Two-dimensional porphyrin sheet as an electric and optical sensor material for pH detection: A DFT study

Highlights

• Two-dimensional porphyrin sheet was a novel material that was used to develop electric and optical devices.

• Two-dimensional porphyrin sheet could been as a potential sensor for pH detection.

Abstract

The two-dimensional porphyrin sheet (2D porphyrin) was as an electric and optical sensor material for pH detection was explored via the periodic density functional theory. The geometric structures, electronic and optical properties of the 2D porphyrin with different amount of protons were calculated in order to explore the mechanism of sensor for pH detection. The band structure and absorption spectra of the 2D porphyrin were dependent on the amount of proton applied. Thus, the conductivity and absorption spectra of 2D porphyrin were all sensitive to solution pH, which can be applied to the electric and optical sensor for pH detection. This concept had potential applications in the design of sensor devices based on the 2D porphyrin.

Introduction

Porphyrins were naturally occurring macrocyclic compounds and contained four pyrroles connected in a macrocyclic manner through the four methine carbons at their α-positions [1], [2], [3]. These α-positions were planar 18 π-electron aromatic molecules [4]. Porphyrins and their derivatives, which played an important role in biological systems [5], such as chlorophylls, heme, and vitamin B12, which were the coenzymes with catalysis in the organism biochemical reaction, had attracted considerable attention for many years [6], [7]. In the past years, graphene as a classical two-dimensional material was a very popular material due to its high signal of electrical conductivity, high surface area, low cost of production and heterogeneous electron transfer rate, which was widely used in electrochemistry-related applications such as sensor [8], [9], [10], environment treatment [11], [12], energy resources [13], [14] and electronic devices [15], Based on this point, the researchers focused on the development of extensively p-conjugated porphyrins, which were greatly used for sensors [16], [17], [18], [2], dye-sensitized solar cells [19], [20], [21], [22], and single atom catalyst [23], [24], [25]. pH was a numeric scale used to specify the acidity or basicity of an aqueous solution. The measurement of the pH was very meaningful in many fields such as biochemistry, clinical medicine, environmental monitoring, and food safety. Over the past decades, many optical pH sensors based on different optical principles have developed, such as evanescent wave absorption [26], surface plasmon resonance [27], surface enhanced Raman scattering [28] and fluorescence [29]. Among them, optical pH sensors based on fluorescence had attracted much attention because of their good sensitivity and fast response [29]. Most of the conjugated porphyrins were created through the introduction of p-conjugated segments at the porphyrinic peripheries. Osuka et al.[30] reported the synthesis of multiply-fused porphyrin sheet. The 2 × 2 repeating units of free porphyrin was also synthesized, indicating that the 2D porphyrin sheet could be synthesized. Li et al. [31] constructed 2D iron-porphyrin sheet and investigated the catalyst for oxygen reduction reaction via the first principle. However, few research articles related to 2D porphyrin sheet were available. Thus, we tried to fill this gap and carried out a series of studies. First, the UV–Vis absorption spectrum of porphyrin was sensitive to solution pH. Thus, the electronic and optical properties of 2D porphyrin were tuned by solution pH. A 2D porphyrin sheet was constructed, which was an electric and optical sensor for pH detection. The electronic and optical properties were calculated by the first principle at different pH levels.