Two fully fused perylenediimide (PDI) tetramers, TFPDI-MFT and TFPDI-FT, were designed and synthesized through an inner-ring-fusion strategy and investigated as nonfullerene acceptors for organic solar cells. The two acceptors contain different arrangements of thiophene- and naphthalene-based fusion motifs, resulting in distinct molecular geometries and torsional distributions. TFPDI-MFT consists of a central thiophene-fused region flanked by two naphthalene-centred fused PDI units, whereas TFPDI-FT contains a central naphthalene-fused segment with laterally extended FPDI-T units. Both tetramers possess rigid, extended π-conjugated frameworks and exhibit strong optical absorption with high molar extinction coefficients. Their fused structures also produce distinct nonplanar molecular conformations, with the major torsional distortion located at different positions within the two tetrameric frameworks. TFPDI-MFT exhibits a relatively less-twisted central region and more-twisted peripheral regions, whereas TFPDI-FT displays the opposite torsional distribution. Spectroscopic, morphological, and charge-transport measurements reveal different intermolecular interactions and film-state behaviors while both acceptors form relatively uniform blend films with PBDB-T. Organic solar cells using PBDB-T as the donor and TFPDI-MFT or TFPDI-FT as the acceptor achieved optimized power-conversion efficiencies (PCEs) of 6.4% and 6.3%, respectively. A more pronounced difference was observed for the as-cast devices, with PCEs of 5.96% and 5.41%, respectively, while the two acceptors also exhibited different responses to processing additives. These results suggest that the spatial position and distribution of local torsion, rather than simply the overall degree of molecular twisting, represent important molecular-design parameters for fully fused PDI-based nonfullerene acceptors.
Solvent-specific chromogenic systems enabling quantitative analysis with clear mechanistic insights remain scarce, especially those where dichloromethane (DCM) acts as the reaction medium and enables the observed chromogenic behaviour. Herein, we report phenyl-bridged N,N,N′,N′-tetrasubstituted bis(2-amino-5-thiazolyl)diamine derivatives (4a–4c) that exhibit exclusive color-to-deep-green chromic switching in halogenated alkanes. DCM delivers the fastest kinetics and strongest ∼650 nm absorbance enhancement. Combined photophysical, electrochemical, and kinetic studies reveal a dual-path mechanism of light-accelerated conversion and spontaneous dark rearrangement, with reactivity following 4c > 4b > 4a. EPR, chemical-oxidation controls, and HRMS confirm the cationic nature of photogenerated products. DFT calculations highlight substituent-tunable electronic effects, where tetramethoxy-substituted 4c shows optimal responsiveness. An excellent linear correlation (R = 0.999) between 672 nm absorbance and DCM fraction in acetonitrile permits accurate DCM quantification. Paper-based test strips further enable naked-eye on-site DCM-vapor detection without sophisticated instrumentation. This work provides a tunable platform for solvent-specific sensing and radical cation chemistry, challenging DCM's conventional role as an inert solvent.
