nanoporous materials 
 have attractive properties for a wide variety 
 of applications in adsorption and separation . the 
 presence of a high density of pores with well - defined dimensions gives these materials superior capacity , an increased surface area , 
 and higher selectivity than mesoporous materials . the fabrication 
 of nanoporous materials has two distinct approaches : 
 top - down fabrication , where the pores are introduced by manipulating 
 a pristine material , and fabrication using self - assembly , where the 
 nanostructure is an intrinsic feature of the material . nanoporous 
 materials based on polymers and organic molecules have been prepared 
 via a range of top - down methods , but the use of self - assembly is attractive 
 because it potentially leads to highly efficient manufacturing processes 
 and can perhaps access even smaller features . a widely used strategy 
 to make self - assembled nanostructured materials is to use microphase 
 separation in block copolymers . when this strategy is combined with 
 selective removal of one of the blocks , nanostructured 
 materials with considerably smaller features than 5 nm have been obtained 
 from liquid crystalline ( lc ) building blocks . in columnar lc phases of disk shaped molecules 
 or complexes , features 
 below 2 nm are usually present . polymerization of these 
 phases followed by selective removal of the core of the disk is a 
 powerful and effective method for the preparation of nanoporous polymer 
 films . such films , which combine very small pore sizes with a high 
 pore density , are of interest because they are expected to have favorable 
 properties for many application , e.g. , water desalination or as ion 
 selective membranes in batteries . the 
 scope of nanoporous materials is significantly broadened by 
 chemical modification of the pore surface , which is common practice 
 for zeolites , porous carbon materials , and covalent organic frameworks . the pore interior of top - down fabricated nanochannels in thin films 
 has been chemically modified to tune their mode of selectivity to 
 discriminate on the basis of size , charge , wettability , recognition , 
 or a combination of these properties . pore 
 surface functionalization of nanoporous materials based on 
 self - assembled block copolymer has also been explored ; e.g. , the group 
 of hillmyer reported the conversion of pores lined with carboxylic 
 acids to amides using coupling reagents and three different amines , 
 whereas in another study pores lined with alkene units were successfully 
 converted to epoxides . other 
 examples report e.g. the preparation of quaternary pyridinium salts 
 in pores lined with polymer segments or the formation of pores lined 
 with carboxylate groups after the hydrolysis of dimethylacrylamide 
 groups . it is known that lc based nanoporous materials 
 can selectively adsorb small molecules ; however , covalent pore surface functionalization 
 has not been reported yet for lc based nanoporous networks and would 
 constitute a distinct step forward in the development of functional 
 nanoporous polymers based on lcs because it creates a handle in the 
 pore facilitating modification of the chemical environment of the 
 pore lining . we expect that this additional functionality will provide 
 crucial tunability of lc based nanoporous films for specific applications . in addition to tuning the exact size of the pore , the chemical environment 
 is also modified and affects properties such as flux , selectivity , 
 and rejection , which depend on the interplay between pore size and 
 the chemical environment . fabrication of 
 nanoporous polymer films based on a noncovalent 
 templated liquid crystal , polymerized via alkene metathesis , has been 
 illustrated previously . facile pore surface 
 functionalization of such materials would be a distinct step forward 
 to functional nanoporous membranes . herein , we report on the 
 design and synthesis of a discotic molecule 
 with a triazine core and nine terminal alkene groups at the periphery . the molecules are designed to polymerize through dimerization of alkene 
 groups using acyclic diene metathesis ( admet ) in the colhex lc phase without affecting structural organization 
 of the disks in the lc phase . the imine and ester groups provide two 
