Synthesis, X‐ray Crystal Structures, and Solid‐State Fluorescence Properties of 5,5‐Dialkyl‐9‐dibutylamino‐5H‐benzo[b]naphtho[1,2‐d]furan‐6‐one and 3,3‐Dialkyl‐9‐dibutylamino‐3H‐benzo[kl]xanthen‐2‐one

Abstract

AbstractHeterocyclic fluorophores 5,5‐dibutyl‐9‐dibutylamino‐5H‐benzo[b]naphtho[1,2‐d]furan‐6‐one (4) and 3,3‐dibutyl‐9‐dibutylamino‐3H‐benzo[kl]xanthen‐2‐one (7) with dialkyl substituents linked in a nonconjugated fashion to the chromophore skeleton have been derived from quinol‐type compounds 1 and 2, and their photophysical properties were investigated in solution and in the solid state. Fluorophores 4 and 7 exhibit strong fluorescence intensity in the solid‐state relative to that of quinols 1 and 2; however, 1 and 4 or 2 and 7 exhibit similar fluorescence intensities in solution. To elucidate the dramatic effect of the dialkyl substituent on the solid‐state fluorescence excitation and emission spectra, we performed semiempirical molecular orbital calculations (AM1 and INDO/S) and X‐ray crystallographic analysis. On the basis of the results of the calculations and the X‐ray crystal structures, the relation between the solid‐state photophysical properties and the chemical and crystal structures of 4 and 7 were discussed. It was confirmed that introduction of bulky dialkyl substituents to the fluorophore skeleton can efficiently prevent the short π–π contact between the fluorophores in molecular aggregation states and cause a dramatic solid‐state fluorescence enhancement. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)