A new class of donor-bridge-acceptor (D-π-A) π-conjugated light-emitting molecules comprising carbazole as donor and maleimide (Cbz-MI, Cbz-MI(d)), phthalimide (Cbz-Pth) as acceptor units with phenyl ring as spacer have been synthesized in good yields. These compounds exhibit high quantum yield with three distinct emission colors yellowish-green (Cbz-MI), bright yellow Cbz-MI(d), and sky blue (Cbz-Pth) in the solid state. Single-crystal X-ray and quantum chemical calculations reveals that twisting of the phenyl rings with high torsional angle on maleimide and phthalimide units reduce the effective inter-chromophore electronic coupling, furnish dramatic changes in their photophysical properties in solution and solid states. Intriguingly, Cbz-MI(d) and Cbz-Pth exhibits a unique aggregation-induced blue-shifted emission (AIBSE) due to restricted intramolecular rotation (RIR) process, while Cbz-MI shows red-shifted emission in the solid state. The solvatochromic study reveal that combined RIR and excited state migration augment AIE (aggregation-induced emission) properties. The electrochemical properties reveal that Cbz-MI exhibits high oxidation propensity while Cbz-Pth shows low reduction values. Subsequently, organic light-emitting diodes (OLEDs) were fabricated with a simple three-layer device containing Cbz-Pth and Cbz-MI(d) as emitting layers. Cbz-MI(d) exhibits high performance yellow OLED with an external quantum efficiency exceeding ∼4.1% and a brightness exceeding ∼73915 cd/m, which is among the best performance reported for bright yellow fluorescence organic light-emitting diodes.

A series of dicarboxylic quinoline derivatives bearing electron-releasing or -withdrawing substituents have been synthesized using mono- or/and biphasic methodologies. By controlling the regioselectivity of addition into our electrophilic intermediate, we also characterized by which mechanism the Doebner-Miller cyclization step occurred. As anticipated, electron-releasing substituents induce a red shift of the low-energy absorption allowing excitation in the visible region. In addition, by playing on the strength and position of the electron-releasing substituents, chromophore having interesting fluorescent properties such as large Stoke shifts, good fluorescent quantum yields, emission in the visible green-yellow region and reasonable two-photon absorption in the NIR region have been obtained. These small-size fluorophores, which can be made water-soluble and have been shown to be non-toxic, can be hetero- and/or polyfunctionalized and thus represent promising key units for fluorescence-based physiological experiments with low background interactions.

The photochemical and redox properties of two newly synthesized tetrahydroquinoxaline-based squaraine dyes (SQ) are investigated using femto- and nanosecond laser flash photolysis, pulse radiolysis, and cyclic voltammetry. In acetonitrile and dichloromethane, these squaraines exist as monomers in the zwitterionic form (lambda(max) approximately 715 nm, epsilon(max) approximately 1.66 x 10(5) M(-1) cm(-1) in acetonitrile). Their excited singlet states ((1)SQ*) exhibit a broad absorption band at 480 nm, with singlet lifetimes of 44 and 123 ps for the two dyes. Both squaraines exhibit poor intersystem crossing efficiency (Phi(ISC) < 0.001). Their excited triplet states ((3)SQ*), however, are efficiently generated by triplet-triplet energy transfer using triplet excited 9,10-dibromoanthracene. The excited triplet states of the squaraine dyes exhibit a broad absorption band at ca. 560 nm (epsilon(triplet) approximately 4.2 x 10(4) M(-1) cm(-1)) and undergo deactivation via triplet-triplet annihilation and ground-state quenching processes. The oxidized forms of the investigated squaraines (SQ(*+)) exhibit absorption maxima at 510 and 610 nm.