 hydrolyzable units ( figure 1 ) for stepwise removal of the inner imine and outer ester 
 core from each disc of the polymer to introduce amine - functionalized 
 smaller cationic pores ( pore diameter 1.3 nm ) and carboxylate - functionalized 
 bigger anionic pores ( pore diameter 2.6 nm ) in the polymer 
 film . the amine and carboxylate functional groups at the pore wall 
 are amenable to chemical conversion to other functionalities . in addition , 
 the porous polymer with charged moieties at the pore surface is well 
 suited to selectively adsorb oppositely charged dyes . ( a ) chemical structure 
 of the triazine based disk shaped molecule , 
 triz - imine . ( b ) pom of triz - imine at 75 c , showing a focal conic 
 texture typical for a colhex phase . picture obtained during 
 cooling from the isotropic state at a rate of 0.1 c / min ( scale 
 bar represents 200 m ) . ( c ) medium angle xrd pattern of the 
 monomer triz - imine and its polymer . ( d ) schematic illustrations of 
 the formation of the colhex phase by triz - imine , ( e ) its 
 polymerization in the lc phase using grubbs catalyst , second 
 generation , and ( f ) subsequent template removal by hydrolyzing the 
 imine linkage using dmf : hcl ( 11:1 v / v ) to fabricate the porous polymer , 
 pore - nh3cl , with amine functional groups at the pore surface . the thermotropic lc properties 
 of the triz - imine were investigated with differential scanning calorimetry 
 ( dsc ) , x - ray diffraction ( xrd ) , and polarizing optical microscopy 
 ( pom ) . dsc showed a broad endothermic peak at 64.3 c ( h = 2.65 j / g ) , indicating a crystalline to lc phase transition 
 ( figure 2a ) . the sample 
 remains in the lc phase until it melts at 88.6 c ( h = 0.26 j / g ) and returns to the lc phase when cooled to 
 86 c from the isotropic melt . when heated under pom , the sample 
 was birefringent between 64 and 86 c ( figure s1a ) . a focal conic texture typical for a colhex phase could be grown from the isotropic melt on cooling the sample 
 at a rate of 0.1 c / min , indicating the presence of an enantiotropic 
 lc phase ( figure 1b 
 and figure s1b , c ) . the lc phase was further characterized by recording variable temperature 
 xrd ( figure 1c ) . diffraction 
 peaks with q - ratios of 1:3:4 were 
 observed both during the heating and cooling cycle at 75 c , 
 which confirms the existence of a disordered colhex phase 
 with a disk diameter of 4.95 nm . ( b , c ) ft - ir spectra of the monomer 
 triz - imine and its polymer . ( d ) comparison of the ft - ir spectra of 
 the native polymer and the porous polymer , pore - nh3cl . solutions of 
 triz - imine ( 10 mg/30 l chcl3 ) and grubbs 
 catalyst , second generation ( 0.2 mg/20 l chcl3 ) , 
 were prepared separately . the solutions were mixed and dried in a 
 high vacuum for 2530 s and then kept in a vacuum oven at 75 
 c for 12 h to polymerize the terminal double bonds via admet . ft - ir analysis showed high conversion as the 
 end - terminal = c  h bending vibration band at 908 and 
 992 cm of triz - imine had disappeared completely 
 after polymerization ( figure 2b ) . the polymer film with a thickness 
 in the range of 625 m did not show a terminal c = c 
 stretching vibration band at 1640 cm , which is 
 clearly visible in the ft - ir spectrum of triz - imine ( figure 2c ) . in addition , the intensity 
 of the vinylic = c  h stretching vibration band at 3077 
 cm was strongly reduced in the polymer compared 
 to triz - imine ( figure s2 ) . insolubility of the 
 polymer film in chcl3 , etoh , dmf , dmf : hcl ( 11:1 v / v ) , and 
 acetic acid confirmed the high degree of cross - linking . the 
 xrd diffraction patterns of triz - imine after admet polymerization 
 showed retention of the hexagonal lattice ( figure 1c ) . the lattice spacing , d100 , was slightly decreased from 4.29 to 4.21 nm after 
 polymerization . although the d110 and d200 reflections could no longer be observed 
 separately in the polymerized film due to broadening , this indicates 
 that terminal alkene metathesis reaction is enough to form a cross - linked 
 polymer network and fixate the morphology of the lc phase . after the polymerization 
 of triz - imine , the imine linkages in the 
 polymer were hydrolyzed in dmf : hcl , which was a good solvent for the 
 subsequent removal of the template aldehyde triz-3cho from the polymer . 
