Effects of multibranching on 3-hydroxyflavone-based chromophores and the excited-state intramolecular proton transfer dynamics.

A series of one-, two-, and three-branched chromophores based on 3-hydroxyflavones (1-3) have been synthesized as the first example of multibranched chromophores demonstrating excited-state intramolecular proton transfer (ESIPT). Coupling between the 3-hydroxyflavone branches connected by an electron-donating triphenylamine core is manifested in the red-shifted and asymmetric absorption band of 2, whereas the absorption of 3 is governed by the divided donor strength. Their excited-state charge-transfer (ESCT)-coupled ESIPT dynamics is investigated via femtosecond fluorescence upconversion and is proved to be well correlated with the ratio of normal/tautomer emission in the fluorescence spectra.

Design and synthesis of trithiophene-bound excited-state intramolecular proton transfer dye: enhancement on the performance of bulk heterojunction solar cells.

In an aim to harvest UV-near-visible (360-440 nm) photons as well as to increase the morphology in the bulk heterojunction solar cells, we report herein the strategic design, synthesis, and characterization of a novel excited-state intramolecular proton-transfer dye, 3-hydroxy-2-(5-(5-(5-(3-hydroxy-4-oxo-4H-chromen-2-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-4H-chromen-4-one (FT), which bears two key functional groups, namely 3-hydroxychromone chromophore and trithiophene backbone and is then exploited into the blends of regioregular poly(3-hexylthiophene) (RR-P3HT) and phenyl-C(61)-butyric acid methyl ester (PCBM). FT acts as an excellent UV-near visible absorber, which then undergoes excited-state intramolecular proton transfer, giving rise to an orange-red proton-transfer emission that was reabsorbed by P3HT via a Forster type of energy transfer. Introduction of FT to P3HT/PCBM blend films also improves the morphology of phase separated structure, in particular, enhances the interaction of P3HT chains and the hole mobility.

Dual excited-state intramolecular proton transfer reaction in 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one.

The synthesis, characterization and fundamental of the dual excited-state proton-transfer properties of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one (1a) are reported. In the electronic ground state, there exist two competitive hydrogen bonding (HB) isomers for 1a. Conformer 1a(O) reveals a five-membered ring HB structure between O-H and carbonyl oxygen, while conformer 1a(N) possesses a six-membered ring HB formation between O-H and pyridyl nitrogen.