# Fluorescence and phosphorescence of tetracarboxylated ZnPc–perylene diimide organic systems in highly acidic media

## TL;DR

This study explores how combining two organic compounds in acidic solutions can control their light-emitting properties, useful for medical and electronic applications.

## Contribution

The paper introduces tunable excited-state lifetimes and room-temperature phosphorescence in co-assembled organic systems for photosensitizer design.

## Key findings

- TcPcZn and EP-PDI blends show tunable excited-state lifetimes in acidic TFA/H2O.
- Room-temperature phosphorescence lifetimes of up to 10.18 µs were observed in EP-PDI.
- High concentrations are needed to measure singlet-state lifetimes due to solvent quenching.

## Abstract

This study presents a comprehensive analysis of the photophysicochemical properties of zinc(ii) 2,9,16,23-tetracarboxy-phthalocyanine (TcPcZn), N,N′-bis(3-pentyl)perylene-3,4,9,10-bis(dicarboximide) (EP-PDI), and their mixed systems in various TFA/H2O solvent mixtures. Key aspects discussed include molecular arrangement, intra- and intermolecular interactions, protonation effects on absorbance and aggregation, light-induced partial deprotonation of TcPcZn, and Förster Resonance Energy Transfer (FRET) effects on excited-state lifetimes. Due to strong solvent quenching, the singlet-state lifetimes of EP-PDI (1.07 and 2.91 ns), TcPcZn (0.67 and 3.79 ns), and their TcPcZn : EP-PDI mixture (0.64 and 3.96 ns) were measurable only at high concentrations (CM ≥ 0.110 mM). Both individual compounds and their blends exhibit promising triplet-state lifetimes, which are crucial for processes relying on long-lived excited states, such as photodynamic therapy and optoelectronic applications. In this context, particular attention is given to their ability to sustain room-temperature phosphorescence (RTP) : TcPcZn – 8.93 µs, EP-PDI – 10.18 µs, and TcPcZn : EP-PDI – 9.41 µs. Several strategies are proposed to further optimize these parameters and enhance RTP quantum yields.

Co-assembly of TcPcZn and EP-PDI in acidic TFA/H2O enables tunable excited-state lifetimes and room-temperature phosphorescence, providing design principles for efficient organic photosensitizers in photodynamic therapy and optoelectronics.