Development of Polythiophene–Tripeptide Covalent Conjugates Showing Excellent Structure-Dependent Photophysical and Photocurrent Properties

Abstract

Presently, conducting polymer−peptide conjugates have drawn great interest for their interesting optoelectronic and photophysical properties. To understand the structural dependence of the conjugates on their properties, we have covalently coupled poly(3-thiophene acetic acid) (P3TAA) with a Cprotected tripeptide, H 2 N-F-F-V-OMe (TPEP), to produce their conjugate PTCP-I. A carboxylic acid-deprotected tripeptide polythiophene conjugate (PTCP-II) is also produced by alkaline hydrolysis of PTCP-I to delineate any difference in properties due to the change in molecular structure. The stretching frequencies for −NH− and >CO groups of PTCP-II are 11 and 26 cm −1 lower than those of PTCP-I, indicating better intermolecular hydrogen bonding interactions in the former. This alters the seaweed morphology of PTCP-I to a sheet morphology for PTCP-II. The blue shift of the π−π* absorption band of polythiophene with gradually increasing the PTCP-I concentration is attributed to the H-type aggregation in DMF solution, but in the solid state, this peak shows a 17 nm red shift from its solution state for better electron delocalization for closer proximity of molecules. The UV−Vis peak of PTCP-II shows a lower blue shift than that of PTCP-I in DMF, attributed to the uncoiled polythiophene chains of the former. In DMF solution, interestingly, both PTCP-I and PTCP-II conjugates exhibit aggregation-induced emission (AIE), showing maxima at 0.08 mg/mL and then aggregation-induced quenching (AIQ) with further increasing its concentration. PTCP-I and PTCP-II exhibit dc conductivities of 0.04 and 0.55 μS cm −1 , respectively, at 30 °C, and the higher value for PTCP-II is due to its lower band gap (1.91 eV) compared to that of PTCP-I (2.14 eV). The current (I)−voltage (V) plot of both conjugates exhibits semiconducting properties, which are higher for PTCP-II for its lower band gap. The photocurrent behavior of the conjugates indicates that the on−off response in the PTCP-II system is significantly higher than that in PTCP-I due to the unfolded polymer chain of the former, as the photogenerated electrons and holes can move more freely there. Impedance spectra of both the conjugates show single semicircles for the Nyquist plots, and the charge transfer resistance of PTCP-II is 4.4 times lower than that of PTCP-I but the capacitance value is 27 times higher, arising from the more extended chain configuration of the former, signifying structural importance on the optoelectronic and photocurrent properties of the polymer−peptide conjugates.

Peptide‐tethered Perylenebisimide Aggregates with Copper Nanoclusters showing Thermoresponsive and Photoresponsive Properties

“…Samples were prepared by drop‐casting the solutions on the ITO glass and sandwiching it with another ITO glass. The samples were kept under complete vacuum for 24 hours before the experiment to remove any moisture, which may cause for the decrease of current‐voltage property [42] . During the measurement, the voltage was swept between −5 V to +5 V. It is apparent from Figure 8b (PBI) 2 P shows dark current value of 0.14 μA at +4 V bias, whereas CuNCs themselves could not show any promising result.…”

“…The samples were kept under complete vacuum for 24 hours before the experiment to remove any moisture, which may cause for the decrease of current-voltage property. [42] During the measurement, the voltage was swept between À 5 V to + 5 V. It is apparent from Figure 8b (PBI) 2 P shows dark current value of 0.14 μA at + 4 V bias, whereas CuNCs themselves could not show any promising result. Interestingly, upon addition of different wt % of CuNCs into the (PBI) 2 P, the hybrids started showing gradual enhancement of dark current with a highest value of 20.8 mA at + 4 V bias for the hybrid (10 wt %).…”

Tunning of Optoelectronic Properties in Nanohybrids of Peptide-Appended Perylenebisimides and Carbon Nanodots

“…Therefore, we have prepared the samples for this experiment by drop-casting the solutions on an ITO glass and sandwiching it with another ITO strip. The samples were kept under complete vacuum for 24 h before the experiment to remove any moisture, which may be cause for the decrease of the current–voltage property. , The current measurement was conducted by sweeping the bias from −5 V to +5 V.…”

Functionalization of Conductive Polymers through Covalent Postmodification

“…More recently, the covalent coupling of poly(3-thiophene acetic acid) (P3TAA) with a C-protected tripeptide was also reported to produce a bioconjugated conducting polymer [ 172 ]. Through alkaline hydrolysis, a carboxylic-acid-deprotected tripeptide polythiophene conjugate can be obtained [ 173 ]. Istif et al produced aldehyde derivatives of thiophene [ 172 ], which are polymerized into conductive polymer chains with aldehyde pendant groups.…”