We report a computational study on vibronic effects in the spectroscopy, photoinduced processes and
decay back to the ground state of aza[7]helicene, a helicene with an unusually high fluorescence
quantum yield (QY = 0.39). In a first step, we compute and assign the absorption and electronic circular
dichroism (ECD) spectra in its full frequency range from 2.7 to 5.0 eV, accounting for nonadiabatic effects.
Then we compute the quantum dynamics of the cascade of ultrafast internal conversions of the highlyexcited singlet states to the lowest-energy one S1. Finally we adopt Fermi golden rule rates to compute the
QY of the dye, taking into account the competition between the radiative decay and the nonradiative decays
to the ground state and to the energy-accessible triplet states. We use time-dependent density functional
theory (TD-DFT), including solvent (dichloromethane) effects within the polarizable continuum model, to
parameterize a linear vibronic coupling (LVC) model involving the first lowest 12 singlet states and all the
normal coordinates. Nonadiabatic spectra and internal conversions dynamics are then computed through
wavepacket propagations with the Multilayer (ML) extension of the Multiconfigurational Time Dependent
Hartree method (ML-MCTDH). We highlight the molecular vibrations playing a major role in determining the
shape of the spectra and analyse the effect of inter-state couplings. At the same time we report a breakdown
of perturbative Herzberg–Teller approach. The computed QY is in perfect agreement with experiment and
allows us to ascertain that intersystem crossings are the processes limiting the fluorescence from S1. They
involve the three lowest triplet states and are made effective by spin–orbit coupling and vibronic effects.
