it will now be convenient to describe the invention with reference to particular embodiments and examples . these embodiments and examples are illustrative only and should not be construed as limiting upon the scope of the invention . it will be understood that variations upon the described invention as would be apparent to the skilled artisan are within the scope of the invention . similarly , the present invention is capable of finding application in areas that are not explicitly recited in this document and the fact that some applications are not specifically described should not be considered as a limitation on the overall applicability of the invention . fig1 provides an overview of the reaction set - ups for 1 , 3dipolar and diels - alder cycloadditions . the process reaction conditions may be appropriately varied and are dependent on the nature of the chemical reaction in question . reaction pressures may range from 40 to 600 psi . preferably reaction pressures are below 250 psi . the reactor residence time may vary , again depending on the specific chemistry , reagent stoichiometry and temperature . residence times may be in the range of 0 . 1 and 10 hours , preferably in the range of 0 . 25 to 4 hours , more preferably in the range of 0 . 5 to 2 hours . the continuous processes of the present invention may comprise a single reaction step or multiple reaction steps . in the latter case different temperatures or irradiation may be applied at individual process sections to promote or accelerate intermediate steps . the continuous processes of the present invention may be performed in one or more tubular reactors or one or more continuous stirred tank reactors or combinations of both . the reactors may be arranged in series or in parallel depending on the specific nature of the chemical steps and the target product mix . two of the most widely used fullerene derivatives in organic electronics are phenyl - c 61 - butyric acid methyl ester ( pc 61 bm ) and its c 70 analogue ( pc 71 bm ). the synthesis of pc 61 bm is essentially a one - pot reaction with three steps [ hummelen , j . c . ; knight , b . w . ; lepeq , f . ; wudl , f . ; yao , j . ; wilkins , c . l . j . org . chem . 1995 , 60 , 532 - 538 ; mayorova , j . y . ; nikitenko , s . l . ; troshin , p . a . ; peregudova , s . m . ; peregudov , a . s . ; kaplunov , m . g . ; lyubovskaya , r . n . mendeleev commun . 2007 , 17 , 175 - 177 ]. in the first step , the diazo intermediate is generated by the reaction of the tosylhydrazone precursor with sodium methoxide [ bamford , w . r ., stevens , t . s . j . chem . soc . 1952 , 4735 ] in the presence of pyridine . 1 , 3 - dipolar cycloaddition of the diazo intermediate to the c 60 followed by n 2 liberation gives a mixture of two isomers of pc 61 bm , the open - cage [ 5 , 6 ] fulleroid and close - cage [ 6 , 6 ] isomer . the mixture can then be thermally isomerized to give exclusively the desired close - cage [ 6 , 6 ] isomer . while this reaction is relatively simple to perform in conventional batch reaction conditions , there are several problems to overcome if the reaction is to be successfully translated to continuous process methods . the primary challenges are the solubility of reactants and products . it would also be advantageous to use reagents that are less sensitive to oxygen and water . electron acceptor phenyl - c 61 - butyric acid methyl ester ( pc 61 bm ) was synthesized using a continuous process ( see fig2 , a and b ). the soluble c 60 fullerene derivative was functionalized via 1 , 3 dipolar cycloaddition with p - tosylhydrazone of methyl benzoylbutyrate as diazoalkane precursor . the optimization parameters were varied in terms of residence times , temperatures and equivalents of tosylhydrazone , thereby translating to variations in yield and nature of by - products ( see table 1 ). excellent results were obtained using stoichiometric quantities of tosylhydrazone 1 at high reaction temperatures , translating the low yielding overnight prior art batch reaction into moderate yields and direct thermolysis to the [ 6 , 6 ] isomer within 100 min ( table 1 , entry 4 ). the large scale continuous synthesis of pc 61 bm was performed with a reactor setup to allow a continuous feed of reactants from a stock solution reservoir ( fig2 , b ). it is important to note that the anomalous solubility behavior of c 60 must be taken into account in large scale continuous reactions . [ ruoff , r . s . ; malhotra , r . ; huestis , d . l . ; tse , d . s . ; lorents , d . c . nature 1993 , 362 , 140 - 141 ] the fact that the solubility of c 60 decreases ( by as much as ⅔ ) with increasing temperature can have significant impact on the progress of the reaction . as the stock solutions were prepared with near saturated room temperature concentrations of c 60 ( 28 mm ), precipitation of c 60 in the tube reactor at temperature exceeding 150 ° c . is likely . to overcome this solubility problem , the reaction temperature was increased gradually from 70 ° c . ( 10 ml internal volume reator ) to 150 ° c . ( 20 ml internal volume reactor ) and 250 ° c . ( 10 ml reaction volume reactor ). the temperature of the final coil reactor portion was raised to 250 ° c ., ensuring complete isomerization from the [ 5 , 6 ] isomer to the [ 6 , 6 ] isomer . additionally , the reduction of the residence time from 100 min ( table 1 , entry 4 ) to 80 min and 40 min yielded 48 % and 39 % conversion respectively . reducing the reaction time to less than one hour compromises the reaction yield by 20 %, while increasing the throughput by 2 . 5 times . an excess of base with respect to the diazo precursor may be preferred , typically between 2 - 10 equivalents and may vary depending on its reactivity . typically 5 equivalents show good results . one equivalent of diazo precursor based on the fullerene is preferably used for monofunctionalization of the dipolarophile , although the amount may be increased if multiple functionalization is desired . diels - alder adducts of indene with fullerenes have been successfully used to improve polymer / fullerene bulk heterojunction ( bhj ) solar cell device performance . both indene - c 60 bisadduct 9 ( ic 60 ba ) and indene - c 70 bisadduct 10 ( ic 70 ba ) are attractive fullerene acceptor materials for two main reasons . firstly , the lowest unoccupied molecular orbital ( lumo ) energy levels of ic 60 ba and ic 70 ba are elevated compared with their pcbm counterparts leading to a larger open circuit voltage in bhj devices with donor polymers . secondly , the synthesis involves only two reactants ; the diels - alder cycloaddition of indene and fullerene ( fig3 , a ). by using 1 , 2 , 4 - trichlorobenzene as solvent , the yield of the reported batch reaction is 34 % for ic 60 ba [ he , y . j . ; chen , h . y . ; hou , j . h . ; li , y . f ., j . am . chem . soc . 2010 , 132 , 1377 ]. for ic 70 ba , a high molar ratio of indene to c 70 in combination with long reaction times were shown to be necessary for good conversions ( 58 %) [ he , y . ; zhao , g . ; peng , b . ; li , y ., adv . funct . mater . 2010 , 20 , 3383 ]. it is important to note that both bisadducts of c 60 and c 70 consist of complex mixtures of regioisomers as can be observed by hplc analyses . one of the advantageous features of continuous reactions is the ability to perform reactions under pressure with superheated solvents . this means the high temperatures required for the diels - alder addition of indene to fullerenes should translate well to continuous methods . indene is thermally converted to isoindene in a tube reactor , which then reacts with c 60 or c 70 via diels - alder cycloaddition ( fig3 , b ). the experiments were conducted with 20 to 36 equivalents of the indene under superheated conditions at 220 ° c . in a stainless steel reactor with o - dcb as a solvent . ic 60 ba and ic 70 ba were both successfully prepared in less than 2 h in 54 % and 49 % yield , respectively ( table1 , entry 7 ) achieving comparable to significantly improved yields over the batch process . it will be apparent to the skilled artisan that the possible applications of the continuous process of the present invention extend well beyond those specific embodiments hereinbefore described . these applications include a wide range of functionalization chemistries . the following examples demonstrate the efficacy of the continuous process of the present invention in the preparation of several functionalized fullerenes . a vapourtec microreactor consisting in a r2 - and a r4 - module with four temperature controllable zones was used ( see www . vapourtec . co . uk ). perfluoroalkoxy ( pfa ) or stainless steel ( 10 ml internal volume ) tubing material was used in the reactor setups . the vapourtec r4 - pumping module was operated in the small scale fluid connection mode with manual loaded sample loops . the reactants were channeled into the tube reactor by pumping solvent from a reservoir at 0 . 1 or 0 . 2 ml / min ( equivalent to residence times of between 50 and 100 min ). all reactions were performed either thermally ( r4 - module , vapourtec ) and / or photochemically ( using a halogen lamp ), in o - dichlorobenzene ( o - dcb ), at concentration ranging from 22 to 28 mm ( based on fullerene component ) and under approximately 6 - 19 bar system pressure . 