 for template hydrolysis and removal , a polymer sample was shaken gently 
 overnight at room temperature in dmf : hcl ( 11:1 v / v ) . uv / vis absorption 
 spectra of the solutions showed that after two extractions the template 
 had been quantitatively removed ( figure s3 ) . this was confirmed by the disappearance of the c = n stretching 
 vibration at 1627 cm in the ft - ir spectrum of 
 the polymer ( figure 2d ) . h stretching band of 
 nh3cl functional groups of the anilinium salt in 
 the pores was not observed in the ft - ir spectrum , presumably because 
 of spectral overlap . performing xrd on the films showed that 
 the diffraction pattern of the porous polymer was the same as the 
 native polymer film . however , the lattice spacing , d100 , increased from 4.21 to 4.39 nm upon removal of the 
 template , which we attributed to the reduction of the cross - link density 
 and concomitant stress relaxation ( figure 4c ) . this result indicates structural integrity 
 and the formation of nanopores with an estimated pore diameter of 
 1.3 nm ( figure 3 , path a , and figure s4 ) . schematic illustrations 
 of the pore surface engineering of the 
 porous polymers : ( a ) hydrolysis of the imine linkage of the native 
 polymer using dmf : hcl ( 11:1 v / v ) to fabricate the porous polymer , 
 pore - nh3cl . the amino groups in the pores reacted with 
 different aldehydes , ( b ) benzaldehyde ( where x = h ) , benzene-1,3,5-tricarboxaldehyde 
 ( where x = cho ) , and ( c ) the template aldehyde , triz-3cho , to transform 
 back to the original polymer . ( d ) the ammonium groups in the pores 
 of pore - nh3cl were converted to diazonium salt ( n2cl ) by reacting with aqueous nano2/hcl solution 
 at 05 c for 1 h. ( e , f ) pore - n2cl was further 
 reacted with nan3 and h3po2 in water 
 and thf , respectively , at 21 c to fabricate porous polymers 
 with neutral azide ( n3 ) and phenyl ( ph ) 
 groups at the pore surface ( pore - n3 and pore - ph ) , respectively . ( g ) the ester groups present in the inner core of pore - nh3cl were successfully hydrolyzed using 1 m naoh in etoh : h2o ( 23:1 v / v ) at 75 c for 12 h to furnish a porous polymer containing 
 anionic coona groups at the pore surface . ( h ) pore - coona could 
 be directly obtained in one step by reacting the native polymer with 
 1 m naoh in etoh : h2o ( 23:1 v / v ) at 75 c for 12 h. 
 ( i ) pore - coona was converted to a porous polymer with cooh 
 groups at the pore surface ( pore - cooh ) by reacting with ethanolic 
 hcl solution for 1012 min at ambient condition . ( j ) treatment 
 of pore - cooh with hydroxides salt of li , na , k , cs , and nh4 resulted 
 in the formation of pore - coom ( where m = li , na , k , cs , and nh4 ) . after drying the porous polymer 
 under vacuum ( < 1 mbar ) at 21 
 c for 2 days , a relatively broad absorption band at 1667 cm persisted in the ft - ir spectrum , which was assigned 
 to the c = o stretching vibration of dmf ( figure 2c ) . in line with the porosity of the polymerized 
 material , dmf molecules were strongly h - bonded with the nh3cl surface groups in the pores and retained in the porous 
 polymer , pore - nh3cl . thermogravimetric analysis ( tga ) 
 of the porous polymer showed around 
 4% weight loss at 145 c , a temperature at which the polymer 
 and the catalyst embedded in the polymer are stable ( figure s5a ) . the native polymer before template removal showed 
 no weight loss at that temperature ( figure s5b ) . the 4% weight loss of dmf indicates the presence of approximately 
 1 molecule of dmf per disk in pore - nh3cl . the adsorbed 
 dmf molecules could be removed , however , by soaking the polymer in 
 meoh for 24 h at room temperature , followed by drying ( figure s6a ) . the nh3cl groups at the pore surface were converted 
 to imines by reacting 
 with different aldehydes in thf at room temperature , with a trace 
 of acetic acid as catalyst . reaction of pore - nh3cl with 
 benzaldehyde ( ben - cho ) , resulted in an imine , as was evident from 
 the reappearance of the c = n stretching absorption at 1627 cm ( figure 4a ) , while the band of pore - adsorbed dmf 
 at 1667 cm was reduced in intensity after the 
 reaction . it is noteworthy to mention that the native polymer before 
 template removal did not swell in dmf . the ft - ir spectrum of the native 
 polymer soaked with dmf for 24 h only has a minor band at 1678 cm which can be ascribed to surface bound dmf ( figure s6b ) . ( a ) ft - ir spectra of the nonporous polymer , the porous 
 polymer 
 film , pore - nh3cl , and after reacting pore - nh3cl with different aldehydes . ( b ) ft - ir spectra of the diazonium lined 
