Aggregation-induced enhanced emission and twisted intramolecular charge transfer in a pyridylcarbodinitrile with tunable photoluminescence in solution, films, and OLEDs

Abstract

Novel phenylpyridylcarbodinitrile (PPC) derivatives were synthesized to develop materials whose emission properties can be tuned by changes in their dissolving/dispersing environment. In solution these compounds exhibit blue to green fluorescence with quantum yields between 0.01 and 0.70. The large Stokes shifts, along with the significant rotational freedom of the rings and computational data indicate twisted intramolecular charge transfer (TICT) excited states for these PPCs. The dimethylmethoxyaryl-substituted PPC (MT-PPC) exhibited distinctive emissive properties, featuring highly environment-dependent fluorescence in solution, with a Δλem = 118 nm. Additionally, this compound exhibits aggregation-induced enhanced emission (AIEE), with a 19-fold photoluminescence quantum yield enhancement upon aggregation, whose emission profile is very similar to those observed with MT-PPC as a pure thin film. Conversely, in SF3PO films doped with MT-PPC, the emission is dependent on MT-PPC percentage. Films with 5 % and 10 % exhibit blue-shifted fluorescence (433 and 436 nm) compared to the 20 % film (445 nm), and especially compared to the pure film (468 nm). Interestingly, OLEDs with the same doped films also present environment-dependent behavior, with similar trends regarding the emission maximum. OLEDs with 5 % and 10 % show electroluminescence maxima at 437 nm, while the OLED with 20 % MT-PPC exhibits emission centered at 463 nm. Furthermore, these changes in dopant content shift the chromaticity coordinates from (0.18, 0.15) to (0.20, 0.26), demonstrating that the emissive properties of MT-PPC are environment-dependent, and consequently tunable in solution, thin films, and OLEDs.