S/Se-Annulated Star-Shaped Perylene Diimides (PDIs) with Large Two-Photon Absorption (TPA) Cross-Section in NIR-I Region

Two-photon absorption (TPA) has attracted growing attention over recent years owing to the wide range of applications in organic nonlinear optical (NLO) materials. The quantitative sensitivity of a two-photon molecular entity is determined by its TPA cross-section (δ_TPA). Perylene diimides (PDIs) are excellent n-type organic semiconductor materials demonstrating distinguished thermal, optical, and chemical stability. Nonetheless, PDIs-based scaffolds exhibit poor δ_TPA in the NIR-I region (700-900 nm) due to the lack of suitable molecular design. Here, two novel star-shaped PDIs fluorophores, namely PDI-S and PDI-Se, were constructed by four periphery S/Se-fused PDIs connected with bicarbazole core. PDI-S manifested excellent δ_TPA of 3775 GM, which are among the highest values reported for PDIs excited in the NIR-I region.