 porous polymer , pore - n2cl , and its further modification 
 to the porous polymers containing azide ( n3 ) and 
 phenyl ( ph ) groups at the pore surface ( pore - n3 and pore - ph ) . ( c ) wide - angle xrd patterns of the porous polymer 
 film , pore - nh3cl , and after reacting pore - nh3cl with benzaldehyde and triz-3cho . the nh3cl groups were not fully converted 
 when 
 benzene-1,3,5-tricarbaldehyde ( ben-3cho ) was used as the reactant , 
 even though it has three reactive aldehyde groups and is smaller than 
 the initial template ( figure 4a ) . in addition , the presence of a band at 1700 cm in ft - ir , which is not present when reacted with 
 benzaldehyde , suggests that unreacted aldehyde groups are present 
 in the resulting polymer film ( figure s6c ) . the amino groups lining the pores also react only partially with 
 the larger triz-3cho , the trialdehyde that was used as template ( figure 4a ) . under identical 
 conditions , the polymer film did not react at all with the smaller 
 1-pyrenecarboxaldehyde ( figure s6d ) , indicating that imine formation is dependent on more than just 
 the size of the aldehyde . in addition , the anionic dye sodium fluorescein 
 ( sf ) was also not taken up in the cationic pores probably because 
 of its larger size ( figure s6e ) . the porous polymers functionalized with different aldehydes were 
 further characterized with xrd ( figure 4c ) . the d100 lattice spacing 
 decreased slightly from 4.39 to 4.22 and 4.13 nm for the films treated 
 with benzaldehyde and triz-3cho , respectively , while the diffraction 
 patterns remained the same . the presence of primary amines opens up multiple 
 possibilities 
 to modify the pore surface by further chemical transformations , for 
 which the diazonium group is a convenient intermediate . amine groups 
 in the pores were converted to the diazonium salt with nano2 in cold aqueous hcl solution . the resulting film showed a strong 
 absorption band at 2277 cm ( figure 4b ) , characteristic of the n2 group , confirming the formation of diazonium groups 
 in the pores , pore - n2cl , ( figure 3 , path d ) . the 
 ester groups in the polymer did not hydrolyze during the diazotization 
 reaction as is indicated by the persistence of the ester c = o 
 stretching band at 1730 cm . the n2cl group , a relatively unstable intermediate when in solution , 
 showed remarkable stability in the film , where it decomposes only 
 partially after 20 days at room temperature as evidenced from the 
 ft - ir analysis ( figure s7a ) . treatment of 
 the porous polymer , pore - n2cl , with aqueous 
 nan3 resulted in conversion of the n2 groups to n3 groups . the intensity 
 of the absorption band at 2277 cm ascribed to 
 the n2 stretching vibration decreased 
 considerably at the expense of a new band at 2114 cm ( figure 4b ) , which 
 confirms the formation of porous polymer , pore - n3 , with 
 azide functionalized neutral pores ( figure 3 , path e ) . the 
 n2 groups in the pores were also replaced 
 with protons by reaction with h3po2 in thf at 
 room temperature ( figure 3 , path f , and figure 4b ) . the porous polymer , pore - nh3cl , contains ester groups in the core ( figure 1a ) . the small cationic pores were converted 
 to bigger anionic pores by hydrolysis of the ester groups . to this 
 end , the porous polymer was treated with 1 m naoh in etoh : h2o ( 23:1 v / v ) at 75 c overnight . analysis of the ft - ir spectrum 
 of the resultant polymer showed the c = o stretching vibration 
 at 1730 cm and the peak for dmf ( 1667 cm ) had disappeared in the resultant film , with the emergence of two 
 new absorption peaks at 1556 and 1404 cm ( figure 5a ) , assigned to asymmetric 
 and symmetric c = o stretching vibrations of coona groups , 
 respectively . therefore , we have been 
 able to convert the cationic small pores ( diameter 1.3 nm ) 
 to anionic bigger ones ( diameter 2.6 nm ) ( figure 3 , path g ) . ft - ir spectra depicting 
 ( a ) the transformation of pore - nh3cl to an anionic porous 
 polymer , pore - coona , and ( b ) the conversion 
 of the porous polymer , pore - coona , to pore - cooh . ( c ) xrd patterns 
 of the porous polymers , pore - coona and pore - cooh . direct treatment of the native polymer with 1 m naoh in etoh : h2o ( 23:1 v / v ) at 75 c for 12 h led to a one - step removal 
 of the core template as the resultant polymer showed same ft - ir absorption 
 spectrum as that of pore - coona ( figure 3 , path h , and figure s7b ) . the porous polymer , pore - coona , was further treated with 
 etoh : hcl 
 ( 11:1 v / v ) for 1012 min at 21 c . as a result , the asymmetric 
