# Enhanced Photostability through Rapid Exciton Decay in Desymmetrized Cyclopentannulated Acenes with Strong Face-to-Face pi Stacking

## TL;DR

Researchers designed acene molecules that rapidly return to their ground state, preventing triplet formation and improving photostability in optoelectronic applications.

## Contribution

The study introduces desymmetrized cyclopentannulated acenes with rapid exciton decay and suppressed triplet formation through molecular design.

## Key findings

- The synthesized acenes exhibit rapid exciton decay and photostability in both solution and single crystals.
- Strong face-to-face pi stacking does not affect the rapid decay due to short excited-state lifetimes.
- DFT calculations suggest five-membered ring twisting drives internal conversion.

## Abstract

The photophysics of organic semiconductors impacts their
efficiency
in optoelectronic devices where exciton transitions, including singlet
fission, intersystem crossing and the formation of charge transfer
states influence the ability to convert between bright and dark states
and to dissociate into free charges. Unfortunately, photodegradation
and spurious signals often confound the results of optical studies,
especially of important triplet states. Here four asymmetric cyclopentannulated
acenes are synthesized and studied. This system represents an extreme
in photophysics achieved via molecular design to fully quench the
photoluminescence and bypass triplet formation allowing for comparative
studies with other highly absorbing acenes. Rapid molecular exciton
decay that is unaffected by strong electronic coupling induced by
the crystal packing is found. The quick return to the ground state
inhibits the formation of triplets and leads to heating in the solid
state. These aceacenes are photostable both in solution and as single
crystals, likely because the short excited-state lifetime diminishes
the chances for deleterious photoreactions. Density functional theory
calculations highlight excited state twisting in the five-membered
ring, indicating a key driver of rapid internal conversion.