# Tuning Excited-State Properties in Pyrrolo[3,2-b]pyrrole-Based Donor–Acceptor Emitters via Molecular Conformation and Conjugation Control

## TL;DR

This paper shows how adjusting molecular structure in nitrogen-based compounds can control their light-emitting properties for better optoelectronic applications.

## Contribution

A strategy for tuning excited-state properties in PP-based emitters through molecular conformation and conjugation control is demonstrated.

## Key findings

- PP-6F shows efficient π-electron delocalization and dominant local excitation emission.
- PPA-3F exhibits a hybrid ICT/LE excited state due to increased dihedral angle and reduced conjugation.
- Rigid anthracene in PPA-3F suppresses nonradiative decay and maintains high oscillator strength.

## Abstract

Nitrogen-fused conjugated heterocycles have attracted growing interest owing to their tunable electronic properties and potential in organic optoelectronics. In this study, two centrosymmetric donor–acceptor-type emitters PP-6F and PPA-3F were designed by incorporating trifluorophenyl and anthracene acceptor units into a pyrrolo[3,2-b]pyrrole (PP) framework. The experimental and theoretical results reveal that subtle modulations in molecular conformation and π-conjugation pathways strongly affect the excited-state characteristics. PP-6F, featuring a nearly coplanar donor–acceptor configuration, exhibits efficient π-electron delocalization and a dominant local excitation (LE) emission with a large oscillator strength. In contrast, the bulky anthracene in PPA-3F increases the donor–acceptor dihedral angle, reduces conjugation coupling, and promotes orbital separation, leading to a hybrid intramolecular charge transfer and local excitation (ICT/LE) excited state. The rigid anthracene framework suppresses structural reorganization and nonradiative decay, allowing PPA-3F to retain a relatively high oscillator strength despite its charge-transfer nature. This work demonstrates that fine-tuning donor–acceptor dihedral angles and conjugation continuity within PP-based systems is an effective strategy for balancing LE and ICT emissions and developing high-efficiency nitrogen-fused organic emitters and scintillators.