Formyl‐Group Multiplicity Regulates Nonradiative Decay Through Intermolecular Locking in Tetraphenylethylene‐Based Aggregation‐Induced Emission Luminogens

Abstract

ABSTRACT Aggregation‐induced emission (AIE) is commonly attributed to the restriction of intramolecular motion upon aggregation. However, aggregation alone does not guarantee high solid‐state photoluminescence efficiency, because residual molecular motions may still promote nonradiative decay. Here, four formyl‐substituted tetraphenylethylene (TPE) derivatives, denoted TPE‐nCHO, were comparatively investigated to clarify how substituent multiplicity and arrangement influence aggregate‐state emission. Although all compounds exhibit typical AIE behavior, their solid‐state photoluminescence quantum yields differ markedly: TPE‐CHO shows only 20 ± 2%, whereas ( Z )‐TPE‐2CHO, ( E )‐TPE‐2CHO, and TPE‐4CHO reach 89 ± 2%, 99 ± 1%, and 99 ± 1%, respectively. Fluorescence lifetime analysis shows that the low efficiency of TPE‐CHO is associated with a substantially larger nonradiative decay contribution. Single‐crystal structures and quantitative short‐contact statistics indicate that the highly emissive ( E )‐TPE‐2CHO and TPE‐4CHO crystals possess more extensive and spatially distributed intermolecular contact networks than TPE‐CHO. These structural trends are consistent with stronger intermolecular confinement and reduced nonradiative relaxation. Overall, efficient solid‐state emission in this TPE series requires both a twisted geometry that avoids detrimental cofacial π–π stacking and a sufficiently developed intermolecular contact network; the actual degree of confinement is governed by both substituent multiplicity and packing topology.