Effect of the Linkage Position on the Conjugation Length of Truxene-Based Porous Polymers: Implications for Their Sensing Performance of Nitroaromatics

Abstract

Four highly porous truxene-based organic polymers have been synthesized via C–C cross coupling methodologies (under Yamamoto and Suzuki–Miyaura conditions) starting from two different brominated hexamethyltruxene isomers (2,7,12- and 3,8,13-tribromohexamethyltruxene). We have found that the linkage position in these polymers has a strong influence not only on the porosity but also on the absorption and light emitting properties of the final materials. We have performed a joint theoretical and experimental investigation to shed light on the role of the positional isomeric effect of the monomers on the degree of π-conjugation of the final materials. Our study indicates that the 2,7,12 linkage significantly enhances the electronic communication between the covalently linked building units, thus strongly influencing the conjugation length and the position of the energy levels of the final materials. The result of this work provides us with a new design tool to fine-tune the electronic properties of conjugated porous polymers with important implications for their potential applications, as demonstrated by their sensing performance for the detection of nitroaromatic compounds.

In silico design of 2D polymers containing truxene-based platforms: insights into their structural and electronic properties

“…(iii) A moderate increase of the HOMO-LUMO gaps was observed when varying the linkage position from T 2 to T 3 due to the similar LUMO destabilization and HOMO stabilization. This is in line with our previously reported study on Tx-based porous polymers, 25 where we demonstrated that polymers with truxene cores covalently linked in para positions are better conjugated than their meta-substituted isomers. A comparison of the molecular orbitals for the T 2 and T 3 models (Fig.…”

“…S17, ESI †). A good correlation can be found with the experimental results previously reported for truxene-based (Tx 2 , Tx 3 , Ph-Tx 2 and Ph-Tx 3 ) 25 polymers. Please note that UV-Vis absorption (photoexcitation) spectra are of fundamental importance for applications ranging from sensing to photocatalysis and photovoltaics.…”

In silico design of 2D polymers containing truxene-based platforms: insights into their structural and electronic properties

“…(iii) A moderate increase of the HOMO-LUMO gaps was observed when varying the linkage position from T 2 to T 3 due to the similar LUMO destabilization and HOMO stabilization. This is in line with our previously reported study on Tx-based porous polymers, 25 where we demonstrated that polymers with truxene cores covalently linked in para positions are better conjugated than their meta-substituted isomers. A comparison of the molecular orbitals for the T 2 and T 3 models (Fig.…”

“…S17, ESI †). A good correlation can be found with the experimental results previously reported for truxene-based (Tx 2 , Tx 3 , Ph-Tx 2 and Ph-Tx 3 ) 25 polymers. Please note that UV-Vis absorption (photoexcitation) spectra are of fundamental importance for applications ranging from sensing to photocatalysis and photovoltaics.…”

Donor‐Acceptor Truxene‐Based Porous Polymers: Synthesis, Optoelectronic Characterization and Defense‐Related Applications

“…As this ratio increases, the conjugation becomes more efficient. [ 24,30,32 ] If we compare the polymers having the same symmetric C 3 monomer we can clearly see that the intensity ratio is higher in the polymers connected through the 2,7,12 position than in those connected through the 3,8,13 position, indicating more efficient conjugation in line with their less distorted structures. Interestingly, the band localized at ≈1544 cm −1 arising from the CC stretching mode of the BTD acceptor units is very sensitive to the electronic communication between truxene or triindole platforms, shifting toward lower frequency on going from Tx3‐BTD (1549 cm −1 ), Tx2‐BTD (1547 cm −1 ), Tri3‐BTD (1544 cm −1 ) to Tri2‐BTD (1543 cm −1 ) porous polymers.…”

“…It is well known that Raman spectroscopy provides valuable information about the electronic coupling between covalently connected conjugated moieties in organic semiconductors. [ 24,30 ] As shown in Figure the most intense Raman bands of the four polymers under study are located in the spectral region of 1500–1650 cm −1 and can be deconvoluted into three distinct peaks. With the help of DFT calculations, the different peak contributions are assigned to the same CC stretching mode (i.e., mode 8a of benzene) [ 31 ] but localized in different rings: (i) the Raman band at ≈1610 cm −1 (colored red) involves the outer benzene rings of the C 3 platform, (ii) the observed band at ≈1580 cm −1 (colored blue) corresponds to the inner benzene rings, and (iii) the band at ≈1544 cm −1 (colored orange) is located at the BTD linking units.…”

Natural‐Sunlight‐Driven H 2 O 2 Photosynthesis Over Bandgap Engineered Truxene‐Based Porous Aromatic Frameworks

“…The peaks located at 20 and 46 ppm correlate with the methyl and quaternary carbons of the Tx moiety [35]. Signals falling within the range of 115–155 ppm are probably attributed to the aromatic carbons [36–38]. The characteristic signals of C─N bonds in PAF‐457 and C═O bonds in PAF‐458 could be found at around 138 and 190 ppm, respectively [39].…”

In silico design of 2D polymers containing truxene-based platforms: insights into their structural and electronic properties

“…(iii) A moderate increase of the HOMO-LUMO gaps was observed when varying the linkage position from T 2 to T 3 due to the similar LUMO destabilization and HOMO stabilization. This is in line with our previously reported study on Tx-based porous polymers, 25 where we demonstrated that polymers with truxene cores covalently linked in para positions are better conjugated than their meta-substituted isomers. A comparison of the molecular orbitals for the T 2 and T 3 models (Fig.…”

