Single-Component Organic Light-Harvesting Red Luminescent Crystal

Highly efficient photoinduced energy transfer is observed in an orthogonal bichromophore naphthalenimide-perylenimide (NP), leading to strong solid-state luminescence (Φ = 0.5 ± 0.04) in the red region (λem = 631 nm). Steric hindrance imparted by orthogonal naphthalenimide and diisopropyl phenyl units prevents the association of perylenimide moieties, thereby retaining a high quantum yield of fluorescence emission even in the crystalline state. Upon photoexcitation at 340 nm, the intramolecular parallel orientation of the transition dipoles permits efficient Coulombic coupling between naphthalenimide and perylenimide in combination with weak H-type excitonic interactions between the intermolecular perylenimide units that results in intense red fluorescence in the crystalline state of dyad NP. Negligible photoinduced electron transfer from the singlet excited state of the perylenimide to the naphthalenimide unit (ΔG = 0.44 eV) and a marginal feasibility (ca. 10%) of photoinduced electron transfer from the singlet excited state of the naphthalenimide to the peryleninimide unit (ΔG = −0.17 eV) makes the dyad strongly fluorescent when excited at both 340 and 475 nm, corresponding to the naphthalenimide and perylenimide units, respectively. A narrow emission at 631 nm, wide absorption window (300–600 nm), and high fluorescence quantum yield in the crystalline state make the dyad NP a potential candidate for optoelectronic and photonic applications.