This is the case of π-conjugated molecules and oligomers, which are being utilized to

trigger electron injection or for photostimulation. In this section, we will focus on three

main classes of photosensitive bioelectronic molecules: conjugated oligomers, organic

dyes/pigments, and photoswitches.

4.4.1 Conjugated Oligomers

Conjugated oligoelectrolytes (COEs) consist of a π-delocalized backbone and ionic pen­

dant groups, have been demonstrated to modify the abiotic/biotic interface via efficient

insertion in the plasma membrane (Figure 4.5a,b) [39]. The COE chromophore mainly

undergoes radiative decay via emission or nonradiative decay via heat generation or

energy/electron transfer to acceptors (such as dyes and/or oxygen) upon light excitation.

This molecular unit is ultimately responsible for some important bioelectronic properties

of COEs, i.e. the photoinduced production of reactive oxygen species, [40] increase of

the local temperature, and the facilitation of extracellular electron transport to abiotic

electrode surface via direct electron transfer and/or meditated electron transfer. In ad­

dition, emission enables facile tracking of the chromophore via simple fluorescence mi­

croscopies. On the other hand, the ionic side chains confer water solubility and enable

specific interaction with targets via electrostatic interactions, leading to the disruption or

stabilization of the plasma membrane, depending on the COE molecular size. For in­

stance, disruption can occur via membrane thinning, as the lipid phosphate head groups

are drawn toward the center of the bilayer. For all these reasons, COE have been em­

ployed for a plethora of applications, including in microbial fuel cells, as light-driven

antibacterial agent, as biosensors and in photodynamic and photothermal therapy [39,41].

4.4.2 Organic Dyes and Pigments

Historically, dyes and pigments have been used as electronic materials. One of the most

famous examples is perhaps Tang’s photovoltaic cell, consisting of a bilayer of copper

FIGURE 4.5

(a) Schematic of the COE structure with a π-conjugated internal region (rectangle) and polar pendant group

terminals (circle) intercalating into a lipid bilayer. b) Typical COE chemical structure.

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Bioelectronics