Solid state photophysics of a π-stacked 9,10-anthraquinone derivative oriented by cooling through a liquid crystalline phase

The absorption spectrum of a solid state film of anthraquinone derivative 1 differs significantly from that observed in solution and depends on the degree of film crystallinity. At room temperature, a solution of 1 exhibits weak fluorescence (Φf ≈ 0.001 in 2-propanol), but is totally non-emissive in aprotic solvents (e.g., in diethyl ether or chloroform). Stronger fluorescence can be observed in rigid glasses, suggesting that rapid and efficient internal conversion deactivates the lowest excited state in fluid solution. An ordered solid state film of 1 exhibits weak luminescence at room temperature, and emission intensity increases more than 100-fold upon cooling to 77 K.