Electronic, optoelectronic, photophysical, and NLO properties analysis of the photochromic 1,2-bis(2-methyl-5-phenylthien-3-yl)cyclopentene (DAE) based on the pyromelllitic diimide (PMDI): DFT investigation

• DTEPMPI-o exhibits a bandgap of 2.135 eV, again 1.272 eV for DTEPMPI-c, making DTEPMPI good organic semiconductors. • Both DTEPMPI isomers exhibit the stable LUMO properties required for efficient election injection. • DTEPMPI-o is suitable for p-type organic semiconductors, while DTEPMPI-c is the best candidate for ambipolar FET. • DTEPMPI-c exhibits the highest first- and second-order NLO response. • DTEPMPI-c exhibits a quadratic nonlinear refractive index value of 54.855 × 10 −20 m 2 w −1 . • DTEPMPI-o absorbs in the UV with better LHE, whereas DTEPMPI-c absorbs in both the UV and visible with low LHE. Using the insulating pyromellitic diimide (PMDI) as a starting point, two stable aromatic diimide isomers, namely DTEPMPI-o and DTEPMPI-c, designated open (o) and closed (c) ring, based on photochromic diarylethene (DAE) were investigated using density functional theory (DFT) and its time-dependent extension (TD-DFT). To this end, the B3PW91, PBE0, and ωB97XD functionals were employed, alongside the 6-311G(d,p) basis set. Thus, the impact of isomerization on electronic, optoelectronic, photophysical, charge transport, and nonlinear optical (NLO) properties, as well as on structural parameters, was analyzed. The air stability, reactivity, and solubility of these semiconductors were also studied in depth. The findings indicate a bandgap of 2.135 eV for DTEPMPI-o and 1.272 eV for DTEPMPI-c, making these compounds good organic semiconductors. In addition, DTEPMPI-o is suitable for p-type organic semiconductors, while DTEPMPI-c is the best candidate for ambipolar field-effect transistors (FETs). In addition, the LUMO levels of both isomers fall within the −3.4 to −4.6 eV range of n-type semiconductors. Both compounds show enhanced stability as p-type organic field effect transistors (OFET) materials and good solubility in N-Methyl-2-pyrrolidone (NMP). Optoelectronic results revealed that the average electric field of DTEPMPI-o is at least 1.1 and 1.4 times higher than that of poly (3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxyselenophene) (PEDOS), respectively, which are good optoelectronic materials used in industry; while that of DTEPMPI-c is at least 1.6 and 2.0 times higher, making the studied compounds excellent candidates for potential optoelectronic applications. Photophysical findings in toluene revealed that DTEPMPI-o absorbs in the ultraviolet (UV) with better light-harvesting efficiency (LHE), whereas DTEPMPI-c absorbs in both the UV and visible with low LHE. DTEPMPI-o is therefore a more promising candidate for photocurrent enhancement in organic solar cell devices. On the other hand, emission spectra revealed that DTEPMPI-o emits only in the UV with a medium Stokes shift (61.7 nm), while DTEPMPI-c emits both in the UV with a medium Stokes shift (56.2 nm) and in the near infrared (NIR) with a very large Stokes shift. In terms of NLO, the closed ring exhibits the highest first- and second-order NLO response. Furthermore, DTEPMPI-c exhibits a quadratic nonlinear refractive index value of 54.855 × 10 −20 m 2 w −1 , very high compared to standard values commonly used for degenerate four-wave mixing.