“…S17, ESI †). A good correlation can be found with the experimental results previously reported for truxene-based (Tx 2 , Tx 3 , Ph-Tx 2 and Ph-Tx 3 ) 25 polymers. Please note that UV-Vis absorption (photoexcitation) spectra are of fundamental importance for applications ranging from sensing to photocatalysis and photovoltaics.…”

Donor‐Acceptor Truxene‐Based Porous Polymers: Synthesis, Optoelectronic Characterization and Defense‐Related Applications

“…As this ratio increases, the conjugation becomes more efficient. [ 24,30,32 ] If we compare the polymers having the same symmetric C 3 monomer we can clearly see that the intensity ratio is higher in the polymers connected through the 2,7,12 position than in those connected through the 3,8,13 position, indicating more efficient conjugation in line with their less distorted structures. Interestingly, the band localized at ≈1544 cm −1 arising from the CC stretching mode of the BTD acceptor units is very sensitive to the electronic communication between truxene or triindole platforms, shifting toward lower frequency on going from Tx3‐BTD (1549 cm −1 ), Tx2‐BTD (1547 cm −1 ), Tri3‐BTD (1544 cm −1 ) to Tri2‐BTD (1543 cm −1 ) porous polymers.…”

“…It is well known that Raman spectroscopy provides valuable information about the electronic coupling between covalently connected conjugated moieties in organic semiconductors. [ 24,30 ] As shown in Figure the most intense Raman bands of the four polymers under study are located in the spectral region of 1500–1650 cm −1 and can be deconvoluted into three distinct peaks. With the help of DFT calculations, the different peak contributions are assigned to the same CC stretching mode (i.e., mode 8a of benzene) [ 31 ] but localized in different rings: (i) the Raman band at ≈1610 cm −1 (colored red) involves the outer benzene rings of the C 3 platform, (ii) the observed band at ≈1580 cm −1 (colored blue) corresponds to the inner benzene rings, and (iii) the band at ≈1544 cm −1 (colored orange) is located at the BTD linking units.…”

Natural‐Sunlight‐Driven H 2 O 2 Photosynthesis Over Bandgap Engineered Truxene‐Based Porous Aromatic Frameworks

“…The peaks located at 20 and 46 ppm correlate with the methyl and quaternary carbons of the Tx moiety [35]. Signals falling within the range of 115–155 ppm are probably attributed to the aromatic carbons [36–38]. The characteristic signals of C─N bonds in PAF‐457 and C═O bonds in PAF‐458 could be found at around 138 and 190 ppm, respectively [39].…”

In silico design of 2D polymers containing truxene-based platforms: insights into their structural and electronic properties

“…(iii) A moderate increase of the HOMO-LUMO gaps was observed when varying the linkage position from T 2 to T 3 due to the similar LUMO destabilization and HOMO stabilization. This is in line with our previously reported study on Tx-based porous polymers, 25 where we demonstrated that polymers with truxene cores covalently linked in para positions are better conjugated than their meta-substituted isomers. A comparison of the molecular orbitals for the T 2 and T 3 models (Fig.…”

“…S17, ESI †). A good correlation can be found with the experimental results previously reported for truxene-based (Tx 2 , Tx 3 , Ph-Tx 2 and Ph-Tx 3 ) 25 polymers. Please note that UV-Vis absorption (photoexcitation) spectra are of fundamental importance for applications ranging from sensing to photocatalysis and photovoltaics.…”

Donor‐Acceptor Truxene‐Based Porous Polymers: Synthesis, Optoelectronic Characterization and Defense‐Related Applications

“…As this ratio increases, the conjugation becomes more efficient. [ 24,30,32 ] If we compare the polymers having the same symmetric C 3 monomer we can clearly see that the intensity ratio is higher in the polymers connected through the 2,7,12 position than in those connected through the 3,8,13 position, indicating more efficient conjugation in line with their less distorted structures. Interestingly, the band localized at ≈1544 cm −1 arising from the CC stretching mode of the BTD acceptor units is very sensitive to the electronic communication between truxene or triindole platforms, shifting toward lower frequency on going from Tx3‐BTD (1549 cm −1 ), Tx2‐BTD (1547 cm −1 ), Tri3‐BTD (1544 cm −1 ) to Tri2‐BTD (1543 cm −1 ) porous polymers.…”

“…It is well known that Raman spectroscopy provides valuable information about the electronic coupling between covalently connected conjugated moieties in organic semiconductors. [ 24,30 ] As shown in Figure the most intense Raman bands of the four polymers under study are located in the spectral region of 1500–1650 cm −1 and can be deconvoluted into three distinct peaks. With the help of DFT calculations, the different peak contributions are assigned to the same CC stretching mode (i.e., mode 8a of benzene) [ 31 ] but localized in different rings: (i) the Raman band at ≈1610 cm −1 (colored red) involves the outer benzene rings of the C 3 platform, (ii) the observed band at ≈1580 cm −1 (colored blue) corresponds to the inner benzene rings, and (iii) the band at ≈1544 cm −1 (colored orange) is located at the BTD linking units.…”

Natural‐Sunlight‐Driven H 2 O 2 Photosynthesis Over Bandgap Engineered Truxene‐Based Porous Aromatic Frameworks

“…The peaks located at 20 and 46 ppm correlate with the methyl and quaternary carbons of the Tx moiety [35]. Signals falling within the range of 115–155 ppm are probably attributed to the aromatic carbons [36–38]. The characteristic signals of C─N bonds in PAF‐457 and C═O bonds in PAF‐458 could be found at around 138 and 190 ppm, respectively [39].…”