Conformational Control of Excited-State Properties in Ortho-Linked Triarylamine-Based Donor–Acceptor Conjugates

Abstract

A series of intensely blue-emissive ortho-linked donor–acceptor conjugates comprising triarylamine donors and cyanopyridine or benzonitrile acceptors was readily synthesized via the bromine–lithium exchange–borylation–Suzuki (BLEBS) sequence in moderate to good yields. The modular synthetic approach enables systematic variation of conformational constraint as a molecular design element for tailoring excited-state properties. Cyclic voltammetry reveals irreversible dimerization of triarylamine derivatives lacking para-substituents. Photophysical studies in the solid state, solution, and polymethylmethacrylate (PMMA) matrix reveal photoluminescence quantum yields (PLQY) of up to 70%, emission bandwidths as narrow as 2480 cm⁻¹ (47 nm), and CIE 1931 coordinates approaching the standard blue point. Phenylene extension increases conformational constraint around the acceptor, inducing hypsochromically shifted emission and providing an additional structural handle for tuning the optical properties. Pronounced positive emission solvatochromism, aggregation-induced emission enhancement (AIEE), temperature-dependent spectroscopy, and quantum-chemical calculations consistently indicate that conformational modulation governs charge-transfer interactions, excited-state relaxation, and triplet-state accessibility. Together, the experimental and theoretical results establish structure–property relationships that provide design principles for the rational engineering of future blue-emissive organic chromophores.