 4-position thiophene proton at 6.98 
 ppm . by assuming that residual bromine content of 4 is 
 the same as the contents of 3c ( that is , 6% ) , 70% of 
 the monomers contained a deuteron ( z = 0.70 , scheme 2 ) . this result demonstrates that with this methodology 
 p3hts containing up to 70% modification at the 4-position can be achieved . it should be noted that lower degrees of functionalization can also 
 be achieved by controlling the levels of bromination . the possible avenue for introduction of the recovered 4-position 
 proton in 4 could be e2 elimination of n - butyl bromide formed in situ by li however , the direct introduction of n - butyl bromide 
 did not increase the recovered 4-position proton ( see supporting information ) , suggesting this is not 
 a significant source of recovered proton . the efficient lithiation 
 and quenching suggested that this methodology 
 could be a versatile , efficient approach for the synthesis of 4-position 
 functionalized p3ht by introducing lithiated intermediate 2 to a variety of electrophiles . we first applied this methodology 
 to the synthesis of ketone - functionalized p3hts ( 511 in scheme 3 ) by the introduction 
 of anhydrides to 2 . we found that short , long , and bulky 
 alkyl ketones ( 57 ) , trifluoromethyl 
 ketone ( 8) , and aryls with different substituents ( 911 ) can all be appended to p3ht . the 
 conversions ( z values in scheme 3 ) range from 4765% as determined by nmr spectroscopy . infrared ( ir ) spectroscopy confirms the appearance of distinct ketone 
 peaks at around 16501800 cm for all cases 
 ( 511 , see supporting 
 information ) . secondary alcohol p3ht derivatives ( 1214 ) were obtained by quenching the intermediate 2 with the corresponding aldehydes . despite being weaker electrophiles 
 than anhydrides , trimethylsilyl ( tms ) functionalized p3ht ( 15 ) was synthesized 
 by quenching the lithiated p3ht with tms chloride to result in 59% 
 incorporation of tms groups . fluoride and azide moieties could also 
 be installed at the 4-position using n - fluorobenzenesulfonimide 
 ( nfsi ) and tosyl azide as electrophiles , respectively ( vide infra ) . the dispersity of most of the synthesized polymers is increased during 
 the chemical transformation as shown in the gpc traces ( supporting information ) . although there could 
 be multiple interpolymer coupling in the ketone - functionalized p3hts , 
 it is most likely that the increased dispersity is primarily due to 
 the lithium  bromine exchange , since 3a3d have already possessed the increased dispersity . the conversion determined 
 by f nmr with trifluorotoluene as an internal standard 
 in nmr solvent . the conversion is slightly overestimated due to overlapped 
 peaks in the aryl region of the h nmr spectra with cdcl3 . the conversion can not be 
 calculated with a single value due to the overlapped peaks of -ch2 of hexyl chain with ar - me . recently , roncali and co - workers have 
 proposed 4-fluoro - p3ht ( f  p3ht , 16 ) as an advantageous 
 material for organic photovoltaics due to the combination of its high 
 electronegativity and small size , which will lower the homo and lumo 
 levels yet not significantly alter the crystal packing . despite attempts 
 to synthesize f p3ht with a fluorine atom at each 4-position 
 through a monomer - modification approach , roncali s efforts 
 were unable to surpass 33% fluorination of pt using a monofluorinated 
 terthiophene as the monomer unit . p3ht with higher percent 
 fluorine in fewer steps . upon subjecting lithiated p3ht to nfsi ( figure 2a ) , the introduction of fluorine atoms onto the 
 4-position was immediately evident by the broad singlet at 123.60 
 ppm in the f nmr spectrum ( supporting 
 information ) . the conversion was calculated by determining 
 the amount of 4-position proton by h nmr spectroscopy 
 and 4-position residual bromine by ea . from these values , the amount 
 of 4-position fluorine was inferred to be 67% , twice as much as previously 
 possible by the monomer - modification approach . we further investigated 
 the electronic properties of the f  p3ht and compared it to 
 p3ht and br p3ht through absorption spectroscopy , photoluminescence 
 spectroscopy , and cyclic voltammetry ( cv ) ( figure 2 and supporting information ) . as 
 predicted by roncali and co - workers , the small size of the fluorine 
 atom resulted in minimal twisting of the backbone and thus longer 
 conjugation lengths as compared to br p3ht , although p3ht still 
 appeared to have a superior conjugation length as indicated by solution 
 spectra ( figure 2b , chloroform ) and thin films 
 ( figure 2c ) . p3ht 
 ( 1.97 ev ) , measured from the absorption spectra of the thin film ( figure 2c ) , is similar to p3ht ( 1.90 ev ) , but much smaller 
 than br  p3ht ( 2.80 ev ) . the homo is measured by carrying out 
 cyclic voltammetry in 0.1 m tetrabutylammonium hexafluorophosphate 
 in acetonitrile as an electrolyte , along with a spin - coated polymer 
 film on ito - coated glass , pt wire , and ag / agcl electrode as the working , 
 counter , and reference electrode , respectively . a ferrocene / ferrocenium 
 redox couple was used as an internal standard , assuming its redox 
 positioned at 4.8 ev from vacuum level . p3ht is at 5.38 ev , which is 0.51 ev lower than 
 p3ht ( 4.87 ev ) , indicating increased oxidative stability in 
 the atmosphere . p3ht did not show any significant current 
 peak , indicative of its nonconductive nature and absence of  
 stacked polymer backbone . p3ht thin films exhibit 
 bathochromic shifts as compared to solution ( 451 to 530 nm for p3ht ; 
