Tetraphenylethene (TPE) substituted phenanthroimidazoles 3a and 3b were designed and synthesized by the Suzuki cross-coupling reaction. They show reversible mechanochromic behavior with contrast colors between sky-blue and yellow green. The powder XRD studies show that destruction of a crystalline state into an amorphous state is responsible for mechanochromism. Hydrogen bonding interaction of a cyano-group in 3b results in enhanced AIE and improved thermal stability.

A series of new naphthalimide and phenothiazine-based push–pull systems (NPI-PTZ1–5), in which we structurally modulate the oxidation state of the sulfur atom in the thiazine ring, i.e., S(II), S(IV), and S(VI), was designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. The effect of the sulfur oxidation state on the spectral, photophysical, and electrochemical properties was investigated. The steady-state absorption and emission results show that oxygen functionalization greatly improves the optical (absorption coefficient and fluorescence efficiency) and nonlinear optical (hyperpolarizability) features. The cyclic voltammetry experiments and the quantum mechanical calculations suggest that phenothiazine is a stronger electron donor unit relative to phenothiazine-5-oxide and phenothiazine-5,5-dioxide, while the naphthalimide is a strong electron acceptor in all cases. The advanced ultrafast spectroscopic measurements, transient absorption, and broadband fluorescence up conversion give insight into the mechanism of photoinduced intramolecular charge transfer. A planar intramolecular charge transfer (PICT) and highly fluorescent excited state are populated for the oxygen-functionalized molecules NPI-PTZ2,3 and NPI-PTZ5; on the other hand, a twisted intramolecular charge transfer (TICT) state is produced upon photoexcitation of the oxygen-free derivatives NPI-PTZ1 and NPI-PTZ4, with the fluorescence being thus significantly quenched. These results prove oxygen functionalization as a new effective synthetic strategy to tailor the photophysics of phenothiazine-based organic materials for different optoelectronic applications. While oxygen-functionalized compounds are highly fluorescent and promising active materials for current-to-light conversion in organic light-emitting diode devices, oxygen-free systems show very efficient photoinduced ICT and may be employed for light-to-current conversion in organic photovoltaics.

Phenothiazine is one of the most extensively investigated aromatic compounds owing to its unique optical and electronic properties. This review highlighted the recent advances in the development of phenothiazine-based fluorescent materials for applications in various fields.

The present review focuses on the design, synthesis, functionalization, and application of BODIPY dyes in dye-sensitized solar cells and photodynamic therapy.

Organic–inorganic halide perovskite solar cells (PSCs) have attracted great attention as an alternative renewable photovoltaic technology with a power conversion efficiency (PCE) > 22%, which is on par with established technologies. The state-of-the-art spiro-OMeTAD (2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene) is the most successful hole-transport material (HTM) employed in PSCs. Recently, various types of spiro-linked organic small molecules have been reported to overcome the reported disadvantages of spiro-OMeTAD, such as a complex synthetic route, high synthetic cost, and requirement for hygroscopic dopants to improve the charge-carrier mobility and device performance, which significantly limits spiro-OMeTAD for large-scale application in the future. Herein, we provide an overview of recent developments in the design, synthesis, and characterization of spiro-linked organic small molecules as hole-transport materials (HTM) in perovskite solar cells (PSCs).

The development of mechanochromic materials by incorporating aggregation induced emission (AIE) luminogens has gained momentum owing to their wide range of applications in optoelectronics. In this work, the authors contribute to the development of AIE active mechanochromic phenanthroimidazole derivatives. The positional isomers of phenanthroimidazoles 1 and 2 were designed to study the effect of the position of triphenylamine (TPA) and tetraphenylethylene (TPE) units on their AIE and mechanochromism. Phenanthroimidazoles 1 and 2 were synthesized using the Suzuki cross-coupling reaction of TPE boronate ester with iodo-phenanthroimidazole of TPA and bromo-phenanthroimidazole of TPA, respectively. The single crystal X-ray analysis of 1 reveals a propeller orientation of multiple phenyl rings of the TPA and TPE units, confirming strong AIE characteristics of 1 and 2. Phenanthroimidazoles 1 and 2 exhibit reversible mechanochromism between blue and green colours, which was studied using powder X-ray diffraction (PXRD). The PXRD studies suggest that a phase transition from a crystalline state to an amorphous state is associated with the colour change. Moreover, phenanthroimidazoles 1 and 2 worked efficiently as non-doped emitters based on the AIE character and provided a high external quantum efficiency of 2.8 and 4.0%, respectively.