Nonlinear Optical Switching in Regioregular Porphyrin Covalent Organic Frameworks

Abstract

Covalent organic frameworks (COFs) have garnered immense scientific interest among porous materials because of their structural tunability and diverse properties. However,the response of such materials towardlaser-induced nonlinear optical (NLO) applications is hardly understood and demands prompt attention. Three novel regioregular porphyrin (Por)-based porous COFs-Por-COF-HH and its dual metalated congeners Por-COF-ZnCu and Por-COF-ZnNi-have been prepared and present excellent NLO properties.N otably,i ntensity-dependent NLO switching behavior was observed for these Por-COFs,w hichi sh ighly desirable for optical switching and optical limiting devices. Moreover,t he efficient p-conjugation and charge-transfer transition in ZnCu-Por-COF enabled ahigh nonlinear absorption coefficient (b = 4470 cm/GW) and figure of merit (FOM = s 1 /s o ,3565) value compared to other state-of-the-art materials, including molecular porphyrins (b % 100-400 cm/GW), metalorganic frameworks (MOFs; b % 0.3-0.5 cm/GW), and graphene (b = 900 cm/GW). Molecules/materialswithinherentnonlinearoptical(NLO)properties have profound importance in telecommunications, data storage,d isplay technologies,s ensors,a nd biomedical devices. [1] In this regard, molecular porphyrins have been widely studied because of their versatile optical and electrochemical properties,large and fast NLO responses,possibility of incorporating aw ide range of metals,a nd their good thermochemical stabilities for optical limiting and optical switching applications. [2] Nonetheless,t oenhance and tune optical nonlinearities of singular porphyrin moieties,b athochromic shifting of their absorption bands by large p-electron delocalization is crucial, which becomes possible through de novo design of integrated porphyrin units featuring extended p-conjugation. [3, 4] Along this line,w ep ropose ap orphyrin-linked covalent organic framework (COF) [5] as model system, wherein enhancement and switching of the NLO response can be studied by manipulation of the framework. Among the recognized crystalline materials, COFs are known for being mechanically robust and offering ahighly accessible surface area. Thestructural and electronic tunability of COFs have garnered particular interest in research areas such as adsorption/storage, [6] chemical sensors, [7] electronics, [8] and catalysis. [9] Despite such potential, COFs comprising porphyrin units have not been explored as NLO materials.F or this purpose,aregioregular ordering of multiple metal centers in ac rystalline 2D porphyrin framework-preferably without ap ost-synthetic modification-is desirable.T his challenging objective [10] has great potential in optoelectronics and photo/electrocatalysis applications.Herein, we present aconjugated imine-linked porphyrinhomopolymeric COF (Por-COF-HH; Figure 1a)prepared by Schiff base A4B4 condensation of 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin (TFPP) and 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TAPP). Adopting the same pathway,w ea lso synthesized regioregular...

Electroactive Organic Building Blocks for the Chemical Design of Functional Porous Frameworks (MOFs and COFs) in Electronics

“…More recently,F eng et al have reported af amilyo fc onjugated 2D Pc-based MOFs exhibiting high electrical conductivityt hat were used for electrocatalysis. [207,208] Porphyrin- [209][210][211][212][213][214][215][216][217] and phthalocyanine-based [32,[218][219][220][221] COFs have also received al ot of attention in recent years due to their photocurrent generation properties and possible applications in optoelectronics. For example, ambipolar conducting 2D porphyrin-based COFs bearing different metalsw ere synthesized providing efficient charge transport pathways,w hich have adirect influence on their photoconductivep roperties.…”

“…[212,215] More recently,e lectronic and optical properties of Por-based COFs have also been exploited towards energys torage [213] and NLO applications. [217] Phthalocyanines are also excellent building blocks for the preparation of functional COFs in optoelectronics.D ifferent crystalline boronate ester-linked Pc-based COFs have been prepared and some of them exhibitedh igh chargec arrier and photoconductivity. [219,220] Feng et al reported ad etailed study on the electronic properties of some metal-phthalocyanine-based pyrazine-linked 2D COFs exhibiting high mobility towards their use in electronics.…”

A thiazolo[5,4-d]thiazole-bridged porphyrin organic framework as a promising nonlinear optical material

“…12 Moreover, the obtained figure of merit (FoM = s 1 /s 0 ; 5571) for the Por-TzTz-POF is also higher than that of our recently reported porphyrin based COFs; Por-COF-HH (FoM = 3534), Por-COF-ZnCu (FoM = 3565) and Por-COF-ZnNi (FoM = 3762), tabulated in Table S2 (ESI †). 11 Overall, these results signify a structure-activity relationship in porphyrin based porous organic materials that can be useful in optical switching applications. 16,17 In summary, we have synthesized a conjugated TzTz-linked porphyrin organic framework employing single-step direct condensation of A4 porphyrin tetra-aldehyde and DTO.…”

“…It is worth Fig. 1 Schematic representations of the synthesis of the Por-TzTz-POF and Por-CQN-COF (previously reported as Por-COF-HH), 11 (b) and (c) experimental (red) PXRD profiles of the Por-TzTz-POF and Por-CQN-COF (the black pattern is the simulated one derived from the eclipsed model) respectively with molecular models (C: grey; N: blue; S: yellow and H: white).…”

Proximity Effect in Crystalline Framework Materials: Stacking-Induced Functionality in MOFs and COFs

“…Up to date, a huge variety of 2D COF structures has been synthesized and studied, e.g., in the direction of photoactivity and photosensitivity. [61,78,[82][83][84][85][86][87] However, electronic structures are seldom discussed and, even then, mostly only single layers are considered. [60,[88][89][90] Thomas et al [60,90] investigated electronic structures of 2D -conjugated polymers with three-and fourarm connections, which correspond to kagome and Lieb (Archimedean) lattices, and explained occurrence of flat and disperse bands.…”