Substituent effect on quantum efficiency in 4-aryloxy-N-(2′,6′-diisopropylphenyl)-1,8-naphthalimides: Experimental and computational investigations

• The substituent effect on quantum yields of 4-aryloxy-N-(2′,6′-diisopropylphenyl)-1,8-naphthalimides was studied.
• The photo-induced electron transfer process was hypothesized and justified by a computational calculation.
• The experimentally determined quantum yield of an additional compound agreed with the calculated value.

A series of potential optical brightening agents – 4-aryloxy-N-(2′,6′-diisopropylphenyl)-1,8-naphthalimides – are synthesized and their photo-physical properties are experimentally determined. Interestingly, it is found that their quantum efficiencies or quantum yields are exclusively dependent on the substituents on the aryloxy group at the 4-position. It is postulated that the electronic effect of the substituents influences the photo-induced electron transfer process, which causes a variation in quantum efficiencies. Due to analysis of charge transfer from 1,8-naphthalimide molecular part to its substituents in dichloromethane based on the time-dependent density functional theory at Becke 3-parameters Lee-Yang-Parr level coupling with the 6–31G(d) basis set in the conductor-like polarizable continuum model with the united atom topological model computations, it is found that computed charge transfers of these serial compounds correspond well with their experimental quantum yields. Validation of the calculation method is performed by experimental determination of the quantum yield of the nitro-substituted compound.