Two novel sensitizers, 2a and 2b, with D/A–π–D–π–A architectures were designed and synthesized based on a phenothiazine framework connected via ethylene with 3,5-bis(trifluoromethyl)phenyl (A) and p-methoxyphenyl (D), and with cyanoacrylic acid as an anchoring group, acting as an acceptor (A). A comparative analysis was performed to investigate the effect of the electronic character of end-capped D and A groups on the photophysical properties and photovoltaic performance of 2a and 2b. The optical, thermal, electrochemical and photovoltaic properties of the dyes were thoroughly investigated and confronted with DFT and TD-DFT calculations. Compound 2b of D–π–D–π–A type showed better photovoltaic parameters, which verify the general trends, although the parameters for compound 2a of A–π–D–π–A type do not differ significantly from those for 2b. The metal-free 2a and 2b-based DSSC devices exhibited higher power conversion efficiencies of 6.11% (2a) and 5.03% (2b) compared to 3.56% for the N719-based device.

New D-π-D-π-A low-molecular-weight compounds, based on a phenothiazine scaffold linked via an acetylene unit with various donor moiety and cyanoacrylic acid anchoring groups, respectively, were successfully synthesized. The prepared phenothiazine dyes were entirely characterized using nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The compounds were designed to study the relationship between end-capping donor groups’ structure on their optoelectronic and thermal properties as well as the dye-sensitized solar cells’ performance. The effect of π-conjugation enlargement by incorporation of different heterocyclic substituents possessing various electron–donor affinities was systematically experimentally and theoretically examined. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were implemented to determine the electronic properties of the novel molecules.