A Systematic Approach toward Designing Functional Ionic Porphyrin Crystalline Materials

Abstract

Synthetic ionic porphyrin self-assembled structures possess remarkable optoelectronic properties that are useful for energy and sensor related technological application, and there is a continued interest in tailoring their molecular structure and interactions in order to control their various functions. Central to these efforts is the fundamental understanding of the structure, the chemical and physical properties, and the relationship between the structural organization of the chromophores and their functions. In this Feature Article, we demonstrate the capability of a nucleation and growth algorithm to reproducibly synthesize nano- to millimeter size single crystals of several different ionic binary porphyrin (BP) systems under chemically controlled conditions. Single crystal X-ray diffraction analysis, morphology, sensing, and mechanical measurements are presented. UV–vis and X-ray photoelectron spectroscopy of these materials is also discussed. The crystalline porphyrin assemblies have varying degrees of dark conductivity (depending on their chemical and structural composition) but all appear to be sensitive to light; i.e., they absorb radiation and become conductive and/or persistently photoconductive (PPC). In addition, some of these crystalline porphyrins show persistent ion beam induced conductivity. This rich photo and ion response provides opportunities for the selective light control of these semiconductors. Exposure of the BP crystals to small gas molecules such as O2 strongly modifies their photocurrent in sensing experiments. The range of the Young’s modulus values extracted from nanoindentation experiments indicates that the BP crystals have a Young’s modulus intermediate between “soft” polymers and composite materials, making them excellent candidates for deformable optoelectronic devices. Both the experimental photoconductive and mechanical properties of the porphyrin self-assembled structures can be correlated with their molecular organization and morphology. In addition, quantum mechanical calculations provide the electronic band structure and the density of states and help explain experimental prompt photoconductivity measurements. Theory was also used to develop strategies for precise manipulation of the photoresponse of the BP crystals by selective structure modification. This work shows that combining the results from structural and theoretical studies and correlating them with electronic and optoelectronic properties can assist in engineering highly organized functional materials from organic π-conjugated molecules.

Mechanical behavior of crystalline ionic porphyrins

“…Single crystal data obtained from high quality TMPyP:TSPP and its metallated analogues indicate that these BPs all share nearly identical structural geometry. (CSD reference codes for TMPyP:TSPP and TMPyP:NiTSPP structures are AYULOX and ZETKUH, respectively [28,29,34].) Similar results were obtained from powder X-ray diffraction data (Fig.…”

“…They include: TMPyP:TSPP, NiTMPyP:TSPP, TMPyP:NiTSPP, CuTMPyP:TSPP, TMPyP:CuTSPP, TPyP:TSPP and TAPP:TSPP. Each crystal was examined by XPS (x-ray photoelectron spectroscopy) to verify its stoichiometry and the actual protonation of the porphyrin tectons; spectra and analysis were published earlier [18,20,28,29,[34][35][36]. We note that heating the BP solids up to 130 °C did not modify their elemental charges or composition, based on X-ray photoelectron spectroscopy, (XPS) measurements [18,20,28,29,36].…”

“…These materials are known to serve as active components in many optoelectronic devices such as solar cells [21][22][23][24], photovoltaics [1,17,25], and photosensors [26][27][28][29][30]. Until recently, reports of crystal structures of BPs were rare because synthesized crystals were not suitable for single crystal X-ray diffraction (XRD) [31][32][33][34]. However, by employing a newly developed crystal growth algorithm by Adinehnia and coworkers, it is now possible to efficiently produce nano-to millimetersized BP crystals in a controlled and reproducible manner [28,29,33,34].…”

“…Until recently, reports of crystal structures of BPs were rare because synthesized crystals were not suitable for single crystal X-ray diffraction (XRD) [31][32][33][34]. However, by employing a newly developed crystal growth algorithm by Adinehnia and coworkers, it is now possible to efficiently produce nano-to millimetersized BP crystals in a controlled and reproducible manner [28,29,33,34]. Thus, this report is the first to relate the elastic modulus of single crystal ionic BPs to their molecular organization within the lattice of these anisotropic crystals.…”

1D materials from ionic self-assembly in mixtures containing chromonic liquid crystal mesogens

“…Porphyrin are examples of such blocks and are associated to chromophores found in Nature that play an important role in biological functions, such as photosynthesis, molecular recognition and catalysis. 2,3 These molecules can also hold different metals in the macrocycle via complexation with the pyrrole nitrogens; some of these porphyrin-metal complexes are found in nature and are biologically relevant (e.g. heme porphyrin).…”