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Published on: January 1, 2016
Core-wing modulated squaraines with enhanced two-photon absorption and efficient photothermal eradication of bacteria
Xin-Ao Liu1, Xingtong Zhou1, Tong Zhang2
1Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, Shaanxi Provincial Key Laboratory of New Concept Sensors and Molecular Materials, School of Chemistry and Chemical Engineering, Shaanxi Normal University Xi'an 710119 P. R. China liuth121@snnu.edu.cn dinglp33@snnu.edu.cn.
None:
Predictable structure-property relationships for near-infrared (NIR)-emitting chromophores and sustainable photothermal agents remain challenging. Herein, two series of indolenine-based squaraines are synthesized to investigate how core-wing structural modulation influences photophysical properties. Dicyanovinylene modification of the squaraine carbonyl core induces a substantial bathochromic shift and enriches de-activation pathways, while further wing functionalization strengthens intramolecular charge transfer (ICT) efficiency and enhances nonlinear two-photon absorption (2PA). Intrinsic zwitterionic stabilization and the bent-shaped molecular skeleton of bis(dicyanovinylene)-cored squaraines are also supported by theoretical calculations. Optimal benzindolenine-winged squaraine dye SQ2-4CN demonstrates a strong two-photon absorption cross-section (δ 2PA) of 2140 GM at 890 nm within the NIR biological spectral window, approximately 8.95-fold enhancement over that of the indolenine-winged counterpart SQ1-2O. Femtosecond transient absorption spectroscopies further reveal the ICT character and plausible excited-state dynamics. Moreover, efficient bio-staining capability and photothermal eradication of bacteria with a significant photothermal conversion efficiency of 42.4% under 808 nm laser irradiation are initially validated for SQ2-4CN. The present work opens a pathway for designing core/wing-modified squaraines with superior nonlinear optical properties for potential bioimaging and photothermal applications.
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