Which strategy for molecular probe design? An answer from the integration of spectroscopy and QM modeling.

With this study we show that the maturity reached by quantum-mechanical (QM) modeling has allowed a new analytical approach to the design of molecular probes. In this approach, the strategy is to integrate suited computational tools with multi-spectroscopic measurements to identify specific signals for the characterization of the molecular probe with respect to the perturbation used and the environmental conditions applied. The application of the strategy to a typical optical probe (2-acetylanthracene) has allowed the identification of specific IR and NMR signals for the characterization of the conformational states in both solid and solution states. This analysis has been successively extended to the investigation of specific optical signals. In particular we have shown that the introduction of a substituent in specific positions of the aromatic structure induces a different perturbation in the different excited states of the precursor anthracene with consequent differentiations of the states with respect to their solvent sensitivity (both in terms of bulk and specific effects). Finally, the integration of simulated and experimental emission spectra has revealed a possible isomerization in the excited state with resulting change of the conformational state in the absorbing and the emitting species.