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Modern technological breakthroughs depend on nonlinear optical (NLO) and photovoltaic (PV) materials, essential for creating advanced photonic devices and efficient solar cells. Herein, the NLO, PV, electrical, and photophysical characteristics of proposed chromophores (WLK-1-WLK-6) designed from pyridoquinazolindone-containing triphenylamine have been systematically altered by the addition of different spacers categorized as K1, K2, K3, K4, K5, and K6 (named as i-series). This fine-tuning was accomplished using TD-DFT, DFT computations, and the Scharber model. The impact of spectrum of medium polarity, ranging from the least polar to the most polar, including water ( ε = 78.36), methanol ( ε = 32.61), DMSO ( ε = 46.83), tetrahydrofuran ( ε = 7.43), benzene ( ε = 2.27) and chloroform ( ε = 4.71), is explored in detail utilizing the IEFPCM model on NLO and PV properties. Moreover, the response of different analyses like DOS, NCI, NBO, FMO, dipole moments ( µ ), and hyperpolarizability ( β ) in both gas, polar and non-polar solvents was analyzed. Our structure-property relationship studies revealed that adding extra spacer groups, particularly those containing thiophene spacers, considerably impacted the lowering of the energy gap (3.853-4.190 eV). The simulated UV-Vis spectra illustrate significant π → π* transitions and lower n → π* transitions, primarily in the near-infrared (IR) range of 558.613 to 429.844 nm. Push-pull chromophores showed extraordinary frequency-dependent NLO properties, SHG β (-2 ω , ω , ω ), and EOPE β (- ω , ω , 0) effect computed at laser frequencies of 1064 and 532 nm. Among the proposed compounds, WLK-6 with the K6 spacer demonstrated a smaller energy gap (3.853 eV), resulting in a maximum optical absorption peak at λ max = 558.613 nm and the maximum hyperpolarizability in benzene (9.00 × 10 4 a.u.), methanol (1.22 × 10 5 a.u.), THF (1.12 × 10 5 a.u.), DMSO (1.23 × 10 5 a.u.), and water (1.23 × 10 5 a.u.). Our study found that WLK-6, WLK-5, and WLK-1 compounds also had good photovoltaic (PV) capabilities, reaching a power conversion efficiency (PCE) of around 5% and an injection efficiency (Δ G inject ) of 0.191. In addition to these analyses, we performed topologic studies, such as TDM, ELF, NCI, MEP, LOL, and electron-hole overlap plots to better understand both intra and intermolecular interactions. Based on these results, it is clear that modifying longer π-linker groups in A-D-π-A conjugated systems benefits the optoelectronic characteristics and NLO responses for organic PV devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Context: Dye-sensitized solar cells (DSSCs) present a convincing substitute for conventional silicon-based solar cells because of their possible lower manufacturing costs and versatile uses. Electron injection and dye regeneration processes are important in meeting the need for photosensitizers with improved efficiency and stability. Aimed at enhancing the performance and efficiency of DSSCs, this study focuses on the structural engineering to performance metrics of novel indoline-benzo[d][1,2,3]thiadiazole based push-pull sensitizers (LHZ1 to LHZ9) with D-D-A-π-A framework. The current study provides insights into the photovoltaic and optoelectronic properties of the investigated dyes, which are significantly influenced by the modification of auxiliary donors (D), internal acceptors with thiophene as a spacer, and cyanoacrylic acid (A) as the terminal acceptor. These modifications enhance rapid charge transfer among the dyes, highlighting the critical role of dye-semiconductor interactions., Methods: The suitability of developed sensitizers for DSSCs applications is confirmed by executing quantum methods like NBO, TDM, FMO, DOS, E b , ΔG reg , ΔG inject , VRP, and ICT parameters q CT (e - ), D CT ( A ∘ ), H index ( A ∘ ), ∆( A ∘ ), t index ( A ∘ ), and μ CT (D). All of the investigated dyes have HOMO levels lower than the electrode I-/I 3 -'s redox potential (-4.8 eV) and LUMO values that are appropriately higher than the conduction band of TiO 2 (-4.0 eV). The novel dyes showed a closing of the energy gap (2.38-1.84 eV). The LHZ7 and LHZ8 molecules with the lowest E g (1.97 eV and 1.84 eV) demonstrated the highest absorption (up to 746 nm > 402 nm for LHZ), which was caused by the insertion effect of varied donors and internal acceptors. Almost all photosensitizers appeared with remarkable properties, i.e., red-shifted absorption maxima (746 nm), lowest E x (1.66 eV), E b (0.02 eV), and highest values of LHE (0.958). The TDM analysis revealed high charge density on HOMO of donor and LUMO of acceptors in designed dyes. DOS analysis revealed that the donor parts of the molecules delocalized the highest occupied molecular orbitals of dye particles. The electronic properties predicted by the NBO analysis showed that donor groups donate high and faster transfer of charge, and internal acceptor groups rapidly accept them. The electron injection (ΔG inject ) and dye regeneration (ΔG reg ) analysis of photosensitizers attached with TiO 2 proved efficient charge transfer properties from the donor of newly designed dyes onto the conduction band of TiO 2 . This study, also supported by the thermodynamic stability of dyes with negative values of Gibbs free energy, revealed that the performance of the designed dyes is augmented by modifying the donor and internal acceptors of the reference photosensitizer for effective application in the experimental community. All of the dyes are suitable for DSSCs based on the calculated parameters. Still, the LHZ9 dye proved proficient in applying dye-sensitized solar cells due to its remarkable properties, i.e., lowest gap and red-shifted absorption maxima., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Nanoscale nonlinear optical (NLO) materials have received huge attention of the scientists in current decades because of their enormous applications in optics, electronics, and telecommunication. Different studies have been conducted to tune the nonlinear optical response of the nanomaterials. However, the role of alkali metal (Li, Na, K) doping on triggering the nonlinear optical response of nanomaterials by converting their centrosymmetric configuration into noncentrosymmetric configuration is rarely studied. Therefore, to find a novel of way of making NLO materials, we have employed density functional theory (DFT) calculations, which helped us to explore the effect of alkali metal (Li, Na, K) doping on the nonlinear optical response of tetragonal graphene quantum dots (TGQDs). Ten new complexes of alkali metal doped TGQDs are designed theoretically. The binding energy calculations revealed the stability of alkali metal doped TGQDs. The NLO responses of newly designed complexes are evaluated by their polarizability, first hyperpolarizability (β o ), and frequency dependent hyperpolarizabilities. The Li@r8a exhibited the highest first hyperpolarizability (β o ) value of 5.19 × 10 5 au. All these complexes exhibited complete transparency in the UV region. The exceptionally high values of β o of M@TGQDs are accredited to the generation of diffuse excess electrons, as indicated by NBO analysis and PDOS. NCI analysis is accomplished to examine the nature of bonding interactions among alkali metal atoms and TGQDs. Our results suggest alkali metal doped TGQD complexes as potential candidates for nanoscale NLO materials with sufficient stability and enhanced NLO response. This study will open new doors for making giant NLO response materials for modern hi-tech applications., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)