Synthesis and photophysical properties of three ladder-type chromophores with large and rigid conjugation structures

•Three novel ladder-conjugated chromophores were synthesized and characterized.•Linear optics, two-photon absorption and electrochemical properties illustrated their photophysical features.•Structure–function relationship is further discussed, suggesting a rational design to develop ladder-conjugated small molecules.

Three novel ladder-conjugated chromophores indicated as LT1–LT3 were synthesized and characterized. Further studies on linear, nonlinear optics and electrochemical properties demonstrated their photophysical features respectively. Compound LT1 shows good two-photon absorption cross-section (δ) up to ∼1200 GM at 810 nm in tetrahydrofuran, which is attributed to intramolecular charge transfer effect, as supported by density functional theory theoretical calculations. Compound LT2 and LT3 show considerable molar extinction coefficients, which are more than 105, and higher quantum yields. Structure–function relationship is further discussed, suggesting a rational strategy to develop ladder-conjugated small molecules.

Graphical abstractThree novel ladder-conjugated chromophores LT1–LT3, using TABEF (2, 3, 6, 7-tetraamino-9, 9-bis (2-ethylhexyl) fluorene) as the key intermediate, were synthesized and characterized by NMR and MALDI-TOF mass spectrometry. They had similar structure and conjugated length. But interestingly they show different photophysical features caused by their electron density distribution, and it could be verified by DFT theoretical calculations. Structure–function relationship is further discussed, suggesting a rational strategy to develop ladder-conjugated small dyes.Figure optionsDownload full-size imageDownload as PowerPoint slide