 419 to 491 nm for f p3ht ) as a result of a planarization of 
 the polymer main chain in the solid state . thin film spectra also 
 show shoulder signals at 600 nm for p3ht and 574 nm for f p3ht 
 that are well - defined vibronic transitions from the planarized  stacked ( partially crystalline ) 
 polymer backbone . as expected in the case of br p3ht , no bathochromic 
 shift or shoulder peak is observed , indicating that the steric bulk 
 of the bromine atoms result in a twisted backbone and thus no  
 stacking is present in the br ( b ) absorption 
 ( solid line ) 
 and photoluminescence ( dotted line ) spectra of p3ht ( black ) , f  p3ht 
 ( red ) , and br  p3ht ( blue ) in chcl3 . excitation at 
 400 nm ( p3ht ) , 380 nm ( f  p3ht ) , and 330 nm ( br  p3ht ) . the films are 
 fabricated on glass by spin - coating each polymer from a chlorobenzene 
 solution . (  ) 
 optical bandgap ( bg ) was measured by onset ( drawing a tangent 
 line ) of the thin film absorption spectra . (  ) homo 
 = e(epolymeronset , oxidation + efconset , oxidation  
 4.8 v ) . , we 
 installed an azide group at the 4-position , 
 which could be further modified through copper - catalyzed or strained - promoted copper - free cycloaddition 
 reactions with alkynes . we were able 
 to synthesize poly(3-azido-4-hexylthiophene ) ( n3p3ht , 17 ) by the addition of tosyl azide to lithiate 2 , followed by the addition of an acid , such as glacial acetic acid 
 or hydrochloric acid ( figure 3a ) . the acidic 
 work - up was employed to prevent base - mediated decomposition pathways , 
 such as the formation of amines from 1,3-disubstituted triazenes . the strong peak in the ir spectrum at 2105 cm ( figure 3b ) indicated the 
 presence of azide moieties . next , we modified 17 through 
 click reactions with alkynes . as a result of the insolubility of azido - p3ht 
 after precipitation in methanol , we took measures to avoid precipitation 
 ( see experimental section ) and performed an in situ click reaction on a crude solution ( suspension ) 
 of 17 . a cu - catalyzed click reaction in the presence 
 of copper iodide ( cui ) , diisopropylethylamine ( dipea ) , and phenyl propargyl ether the ir spectrum of 18 ( figure 3b ) reveals the disappearance of the azide peak , 
 associated with the emergence of characteristic triazole ( 1599 cm ) and phenyl ( 1494 cm ) signals . the resulting triazole - containing p3ht ( 19 ) was soluble in common organic solvents , and h nmr spectroscopy , f nmr spectroscopy , as well as the 
 disappearance of the azido group in the ir spectrum ( figure 3b ) confirmed that the cycloaddition had occurred 
 on the polymer . the analysis of f nmr spectrum indicated 
 that 19 is the major regioisomer . the ability to easily 
 synthesize n3p3ht and its click reaction offer 
 a plethora of opportunities for custom p3ht derivatives to be prepared 
 from commercially available p3ht . ( a ) click reactions with azido - p3ht ( 17 ) in the cu - catalyzed 
 ( 18 ) and strain - promoted cu - free ( 19 ) conditions . ( b ) comparison of ir of 17 ( black ) , 18 ( red ) , 
 and 19 ( blue ) . 17 was prepared by quenching 
 with hcl and resulted in a strong azide peak at 2105 cm . a variety of functionalized 
 p3hts were synthesized in a simple 
 two - step approach bromination of p3ht followed by lithium  bromine exchange and quenching  from 
 commercial p3ht . in contrast to the conventional belief that the generation 
 of multiple reactive anions on one molecule is not favorable , we observed nearly quantitative lithium the multilithiated p3ht is highly reactive , 
 yet stable enough to undergo the next reaction in situ with functional electrophiles , resulting in an array of modified 
 p3hts . we successfully prepared ketone- , 2 alcohol- , tms- , f- , 
 and n3-containing p3hts , many of which could not be synthesized 
 by direct grim polymerization . p3ht 
 in solution and thin films as well as cyclic voltammetry were investigated 
 to infer the electronic properties , chain configuration , and solid 
 state behavior in comparison to p3ht and br  p3ht . additionally , 
 we demonstrated that n3p3ht could be further derivatized 
 with alkynes using click chemistry . this novel , efficient methodology , 
 and more generally the ability to generate polyanions through lithiumhalogen exchange , will 
 allow for the 
 synthesis of many new functional polymers .
poly(3-hexylthiophene ) ( p3ht ) is 
 one of the most extensively investigated 
 conjugated polymers and has been employed as the active material in 
 many devices including field - effect transistors , organic photovoltaics 
 and sensors . as a result , methods to further tune the properties of 
 p3ht are desirable for specific applications . 
 herein , we report a 
 facile postpolymerization modification strategy to functionalize the 
 4-position of commercially available p3ht in two simple steps  bromination 
 of the 4-position of p3ht ( br  p3ht ) followed by lithiumbromine 
 exchange and quenching with an electrophile . 
 we achieved near quantitative 
 lithium  bromine exchange with br 
 p3ht , which requires 
 over 100 thienyl lithiates to be present on a single polymer chain . 
 the lithiated - p3ht is readily combined with functional electrophiles , 
 resulting in p3ht derivatives with ketones , secondary alcohols , trimethylsilyl 
 ( tms ) group , fluorine , or an azide at the 4-position . 
 we demonstrated 
 that the azide - modified p3ht could undergo cu - catalyzed or cu - free 
 click chemistry , significantly expanding the complexity of the structures 
 that can be appended to p3ht using this method .