# Reversing the Photovoltage of a Photoacid in Aqueous Glycerol and Ethylene Glycol Solutions

## TL;DR

This paper shows that the voltage produced by a light-sensitive acid can reverse when dissolved in glycerol or ethylene glycol instead of water.

## Contribution

The study reveals that the polarity of photovoltage in glycerol and ethylene glycol solutions is reversed compared to water.

## Key findings

- Photovoltage polarity reverses in glycerol and ethylene glycol solutions compared to water.
- Voltage kinetics depend on the ratio of glycerol/ethylene glycol to water.
- A model explains the photovoltage based on differing diffusion rates of charges.

## Abstract

Pyranine is a photoacid, which upon illumination in water,
deprotonates.
It has been well studied and can therefore be used as a model system
for developing sensors and energy-harvesting devices based on photoacids.
Under normal circumstances, the release of protons results in an open-circuit
voltage of a fixed polarity. Here, it is demonstrated that the polarity
of the photovoltage in glycerol and ethylene glycol is reversed compared
to that in water. The polarity and kinetics of the photovoltage are
found to depend on the ratio of glycerol or ethylene glycol to water.
A simple model for the observed photovoltage kinetics is proposed,
based on the assumption that both positive and negative charges are
released and exhibit different diffusion constants.