Highly-efficient upconversion via direct one-photon absorption of xanthene-based chromophores

Abstract

A series of xanthene-based chromophores, including rhodamines (Rh6G, RhA, RhB and RhBS) and luciferin derivatives (fluorescein, eosin and rose bengal), were firstly reported to obtain the structure-performance correlations in the upconversion via one-photon absorption (OPA-UC). These xanthene derivatives capped with different aryl groups contain the varying tautomeric donor-acceptor pairs at both ends. Electron cloud density calculations show that attaching different tautomeric donor-acceptor pairs and aryl group can change the intramolecular charge-transfer (ICT) strength and the restricted intramolecular rotation (RIR) degree. Under the excitation of CW diode laser (655 nm, < 2 W cm−2), all the chromophore solutions (5 × 10−5 M) radiate yellow upconversion (UC), but the UC efficiency (ΦUC) showed a difference of more than two orders of magnitude, ranging from 7.56% for RhBS to 0.01% for fluorescein. The results show that strong ICT and large RIR lead to highly-efficient OPA-UC. Finally, the OPA-UC microscopy imaging and OPA-UC detection were briefly investigated under the conditions of neither deaerating nor the high-power excitation light, suggesting that OPA-UC of this system possesses practical applications.