Photophysics of 1-Aminonaphthalene: A Theoretical and Time-Resolved Experimental Study

The photophysics of 1-aminonaphthalene (1-napthylamine, AMN) has been investigated on the basis of a constructive experimental-theoretical interplay derived from time-resolved measurements and high-level quantum-chemical ab initio CASPT2//CASSCF calculations, Transient ionization signals at femtosecond resolution were collected for AMN cold isolated molecules following excitation from the vibrationless ground level to a number of vibrational states (within the pump resolution) in the lowest accessible excited state and further multiphoton ionization probing at 500, 800, and 1300 nm. Theory predicts two pi pi* states, L-1(b) and L-1(a), as the lowest singlet electronic excitations, with adiabatic transitions from S-0 at 3.50 and 3.69 eV, respectively. Since the associated oscillator strength for the lowest transition is exceedingly small, the L-1(b) state is not expected to become populated significantly and the L-1(a) state appears as the main protagonist of the AMN photophysics. Though calculations foresee a surface crossing between L-1(a) and the lower L-1(b) states, no dynamical signature of it is observed in the time-dependent measurements. In the relaxation of L-1(a), the radiant emission competes with the intersystem crossing and internal conversion channels. The rates of these mechanisms have been determined at different excitation energies. The internal conversion is mediated by a L-1(a)/S-0 conical intersection located 0.7 eV above the L-1(a) minimum. The relaxation of a higher-lying singlet excited state, observed above 40 000 cm(-1) (4.96 eV) and calculated at 5.18 eV, has been also explored.