Charge Carrier Mobility of Phenothiazine Functionalized TCBD Derivatives of Naphthalimide

A set of naphthalimide functionalized push-pull chromophores NPI 1-3 were designed and synthesized via Pd-catalyzed Sonogashira cross-coupling followed by [2 + 2] cycloaddition-electrocyclic ring-opening reaction. The 1,8-naphthalimide (NPI) and 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) moiety acts as an acceptor unit, whereas phenothiazine (PTZ) unit acts as a donor unit. Their photophysical, electrochemical properties, and charge carrier mobilities were investigated. Density functional theory (DFT) and TD-DFT calculations were performed on NPI 1-3 to analyze the molecular geometry, frontier molecular orbitals, molecular electrostatic potentials (MEPs), and electronic transitions related to their absorption spectra. The incorporation of cyano-based strong electron acceptor TCBD in the phenothiazine functionalized naphthalimide derivatives NPI1 resulted in TCBD incorporated chromophore NPI 2-3 which exhibits red-shifted electronic absorption spectra in the near IR region. The electrochemical properties reveal that the naphthalimide derivatives NPI 1-3 exhibit multiple redox waves, attributed to the presence of NPI and TCBD acceptor units and phenothiazine donor units. The measured hole and electron mobilities for NPI 1-3 are 4.06 × 10^-3 and 3.16 × 10^-3 cm² V^-1 s^-1, 7.5 × 10^-3 and 4.48 × 10^-3 cm² V^-1 s^-1, 6.76 × 10^-3 and 3.1 × 10^-3 cm² V^-1 s^-1, respectively, obtained by space-charge limited current (SCLC) measurements.