Higher emotional synchronization is modulated by relationship quality in romantic relationships and not in close friendships

•Couples exhibit significantly greater prefrontal alpha synchronization compared to close friends even in a non-interactive and natural context.•Low-relationship-quality couples required heightened neural compensation to maintain robust behavioral synchronization, indicating the significance of relationship quality on couple emotional coordination.•Support vector machine analysis highlights the crucial role of prefrontal activity in differentiating couples from friends, suggesting its importance in romantic emotional coordination.•This research contributes to our understanding of the neural mechanisms underlying emotional coordination within romantic relationships, shedding light on the intricacies of romantic emotions. Emotions are fundamental to social interaction and deeply intertwined with interpersonal dynamics, especially in romantic relationships. Although the neural basis of interaction processes in romance has been widely explored, the underlying emotions and the connection between relationship quality and neural synchronization remain less understood. Our study employed EEG hyperscanning during a non-interactive video-watching paradigm to compare the emotional coordination between romantic couples and close friends. Couples showed significantly greater behavioral and prefrontal alpha synchronization than friends. Notably, couples with low relationship quality required heightened neural synchronization to maintain robust behavioral synchronization. Further support vector machine analysis underscores the crucial role of prefrontal activity in differentiating couples from friends. In summary, our research addresses gaps concerning how intrinsic emotions linked to relationship quality influence neural and behavioral synchronization by investigating a natural non-interactive context, thereby advancing our understanding of the neural mechanisms underlying emotional coordination in romantic relationships.