Franck Condon spectra of the 2-tolunitrile dimer and the binary 2-tolunitrile water cluster in the gas phase

We present fluorescence emission spectra of the 2-tolunitrile dimer and the 2-tolunitrile water cluster through various vibronic bands in the electronically excited state. From the transition dipole moments in the individual monomers, the 2-TN dimer has shown to form J-aggregates, which is why the one-photon allowed transition is the S1 state in this cluster in contrast to other symmetric dimers, which tend to form H-aggregates. The changes of the molecular structures upon electronic excitation have been determined from a fit of the intensities in various fluorescence emission spectra. The excited state structure of the 2-TN dimer has been found to be asymmetric, in contrast to the ground state structure. Thus, emission takes place from one of the locally excited monomer moieties in the 2-tolunitrile dimer.