Nature of the N‐Substituted Alkyl Chain Influencing Emission Properties of Naphthalene Diimide (NDI) Via Excimer, and Exciplex Formation

Abstract

AbstractIn this paper, the effect of structural differences in alkyl chains substituted at the imide position of naphthalene diimide (NDI) derivatives were compared using oleylamine (NDI‐OL) and octadecylamine (NDI‐OD) in different solvents, solvent mixture, gel, and solid‐state inferring the photophysical properties at different states. The difference in alkyl chains renders a range of emission (∼90 nm) for NDI‐OL due to the steric reasons when self‐assemble from a non‐aromatic solvent mixture [CHCl3/MCH (1 : 9, v/v)] and aromatic solvents, wherein such emission tuning was absent for sterically less hindered NDI‐OD. Further, the emission tuning and enhancement were also observed via a host‐guest method, aggregation from a solvent mixture [aggregation induced emission enhancement (AIEE)], and by applying mechanical [mechanochromic behaviour] force deciphering these properties as the favourable formation of exciplex/excimer by NDI derivatives with excellent emission quantum yield enhancement (ϕf,%≈1–5) compared to the monomeric form of NDI (ϕf,%≈0.2). Further, the NDI compound was also found to be useful for distinguishing pH 14 among other ranges of pH solutions visually and spectroscopically.