 and symmetric c = o stretching vibration of coona groups 
 shifted from 1556 to 1685 and 1404 to 1585 cm , 
 respectively , indicating formation of pores with a cooh groups 
 at the surface ( figure 3 , path i , and figure 5b ) . the structural integrity in pore - coona 
 and pore - cooh was retained without collapsing the pores as was evident 
 from the xrd patterns ( figure 5c ) . films of pore - cooh were treated with 1 m solutions of 
 the hydroxide salts of li , na , k , cs and nh4 ions in etoh : h2o ( 23:1 v / v ) for 2 h. after treatment , the asymmetric and 
 symmetric stretching band of cooh have shifted from 1685 to 
 1560 cm and from 1585 to 1404 cm , respectively ( figure s7c ) . the data 
 clearly indicates the formation of a porous polymer lined with cooli , 
 coona , cook , coocs , and coonh4 functional groups at the pore surface ( figure 3 , path j ) . in this regard , it is important 
 to mention that we previously reported selective binding of na and k ions among hydroxide salts in cooh 
 functionalized porous polymer with a pore diameter of 1.6 
 nm , while in the present case , also cs ions were taken 
 up as a countercation in the bigger anionic pores . the anionic pores 
 in pore - coona are likely to selectively adsorb cationic dyes . to check 
 this hypothesis , adsorption of cationic and anionic dyes was studied . methylene blue ( mb ) , a cationic dye , was found to be adsorbed from 
 its aqueous solution when pore - coona was immersed in 10 m aqueous 
 solution of mb , 1.5 ml . dye adsorption was monitored by recording 
 uv / vis spectra of the solution at different time intervals ( figure 6a ) . mb was adsorbed 
 rapidly by the porous polymer , turning the solution from deep blue 
 to nearly colorless , while the porous polymer became bluish ( figures 6a and 6b , insets ) , adsorption reached a plateau within 1 h as determined 
 from the decrease of the absorption intensity at 665 nm ( figure 6b ) . after saturation 
 with mb from a 10 m aqueous solution over 12 h , approximately 
 13% of the coona groups was associated with a dye molecule 
 ( figure s8 ) . ( a ) monitoring adsorption 
 of the cationic dye , mb ( 10 m ) , 
 by the coona functionalized anionic pores of pore - coona , in 
 aqueous medium using uv / vis absorption spectroscopy and ( b ) the plot 
 of absorbance at 665 nm versus time . the inset in parts a and b showing 
 the color of the porous polymer , pore - coona and mb solution before 
 and after adsorption experiment , respectively . ( c ) uv / vis absorption 
 spectra of the anionic dye , sf , solution before and after exposure 
 to pore - coona . ( d ) selective adsorption of the cationic dye , mb , over 
 the anionic dye , sf , by pore - coona was monitored by the uv / vis spectroscopy . the inset in part d showing the color of the [ mb ( 20 m ) + sf 
 ( 30 m ) ] solution before and after adsorption by pore - coona . in contrast , hardly any of the 
 anionic dye , sodium fluorescein 
 ( sf ) , was adsorbed from an aqueous solution by pore - coona ( figure 6c ) . ion selectivity 
 is illustrated by treating a mixture of sf and mb with pore - coona , 
 the green solution ( mb plus sf ) turned yellow - green ( the color of 
 an sf solution ) after the treatment with the anionic material ( figure 6d ) . the fabrication of nanoporous polymers by hydrolysis of the discotic 
 core from a polymerized lc - film has been demonstrated . pore - nh3cl ( pore diameter 1.3 nm ) , with ammonium groups in 
 the pore interior , reacts faster with smaller aldehydes than with 
 larger ones , but reactivity is not determined by size alone . the ammonium 
 groups in pore - nh3cl were successfully converted to the 
 diazonium salt , which is shown to be a versatile reactive intermediate 
 for further chemical modification of the pores . a nanoporous 
 material , pore - coona , with larger , anionic functionalized 
 pores of 2.6 nm was obtained either from pore - nh3cl or directly in one step from the native polymer thin film . selective 
 adsorption of cationic over anionic dyes in the anionic pores of pore - coona 
 was demonstrated . the cations in pore - coona could be exchanged by 
 converting to the carboxylic acid , followed by treatment with the 
 hydroxides of li , na , k , cs , and nh4 . the demonstrated possibility 
 to covalently modify the pore surface in nanometer sized pores of 
 a polymer thin film offers ample opportunities to develop functional 
 materials . we believe that the present strategy , to modify the pore 
 surface , can be extended to other functions . further pore surface 
 engineering , adsorption , and filtration studies with these porous 
 materials are under way .