1 h - nmr measurements were carried out from cdcl 3 solutions on a varian lnova - 400 ( 400 mhz ) or a varian lnova - 500 ( 500 mhz ) instrument . hplc - analysis was carried out using a gilson 712 hplc system , consisting of a gilson 118 uv / vis detector , gilson 307 and 303 pumps . the product ratios and yields are based on the peak integrations of the hplc trace ( detection at 330 and 313 nm ). silica gel ( merck 9385 kieselgel 60 ) was used for flash chromatography . thin layer chromatography was performed on merck kieselgel 60 silica gel on glass ( 0 . 25 mm thick ). a degassed homogeneous solution of c 60 ( 40 mg , 5 . 5 × 10 − 2 mmol ), p - tosylhydrazone of methyl benzoylbutyrate ( 21 mg , 1 equiv .) and tetramethylpiperidine ( 50 μl , 0 . 3 mmol ) in 2 ml o - dcb was pumped through a preheated reactor ( at 135 ° c ., 150 ° c . or 180 ° c .) using a hplc pump at the corresponding flow rate . a backpressure regulator ( 75 psi ) was connected to the outflow . an analytical sample diluted with toluene , washed with water , dried with magnesium sulfate and the yield determined by analytical hplc . a premixed homogeneous solution containing c 60 ( 6 g , 8 . 3 mmol ), p - tosylhydrazone of methyl benzoylbutyrate ( 3 . 18 g , 1 equiv .) and tetramethylpiperidine ( 5 . 7 ml , 34 mmol ) in 360 ml o - dcb was pumped through a preheated reactor at 70 ° c . ( 10 ml internal volume reactor ), followed by a 150 ° c . ( 20 ml internal volume reactor ) and a 250 ° c . ( 10 ml reactor volume ) temperature sector using a hplc pump at 1 ml / min flow rate . a backpressure regulator ( 250 psi ) was connected to the outflow . the product was purified by column chromathography using toluene as eluent to give 2 . 6 g ( 2 . 9 mmol , 35 %) of pc 61 bm . hplc ( min ., detection at 330 nm , 100 % toluene , 1 ml / min ) pc 61 bm : 7 . 5 1 h - nmr ( cdcl 3 , 500 mhz ) δ ppm : 7 . 94 ( d , 2 h , j = 8 hz ), 7 . 56 ( t , 2 h , j = 7 . 5 hz ), 7 . 48 ( t , 1 h , j = 7 . 4 hz ), 3 . 69 ( s , 3 h ), 2 . 92 ( m , 2 h ), 2 . 54 ( t , 2 h , j = 7 . 4 hz ), 2 . 2 ( m , 2 h ). a degassed solution of c 70 ( 40 mg , 4 . 8 × 10 − 2 mmol ), p - tosylhydrazone of methyl benzoylbutyrate ( 20 mg , 1 . 1 equiv .) and tetramethylpiperidine ( 40 μl , 0 . 2 mmol ) in 2 ml o - dcb was pumped through a tube reactor using a hplc pump at the corresponding flow rates and irradiated with a white halogen lamp . an analytical sample was diluted with toluene , washed with water dried with magnesium sulfate and the yield determined by analytical hplc . hplc ( min ., 330 nm , 100 % toluene , 1 ml / min ) pc 71 bm : 6 . 5 1 h - nmr ( cdcl 3 , 500 mhz ) ppm : 7 . 2 - 7 . 95 ( m , 5 h ); 3 . 52 , 3 . 69 ( major isomer ), 3 . 76 ( s , 3h , ratio 1 : 10 : 1 ); 2 . 41 - 2 . 94 ( m , 4 h ); 1 . 79 - 2 . 24 ( m , 2 h ). 13 c - nmr ( cdcl 3 , 500 mhz ) ppm : 173 . 3 , 156 . 0 , 155 . 3 , 152 - 138 ( forest of peaks belonging to sp 2 carbons on the fullerene cage ), 131 . 6 , 130 . 8 , 128 . 6 , 128 . 3 , 72 . 9 , 69 . 9 , 51 . 8 , 36 . 0 , 34 . 2 , 33 . 9 , 21 . 8 . a degassed solution of c 60 ( 40 mg , 5 . 5 × 10 − 2 mmol ) and indene ( 130 μl , 1 . 1 mmol , 20 equiv .) in 2 ml o - dcb was pumped through a preheated reactor ( 220 ° c .) at 100 μl / min . an analytical sample was diluted with toluene / hexane ( 1 : 10 ) and the yield determined by analytical hplc . after precipitation from ethanol , 40 mg of crude product was purified by column chromatography ( 30 % toluene in hexane ). hplc ( min , 313 nm , toluene / hexane ( 1 : 10 ) 1 ml / min ) 1c 60 ba : 16 - 20 1 h - nmr ( cdcl 3 , 500 mhz ) δ ppm : 7 . 91 - 7 . 20 ( m , 8h ), 2 . 57 - 4 . 44 ( m , 4h ), 48 . 08 - 3 . 22 ( m , 2h ), 3 . 06 - 2 . 49 ( m , 2h ). 13 c - nmr ( cdcl 3 , 500 mhz ) δ ppm : 161 - 136 ( forest of peaks belonging to sp 2 carbons on the fullerene cage ), 127 , 124 ( sp 2 carbons on the indene addend ), 74 , 57 , 46 ( sp 3 on the indene addend ). c 70 ( 40 mg , 4 . 7 × 10 − 2 mmol ) and indene ( 200 μl , 36 equiv .) were reacted following the procedure described for ic 60 ba . hplc ( min , 313 nm , toluene / hexane ( 1 : 10 ) 1 ml / min ) ic 70 ba : 30 - 49 1 h - nmr ( cdcl 3 , 500 mhz ) δ ppm : 7 . 73 - 7 . 24 ( m , 8h ), 4 . 79 - 4 . 45 ( m , 2h ), 4 . 33 - 4 . 14 ( m , 2h ), 2 . 92 - 2 . 70 ( m , 2h ), 2 . 50 - 2 . 37 ( m , 2h ). 13 c - nmr ( cdcl 3 , 400 mhz ) δ ppm : 162 - 129 ( forest of peaks belonging to sp 2 carbons on the fullerene cage ), 127 , 124 ( sp 2 carbons on the indene addend ), 68 . 2 , 67 . 4 , 58 . 0 , 55 . 9 , 46 , 38 . 7 ( sp 3 on the indene addend ).