Dynamics of Isolated 1,8-Naphthalimide and N-Methyl-1,8-naphthalimide: An Experimental and Computational Study

Abstract

In this work we investigate the excited-state structure and dynamics of the two molecules 1,8-naphthalimide (NI) and N-methyl-1,8-naphthalimide (Me-NI) in the gas phase by picosecond time- and frequency-resolved multiphoton ionization spectroscopy. The energies of several electronically excited singlet and triplet states and the S1 vibrational wavenumbers were calculated. Nonadiabatic dynamics simulations support the analysis of the radiationless deactivation processes. The origin of the S1 ← S0 (ππ*) transition was found at 30, 082 cm(-1) for NI and at 29, 920 cm(-1) for Me-NI. Furthermore, a couple of low-lying vibrational bands were resolved in the spectra of both molecules. In the time-resolved scans a biexponential decay was apparent for both Me-NI and NI. The fast time constant is in the range of 10-20 ps, whereas the second one is in the nanosecond range. In accordance with the dynamics simulations, intersystem crossing to the fourth triplet state S1 (ππ*) → T4 (nπ*) is the main deactivation process for Me-NI due to a large spin-orbit coupling between these states. Only for significant vibrational excitation internal conversion via a conical intersection becomes a relevant deactivation pathway.

Ultrafast Intersystem Crossing in Acetylacetone via Femtosecond X-ray Transient Absorption at the Carbon K-Edge

“…( 3 nπ*) state, as also noted for many other organic molecules. 1,[56][57][58] A new peak at 287.4 eV, although barely evident in Figure 3b, gains prominence at longer timescales (10-100 ps, Figure S13) and is possibly also arising from the T 1 state; the computed spectrum of this state predicts an absorption peak at 287.8 eV (within experimental resolution). In fact, it appears that the seeming recovery of the ground-state bleach (peak 5) also owes its origin to an overlapping resonance with the T 1 state (which gives rise to peaks 1 and 2), as all three peaks are characterized by similar temporal behavior.…”

Intersystem Crossing and Electron Spin Selectivity in Anthracene‐Naphthalimide Compact Electron Donor‐Acceptor Dyads Showing Different Geometry and Electronic Coupling Magnitudes

“…[55] Interestingly, Ph-NI shows a strong structureless fluorescence band centered at 410 nm (Figure 3a, Φ F = 95 %, Table 1), which is drastically different from the extremely weakly fluorescent unsubstituted NI. [54,55] This result is due to the coupling between the phenyl moiety and the NI moiety in Ph-NI (54°, Figure S55 in the Supporting Information). Structured emission band was observed for Ph-An, centered at 398 nm (Figure 3a, and Φ F = 74 % in Table 1), which is similar to the emission of anthracene, indicating the electronic coupling between the phenyl and the anthryl moieties is limited, which agrees with the dihedral angle between the two moieties (83°, Figure S55 in the Supporting Information).…”

“…[54,55] The fast ISC (10-100 ps) is due to the strong coupling of the S 1 /T 4 states (ππ*!nπ*), which share similar energy and there is change of the molecular orbital angular momentum to compensate the electron spin angular momentum change of the ISC. [55] Interestingly, Ph-NI shows a strong structureless fluorescence band centered at 410 nm (Figure 3a, Φ F = 95 %, Table 1), which is drastically different from the extremely weakly fluorescent unsubstituted NI. [54,55] This result is due to the coupling between the phenyl moiety and the NI moiety in Ph-NI (54°, Figure S55 in the Supporting Information).…”

Long‐Lived Charge‐Transfer State Induced by Spin‐Orbit Charge Transfer Intersystem Crossing (SOCT‐ISC) in a Compact Spiro Electron Donor/Acceptor Dyad

“…Femtosecond TA (fs TA) spectra of NI‐Br in toluene shows that ISC occurs within 30 ps (Figures S19), similarly to what reported for non‐brominated NI, with ISC time constants of 10–20 ps . To obtain the absorption of the 3 NI state and the NI radical anion (NI −.…”